Science Priorities Related to the Organic Contamination of Martian
Landers

November 15, 2004

Paul Mahaffy and David Beaty (co-chairs)

Mark Anderson, Glen Aveni, Jeff Bada, Simon Clemett,\
Dave Des Marais, Susanne Douglas, Jason Dworkin, Roger Kern, Dimitri
Papanastassiou, Frank Palluconi, Jeff Simmonds,\
Andy Steele, Hunter Waite, and Aaron Zent

# (For correspondence, please contact [**paul.r.mahaffy@nasa.gov**](mailto:paul.r.mahaffy@nasa.gov), 301 614-6379, or [**David.Beaty@jpl.nasa.gov**](mailto:David.Beaty@jpl.nasa.gov), 818-354-7968) 

# This report has been approved for public release by JPL Document Review Services (CL#03-3455), and may be freely circulated. Suggested citation:

# 

Mahaffy, P.R., Beaty, D.W., Anderson, M., Aveni, G., Bada, J., Clemett,
S., Des Marais, D., Douglas, S., Dworkin, J., Kern, R., Papanastassiou,
D., Palluconi, F., Simmonds, J. Steele, A., Waite, H., and Zent, A.
(2004). Science Priorities Related to the Organic Contamination of
Martian Landers. Unpublished white paper, 32 p, posted Nov., 2004 by the
Mars Exploration Program Analysis Group (MEPAG) at
http://mepag.jpl.nasa.gov/reports/index.html.

or

Mahaffy, Paul R. and 15 co-authors (2004), Science Priorities Related to
the Organic Contamination of Martian Landers. Unpublished white paper,
32 p, posted Nov., 2004 by the Mars Exploration Program Analysis Group
(MEPAG) at http://mepag.jpl.nasa.gov/reports/index.html.

1\. Introduction 2

2\. Organics of Interest and Contaminants of Concern 3

2.1 Sources of martian organic molecules 3

2.2 Transformation of organics on Mars 3

2.3 Contamination issues, driven by mission science goals 5

2.4 OCSSG definition of clean 5

2.5. Derivation of cleanliness thresholds for MSL 5

2.6 Sources of terrestrial organic contamination of Mars samples 7

2.6.1 Organic materials contained in spacecraft hardware 7

2.6.2 Personnel handling or exposure of instruments or\
spacecraft components 8

2.6.3 Microorganisms (dead or alive) 8

> 2.7 OCSS proposals regarding identification of potential contaminants
> of\
> concern and their thresholds 8

3\. Quantification of Contamination: 8

3.1 Analytical techniques 9

3.2 Hardware sampling 9

3.3 Typical contamination levels 9

3.4 Contamination Migration 10

3.5 Models of Chemical Migration 10

3.6 OCSS proposals regarding quantification of contamination and its
migration 11

4\. Contamination Mitigation 11

4.1 Identification of sensitive areas 11

4.2 Materials selection 12

4.3 Cleaning procedure examples 12

4.4 Cleaning procedures and planetary protection requirements 13

4.5 Primary system level cleaning requirements 13

4.6 Derived cleaning requirements 14

4.7 Designs that isolate sample acquisition and processing hardware 14

4.8 In situ operations and processing 14

4.9 Summary of OCSSG proposals for contamination mitigation 15

5\. Standards and Controls 15

5.1 The use of terrestrial organic materials in standards 15

5.2 Organic-free blank standards 15

#  5.3 Summary of OCSSG proposals for use of standards and controls 16

6\. Conclusions 16

7\. References 16

Appendix A. Extended list of contaminants\
Appendix B. Common spacecraft contaminants\
Appendix C. Organic Materials Inventory for the Mars Exploration Rovers\
Appendix D. Physical Transfer of Organic Contaminants from Hardware
Surfaces\
to Simulated Mars Soil

# 1. Introduction

A current goal of the Mars Exploration Program is to achieve an
understanding of the possible emergence and duration of life on that
planet. This demands an increasing focus on the quality of measurements
that address Astrobiology objectives. Continuing advances in instrument
technology lead to the possibility of measurements of increasing
sensitivity and selectivity. Thus the steps necessary to reduce the
potential impacts of terrestrial contamination on *in situ* Mars
measurements require increasing attention. The Mars Program Office at
NASA Headquarters chartered the Organic Contamination Science Steering
Group (OCSSG) to address this issue following the recommendation of the
Mars Exploration Program Analysis Group (MEPAG) at its September 2003
meeting \[MEPAG, 2003\]. The charter of the group was to define the
contamination problem and suggest plans and priorities for solution that
could provide direction for the engineering teams responsible for the
design, fabrication, assembly, and processing of Mars landed systems.
The group consisted of scientists conversant with a range of *in situ*
measurement techniques for organics and engineers familiar with Mars
lander designs as well as spacecraft cleaning and contamination
characterization techniques. This report is a summary of the analysis of
the OCSSG.

The primary focus of the study was organic contamination introduced into
those Mars samples that would be delivered to sensitive analytical
instruments after processing by lander acquisition and sampling devices.
It is recognized that requirements set by the Planetary Protection
Policy in effect for any specific mission only indirectly address the
larger question of the potential interference from terrestrial
contaminants during *in situ* measurements. Furthermore, we considered
certain non-organic molecular or particulate contaminants that might
also impact Astrobiology-focused measurements. The contamination issues
were considered most specifically in this report with reference to the
2009 Mars Science Laboratory (MSL) Mission, currently under definition.
However, the relevance to other lander missions including the Mars Scout
Phoenix Mission and a Next Decade Astrobiology Mission was also
considered by the OCSSG. Phoenix is presently under development for a
2007 launch \[Smith, 2003\] and a possible Next Decade Astrobiology
Mission has been described in very general terms by the Mars Program
Science Synthesis Group \[MPSSG, 2003\] as a candidate Astrobiology
focused mission that would employ the next generation of measurement
tools. Although the primary focus of the analysis of the OCSSG was on
the impact of terrestrial contamination, the issue of cross
contamination of organic material between different Mars samples was
also considered. Because strategies utilized by the Viking mission
successfully reduced terrestrial contamination, they served as valuable
reference points for the present study.

The OCSSG divided the issues highlighted in its Charter into four
primary areas of focus:

1.  Identify and quantify the contaminants of most concern with regard
    to their possible adverse impact on the goals of each lander
    mission,

2.  Understand methods of quantifying residual contamination, its
    abundance and transport during all stages of lander development and
    operation,

3.  Suggest possible contamination mitigation options, and

4.  Examine the use of controls and facility-provided standards to be
    analyzed by lander instruments after arrival at Mars.

As detailed in Sections 2 and 3 of this report, the first two items can
provide direction and contamination requirements for the engineering
teams that design, fabricate, and test the landers. For example, a
comprehensive contamination-monitoring plan during the development of
MSL can provide not only an understanding of the level of organics that
are transported to Mars in this mission, but also a documented reference
for future missions. Items 3 and 4 are addressed in Sections 4 and 5.
Section 4 of this report addresses strategies for contamination
mitigation. Success in the area of contamination mitigation is important
for Phoenix and is also likely to be key to achieving major goals of the
MSL and future astrobiology landed missions. Section 5 addresses the
possible use of standards and controls. Some residual contamination is
likely to be observed by sensitive instruments on the surface of Mars,
even with the best efforts at mitigation and the use of controls may
then be important for achieving definitive scientific conclusions.

# 2. Organics of Interest and Contaminants of Concern

**2.1 Sources of martian organic molecules:** The search for reduced
carbon species relevant to Astrobiology will be an important aspect of
the missions considered by the OCSSG. However, organic compounds in
near-surface materials on Mars may be derived not only from possible
biotic or prebiotic processes, but also from various abiotic processes
such as exogenous delivery from meteoritic or cometary material or
synthesis in hydrothermal systems. Furthermore, reduced carbon species
from any source will likely be transformed over time to some degree
through chemical processes, including the transformation to more highly
oxidized species. However, these mechanisms are presently not well
understood. The identification of the source of organic compounds that
might be discovered on or near the surface of Mars can be addressed by a
variety of investigations. These include identification of specific
molecules known to be associated with meteoritic sources, analysis of
the distribution of organic molecules in different oxidation states, the
determination of the molecular weight (mw) distribution in homologous
series of these molecules, and a determination of the ^13^C/^12^C and
D/H ratio in organic compounds (Kerridge, 1999, Cronin, 1993). For
example, the amino acid α-aminoisobutyric acid (AIB) found in some
meteorites, such as Murchison, is often used as a marker for
extraterrestrial amino acids, since this molecule is not found in
measurable amounts in sediments. The scientific objectives of MSL and
follow-on missions are not only to search for specific biomarkers, but
also to understand geochemical cycles that include reduced carbon
compounds. Very little is presently known about the distribution,
abundance, or chemical reaction products of reduced carbon-containing
compounds in near-surface materials on Mars, although aromatic
hydrocarbons, phenol, and benzonitrile have been detected by pyrolysis
of small samples of the martian meteorites EET A79001 and Nakhla
\[Sephton et al., 2002\]. Table 1 illustrates a range of molecular
classes and compounds that are potential contaminants. Appendix A
expands this list by giving estimates of contamination levels of concern
and first order estimates of the possibility of migration of the
contaminant to a sample delivered to an analytical instrument.

**2.2 Transformations of organics on Mars:** Although the Astrobiology
objectives will place a high priority on characterization of reduced
carbon compounds in samples collected for analysis, it is recognized
that several chemical processes that potentially exist in the martian
environment may transform these species. Models of such processes of
organic degradation fall into several categories and it is likely that
more than one mechanism operates. Each proposed mechanism has a
potentially different consequence for the fate of organics.

For example, hydrogen peroxide would be expected to selectively oxidize
organic compounds, resulting in the formation of species that may not
have been detected by the Viking GCMS, such as mellitic acid salts
(Benner 2000). Solar ultraviolet radiation may cause photolysis of
atmospheric species resulting in the formation of "odd-H" (H, OH, HO~2~,
and H~2~O~2~) compounds (e.g. Hunten, 1974, Barth et al. 1992).
Subsequent recombination of these reaction products may produce
oxidizing species that precipitate onto the surface.

Alternatively, superoxide radicals, which are more strongly oxidizing
than hydrogen peroxide, are generally responsible for \"deep oxidation\"
of organics, resulting in more complete oxidation (Yen et al., 1999;
Haber, 1996) and, possibly, the complete removal of organic material
from the surface of Mars (Chun et al. 1979). UV-silicate interactions
may produce radical species (Yen et al., 2000) directly in the silicate
matrices. The non-bridging oxygen defects resulting from broken Si-O
bonds are mobile, and can migrate through silicate lattices. The soil
and dust surfaces would then be strongly oxidizing, but the atmosphere
itself need not be oxidizing.

Other mechanisms require both UV and atmospheric oxidants. The free
radicals from radiation damage are highly reactive, and could easily
form semi-permanent complexes, such as such as perchlorates from
photolyzed, complexed halide compounds (Zent and McKay, 1994).

+---------------+-----------------+---+--------------+------------------+
| ### Tabl      |                 |   |              |                  |
| e 1. Contamin |                 |   |              |                  |
| ants of conce |                 |   |              |                  |
| rn for Mars l |                 |   |              |                  |
| anded mission |                 |   |              |                  |
| s (expanded i |                 |   |              |                  |
| n Appendix A) |                 |   |              |                  |
+---------------+-----------------+---+--------------+------------------+
| Molecular     | Examples        |   | Molecular    | Examples         |
| class         |                 |   | class        |                  |
+---------------+-----------------+---+--------------+------------------+
| ### C         | benzene,        |   | #            | Esters, ketones, |
| , H aromatics | toluene, higher |   | ## Carbonyl  | aldehydes and    |
|               | molecular       |   |              | their mw         |
|               | weight          |   |              | distributions    |
|               | aromatics, PAH  |   |              |                  |
+---------------+-----------------+---+--------------+------------------+
| **S, N, O     | furan,          |   | **Sulfonic,  | Methanesulfonic  |
| heterocyclic  | pyridine,       |   | phosphonic   | acid             |
| aromatics**   | pyramadine,     |   | acids**      |                  |
|               | benzothiophene  |   |              |                  |
+---------------+-----------------+---+--------------+------------------+
| **Carboxylic  | Alkyl &         |   | **Lipids and | HC chains, fatty |
| acids and     | aromatic acids, |   | d            | acids, fats,     |
| their salts** | fatty acids     |   | erivatives** | phospholipids.   |
|               |                 |   |              | Hopanes,         |
|               |                 |   |              | steranes         |
+---------------+-----------------+---+--------------+------------------+
| **Non         | Alkanes,        |   | **Sugars and | glucose          |
| aromatic      | alkenes (i.e.   |   | d            |                  |
| h             | isoprenoids     |   | erivatives** |                  |
| ydrocarbons** | such as         |   |              |                  |
|               | pristane,       |   |              |                  |
|               | phytane)        |   |              |                  |
+---------------+-----------------+---+--------------+------------------+
| **Nitrogen    | Amino acids,    |   | **Proteins** | Polar and        |
| containing    | amines, amides, |   |              | non-polar        |
| compounds**   | purines,        |   |              |                  |
|               | pyrmidines,     |   |              |                  |
|               | porphyrins      |   |              |                  |
+---------------+-----------------+---+--------------+------------------+
| **Alcohols**  | Methanol,       |   | **Nucleic    | DNA fragment     |
|               | higher          |   | acids,       |                  |
|               | molecular       |   | n            |                  |
|               | weight linear   |   | ucleotides** |                  |
|               | and branched    |   |              |                  |
|               | chain alcohols  |   |              |                  |
+---------------+-----------------+---+--------------+------------------+

**2.3 Contamination issues driven by mission science goals:** The OCSSG
considered contamination most specifically in the context of three
example missions.

(1) the recently selected Phoenix Scout Mission, is designed to land in
    what is predicted to be an ice-rich region and analyze near-surface
    and sub-surface samples. Organic contamination is of concern to this
    mission team, since a mass spectrometer is part of the payload. This
    instrument will search for organic molecules evolved from surface
    and near-surface samples and will also analyze atmospheric gases.

(2) The 2009 Mars Science Laboratory (MSL), presently under definition,
    is expected to carry out an ambitious search for organic molecules
    in a wide variety of locations that can be accessed by this lander.
    A powerful analytical laboratory is in the baseline for this mission
    with sample preparation using a facility acquisition and processing
    station. A concept for this station on the MSL is illustrated in
    Figure 1, taken from the Proposal Information Package \[MSL PIP,
    2003\] for this mission.

(3) A Next Decade Astrobiology Mission was defined by the Mars Planning
    Science Synthesis Group as a candidate Astrobiology-focused mission
    with life detection experiments as likely elements of the payload.
    The MEPAG Astrobiology Field Lab Science Steering Group further
    defined (Steele et al., 2004) the objectives of this mission. It is
    assumed that this mission might carry advanced extinct or extant
    life detection experiments that would be sensitive to even lower
    abundances of complex organic materials, and that stringent control
    of the terrestrial bioload will be critical to the success of this
    mission.

The specific contamination thresholds described in this report are
primarily directed toward MSL, although the Phoenix Mission Team may
consider implementation of elements of this approach as resources allow.
Contamination thresholds for future missions will need to be revisited
as measurement capabilities and contamination mitigation technologies
develop.

**2.4 OCSSG definition of clean:** Since analytical laboratory
instruments are expected to play a key role in identifying and
characterizing organic molecules, terrestrial contamination introduced
during sample acquisition and processing is a significant concern. The
instruments in the analytical laboratory of MSL will accept samples that
not only have contacted sample acquisition tools, but also have been
processed by crushing and grinding tools. However, contaminants on this
lander will not be of concern if they are not incorporated into these
samples above a certain threshold. Thus, the OCSSG adopted a
system-level definition of "a clean sample" as a sample that is
delivered to an instrument with LESS THAN a specific level of organic
contamination.

**2.5. Derivation of cleanliness thresholds for MSL:** Example levels of
cleanliness in samples delivered to analytical instruments as specified
for the MSL rover are given in Appendix A. These levels are based on
consideration of the science objectives for MSL and likely science
objectives for astrobiology-focused follow-on lander missions.

Contamination levels of concern can be derived from estimates of the
abundance of reduced organic material that is expected to be delivered
by meteorites to the surface of Mars and mixed into the regolith. For
depths of gardening from meters to a kilometer, reduced organic groups
such as aromatics or their oxidation products at mixing ratios of
hundreds of parts per billion to hundreds of parts per million are
expected \[Benner, 2000\]. However, in order to understand the
distribution of species within these groups and the effects of chemical
transformation processes on Mars, it is highly desirable to measure a
range of species to parts per billion (mass mixing ratio to the matrix).
Keeping terrestrial contamination to below 1-10 parts per billion in
Mars samples should allow significant scientific conclusions to be
reached concerning the fate of organic material delivered by meteorites.
The total molecular carbon contamination allowed could be substantially
higher (for example, 40 ppb) if the contamination by specific critical
species or classes was maintained at dependably constant levels.
Although extinct or extant life on Mars has the potential to leave
signature organic material in either much higher abundance than the
parts per billion levels discussed above, the OCSSG concluded that a
definitive search for such signatures could be implemented on MSL by
maintaining terrestrial contamination below levels of 1-10 ppb for
relevant biomarkers.

![](media/image1.png){width="6.622047244094488in"
height="4.3251968503937in"}The present state of the art for detection
thresholds for analysis of volatile organic compounds in meteoritic
materials in terrestrial laboratories can be as low as 10^-13^ mole/g
using gas chromatograph mass spectrometers and on the order of 10^-12^
to 10^-11^ mole/g for a single liquid chromatography analysis of amino
acids \[Glavin et al., 1999,2003\], although highly specific analysis
techniques may detect even smaller quantities (i.e. sub 10^-18^ mole for
immunochemical reactions \[Guomin et al., 2000\]). These detection
limits equate to sub parts per billion mixing ratios by mass.
Miniaturized laser desorption mass spectrometers developed for space
flight applications can detect several parts per billion by mass of
polyaromatic hydrocarbons. The OCSSG concluded that the thresholds
driven by the scientific goals of MSL were well within the capability of
*in situ* instruments that were likely to be selected for this mission.

**2.6 Sources of terrestrial organic contamination of Mars samples:**
Several potential sources of terrestrial contamination could adversely
impact the *in situ* search for organic molecules and their sources and
sinks on Mars. These include moderately volatile organic molecules that
might be released from materials used in spacecraft fabrication,
particulate material that might contain organic residues, and organic
molecules produced from the residual terrestrial bioload. Even with
careful cleaning of sample acquisition and processing systems, transport
of contaminants to these systems in various phases of the missions may
occur. These contaminants are of concern if they interfere with the
measurement of organic molecules that are targets of payload
instruments. Most terrestrial, reduced carbon containing species that
might be incorporated into a martian sample are a potential source of
interference with high quality *in situ* measurements.

***2.6.1 Organic materials contained in spacecraft hardware:*** Organic
compounds are utilized extensively in spacecraft hardware. Complex
mixtures of branched and straight chain aliphatic hydrocarbons are the
most common contaminants. Lubricants and pump oils found in many
industrial environments are sources of these compounds. These can
generally be removed with most common solvents (Freons, alcohol,
acetone). Silicones are also very commonly employed as lubricants,
materials, sealants and adhesives. Silicones can outgas or leach out of
silicone based polymers. Like aliphatic hydrocarbons, silicones exhibit
a broad range of molecular weights. The most common silicones are
polydimethylsiloxane and polymethylphenylsiloxane. This class of organic
contaminants is difficult to remove completely; although freon and
toluene are at least partially effective as solvents.

Salts of organic acids are used in mold release agents, soaps, silicone
polymer activators, and fluxes and are best removed by polar solvents
such as alcohols. In thermal vacuum systems the copper cold-finger may
react with hydrolyzed esters to form (green) organic copper salts.

Esters are found in plasticizers, pump oils, adhesives, polymer
degradation products and many other materials. Phthalates are common
contaminants.. Phthalate esters such as Bis 2-ethylhexyl phthalate (DOP)
are used to make vinyl plastics and in many other polymer formulations.
DOP is a common catastrophic contaminant often discovered after a
thermal vacuum processing. Acetone, methyl ethyl ketone (MEK), and
alcohol solvents are often used to remove these phthalate esters.

Epoxy is frequently used in spacecraft construction and consists of a
class of compounds with a range of molecular weights and
chemical/physical properties. These may have complex formulations and
can be a source of other compounds. Epoxy consists of a mixture of two
compounds that requires "curing", usually by adding a chemical catalyst
and applying heat. Curing is not 100 percent complete and uncured
components of epoxies can outgas or selectively leach a variety of
compounds from the structural materials to which they are applied. These
volatile products are generally amines and phenol ethers. The best
strategy for removing uncured epoxy is to treat or wipe surfaces with
solvents such as alcohol, acetone and aromatic solvents (e.g., toluene).
Cured epoxy is difficult to remove by common solvents.

Inorganic particulates can also be released from the spacecraft.
Metallic and device-shed particles can be released from the spacecraft
hardware either from wear or machining debris. Carbonates are used as
fillers in materials and are a major component of "water spots."
Carbonates are also encountered as a corrosion product from paints using
potassium silicate binders (micas). Inorganic particulates may adsorb
molecular contamination prior to their migration to other locations.

***2.6.2 Personnel handling or exposure of instruments or spacecraft
components:*** Manipulation of spacecraft elements often introduces a
variety of contaminants into the instruments and spacecraft components.
Fingerprints contain a complex mixture of compounds. These residues
consist mainly of high molecular weight, long-chain alkyl esters of
fatty acids while the more volatile fractions contain free fatty acids.
Fingerprints also contain sodium chloride, protein, and urea. Organic
acid salts can form when fingerprints react with some metallic surfaces.
Fingerprints can be removed by wiping with most common solvents (Freon,
alcohol, acetone, and MEK).

Some additional types of particulates can be introduced during handling
and construction. Cloth fibers such as cotton, nylon, polyester, lycra,
silk, cellulose etc. can be inadvertently introduced from a variety of
sources including clothing and cleaning wipes.

Bio-organic materials of concern include dead skin, hair, spores,
pollen, and organic wind-blown matter. These comprise the majority of
"dust." The Planetary Protection group at JPL monitors a crucial subset
of this vast class of materials with separate biological assays. The
remainder of dust consists of silicates that are commonly fine
components of soil. The composition is mainly fine quartz and mixed
silicates. These are also found in construction materials such as
wallboard, wood fibers, etc.

Exposure of spacecraft materials to smoke, smog and associated particles
can introduce polycyclic aromatic hydrocarbons and tars. Ablation of the
entry heat shield and propulsion chemicals may introduce additional
levels of contamination to the spacecraft during landing.

**2.6.3 Microorganisms (dead or alive):** Microorganisms contain a
complex mixture of organic compounds. Sterilization does not remove the
organic contaminants and therefore dead terrestrial organisms could
contribute to the analyzed organic material. A "typical" microbe weighs
approximately 10^-12^ g per cell and is comprised of 55% protein, 20%
RNA, 9% lipid and 3% DNA. Microbes, a small fraction of which are
spores, detected by planetary protection NASA standard methods, are
themselves only a fraction of the organic contamination on a spacecraft.
The current allowable level for Planetary Protection Level IVA is 300
spores per square meter with the total available bioburden of the
landing event to be less than 300,000 spores.

2.7 OCSSG proposals regarding identification of potential contaminants
of concern and their thresholds:

1.  The OCSSG proposes that each project adopt the "system" definition
    of clean given in Section 2.4 to assess the degree of terrestrial
    contamination in samples that are physically processed by sample
    handling mechanisms.

2.  The OCSSG proposes that each project consider maintaining a list of
    contaminants and their thresholds of concern such as that found in
    Appendix A, as a guide for both members of the lander development
    teams and the instrument providers.

# 3. Quantification of Contamination

Appendix B gives an overview of the contaminants, including their
functional groups that are often found on spacecraft surfaces prior to
launch. Appendix C lists organic materials that were used in MER. In
unusual cases, a spacecraft's payload includes instruments that can
measure specific contaminants . More typically, contamination is assayed
prior to launch and it is mitigated only if it might substantially
degrade the performance of the spacecraft or the key instruments.

**3.1 Analytical techniques:** Although a wide range of analytical
techniques can be used to analyze spacecraft contamination, the primary
methods for molecular contamination measurements use Fourier transform
infrared spectroscopy (FTIR), gas chromatograph mass spectrometry, or
ion chromatography. FTIR provides chemical functional group information
for quantitative analysis and qualitative identification of materials.
FTIR allows complex mixtures to be classified while still providing
quantitative information on chemical and spectroscopic effects. Time of
flight secondary ion mass spectrometry (TOF-SIMS) may be used to
supplement the above approaches by providing spatial information on
distribution of contamination allowing eluciation of outgassing or
contact contamination.

**3.2 Hardware sampling:** Organic molecular contamination may be
sampled using witness plates strategically positioned near in the
spacecraft or by directly sampling the hardware with solvents and porous
Teflon swabs. Solvents are carefully selected for compatibility with
hardware materials. The solvents used include Freon TF, 2-propanol,
ethanol, methanol, hexane, dichloromethane, acetone, and various
azeotropic combinations. Proper use of solvents removes most residues
that may have outgassed and collected on critical surfaces. Very high
molecular weight, cross-linked materials are not readily removed by
solvents; however, these materials tend to neither migrate nor outgas
appreciably. The monomolecular contaminant layer may strongly bind to
its host surface and is not easily removed in most cases. Here, the
distinction between contamination and corrosion is blurred.

Contamination control methods on Earth can establish more quantitatively
the transfer of molecular contamination from a source material or
contaminated surface to a sensitive surface by testing the parent
material at its assumed operational temperatures. The outgassing or
off-gassing constituent flux (contaminant mass per unit collection area
per time) can be measured with quartz crystal microbalances (QCM)
operating at the assumed temperatures mimicking those of the sensitive
hardware. The mass of molecular contamination that will collect on the
sensitive surfaces can be estimated. A QCM that operates at 15 MHz
(using the principle of beat frequency change between a reference
crystal and the collection crystal) can detect 1.56 ng/cm^2^ of
collected material. Under optimal conditions, transferred molecular
contamination can be quantified at this level.

**3.3 Typical contamination levels:** The amount of molecular
contamination found on nominal spacecraft surfaces is generally in the
range of 0.05 to 0.3 micrograms per square centimeter (μg/cm^2^). A
level of 1.0 μg/cm^2^ equates to an average thickness of 10 nanometers
(nm) for a residue having a density of 1.0 g/cm^3^. A rule of thumb is
that a monomolecular layer is about 1 nm (0.1 μg/cm^2^). After system
thermal vacuum testing, contaminants migrate, create a more uniform
distribution on accessible surfaces, and, under optimal circumstances,
lower the levels of contaminants in areas of critical importance.

Microbial contamination of space craft has been measured in several
surveys most recently by Venkateswaran et al., (2001). This research has
shown typical bioburdens of spores in the range of 10^6^ m^-2^. This
would approximately indicate a contamination level in the range of
\~0.1ppb of carbon from bacterial compounds which can be further divided
into the relevant classes of molecules to be detected. This does not
represent a significant problem to the levels of contamination
restriction needed for the instrumentation suggested above, if
contamination stays at this level. It is only when these organisms find
food and nutrients to grow that this will lead to problems. The most
likely place for this to happen is in any place harboring liquid water
and shielded from external radiation or upon landing on Mars. Further
studies to understand the possible niches microbes may proliferate in on
spacecraft hardware are a necessity. This need has been identified in
several studies including the NRC Signs of Life Report \[NRC, 2002\],
updated MEPAG documents, and the 1992 report of the National Research
Council\'s (NRC\'s) Space Studies Board, [*Biological Contamination of
Mars: Issues and
Recommendations*](http://www7.nationalacademies.org/ssb/an92ch3), \[SSB,
1992\] that rapid *in situ* methods for measurement of contamination be
developed and implemented in replacement of the reliance on culturing
methods. Such methods as rapid immunoassays, enzymes assays, ATP
detection, RT-PCR etc., can give real time data on the bioload of a
space craft assembly. This will allow faster more sensitive and
efficient monitoring of bioloads, testing of the efficiency of
sterilization procedures and secondary site specific sterilization of
hotspots formed after any primary space craft sterilization.

**3.4 Contamination Migration:** Molecular cleanliness does have a time
dependency due to migration of contaminants. Immediately after cleaning,
the surface will begin to collect molecular and particulate
contamination. Parts cleaned to a very high degree, such as the sample
path on the Viking lander, were cleaned to the submonolayer level. At
the other extreme, surfaces of any kind left exposed to Class 100,000
cleanroom air will collect particulates over time. This can be minimized
by mitigation approaches such as conducting assembly in more stringent
class cleanrooms and housing components and systems in particle and
vapor barriers. In the extreme case of the Hubble Wide Field Planetary
Camera, recontamination is limited to a rate of 47 nanogram/ cm^2^/
month and the cameras undergo a monthly decontamination cycle that
reduces the level to 1 nanogram/cm^2^.

The transfer of particulate contamination occurs particularly through
extensive vibration during the launch and landing operations. For this
reason, the entire Viking payload was encased in a contamination barrier
that was removed in space after launch. Sensitive volumes should be
manufactured with non-debris producing materials in clean environments
(ISO Class 5, Class 100) and maintained to specific clean levels (PCL
50) prior to enclosure.

Molecular contamination that has accumulated on tools that physically
contact martian materials can be directly transferred during sample
collection and manipulation. In order to better understand the fraction
of contamination that might be transferred during the required sample
manipulation, laboratory studies were implemented by OCSSG members at
JPL to model these operations. The variables in these studies were the
tool materials, the sample analogues, the contaminants, and the
temperature. The results of these studies are fully described in
Appendix D and provide a basis for estimates of sample/tool organic
contamination exchange during collection and manipulation of samples
such as will take place during the upcoming Phoenix mission.

**3.5 Models of Chemical Migration:** Contaminants will migrate at
different rates in the 6 to 10 millibar pressure of the Martian
atmosphere than in the high vacuum of space. Contamination models
developed for space environments should be modified to account for the
higher pressure regime of the martian surface and also the range of
thermal environments encountered by the lander over the course of the
mission.

**3.6 OCSS proposals regarding quantification of contamination and its
migration:**

1.  Contamination monitoring should be employed in lander missions that
    seek to measure reduced carbon compounds and their alteration
    products on Mars. An important focus of the analysis, during all
    phases of the development cycle, should be on molecular
    contamination and its transport.

2.  Samples of organic-containing materials, such as plastics and
    epoxies, employed in spacecraft fabrication should be archived for
    possible use in studies after MSL organic detection studies are
    underway. This archive should include different batches of the same
    component when necessary.

3.  Although the tools to monitor organic contamination are largely in
    place with a focus on quantification of molecular functional groups,
    these tools may need to be enhanced with more detailed molecular
    identification if contamination is determined to be above a desired
    threshold.

4.  DNA assays should be carried out over the course of the development
    for selected critical elements of MSL.

5.  Rapid *in situ* methods of bioload monitoring should be implemented
    and protocols established to ensure that these methods replace the
    older culture based criteria.

6.  The relevance of existing contamination transport models to predict
    migration of contaminants during long-term MSL operations should be
    assessed. The feasibility of adapting these models to pressure and
    temperature conditions present on the surface of Mars should be
    evaluated.

7.  The primary analysis of contamination levels on the surface of Mars
    will be derived from measurements made by the selected payload.
    After this selection, the MSL team should evaluate the cost/benefit
    trade of including simple sensors such as quartz microbalance
    devices for contamination monitoring during cruise and after
    landing.

# 4. Contamination Mitigation

The process of contamination mitigation involves many steps that start
with the design of key isolation barriers and include fabrication
material selection, spacecraft and instrumentation cleaning,
identification of key contaminant levels throughout the development
project, and monitoring a subset of the contaminant levels during the
mission. The most critical areas are those that come into physical
contact with Mars solid phase or atmospheric samples. These areas
require higher standards of cleanliness and more attention to monitoring
of contaminants. However, due to the possibility of contamination
migration from other parts of the spacecraft over the course of
development and implementation of a lander mission, great attention must
also be paid to the cleanliness of all elements of a lander system and
the assembly and test environments to which each lander is exposed.

**4.1 Identification of sensitive areas:** Surfaces of sample
acquisition and processing mechanisms, or surfaces in close proximity to
these surfaces, have the highest potential to compromise the scientific
detection of organic material in the Martian soil by terrestrial
contamination. It is important that the sensitive areas be identified
early in the design of a lander such as MSL. These areas should then be
isolated from terrestrial organic sources to the greatest extent
possible during all on ground integration and test operations as well as
during flight and operation. Selected surfaces should be designed to
operate at elevated temperatures to reduce their collection of
terrestrial contaminants. **The spacecraft design should minimize, to
the greatest extent possible, the total surface area, volume and
geometric complexity of those regions where samples are processed.**

**4.2 Materials selection**: Consideration should be given in materials
selection to reduction or elimination of materials that produce the
molecular compounds identified in Table 1. Although this may not always
be possible, attention should be paid to the quantity and location of
these materials. Of particular importance, for example, are materials in
the MSL Analytical Laboratory instruments and the MSL sample acquisition
and processing mechanisms. The information on materials throughout the
MSL system should be specified as accurately as possible as it will then
be used to develop contamination models of the spacecraft. This
consideration should extend not only to an examination of materials
lubricants, epoxies, and resins, but also to selection of solvents used
to clean and reduce the bioload of spacecraft materials. For example, if
a solvent, such as isopropyl alcohol, or an oxidizing agent, such as
hydrogen peroxide, is used to clean, sample, or reduce the bioload on
spacecraft materials, consideration should be given to the residue from
that material that might remain on the lander at Mars and migrate to a
sample. Materials in sensitive areas should generally meet total mass
loss (TML) and volatile condensable material (VCM\_ levels of less than
1.0% and 0.1% respectively.

**4.3 Cleaning procedure examples:** Organic contamination comprises a
significant fraction, usually over 50%, of both the volatile (film) and
non-volatile (particulate) portion of the spacecraft hardware surface
contamination. Spacecraft are typically cleaned to a non-volatile
residue cleanliness level of 1 microgram/ cm^2^ which is known as level
A. Level A10 is 0.1 microgram/ cm^2^, and is considered extremely clean
for most missions. One of the most extreme cases of flight hardware
surface cleanliness is the Viking sample handling hardware. The sample
path hardware was cleaned to 1 nanogram/cm^2^ and the sample path
hardware was sealed and pressurized after cleaning to protect against
recontamination. The following techniques serve to clean or reduce
organic contamination:

-   **Precision cleaning** is a general name for a process that is
    targeted at removing both particles and molecular films. It consists
    of a series of steps beginning with wiping gross contamination off
    the article, following by a series of rinses with organic solvents
    and aqueous rinses with or without ultra sonic treatment. The test
    article is then subjected to a Freon vapor degreasing process,
    followed by a final rinse. A final isopropyl alcohol rinse is
    performed and the rinse is analyzed for particles shed. This process
    commonly achieves level 100 cleanliness, which equates to1 particle
    /ft^2^ of 100 micrometers diameter (IEST-STD-CC1246D). Other
    treatments that are less harsh to sensitive plastics and polymers
    are also being developed. These include chemical, gamma and beta
    sterilization and RF plasma or E-beam treatments that may provide
    for better removal of organics in some cases.

-   **The "thermal bakeout"** is a process by which spacecraft
    components that are known to outgas organic vapor are treated by
    heat to reduce the subsequent outgassing rate of the process at room
    temperature. "Typical" bakeouts can range from 70^o^C to 105^o^C and
    can last from 72 to over 160 hours, depending on the material.

-   **Repeated wipes** with clean room cloths saturated with isopropyl
    or ethyl alcohol remove molecular contamination during the course of
    spacecraft assembly. Both the flight hardware and ground support
    equipment are subjected to this treatment. The isopropyl alcohol
    method is the only method that has been evaluated for its ability to
    remove bacterial spores from a surface. While there is considerable
    practical experience with cleaning spacecraft materials, none of the
    above methods has been systematically studied with regard to ability
    to remove the organics appearing on the reports list generated by
    the OCSSG.

-   **The cleanroom** itself is a cross contamination mitigation tool. A
    "typical" aerospace cleanroom is class 100,000, i. e., contains
    100,000 or fewer particles of 0.5 microns in diameter per cubic foot
    of air. In practice, a clean room classified at this level will for
    the majority of the time maintain particle counts at levels that are
    more than two orders of magnitude lower. The most extreme case of
    flight hardware assembly environment, sample collection hardware
    flown on Genesis was cleaned and assembled in a class 10 cleanroom
    that contained only one 10 0.5 micron size particles per cubic foot
    of air. This required that the personnel be isolated in clean suits
    during the assembly process.

**4.4 Cleaning procedures and planetary protection requirements:**
Current planetary protection regulations specify residual levels of
viable aerobic spores per square meter of spacecraft surface. Since
procedures that address this requirement do not directly address removal
of organic contamination produced from either synthetic materials or
non-viable spores, these are not considered relevant by the OCSSG for
the proposals of this study.

**4.5 Primary system level cleaning requirements:** The OCSSG proposes
the primary system level requirements specified in Table 2. Solid phase
samples delivered to analytical instruments for organic and molecular
analysis should contain less than the specified amounts of example
organic contaminants.

+--------------------------------+---+---+------+------+----+-------------+
| **Table 2. Maximum amount of   |   |   |      |      |    |             |
| contamination in nanograms     |   |   |      |      |    |             |
| (ng) that can be transferred   |   |   |      |      |    |             |
| to organic and molecular       |   |   |      |      |    |             |
| analysis experiments prior to  |   |   |      |      |    |             |
| their delivery to the          |   |   |      |      |    |             |
| instruments.**                 |   |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
|                                |   |   | **ng |      | *  |             |
|                                |   |   | / g  |      | *N |             |
|                                |   |   | samp |      | ot |             |
|                                |   |   | le** |      | es |             |
|                                |   |   |      |      | ** |             |
+--------------------------------+---+---+------+------+----+-------------+
| ### Be                         |   |   | 8    |      | M  |             |
| nzene or aromatic hydrocarbons |   |   |      |      | SL |             |
|                                |   |   |      |      | wi |             |
|                                |   |   |      |      | ll |             |
|                                |   |   |      |      | de |             |
|                                |   |   |      |      | li |             |
|                                |   |   |      |      | ve |             |
|                                |   |   |      |      | ry |             |
|                                |   |   |      |      | a  |             |
|                                |   |   |      |      | pp |             |
|                                |   |   |      |      | ro |             |
|                                |   |   |      |      | xi |             |
|                                |   |   |      |      | ma |             |
|                                |   |   |      |      | te |             |
|                                |   |   |      |      | ly |             |
|                                |   |   |      |      | 5  |             |
|                                |   |   |      |      | g  |             |
|                                |   |   |      |      | of |             |
|                                |   |   |      |      | sa |             |
|                                |   |   |      |      | mp |             |
|                                |   |   |      |      | le |             |
|                                |   |   |      |      | to |             |
|                                |   |   |      |      | t  |             |
|                                |   |   |      |      | he |             |
|                                |   |   |      |      | pr |             |
|                                |   |   |      |      | oc |             |
|                                |   |   |      |      | es |             |
|                                |   |   |      |      | si |             |
|                                |   |   |      |      | ng |             |
|                                |   |   |      |      | s  |             |
|                                |   |   |      |      | ys |             |
|                                |   |   |      |      | te |             |
|                                |   |   |      |      | m. |             |
|                                |   |   |      |      |    |             |
|                                |   |   |      |      | In |             |
|                                |   |   |      |      | di |             |
|                                |   |   |      |      | vi |             |
|                                |   |   |      |      | du |             |
|                                |   |   |      |      | al |             |
|                                |   |   |      |      | e  |             |
|                                |   |   |      |      | xp |             |
|                                |   |   |      |      | er |             |
|                                |   |   |      |      | im |             |
|                                |   |   |      |      | en |             |
|                                |   |   |      |      | ts |             |
|                                |   |   |      |      | m  |             |
|                                |   |   |      |      | ay |             |
|                                |   |   |      |      | r  |             |
|                                |   |   |      |      | eq |             |
|                                |   |   |      |      | ui |             |
|                                |   |   |      |      | re |             |
|                                |   |   |      |      | on |             |
|                                |   |   |      |      | ly |             |
|                                |   |   |      |      | a  |             |
|                                |   |   |      |      | f  |             |
|                                |   |   |      |      | ew |             |
|                                |   |   |      |      | mi |             |
|                                |   |   |      |      | ll |             |
|                                |   |   |      |      | ig |             |
|                                |   |   |      |      | ra |             |
|                                |   |   |      |      | ms |             |
|                                |   |   |      |      | of |             |
|                                |   |   |      |      | sa |             |
|                                |   |   |      |      | mp |             |
|                                |   |   |      |      | le |             |
|                                |   |   |      |      | f  |             |
|                                |   |   |      |      | or |             |
|                                |   |   |      |      | t  |             |
|                                |   |   |      |      | he |             |
|                                |   |   |      |      | ir |             |
|                                |   |   |      |      | an |             |
|                                |   |   |      |      | al |             |
|                                |   |   |      |      | ys |             |
|                                |   |   |      |      | is |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Carbonyl and hydroxyl        |   |   | 10   |      |    |             |
| containing compounds**         |   |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Amino acids**                |   |   | 1    |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Amines, or amides**          |   |   | 2    |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Non-aromatic hydrocarbons**  |   |   | 8    |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **DNA**                        |   |   | 1    |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Total reduced carbon**       |   |   | 40   |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| **Assumptions**: State of      |   |   |      |      |    |             |
| organic cleanliness can be     |   |   |      |      |    |             |
| assessed by analyzing specific |   |   |      |      |    |             |
| representative molecules.      |   |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| ### Table 3. Ex                |   |   |      |      |    |             |
| ample of derived requirements  |   |   |      |      |    |             |
| on cleaning of lander surfaces |   |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| Lander element                 |   | C |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | a |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | i |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | R |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | q |      |      |    |             |
|                                |   | u |      |      |    |             |
|                                |   | i |      |      |    |             |
|                                |   | r |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | m |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | t |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| General surfaces of the        |   | M |      |      |    |             |
| spacecraft carrying organics   |   | u |      |      |    |             |
| detectors                      |   | s |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | m |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | o |      |      |    |             |
|                                |   | r |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | x |      |      |    |             |
|                                |   | c |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | d |      |      |    |             |
|                                |   | C |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | a |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | i |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | L |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | v |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | 1 |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| General sample handling and    |   | M |      |      |    |             |
| processing facility surfaces   |   | u |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | m |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | o |      |      |    |             |
|                                |   | r |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | x |      |      |    |             |
|                                |   | c |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | d |      |      |    |             |
|                                |   | C |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | a |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | i |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | L |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | v |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | 2 |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| Specific sample handling       |   | M |      |      |    |             |
| elements coming in direct      |   | u |      |      |    |             |
| contact with samples           |   | s |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | m |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | t |      |      |    |             |
|                                |   | o |      |      |    |             |
|                                |   | r |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | x |      |      |    |             |
|                                |   | c |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | d |      |      |    |             |
|                                |   | C |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | a |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | i |      |      |    |             |
|                                |   | n |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | s |      |      |    |             |
|                                |   | L |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | v |      |      |    |             |
|                                |   | e |      |      |    |             |
|                                |   | l |      |      |    |             |
|                                |   | 3 |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| ###                            |   |   |      |      |    |             |
|  Cleanliness Level Definitions |   |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
|                                | 1 |   |      | 2    |    | 3           |
+--------------------------------+---+---+------+------+----+-------------+
| Non-volatile residue (NVR)     | 5 |   |      | 10   |    | 1           |
| Contamination                  | 0 |   |      |      |    |             |
| (nanograms/cm^2^)              | 0 |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| Particulate cleanliness level  | 4 |   |      | 200  |    | 25          |
| (PCL)                          | 0 |   |      |      |    |             |
|                                | 0 |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| Outgassing Flux (ng/cm^2^ hr)  | 1 |   |      | 10   |    | 1           |
|                                | 0 |   |      |      |    |             |
|                                | 0 |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+
| Bio-organic proxy molecule(s)  | T |   |      | TBD  |    | TBD         |
|                                | B |   |      |      |    |             |
|                                | D |   |      |      |    |             |
+--------------------------------+---+---+------+------+----+-------------+

**4.6 Derived cleaning requirements:** The primary requirements will
lead to derived requirements for general cleaning of spacecraft
surfaces. Although these may be modified as the fidelity of
contamination migration models increases, example requirements are given
in Table 3.

**4.7 Designs that isolate sample acquisition and processing hardware:**
Contamination barrier technology involves cleaning selected spacecraft
hardware to a specified degree and then encasing it in a lightweight
barrier material for launch and transit to the martian surface. The
contamination barrier is mechanically breached in a manner that allows
the protected instrument to operate. Biobarriers have traditionally been
envisioned as particle barriers, not vapor barriers because of the need
to allow the pressure inside and out to equilibrate during launch and
landing. One such approach incorporates a non-breathable Mylar film in
conjunction with a HEPA filter to enable the structure to breath.

Another uses Tyvek, a woven fiber of polyethylene, which is a 99%
effective barrier and is breathable. In general, the current biobarrier
technology has not been characterized with respect to the specific
compounds of concern. Issues to be addressed with contamination barriers
to protect scientific investigations of organic molecules are the
shedding of particles and outgassing of the materials from which the
biobarrier is made as well as diffusion of volatile species through the
barrier. These considerations may result in the adoption or development
of more suitable materials than those mentioned above. Demonstration of
the effectiveness of cleaning systems to remove compounds and of
barriers to prevent their transport to sensitive instruments is needed.

**4.8 *In situ* operations and processing:** A number of operational and
processing approaches may mitigate the impact of terrestrial
contamination on the desired measurements. For MSL, dilution of samples
by processing multiple samples through the acquisition, crushing, and
grinding systems prior to delivery of samples to the experiments in the
analytical laboratory could provide a substantial reduction in the level
of contamination delivered to analytical laboratory instruments. The
ability to bake sensitive areas of the sample crushing system might also
be studied as a method of removing collected organic compounds.

Other operational mitigation strategies that should be studied during
the MSL development phase include processing solid phase samples at
night when various lander elements are colder and outgassing less or
obtaining atmospheric samples in a lander orientation that places the
inlet tubes upwind from most lander elements.

The cost vs. benefit should be established for such operational
contamination mitigation strategies.

4.9 Summary of OCSSG proposals for contamination mitigation:

1.  Success in contamination mitigation will require a multi-faceted
    approach. Attention must be paid to material selection, and cleaning
    procedures as well as fabrication and assembly procedures.

2.  Contamination barriers for sensitive items should be studied early
    in the design of MSL.

3.  The sample collection and analysis operating plan should take
    contamination mitigation concerns into account.

4.  Contamination monitoring through the use of witness plates and other
    methods should be used in all phases of hardware development for MSL
    so that a comprehensive understanding of organic contaminants and
    their levels can be realized. A subset of the witness plates should
    be archived until the MSL mission is complete for possible analysis,
    in terrestrial laboratories, with different analytical techniques if
    warranted by the results of *in situ* measurements.

5.  Additional technologies for sterilization and cleaning of space
    craft such as RF plasma and E-beam technologies should be studied.

# 5. Standards and Controls

Even with rigorous contamination control some level of organic
contamination will be present in the samples delivered to the analytical
instruments on a surface lander. The OCSSG considered the possibility of
employing facility-provided standards for MSL as a method of quantifying
residual contamination.

**5.1 The use of terrestrial organic materials in standards:** Two
possibilities were considered for facility-provided standards: (1)
employing blank standards free of organic contamination and (2)
employing standards containing one or more selected organic molecules.
The use of standards containing terrestrial organic material might
enable the performance of the instruments of the Analytical Laboratory
to be assessed over the duration of the mission. However, the OCSSG
concluded that **the potential pitfalls of bringing facility standards
containing organic molecules from Earth outweigh the benefits.** The
potential for contamination of the spacecraft by organic standards might
neutralize the ability of the mission to demonstrate conclusively that
it has indeed detected organic carbon on Mars.

**5.2 Organic-free blank standards:** The potential benefits of
employing an organic-free blank to assess the extent of migration of MSL
molecular contamination into the sample acquisition and sampling systems
could be substantial. In the operations dedicated to sampling the
blanks, organic-free material from Earth would pass along all or much of
the sample processing chain and be delivered to the organic detection
instruments in the analytical laboratory. These measurements would then
quantify the extent of molecular contamination migration into the sample
acquisition and processing mechanisms. The blank material would
subsequently be purged from the sample processing elements by repeated
processing of Mars samples through the system. The blank material would
ideally be a material that in any case would itself be easily
distinguishable from Martian samples. The primary objective of the
analysis of the facility provided blank would be to assess the degree of
molecular contamination of the elements of the sample acquisition and
processing system. All other standards would be implemented as necessary
by the individual instruments.

5.3 Summary of OCSSG proposals for use of standards and controls:

1.  The MSL Mission should consider implementation of a facility level
    use of organic-free blank standards to assess the degree of residual
    organic contamination present on surfaces that come in contact with
    Mars samples delivered to instruments of its analytical laboratory.
    While this proposal is supported by a majority of the OCSSG, a
    minority view of the OCSSG is that the expense of this approach and
    the possibility of contamination of MSL instruments that do not
    focus on organic analysis make this implementation undesirable.

2.  Any other standards desired for instrument calibration should be the
    responsibility of the individual investigations and should not be
    provided as a MSL facility.

# 6. Conclusions

Upcoming missions will directly address the nature of the source and
processing of reduced carbon containing species on Mars through
sensitive molecular analysis experiments not attempted since the Viking
Mission in 1976. These measurements are expected to extend our
understanding of the possibility for present or past life on that
planet. Only careful attention to the reduction and quantification of
terrestrial organic species brought to Mars on these lander systems will
insure that definitive conclusions can be made regarding organic
compounds indigenous to that planet.

# 7. References

Barth, C.A., A.I.F. Stewart, S.W. Bougher, D.M. Hunten, S.J. Bauer, A.F.
Nagy, Aeronomy of the current Martian atmosphere, in Mars, 1054-1089
(1994).

Benner, S.A., Devine, K.G., Matveeva, L.N., and Powell, D.H. The missing
organic molecules on Mars, PNAS, 97, 2425-2430, (2000).

Chun, S.F.S, K.D. Pang, J.M. Ajello, Photocatalytic oxidation of organic
compounds in Murchison meteorite under simulated martian conditions,
2^nd^ International Mars Conference Proceedings, 15 (1979).

Cronin, J.R. and Chang, S., "Organic matter in meteorites: Molecular and
isotopic analyses of the Murchison meteorite", In: The Chemistry of
Life's Origins, Kluwer, 209-258, (1993).

Glavin, D.P., G. Matrajt, J.L. Bada, Reexamination of amino acids in
Antarctic micrometeorites, Advances in Space Research, 2003 (in press).

Glavin, D.P., J.L. Bada, K.L.F. Brinton, and G.D. McDonald, Amino acids
in the Martian meteorite Nakhla, Proc. Natl. Acad. Sci, 96, 8835-8838,
(1999).

Guomin S., W. Huang, S. J. Gee, B. A. Buchholz, J. S. Vogel and B. D.
Hammock, Isotope-labeled immunoassays without radiation waste. PNAS 97
2445 -- 2449, (2000).

Kerridge, J., "Formation and processing of organics in the early solar
system", Space Science Reviews 90, 277-288 (1999).

MEPAG,
<http://mepag.jpl.nasa.gov/meeting/mepag-letter-10-11sep03311.pdf>
(2003).

MSL PIP <http://centauri.larc.nasa.gov/msl/PIP-Drft_FBO-RevA-031113.pdf>
(2003).

MSPSG,
<http://mepag.jpl.nasa.gov/reports/Mars_Preliminary_Exploration_Options.doc>
(2003)

NRC (National Research Council Report), Signs of Life: A Report based on
the April 2000 Workshop on Life Detection Techniques, National Academies
Press (2002).

Sephton, M.A., I.P. Wright, I. Gilmour, J.W. de Leeuw, M. M. Grady, C.T.
Pillinger, High molecular weight organic matter in martian meteorites,
Planetary and Space Science 50, 711-716 (2002).

Smith, P. "The Phoenix Scout Mission", 34^th^ Annual Lunar and Planetary
Science Conference, 1855 (2003).

SSB (Space Studies Board), Biological Contamination of Mars: Issues and
Recommendations, Task Group on Planetary Protection, National Academies
Press, (1992).

Steele, A., D. Beaty and 20 members Science Steering Group, Findings of
the Astrobiology Field Lab Science Steering Group,
<http://mepag.jpl.nasa.gov/reports/index.html> (2004).

Venkateswaran, K. M. Satomi, S. Chung, R. Kern, R. Koukol, D. Basic, and
D.C. White, Molecular microbial diversity of a spacecraft assembly
facility. *Syst Appl Microbiol* 24, 311-320. (2001).

Yen, A.S., B. Murray, G.R. Rossman, F.J. Grunthaner, Stability of
hydroxylated minerals on Mars: A study of the effects of exposure to
ultraviolet radiation, JGR 104, 27,031 (1999).

Zent, A.P., C.P. McKay, The chemical reactivity of the martian soil and
implications for future missions, Icarus 108, 146-157 (1994).

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 16%" />
<col style="width: 7%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 20%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="10"><h2
id="appendix-a.-example-potential-contaminants-from-solid-phase-samples-including-soils-rocks-or-samples-with-high-ice-content">Appendix
A. Example Potential Contaminants from Solid Phase Samples Including
Soils, Rocks, or Samples with High Ice Content</h2></td>
</tr>
<tr class="even">
<td><strong>Molecular class</strong></td>
<td><strong>Examples</strong></td>
<td><blockquote>
<p><strong>Scientific<br />
interest</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Exogenous or terrestrial source likely</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Detection goal</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Amount<br />
on lander</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Migration concern</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Concern level</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Species to monitor</strong></p>
</blockquote></td>
<td><strong>Notes</strong></td>
</tr>
<tr class="odd">
<td><h2 id="c-h-aromatics-1">C, H aromatics</h2></td>
<td>Benzene</td>
<td>VH</td>
<td>E T</td>
<td>ppb</td>
<td>H</td>
<td>H</td>
<td>H</td>
<td>Y</td>
<td>Outgassing from coatings, laminates etc. even after cleaning</td>
</tr>
<tr class="even">
<td></td>
<td>PAH’s</td>
<td>VH</td>
<td>E T</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td><strong>S,N, O heterocyclic aromatics</strong></td>
<td>furan, pyridine, pyramadine, benzothiophere</td>
<td>M</td>
<td>E T</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td>Functional group screening may be adequate to test for these species
during development</td>
</tr>
<tr class="even">
<td><strong>carboxylic acids and their salts</strong></td>
<td>alkyl &amp; aromatic acids, fatty acids</td>
<td>VH</td>
<td>E T</td>
<td>10 ppb</td>
<td>M +</td>
<td>L</td>
<td>M</td>
<td></td>
<td>Functional group screening</td>
</tr>
<tr class="odd">
<td><strong>non aromatic hydrocarbons</strong></td>
<td>alkanes, alkenes, atmospheric methane</td>
<td>H</td>
<td>E T</td>
<td>ppb</td>
<td>H</td>
<td>H</td>
<td>H</td>
<td>Y</td>
<td>Outgassing of more volatile members of this class likely. If
significant contamination, MW distribution desired.</td>
</tr>
<tr class="even">
<td></td>
<td>hopanes, steranes</td>
<td>L</td>
<td>T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td><strong>nitrogen containing compounds</strong></td>
<td>racemic amino acids, NH<sub>3</sub>, HCN</td>
<td>VH</td>
<td>E</td>
<td>sub ppb</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td>Y</td>
<td>Functional group screening will identify amines and amino acids if
they are present over a threshold</td>
</tr>
<tr class="even">
<td></td>
<td>L or R enhanced amion acids</td>
<td>VH</td>
<td>T</td>
<td>ppb</td>
<td>M</td>
<td>L</td>
<td>M</td>
<td></td>
<td>Functional group screening will identify amines and amino acids if
they are present over a threshold</td>
</tr>
<tr class="odd">
<td></td>
<td>amines</td>
<td>VH</td>
<td>E T</td>
<td>ppb</td>
<td>M</td>
<td>L</td>
<td>M</td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>amides</td>
<td>M</td>
<td>E T</td>
<td>ppm</td>
<td>M</td>
<td>L</td>
<td>M</td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>purines, prymidines</td>
<td>H</td>
<td>E T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>porphyrins</td>
<td>L</td>
<td>E T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td><strong>Proteins</strong></td>
<td>Polar &amp; non polar</td>
<td>M</td>
<td>T</td>
<td>ppm</td>
<td>M</td>
<td>L</td>
<td>M</td>
<td></td>
<td>Breakdown products of greatest concern</td>
</tr>
<tr class="even">
<td colspan="10"><h2
id="appendix-a-continued.-example-potential-contaminants">Appendix A
(continued). Example Potential Contaminants</h2></td>
</tr>
<tr class="odd">
<td><strong>Molecular class</strong></td>
<td><strong>Examples</strong></td>
<td><blockquote>
<p><strong>Scientific interest</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Exogenous or terrestrial source likely</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Ddetection goal</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Amount<br />
on lander</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Migration concern</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Concern level</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Species to monitor</strong></p>
</blockquote></td>
<td><strong>Notes</strong></td>
</tr>
<tr class="even">
<td><strong>Lipids and derivatives</strong></td>
<td>HC chains, fatty acids, fats, phospholipids</td>
<td>L</td>
<td>T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td>Molecules of this and related classes could become important for
next decade mission</td>
</tr>
<tr class="odd">
<td></td>
<td>pristine, phytane</td>
<td>M</td>
<td>T</td>
<td>ppb</td>
<td>H</td>
<td>H</td>
<td>H</td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td><h2 id="sugars-derivatives">Sugars &amp; derivatives</h2></td>
<td></td>
<td>L</td>
<td>T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td>Molecules of this and related classes could become important for
next decade mission</td>
</tr>
<tr class="odd">
<td><strong>Carbonyl compounds</strong></td>
<td>Esters, ketones, aldehydes etc.</td>
<td>H</td>
<td>E T</td>
<td>ppm</td>
<td>H</td>
<td>H</td>
<td>H</td>
<td>Y</td>
<td>These compounds could be particularly difficult to separate from
terrestrial contamination</td>
</tr>
<tr class="even">
<td><strong>Alcohols</strong></td>
<td></td>
<td>H</td>
<td>E T</td>
<td>ppm</td>
<td>L</td>
<td>H</td>
<td>M</td>
<td>Y</td>
<td>Knowledge of MW distribution of contamination alcohols would be
useful</td>
</tr>
<tr class="odd">
<td><strong>Sulfonic, phosphonic acids</strong></td>
<td>Methanesulfonic acid</td>
<td>M</td>
<td>T</td>
<td>ppm</td>
<td>L</td>
<td>L</td>
<td>L</td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td><strong>Nucleic acids, nucleotides,or DNA fragments</strong></td>
<td></td>
<td>M</td>
<td>T</td>
<td>ppm</td>
<td>M</td>
<td>L</td>
<td>M</td>
<td></td>
<td>DNA assay is standard method that will establish levels on
spacecraft and sensitive areas</td>
</tr>
<tr class="odd">
<td colspan="10"><p><strong>Notes:</strong><br />
MW = molecular weight, VH, H, M, L = very high, high, medium, and low
respectively, Y = yes</p>
<p>E = exogenous, T = terrestrial</p>
<p>The list is intended to be illustrative and not comprehensive. Other
molecular classes containing S and P will also be importance.</p>
<p>The relative importance of molecular classes and specific species may
change after the MSL investigations are selected. However, this method
of assessing the importance of which contaminant species to monitor may
still be followed.</p>
<p>Functional group screening may determine that an entire molecular
class is present below a desired threshold. If contamination levels for
a class are found to be above a threshold, then more detailed
identification of individual species by different techniques may be
desired.</p></td>
</tr>
</tbody>
</table>

+-------------+--------------------------------------------------------+
| ### A       |                                                        |
| ppendix B.  |                                                        |
| Common Cont |                                                        |
| aminates an |                                                        |
| d their Che |                                                        |
| mical Funct |                                                        |
| ional Group |                                                        |
+-------------+--------------------------------------------------------+
| Aliphatic   | AHC's are the most common contamination encountered.   |
| H           | This is generally a saturated (branched and straight   |
| ydrocarbons | chain) mixture of hydrocarbons. It has typically a     |
| (AHC)       | broad molecular weight range. Its source is mainly     |
|             | from lubricants and pump oils. It is found in many     |
|             | industrial environments. AHC's can generally be        |
|             | removed with most common solvents (Freon, alcohol,     |
|             | acetone).                                              |
+-------------+--------------------------------------------------------+
| Silicones   | Silicones are very common contaminates and originate   |
|             | from lubricants, materials, sealants and adhesives.    |
|             | Silicones can outgas or leach out of silicone based    |
|             | polymers (RTV). Like AHC\'s, silicones are found with  |
|             | a distribution of molecular weights. The most common   |
|             | silicones are Polydimethylsiloxane and                 |
|             | Polymethylphenylsiloxane. Silicones are difficult to   |
|             | remove. Freon and toluene are the best to try first.   |
+-------------+--------------------------------------------------------+
| F           | Fingerprints contain a complex mixture of compounds.   |
| ingerprints | The residue consists mainly of high molecular weight,  |
|             | long-chain alkyl esters of fatty acids. The more       |
|             | volatile fractions contain free fatty acids.           |
|             | Fingerprints also contain sodium chloride and protein. |
|             | Fingerprints can be removed by wiping with most common |
|             | solvents (Freon, alcohol, acetone, MEK).               |
+-------------+--------------------------------------------------------+
| Organic     | OAS's are used in mold release agents, soaps, silicone |
| Acid Salts  | polymer activators, and fluxes. OAS's are also formed  |
| (OAS)       | when of fingerprints react with some metallic          |
|             | surfaces. Polar solvents such as alcohols best remove  |
|             | OAS's. In thermal vacuum systems the copper cold       |
|             | finger may react with hydrolyzed esters to form        |
|             | organic copper salts. This gives the copper a green    |
|             | discoloration.                                         |
+-------------+--------------------------------------------------------+
| Phthalates  | Esters are found in plasticiziers, pump oils,          |
| and other   | adhesives, polymer degradation products and many other |
| Esters      | materials. A commonly found class of esters is         |
|             | phthalates. Phthalate esters such as Bis 2-ethylhexyl  |
|             | phthalate (aka DOP) is used to plasticize vinyl        |
|             | plastics and in many other polymer formulations. DOP   |
|             | is a common catastrophic contaminate and is typically  |
|             | discovered after a thermal vacuum processing. Acetone, |
|             | MEK and alcohol are the best solvents to try first.    |
+-------------+--------------------------------------------------------+
| Epoxy       | The uncured components of Epoxies can outgas or leach  |
|             | out a variety of components. These are generally       |
|             | amines (from the \"B\" component) and phenol ethers.   |
|             | The best solvent for these are alcohol, acetone and    |
|             | aromatic solvents. Cured epoxy is difficult to remove  |
|             | by common solvents. Epoxy compounds may have complex   |
|             | formulations and can be a source of other compounds.   |
+-------------+--------------------------------------------------------+
| Particles   | The particles and fibers are usually analyzed          |
| and Fibers  | separately from molecular contamination. They can      |
|             | contribute the molecular contamination by physical     |
|             | transport, solvent extraction and outgassing molecular |
|             | residue. Particles are readily identified by FTIR      |
|             | microscopy (non-metals) and Laser Ablation-ICP         |
|             | (metallic particles).                                  |
|             |                                                        |
|             | *Silicate Dust:* Common fine component of soil. The    |
|             | composition is mainly fine quartz and mixed silicates. |
|             | This is also found in construction materials.          |
|             |                                                        |
|             | *Cloth Fibers:* Cotton, Nylon, polyester, Lycra, Silk  |
|             | etcetera.                                              |
|             |                                                        |
|             | [*Bio-Organic*:]{.underline} This includes dead skin,  |
|             | hair, spores, pollen, and organic wind blown matter.   |
|             | This is a very large class of materials. The           |
|             | *Planetary Protection* group monitors a crucial subset |
|             | of this material with separate biological assays.      |
|             |                                                        |
|             | *Construction Materials*: Wallboard, Wood fibers       |
|             | etcetera.                                              |
|             |                                                        |
|             | *Metallic and Device Shed Particles*: These are        |
|             | particles from the spacecraft hardware. They can be    |
|             | from wear or machining debris.                         |
|             |                                                        |
|             | *Carbonates:* Carbonates are used as fillers in        |
|             | materials and are a major component of "water spots".  |
|             | Carbonates are also encountered as a corrosion product |
|             | from paints using potassium silicate binders.          |
+-------------+--------------------------------------------------------+
| Ionic       | The ionic contaminates of the greatest concern are     |
| Co          | chlorides, fluorides and sulfates. The main effect of  |
| ntamination | this residue is to increase the corrosion rate of      |
|             | sensitive materials before launch when surfaces are    |
|             | exposed to humidity. Ionic contamination is not        |
|             | generally an outgassing concern and the acceptable     |
|             | levels of ionic contamination are not usually          |
|             | established in spacecraft specifications. If ionic     |
|             | contamination is monitored it is usually at the        |
|             | component level. The use of strongly activated solder  |
|             | fluxes (spiked with chlorides or fluorides) is         |
|             | probably the most common source of detrimental ionic   |
|             | contamination. The main background sources of ionic    |
|             | contamination are fingerprints and metal processing    |
|             | residues. Generally ionic contamination is removed by  |
|             | deionized water and to a lesser extent alcohols. Ion   |
|             | Chromatography readily analyzes ionic contamination    |
|             | with excellent sensitivity.                            |
+-------------+--------------------------------------------------------+

  ------------------------------------------------------------------------
  Appendix C: Organic Materials       
  Inventory. Organic materials        
  used on each MER spacecraft in      
  amounts of one kg or more.          
  Materials used in amounts of        
  25 kg or more are marked with       
  an \* symbol.                       
  ------------------------------ ---- ------------------------------------
  Material                            Use

  FM 73 Epoxy Film Adhesive           Bonding of aluminum core to
                                      composite facesheets for RED, WEB,
                                      and Lander

  FM 300 Epoxy Film Adhesive          Bonding of heaters for Cruise Stage
                                      Shunt Radiators

  EA 9309 Epoxy Paste Adhesive        Bonding of fittings for RED, WEB and
                                      Aeroshell

  EA 9394 Epoxy Paste Adhesive        Bonding of fittings for RED, WEB and
                                      Aeroshell

  EX 1541 Polycyanate Paste           Filling aluminum honeycomb core for
  Adhesive                            RED and WEB panels and Aeroshell

  HT 424 Epoxy Paste Adhesive         Core splice adhesive for aluminum
                                      honeycomb core for RED and WEB
                                      panels.

  Eccobond 56C Conductive Epoxy       Bonding of Cruise Stage Shunt
  Adhesive                            Radiators

  Eccobond 57C Conductive Epoxy       Bonding of Cruise Stage Shunt
  Adhesive                            Radiators

  BTCY-1 Polycyanate Resin \*         Used as the matrix resin for carbon
                                      fiber and glass fiber reinforced
                                      panels for WEB, RED and Aeroshell

  RTV 560 Silicone Adhesive           Bonding of SIRCA to the BIP

  Uralane 5750 Polyurethane           Potting and Conformal Coating for
  Resin                               Lander, Rover

  Teflon Polytetrafluoroethylene      Spacers and Standoffs for Lander,
                                      Rover

  G-10 fiberglass epoxy               Standoffs, Insulators, PWBs for
                                      Lander, Rover

  Y966 Pressure Sensitive             Used in tape on Rover, WEB and RED
  Acrylic Adhesiv                     

  Kapton Polyimide Film               Thermal Blankets for Cruise Stage

  Mylar Polyethylene Terphalate       Thermal Blankets for Cruise Stage
  film                                

  Vespel Polyimide                    Standoffs, spacers and antenna
                                      components for the rover and lander

  Polyester\*                         Parachute

  Vectran\*                           Airbag

  Kevlar Tape/Webbing\*               Parachute, Airbags, Bridle, DRL

  S13 Silicone Paint                  Painting of solar array substrates
                                      for Cruise Stage and Rover

  M55J Graphite Fibers                Fiber reinforcement for composites
                                      used in RED, WEB, and Aeroshell

  FlamemasterS1023 Silicone           Exterior paint on Backshell
  Paint                               

  SLA-561V\*                          Thermal Protection System on Heat
                                      Shield

  SLA-561S\*                          Thermal Protection System on
                                      Backshell

  2216 epoxy adhesive                 Potting and staking on Rover and
                                      Cruise Stage

  Xylon (polybenzoxazole)             Straps for the Lander Bridle System

  Torlon polyamide-imide              Bearings and standoffs for Rover and
                                      Lander

  Solithane Polyurethane Resin        Conformal coating for printed
                                      circuit boards for Lander and Rover
  ------------------------------------------------------------------------

**Appendix D. Physical Transfer of Organic Contaminants from Hardware
Surfaces\
to Simulated Mars Soil**

6/15/2004

Mark Anderson, Shirley Chung, Jerami Mennella, Gregory Kuhlman, Gregory
Bearman and Roger Kern

**Summary**

This work addresses the concern that nominal spacecraft surfaces may
contaminate Mars soil prior to chemical analysis. Transfer of surface
residue could compromise the science return particularly for trace
organic experiments. This study was intended to bound the problem by
determining the fraction of molecular contaminants
physically-transferred from external spacecraft surfaces. Contamination
transferred from typical spacecraft surfaces was studied. In addition,
the JPL rock crusher tool was analyzed.

In general we measure 1.3% to 7.6% of the surface contamination is
physically transferred to the soil analogs under conditions of moderate
abrasion. In the case of passive transfer without abrasion, levels
ranging from 0.10 --1.3% were measured. The high abrasion surfaces of
the JPL rock crusher were found to transfer \~60% of surface molecular
contamination. These measurements are based on a variety of organic
compounds, soil analogs and metal surfaces. This work covers room
temperature and low temperature (-40 ^o^C) tests. Experimental
procedures have been developed to address organic transfer for more
specific operational conditions in terms of mechanical stress,
temperature, contamination type and level of hardware contamination.

**Introduction**

A general method was developed to study the physical transfer of organic
films to powders from metals surfaces. This is intended to simulate the
pressing and translation of Mars soil across a nominally contaminated
hardware surface. Methods were developed for the uniform deposition of
the contamination analogs. Several soil analogs were used and this was
dependent on the analytical methods for detecting the transferred
contamination analog. This was not intended to simulate the high stress
conditions of a cutting edge or the grinding surfaces of a rock crusher.

Three simulates of Mars soil were initially chosen for study: Potassium
Bromide (KBr) based on its compatibility with FTIR analysis; Basalt
(USGS, BHVO-2, http://minerals.cr.usgs.gov), a widely uses Mars soil
stimulant; and chromatography grade quartz sand. The contamination
analogs were Dioctyl Phthalate (DOP), adenosine triphosphate (ATP) and
the amino acid lysine. The metal surfaces studied were common spacecraft
alloys of aluminum and titanium. One of the soil analogs evaluated, the
clay montmorillonite, was found to "irreversibly" bind the contaminant
molecules making it difficult to directly extract for the soil analysis.
This issue of the chemical binding of organic analytes and background
residue to clays requires a separate evaluation. In addition, The JPL
rock crusher was tested using the DOP contamination analog and a
Andesite rock sample.

**Experimental**

Hardware Contamination Preparation: The contamination-analogs are
deposited on circular metal plates using a spin coating process. The
contamination-analog is dissolved in solvent and syringed on to the
spinning plate in a uniform coating. This used a standard spin coater
device (Headway Research, Garland, Tx) for deposition uniform polymer
films. The rock crusher back plate was similarly spin coated at a level
of 0.4 micrograms per square centimeter with DOP. The absolute amount
deposited, while uniform, is not consistently the same level of residue
from plate to plate. Therefore the results are reported for the average
percent contamination transferred for plates in a range of contamination
levels.

**Contamination Transfer Process**

**Passive Transfer:** The amount of contamination transferred with no
abrasion was evaluated at 25 ^o^C and --40 ^o^C. The weighed analogs
(0.5 grams) were evenly applied to the surface and after 1 hour were
poured off. The amount of residue was then analyzed. There was little or
no mechanical action was applied other than the particles sliding over
the surface.

**Abrasion Transfer:** The abrasive transfer experiment uses a known
weight of a cleaned, flat-head stainless steel pestle. Weighed powder
(0.5-0.75 grams) is placed between the pestle head and the circular
plate surface (100cm^2^) and the "mechanical transfer" is accomplished
by moving the pestle radically outward and inward from the center of the
plate using only the pestle weight and covering the entire contamination
plate surface. This is done for a prescribed number of passes. The
powder is then lightly brushed off the surface and collected into a vial
and mixed. This powder is either analyzed directly or it is extracted
and evaporated onto potassium bromide (KBr) for DRIFT analysis as
describe below. The residue remaining on the plate is then rinsed with
dichloromethane (DCM) and similarly analyzed. The fraction of the
material transferred to the soil analog from the plate is reported as "%
transferred". Blanks are run on solvents and all hardware that contacts
the powder along surfaces. The error in the measurements is mainly a
function of the grinding process that transfers oil from the surface to
the powder.

> *Below is the apparatus for physical transfer of molecular films. This
> provides uniform pressure on a pestle to the powder-plate interface*

![](media/image2.png)

**FTIR Analysis**

The contamination-analog on the plate and transferred to the soil-analog
are both measured using Diffuse Reflectance/ Fourier Transform Infrared
(DRIFT) spectroscopy. The samples are extracted using dichloromethane.
FTIR provides chemical functional group information for sensitive
quantitative analysis and qualitative identification of materials. The
analysis followed the ACL-120 procedure that complies with Mil-STD-1246C
Notice 3 and is sensitive to the most stringent level (A/100). A paper
(1) co-authored and written under the direction of Mark Anderson details
the quantitative methodology. The method has high precision and
accuracy. The linear correlation coefficient (r2) is 0.980 for bis-ethyl
hexyl phthalate (DOP), 0.982 for Silicone and 0.987 for hydrocarbon pump
oil. This is valid for the range of concentrations used in this study.

**Gas Chromatography- Mass Spectroscopy**

The sample of crushed rock from the rock crusher (with the DOP coated
back plate) was analyzed for DOP using a dichloromethane extraction,
evaporative concentration and analysis using GC/MS. GC/MS provides
separation using gas chromatography and mass analysis using mass
spectroscopy.

**RESULTS**

**Rock Crusher:**

The back plate of the rock crusher was spin coated with 0.4 micrograms
per square centimeter of DOP. A 32-gram Andesite rock was ground to
completion (overnight). The crusher surfaces under high stress have fine
powdered rock marking the surface. This area (\~10 cm^2^) was used to
estimate the contact area. The crushed rock had 5.9 micrograms of DOP as
determined by dichlormethane extraction and GC/MS analysis. This is \~
60% of the residue on the abraded surface area. The resulting crushed
rock sample had 185 parts per billion DOP.

The transfer fractions for the various plate-analog combinations are
based on the average of 3 or 4 measurements (unless otherwise
indicated).

### Table #1 Abrasion: [DOP Transferred to Soil Analog at 22^o^C]{.underline}

# 2 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate/  | DOP Level on    | Fraction        | S       | **Average % |
| Analog  | Plate           | Transferred to  | tandard | Transferred |
|         |                 | Powder (f)      | De      | to Powder** |
|         | Micrograms per  |                 | viation |             |
|         | cm^2^           |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Al/KBr  | 0.07            | 0.063           | 0.033   | **6.3%**    |
+---------+-----------------+-----------------+---------+-------------+
| Al/KBr  | 0.7             | 0.055           | 0.011   | **5.5%**    |
+---------+-----------------+-----------------+---------+-------------+
| Ti/KBr  | 0.06            | 0.066           | 0.021   | **6.6%**    |
+---------+-----------------+-----------------+---------+-------------+
| Ti/KBr  | 0.36            | 0.023           | 0.0072  | **2.3%**    |
+---------+-----------------+-----------------+---------+-------------+
| Ti/Sand | 0.21            | 0.023           | 0.013   | **2.3%**    |
+---------+-----------------+-----------------+---------+-------------+

### Table #2 Abrasion: [DOP Transferred to Soil Analog at -40^o^C]{.underline}

# 2 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate/  | DOP Level on    | Fraction        | S       | **%         |
| Analog  | Plate           | Transferred to  | tandard | Transferred |
|         |                 | Powder (f)      | De      | to Powder** |
|         | Micrograms per  |                 | viation |             |
|         | cm^2^           |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Ti/KBr  | 0.09            | 0.072           | \*      | **7.2%**    |
+---------+-----------------+-----------------+---------+-------------+
| Ti/Sand | 0.20            | 0.025           | \*      | **2.5%**    |
+---------+-----------------+-----------------+---------+-------------+

#### **[Table #3 Passive Transfer: DOP Transferred to Soil Analog at 22^o^]{.underline}**C

+---------+-----------------+-----------------+---------+-------------+
| Plate/  | DOP Level on    | Fraction        | S       | **%         |
| Analog  | Plate           | Transferred to  | tandard | Transferred |
|         |                 | Powder (f)      | De      | to Powder** |
|         | Micrograms per  |                 | viation |             |
|         | cm^2^           |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Al/Sand | 0.07            | 0.01            | \*      | **1.3%**    |
+---------+-----------------+-----------------+---------+-------------+
| Al/Sand | 0.9             | 0.03            | \*      | **2.7%**    |
+---------+-----------------+-----------------+---------+-------------+
| Al/KBr  | 0.10            | 0.04            | \*      | **3.9%**    |
+---------+-----------------+-----------------+---------+-------------+
| Al/KBr  | 0.9             | 0.05            | \*      | **4.6%**    |
+---------+-----------------+-----------------+---------+-------------+

#### 

#### **Table \# 4 Passive Transfer: [DOP Transferred to Soil Analog at -40^o^C]{.underline}**

+---------+-----------------+-----------------+---------+-------------+
| Plate/  | DOP Level on    | Fraction        | S       | **%         |
| Analog  | Plate           | Transferred to  | tandard | Transferred |
|         |                 | Powder (f)      | De      | to Powder** |
|         | Micrograms per  |                 | viation |             |
|         | cm^2^           |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Al      | 1.06            | 0.013           | 0.0047  | **1.3%**    |
| /Basalt |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Al      | 0.175           | 0.0085          | 0.0033  | **0.85%**   |
| /Basalt |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| Al/Sand | 0.073           | 0.0043          | 0.00074 | **0.43%**   |
+---------+-----------------+-----------------+---------+-------------+
| Al/Sand | 1.2             | 0.0013          | 0.00014 | **0.13%**   |
+---------+-----------------+-----------------+---------+-------------+

\* This is based on a single point measurement.

**Bio-Molecular Contamination Experimental**

**ATP (adenosine triphosphate) Determination:**

In this study ATP serves as a surrogate for nucleic acids as it contains
a purine, phosphoric acid and has a negative charge at neutral pH. The
contamination-analog on the plate and that transferred to the soil are
both measured using a bioluminescence-based assay. The bioluminescence
reagent contains firefly luciferin and luciferase. Luciferase
specifically reacts with ATP and the amount of luminescence produced by
the reaction is in direct proportion to the amount of ATP in the sample.
Specifically Kikkoman CheckLite HS plus reagent kit is used as specified
by the manufacturer and the signal is detected with a Kikkoman
Lumitester model K-210 spectrofluorimeter. The instrument has a linear
response over a five decade rang and a lower limit of detection
sensitivity of 10-14 M.

**Amino Acid Determination:** In this study Lysine served as a
representative amino acid as it is the most easily detected since it has
two primary amines. The contamination-analog on the plate and
transferred to the soil were both measured using a fluorescence assay
based on the dye fluorescamine. Upon reaction with primary amines the
product shows absorbance/emission peaks at 381nm and 470nm respectively.
The reaction is detected with a Gemini XS microplate spectrofluorometer
with a detection range from 5 to 2500 ng/ml.

**Compatibility of Assays and Materials:** Like the DRIFT/FTIR both the
ATP and amino acid assays were unable to detect signal from the Mars
soil simulant montmorillonite. It is presumed to "irreversibly" bind the
contaminant molecules making it difficult to directly extract for the
soil analysis. In addition the KBr used is the DRIFT/ FTIR studies was
found to significantly inhibit the biochemistries used in the detection
of ATP and amino acids. Therefore, studies of transfer by this material
were not conducted for this soil simulant This issue of the chemical
binding of organic analytes and background residue to clays requires a
separate evaluation as it may impact operation of some strategies for
chemical detection on the surface of Mars.

**Contaminated Plate Preparation:** The water-based solutions of the
bioorganic contaminants were not suitable for spin coating. The
contamination-analogs, ATP and Lysine were deposited on circular metal
plates (aluminum or titanium) using with micropipter in a 10x10 array of
2 microliter drops and allowed to dry. The contamination-analog was
dissolved in sterile de-ionized water. This is a standard method for
deposition aqueous solutions. The absolute amount deposited is
determined from the known volume and concentration is consistently the
same level of residue from plate to plate although not present as a
contiguous film on the plate. The results are reported for the average
percent contamination transferred for plates from three replicate
experiments. Each experiment also has replicate positive and negative
controls for the presence and absence of the analog contaminant.

**Contamination Transfer Process:** The transfer experiment uses a known
weight of a cleaned, flat-head stainless steel pestle. Weighed sand
(0.75g of SiO~2~) is placed between the pestle head and the plate
surface and the "mechanical transfer" is accomplished by moving the
pestle across the surface of the plate using only the pestle weight and
covering the entire contaminated plate surface. This is done for a
prescribed number of passes. The sand is then poured off the surface and
collected into a vial. This sand is extracted with 1ml of water and the
supernatant used directly for ATP and amino acid. The residue remaining
on the plate is then rinsed with water and similarly analyzed. The
fraction of the material transferred to the soil analog from the plate
is reported as " % transferred". Blanks are run on solvents and all
hardware that contacts the sand along surfaces. The error in the
measurements is mainly a function of the grinding process that transfers
bioorganic molecules from the surface to the sand.

**RESULTS**

The percent transferred to the soil for the various plate-analog
combinations are based on the average of 3 or 4 measurements (unless
otherwise indicated).

### Table \# 6 Abrasion: [Lysine Transferred to Sand at 22^o^C]{.underline}

# 3 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total Lysine on | Lysine          | S       | **%         |
| Type    | Plate           | transferred to  | tandard | Transferred |
|         |                 | sand, Nanograms | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 5,000           | 167.5           | 48.8    | **3.4%**    |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 5,000           | 125.5           | 23.7    | **2.5%**    |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

### Table \# 5 Abrasion: [ATP Transferred to Sand at 22^o^C]{.underline}

# 3 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total ATP on    | ATP transferred | S       | **%         |
| Type    | Plate           | to sand,        | tandard | Transferred |
|         |                 | Nanograms       | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 0.1             | 0.0013          | .0045   | **1.3%**    |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 0.1             | 0.0034          | 0.013   | **3.4%**    |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

### 

### Table #7 Abrasion: [Lysine Transferred to Sand at -40^o^C]{.underline}

# 3 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total Lysine on | Lysine          | S       | **%         |
| Type    | Plate           | transferred to  | tandard | Transferred |
|         |                 | sand, Nanograms | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 5,000           | 75.2            | 31.4    | **1.5%**    |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 5,000           | 378.0           | 128.7   | **7.6%**    |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

### Table #6 Abrasion: [ATP Transferred to Sand at -40^o^C]{.underline}

# 3 Passes over 100 cm^2^ with a Force of 160g/cm^2^

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total ATP on    | ATP transferred | S       | **%         |
| Type    | Plate           | to sand,        | tandard | Transferred |
|         |                 | Nanograms       | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 0.1             | 0.00088         | 0.0015  | **0.9%**    |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 0.1             | 0.0019          | 0.0013  | **1.9%**    |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

### 

### Table #7 Passive Transfer: [ATP Transferred to Sand at 22^o^C]{.underline}

# Static transfer for one hour of direct contact

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total Lysine on | Lysine          | S       | **%         |
| Type    | Plate           | transferred to  | tandard | Transferred |
|         |                 | sand, Nanograms | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 0.1             | 0.00011         | 0.00012 | **0.1%**    |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 0.1             | 0.00013         | 0.00017 | **0.1%**    |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

### Table #7 Passive Transfer: [Lysine Transferred to Sand at 22^o^C]{.underline}

# Static transfer for one hour of direct contact

+---------+-----------------+-----------------+---------+-------------+
| Plate   | Total Lysine on | Lysine          | S       | **%         |
| Type    | Plate           | transferred to  | tandard | Transferred |
|         |                 | sand, Nanograms | De      | to Sand**   |
|         | Nanograms       |                 | viation |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| A       | 5,000           | 46.5            | 24.3    | **0.93%**   |
| luminum |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
|         |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+
| T       | 5,000           | 121.22          | 50.0    | **0.24%**   |
| itanium |                 |                 |         |             |
+---------+-----------------+-----------------+---------+-------------+

**Estimation of Molecular Contamination Transferred to Soil**

The following is a calculation to estimate mechanically transferred
contamination from spacecraft hardware to a soil sample. The resulting
concentration in the soil sample (Cppb) is given as parts per billion
(ppb) by weight (nanograms per gram). The initial surface contamination,
Cs, is given in nanograms per cm^2^. This may be from direct hardware
measurements or contamination modeling. The fraction of the surface
contamination transferred from surface into the soil is given as f. This
transfer fraction is reported in the tables above for various residues,
substrates, temperatures and abrasion conditions. The soil sample
weight, S is express in grams and the area, A is given in cm^2^. The
calculation is Cppb = f x Cs x A / S.

**Example:** Clean hardware (level A/10) with passive contact at
--40^o^C:

f = 0.0085 Transferred fraction (Table 3, Basalt, -40^o^C, passive
transfer)

S = 100 g, Grams of Soil

A = 200cm^2^ Contact Area (scoop area + external funnel)

Cs = 100 nanograms/square centimeter (Level A/10, IEST-STD-CC1246D)

> Cppb = f x Cs x A / S = (0.0085) (100ng/cm^2^) (200cm^2^)/100g = 1.7
> ppb

This is an optimistic estimate and is at a level that could be detected
by the Phoenix TEGA mass spectrometer. Note TEGA has some further
chemical discrimination between synthetics (silicones and
fluoropolymers) and the hydrocarbons of scientific interest. This needs
to be considered when organic detection is being estimated.

**Example:** General spacecraft hardware and light abrasion:

A more pessimistic estimate would assume standard spacecraft limit at
level A cleanliness of 1ug/cm^2^ (1000ng/cm^2^) and a transfer of 7.2
percent (table 2 sand). This gives:

> Cppb = f x Cs x A / S = (0.072) (1000ng/cm^2^) (200cm) /100 = 144 ppb

**Discussion and Recommendations**

The range given above is near the detection limit of Phoenix-TEGA mass
spectrometer (low to sub-ppb) up to 2 orders of magnitude higher. The
lower end is manageable using good blank protocols and relying on the
ability of the mass spectrometer to discriminate certain synthetic
contaminates from organic compounds. The higher end could reduce the
analytical sensitivity and requires greater resources devoted to blank
measurement.

During the course of this study the Phoenix project had the need for an
evaluation of the susceptibility of the TEGA mass spectrometer. This
provides a context and the limitations of this study. The main drawback
is the uncertainty of actual spacecraft contamination levels
particularly for particles. This study does not include particle
transfer estimates and this is of equal importance as the molecular
contamination effects.

Lastly this work underscores the need for flight experiments to have
end-to-end blanks and perhaps self-cleaning of critical surfaces. Given
the uncertainties of spacecraft contamination this may be the only way
to make convincing measurements for the detection organic compounds on
Mars.

**Rock Crusher Implications**

The crushed rock collected 5.9 micrograms of DOP contamination analog in
a 32-gram rock sample. This is \~ 60% of the analog residue removed from
the abrasion surface area. The resulting crushed rock sample has 185
parts per billion DOP. The implications are that the high stress
surfaces of the crusher need to be kept very clean. The amount of
residue on the crusher plate was a "high nominal" surface (0.4
micrograms per square centimeter). Rigorous cleaning and protection of
the critical rock crusher surfaces will greatly improve the levels of
transferred residue.

**References**

1\) M. S. Anderson and J. J. Herrick et al \"Analysis of Semi-Volatile
Residues Using Diffuse Reflectance Infrared Fourier Transform
Spectroscopy\" in Optical System Contamination: Effects, Measurements,
and Control VII; July 2002, edited by Phillip T. C. Chen and O. Manuel
Lee; Proceedings of the SPIE, Vol. 4774, pp. 251-261, (2002).