**NASA ASTROBIOLOGY ROADMAP 2008**

The NASA Astrobiology Roadmap is updated periodically as part of the
space agency's strategic planning process. Accordingly, Dr. J. A.
Rummel, Senior Scientist for Astrobiology in the Science Mission
Directorate at NASA Headquarters, directed that the 2003 version of the
Astrobiology Roadmap^a^ should be revised and updated during 2007-2008.

The ongoing development of the roadmap embodies the contributions of
diverse scientists and technologists, including NASA employees, academic
scientists whose research is partially funded by NASA grants, and many
members of the broader community who have no formal association with
NASA. The members of the roadmap revision team are as follows: D. J.
Des Marais (co-lead), J. A. Nuth III (co-lead), L. J. Allamandola, A. P.
Boss, J. D. Farmer, T. M. Hoehler, B. M. Jakosky, V. S. Meadows, A.
Pohorille, B. Runnegar and A. M. Spormann.

The team's updated draft was recently reviewed by the Executive Council
of the NASA Astrobiology Institute and by the National Academy of
Sciences Space Studies Board Committee on the Origins and Evolution of
Life.

The current version of the roadmap is posted here for a two-month period
in order to solicit your comments. The draft will then be further
revised and presented in near-final form at the 2008 Astrobiology
Science Conference to be held April 14-17, 2008 in Santa Clara, CA.

^a^Des Marais, D. J., Allamandola, L. J., Benner, S. A., Boss, A. P.,
Deamer, D., Falkowski, P. G., Farmer, J. D., Hedges, S. B., Jakosky, B.
M., Knoll, A. H., Liskowsky, D. R., Meadows, V. S., Meyer, M. A.,
Pilcher, C. B., Nealson, K. H., Spormann, A. M., Trent, J. D., Turner,
W. W., Woolf, N. J., Yorke, H. W. (2003) The NASA Astrobiology Roadmap.
*Astrobiology*, Vol. 3, Number 2, 219-235.

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Draft of 28 December 2007

The NASA Astrobiology Roadmap, 2008 Revision

DAVID J. DES MARAIS (CO-LEAD),^a^ JOSEPH A. NUTH III (CO-LEAD),b LOUIS
 J. ALLAMANDOLA,b ALAN P. BOSS,c JACK D. FARMER,d TORI M. HOEHLER,^b^
BRUCE M. JAKOSKY,d VICTORIA S. MEADOWS,e ANDREW POHORILLE,b
BRUCE RUNNEGAR,^f^ ALFRED M. SPORMANNg

^a^ Space Science Division, NASA Ames Research Center, Moffett Field, CA
94035, ^b^Goddard Space Flight Center, Greenbelt, MD 20771;
^c^Department of Terrestrial Magnetism, Carnegie Institution of
Washington, Washington, DC 20015; ^d^Department of Exploration, Arizona
State University, Tempe, AZ 85287; ^d^Laboratory for Atmospheric and
Space Physics and Department of Geological Sciences, University of
Colorado, Boulder, CO 80309; ^e^Department of Astronomy, University of
Washington, Seattle, WA; ^f^Institute of Geophysics, U. C. L. A., Los
Angeles, CA 90024; ^g^Department of Civil and Environmental Engineering,
Stanford University, Stanford, CA 94305.

ABSTRACT

The NASA Astrobiology Roadmap provides guidance for research and
technology development across the NASA enterprises that encompass the
space, Earth and biological sciences. The ongoing development of
astrobiology roadmaps embodies the contributions of diverse scientists
and technologists from government, universities and private
institutions. The Roadmap addresses three basic questions: how does life
begin and evolve, does life exist elsewhere in the universe, and what is
the future of life on Earth and beyond? Seven Science Goals outline the
following key domains of investigation: understanding the nature and
distribution of habitable environments in the universe, exploring for
habitable environments and life in our own solar system, understanding
the emergence of life, determining how early life on Earth interacted
and evolved with its changing environment, understanding the
evolutionary mechanisms and environmental limits of life, determining
the principles that will shape life in the future, and recognizing
signatures of life on other worlds and on early Earth. For each of these
goals, Science Objectives outline more specific high priority efforts
for the next three to five years. These eighteen objectives are being
integrated with NASA strategic planning.

**Introduction**

Astrobiology addresses three basic questions that have been asked in
various ways for generations: how does life begin and evolve, does life
exist elsewhere in the universe, and what is the future of life on Earth
and beyond? Accordingly, the discipline of astrobiology embraces the
search for potentially inhabited planets beyond our Solar System, the
exploration of Mars and the outer planets, laboratory and field
investigations of the origins and early evolution of life, and studies
of the potential of life to adapt to future challenges, both on Earth
and in space. Interdisciplinary research is required that combines
molecular biology, ecology, planetary science, astronomy, information
science, space exploration technologies, and related disciplines. The
broad interdisciplinary character of astrobiology compels us to strive
for the most comprehensive and inclusive understanding of biological,
planetary and cosmic phenomena.

The NASA Astrobiology Roadmap provides guidance for research and
technology development across the NASA Enterprises that encompass the
space, Earth and biological sciences. The Roadmap is formulated in terms
of seven Science Goals that outline key domains of investigation. These
domains of investigation will probably require decades of effort to
consummate. For each of these goals, Science Objectives outline more
specific high priority efforts for the next three to five years. These
eighteen objectives are being integrated with NASA strategic planning.
The Roadmap also includes Example Investigations, which offer examples
of specific research tasks that are both important and timely for their
corresponding Science Objective. It is important to emphasize that these
investigations are intended principally to be illustrative of relevant
tasks, and that additional equally important example investigations can
be envisioned.

The following four basic principles are fundamental to the
implementation of NASA's astrobiology program:

1\. Astrobiology is multidisciplinary in its content and
interdisciplinary in its execution. Its success depends critically upon
the close coordination of diverse scientific disciplines and programs,
including space missions.

2\. Astrobiology encourages planetary stewardship through an emphasis on
protection against forward and back biological contamination and
recognition of ethical issues associated with exploration.

3\. Astrobiology recognizes a broad societal interest in its endeavors,
especially in areas such as achieving a deeper understanding of life,
searching for extraterrestrial biospheres, assessing the societal
implications of discovering other examples of life, and envisioning the
future of life on Earth and in space.

4\. The intrinsic public interest in astrobiology offers a crucial
opportunity to educate and inspire the next generation of scientists,
technologists and informed citizens; thus a strong emphasis upon
education and public outreach is essential.

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**Goals and Objectives**

**GOAL 1 - Understand the nature and distribution of habitable
environments in the Universe.** Determine the potential for habitable
planets beyond the Solar System, and characterize those that are
observable.

A planet or planetary satellite is habitable if it can sustain life that
originates there or if it sustains life that is carried to the object.
The Astrobiology program seeks to expand our understanding of the most
fundamental environmental requirements for habitability. However, in the
near term, we must proceed with our current concepts regarding the
requirements for habitability. That is, habitable environments must
provide extended regions of liquid water, conditions favorable for the
assembly of complex organic molecules, and energy sources to sustain
metabolism. Habitability is not necessarily associated with a single
specific environment; it can embrace a suite of environments that
communicate through exchange of materials. The processes by which
crucial biologically useful chemicals are carried to a planet and change
its level of habitability can be explored through the fields of
prebiotic chemistry and chemical evolution. A major long-range goal for
astrobiology is to recognize habitability beyond the Solar System,
independent of the presence of life, or to recognize habitability by
detecting the presence of life (see Goal 7: Biosignatures). This goal
directly addresses the call for searches for Earth-like planets and for
habitable environments around other stars that is included in the Vision
for Space Exploration.

######### *Background* 

Research in astrobiology supports NASA\'s Origins theme in its attempt
to search for habitable or inhabited environments beyond the Solar
System. Humans have pondered for millenia whether other inhabitable
worlds exist. Now, for the first time, they have an opportunity to look
and see. Of course it is not possible to examine the \~10^10^ Earth-like
planets that simple statistical models predict to exist in our galaxy,
much less the \~10^21^ such planets expected to be in the universe.
Still, it should be possible to determine whether terrestrial planets
are indeed as common as predicted above, whether a substantial fraction
of them show signs of habitability, and whether an appreciable fraction
of these show biosignatures.

A key difference between the search for life in the Solar System and the
search in external planetary systems is that, within the Solar System,
interplanetary transfer of viable microbes seems a plausible process,
and therefore the discovery of life elsewhere in the Solar System seems
plausible. While this is indeed of extraordinary interest, it may not
cast light on whether it is easy or difficult for life to begin. On the
other hand, the fact that dispersion times between stars are \~ 10^5^ to
10^6^ times longer than for dispersion within the Solar System makes
independent origination of life-forms outside the Solar System more
probable.

The research objectives under this goal address three key questions.
First, do terrestrial planets and large satellites tend to form in a
state where they are likely to become habitable, or do habitable
environments emerge only after a sequence of less probable events?
Second, how frequently do habitable environments arise on solid planets,
including large satellites? Third, what are the specific signs of
habitability and habitation, and how do such signs change with the
circumstances of the planet (e.g., mass, distance from its star, history
and relative abundance of volatile compounds)? To address these
questions effectively, we must investigate how habitable planetary
systems form and evolve (Goals 1 and 2), and we must understand the
ultimate environmental limits of life (Goal 5).

Much of this effort focuses upon the presence or absence of liquid water
in bulk form. Water is made from the two most abundant chemically
reactive elements in the universe, and it is the necessary ingredient
for Earth\'s type of life. Liquid water has played an intimate, if not
fully understood, role in the origin and development of life on Earth.
Water contributes to the dynamic properties of an Earth-sized planet,
permitting convection within the planetary crust that might be essential
to supporting Earth-like life by creating local chemical disequilibria
that provide energy for life. Water maintains a strong polar-nonpolar
dichotomy with certain organic substances. This dichotomy has allowed
life on Earth to form independent stable cellular structures. Thus the
primary focus of Goal 1 is concerned with planets having a liquid water
boundary layer, although the focus may expand to include other planets
or satellites as astrobiology matures as a discipline.

There is also a focus - though not exclusive - on molecular oxygen and
ozone as biosignatures (see also Goal 7), and therefore on dealing with
the interface between the understanding of the geological and biological
aspects of oxygen, and the details of the spectral features that can be
observed and interpreted remotely. Oxygen is a very common element that
has provided Earth with its most distinctive biosignature. The chemical
state of an Earth-like planet, as well as the geological activity that
delivers reduced species to the surface environment, will cause
virtually all of the molecular oxygen to be consumed unless it is
produced rapidly (e.g., by oxygen-producing photosynthesis). Also, the
relatively modest ultraviolet fluxes of many stars prevent rapid
production of oxygen from photo-dissociation of water. These factors
will help to prevent the possibility of false positive detections of
oxygen biosignatures.

The challenge of remotely detecting life on a planet that has not
developed a biogenic source of oxygen is fraught with unknowns. What
chemical species and spectral signatures should be sought? What
metabolic processes might be operating? How does one guard against a
false positive detection? Research that is guided both by our knowledge
of Earth's early biosphere (i.e., before the rise of an oxygenated
atmosphere) and by studies of alternative biological systems can help
address these questions and provide guidance to astronomers seeking
evidence of life elsewhere (Goal 7).

**Objective 1.1. Models of formation and evolution of habitable
planets.** Investigate how solid planets form, acquire liquid water and
other volatile species and organic compounds, and how processes in
planetary systems and galaxies affect their environments and
habitability. Use theoretical and observational studies of the formation
and evolution of planetary systems and their habitable zones to predict
where water-dependent life is likely to be found in such systems.

***Example investigations***

Understand how planet formation processes vary with the mass of the
central star and, in particular, whether low mass M dwarf stars are
likely to host habitable planets or satellites.

Model the origin of planetary systems taking into account water delivery
to and loss from terrestrial-like planets of various size and mass.
Determine how water loss affects climate, surface and interior
processes, and how these changes affect habitability.

Develop comprehensive models of the environments of terrestrial-like
planets (including the recently-discovered "Super Earths," planets with
masses in the range of \~1 to \~10 Earth-masses) to investigate the
evolution of habitability.

**Objective 1.2 - Indirect and direct astronomical observations of
extrasolar habitable planets.** Conduct astronomical, theoretical, and
laboratory spectroscopic investigations to support planning for and
interpretation of data from missions to detect and characterize
extrasolar planets.

***Example investigations***

Use ground-based telescopes to detect "Super Earths" that may offer
habitable environments around low mass, M dwarf stars.

Investigate novel methods for detecting and characterizing extrasolar
planets, particularly those that might lead to an improved understanding
of the frequency of habitable Earth-like planets~~.~~

Use atmospheric models to understand the range of planetary conditions
that can be determined from low resolution, full-disk spectra at
visible, near-IR, and thermal wavelengths. Use data on Venus, Earth, and
Mars to validate these models.

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GOAL 2 -- Determine any past or present habitable environments,
prebiotic chemistry and signs of life elsewhere in our Solar System.
Characterize the history of any environments having liquid water,
chemical ingredients and energy sources that might have sustained living
systems. Explore crustal materials and planetary atmospheres for any
evidence of past and/or present life.

This goal seeks to understand the distribution of the basic requirements
for life elsewhere in our solar system and to understand how any
habitable environments and life persisted over geologic time. Although
possible life elsewhere in the solar system may have developed
differently from life on Earth, our understanding of the nature of
terrestrial life provides an important starting point to guide our
exploration strategies. For example, studies of microorganisms in
extreme environments, including the biota sustained by chemical energy
in the deep subsurface, have revolutionized our assessment of the
potential for life on Mars and the icy moons in the outer solar system.
Surface environments on those bodies are presently hostile to life as we
know it, however subsurface environments might be habitable. Ancient
surface environments also might have been habitable, at least
intermittently. By mapping the distribution of any past and present
habitable environments, robotic missions will guide the selection of
samples to be returned to state-of-the-art laboratories on Earth to
conduct life detection experiments.

***Background***

During the past decade, dramatic progress has been made in our
understanding of the potential for past and present habitable
environments elsewhere in the solar system. For example, the Mars Global
Surveyor orbiter, Mars Exploration Rovers and the Odyssey and Mars
Reconnaissance orbiters revealed that, early in Martian history, surface
water environments were widespread over the surface and shallow
subsurface and were sustained by both atmospheric precipitation and
outflows from aquifers. Theoretical models and surface geomorphology
have indicated the potential for a global groundwater system capable of
sustaining an extant subsurface biosphere. The recent discovery of
atmospheric methane indicates that subsurface habitable environments
might exist even today. The Galileo mission found strong evidence of
subsurface brines on three of the four Galilean satellites of Jupiter
(Europa, Ganymede and Callisto), maintained by internal tidal heating.
The Cassini-Huygens mission has confirmed the presence on Saturn's moon,
Titan, of an atmosphere and surface enriched in pre-biotic organic
compounds. Titan can be viewed as a natural laboratory where we might
gain important new insights into the origins of life here on Earth. The
existence of lakes of liquid hydrocarbons on Titan opens up the
possibility for solvents and energy sources that are alternatives to
those in our biosphere and that might support novel life forms
altogether different from those on Earth. The Cassini spacecraft has
imaged plumes of water that erupt episodically from the subsurface of
Enceladus, an icy moon of Saturn. This indicates the possibility that
interior habitable zones with liquid water might exist on yet another
body in the outer solar system. Recent biological research has deepened
our understanding of the nature, environmental limits and evolutionary
history of life on Earth. Such discoveries have contributed to strategic
planning activities that broadly support NASA missions, including the
specification of scientific goals, objectives and measurement
requirements, new instrument designs, and integrated payload concepts.

Building upon such discoveries, logical next steps in the exploration
for extraterrestrial life in the solar system include the following: 1)
continuing to refine our understanding of the nature and distribution of
past and/or present habitable environments in the solar system, 2)
identifying the most favorable landing sites for future *in situ* life
detection missions, 3) developing experiments for the unambiguous
detection of extant and fossil biosignatures in surface/subsurface
rocks, soils and ices on other planetary bodies, like Mars and Europa,
4) developing robotic drilling systems capable of accessing subsurface
environments on Mars and possibly on other bodies in the solar system,
5) collecting and returning samples to Earth from high priority sites on
Mars and possibly other bodies in the solar system to explore for
pre-biotic chemistry and biosignatures utilizing the advanced
capabilities of terrestrial laboratories. Key questions include the
following: If life ever arose elsewhere, is it related to terrestrial
life, or did other bodies in the solar system sustain independent
origins of life? If life never developed elsewhere in our solar system,
is there a prebiotic chemical record preserved in ancient rocks that
might contain clues about how life began on Earth?

Renewed lunar exploration offers opportunities to explore the earliest
history of habitable environments on Earth. The Moon might harbor an
inventory of crustal materials that were delivered from Earth before,
during and after the interval of heavy bombardment. The discovery of
terrestrial meteorites on the Moon could provide important new insights
about the evolution of planetary habitability during the birth of our
biosphere.

Sample return(s) from important Astrobiology targets in the solar system
(e.g. Mars, icy satellites, asteroids and comets) will greatly expand
opportunities to explore for pre-biotic chemistry and life using the
most sophisticated tools available in terrestrial laboratories. Logical
steps toward planning future sample returns include the development of
reliable robotic systems for the *in situ* targeting, collection and
storage of samples, the safe transport and delivery of samples to Earth,
the construction of sample containment facilities on Earth for the safe
handling and storage of extraterrestrial materials, and the distribution
of samples to members of the scientific community for detailed
laboratory analyses.

**Objective 2.1 - Mars exploration.** Through orbital and surface
missions, explore for potentially habitable environments and evidence of
life, as indicated by water, organic matter, atmospheric gases and/or
aqueous minerals. Study Martian meteorites to guide Mars exploration. To
support both exploration at Mars and the first sample return mission,
update astrobiology measurement requirements, support site selection
studies and develop/improve relevant technologies and analytical
methods.

***Example investigations***

Target a well-instrumented robotic rover to a site of past aqueous
activity and analyze rocks for their geochemistry, aqueous minerals
(e.g. sulfates, silica, phyllosilicates, etc.), organic chemistry and
fossil biosignatures (including organic biomarker compounds, atmospheric
gases, biosedimentary structures and microtextures).

Develop flight instruments to characterize samples *in situ*, to select
samples for return to Earth and to analyze atmospheric composition from
orbit.

Develop universal approaches for detecting extant life forms that can be
applied over a broad range of surface environments to distinguish
between forward contamination and *in situ* extraterrestrial life forms.

Analyze results from previous and current missions in the context of
their significance for astrobiology.

**Objective 2.2 - Outer Solar System exploration.** Conduct basic
research, develop instrumentation to support astrobiological
exploration, and provide scientific guidance for outer Solar System
missions. Model the potential for subsurface habitable environments on
icy moons such as Europa, Titan and Enceladus. Support the development
of missions to explore the surface ices and thin atmospheres of these
bodies for evidence of subsurface habitable environments, organic
chemistry and/or biosignatures.

***Example investigations***

Develop flight instrumentation that can survive the surface environments
of Europa and Titan and that can determine the composition (including
any organic compounds) of surface ices and atmospheres, and explore for
cryo-preserved biosignatures.

Develop numerical models to constrain the nature of deep subsurface
environments on Europa, Titan and Enceladus (presence of life-sustaining
solvents, biologically-essential elements and energy sources) that might
sustain life.

Analyze results from the Cassini mission in the context of their
significance for astrobiology.

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**GOAL 3 - Understand how life emerges from cosmic and planetary
precursors.** Perform observational, experimental and theoretical
investigations to understand the general physical and chemical
principles underlying the origins of life.

How life begins remains a fundamental unsolved mystery. The origin of
life on Earth may well represent only one pathway among many along which
life can emerge. This belief forms the intellectual foundations for
observations and missions aimed at searching for extant or extinct life
elsewhere in the universe. Thus the universal principles must be
understood that underlie not only the origins of life on Earth, but also
its possible origins elsewhere. The starting point for establishing
these principles is to determine what raw materials of life can be
produced by chemical evolution in space and on planets. Further, it
should be understood how organic compounds are assembled into more
complex molecular structures and how functions of these biomolecular
structures become coordinated to form complex, evolving systems that lie
at life\'s origins. Such systems must have the capabilities to perform
and coordinate capture of energy and nutrients from the environment,
catalyze the chemical reactions needed for maintenance and growth of
these systems and manufacture copies of key biomolecules. Clues from the
biomolecular and fossil records, as well as from diverse microorganisms,
should be explored in order to define better the fundamental properties
of the living state.

***Background***

We must move beyond the circumstances of our own particular origins in
order to develop a broader discipline, \"Universal Biology.\" Although
this discipline will benefit from an understanding of the origins and
limits of terrestrial life, it also requires that we define the
environmental conditions and the chemical structures and processes that
could support life on other habitable planets. Thus, we need to exploit
universal laws of physics and chemistry to understand polymer formation,
self-organization processes, energy utilization, information transfer
and Darwinian evolution that might lead to the emergence of life in
planetary environments other than Earth. Clearly, an inventory of
molecules must exist that is capable of gaining chemical, structural and
functional complexity and eventually assemble into living systems. This
is strongly conditioned on temperature, solvent, energy sources, etc.
Some conditions that support chemistry sufficiently rich to seed life
might be detrimental to self-organization of biological structures and,
conversely, conditions that promote the emergence of biological
complexity might be unfavorable to organic chemistry. Thus, an
integrative, interdisciplinary approach is necessary to formulate the
principles underlying universal biology. The perspectives gained from
understanding these principles will markedly improve our ability to
define habitability and recognize biosignatures. This in turn, will
guide mission and observational projects aimed at finding life in the
Solar System and beyond from concept to completion.

**Sources of organic compounds required for the origin of life.** To
understand how life can begin on a habitable planet such as the Earth,
it is essential to know what organic compounds were likely to have been
available, and how they interacted with the planetary environment.
Chemical syntheses that occur within the solid crust, hydrosphere and
atmosphere are likely very important sources of biogenic compounds.
Interesting organic compounds are also present in interstellar clouds,
the birthplace of planetary systems. Laboratory simulations of
interstellar ices have recently demonstrated that key prebiotic
molecules can also be synthesized under interstellar cloud conditions
and these materials are incorporated into nascent solar systems. Further
astronomical observations and analyses of extraterrestrial materials
have shown that many compounds relevant to life processes are also
present in meteorites, interplanetary dust particles and comets. It is
likely that substantial amounts of such organic material were delivered
to the Earth during late accretion, providing organic compounds that
could serve as a feedstock for chemical evolution or be directly
incorporated into early forms of life. An important research objective
within this goal is to establish sources of prebiotic organic compounds
and to understand their history in terms of universal processes that
would take place on any newly formed planet. This will require an
integrated program of pan-spectral astronomical observations, sample
return missions, laboratory studies of extraterrestrial materials, and
realistic laboratory simulations of inaccessible cosmic environments.

**Origins and evolution of functional biomolecules.** Life can be
understood as a chemical system that links a common property of organic
molecules - the ability to undergo spontaneous chemical transformation -
with the uncommon property of synthesizing a copy of that system. This
process, unique to life, allows for Darwinian-like selection and
evolution to occur. At the core of the life process are polymers
composed of monomeric species such as amino acids, carbohydrates, and
nucleotides. The pathways by which monomers were first incorporated into
primitive polymers on the early Earth remain unknown, and physical
properties of the products are largely unexplored. A primary goal of
research on the origin of life must be to understand better the sources
and properties of primitive polymers on the early Earth, their initial
evolution towards acquiring increased fidelity, efficiency and diversity
of functions, and the pathway by which polymerization reactions of
peptides and oligonucleotides became genetically linked. In parallel,
catalytic and informational potential of other polymers that can form in
different planetary conditions should be explored. These specific lines
of inquiry should be complemented with theoretical work, based on a
\"general principles\" approach, to elucidate how the various
protobiological properties of molecules and systems, including emergent
behavior and information transfer, depend on and scale with complexity.

**Origins of energy transduction.** Life requires energy to yield, in a
reproducible fashion, specific, very low probability outcomes, such as
the generation and maintenance of locally ordered states of the
biological system, the production of thermodynamically unfavorable
species, and the synthesis of polymers of specific sequence from among
large numbers of alternate sequence possibilities. Thus, the emergence
of complex life depends upon the development of reliable mechanisms for
capturing energy from the surroundings and channeling it, in appropriate
forms, into specific processes. Overarching areas for focus are: (i)
Foundational - understanding the relationship between energy,
information, and complexity; understanding what types of energy can be
captured and utilized by biological systems; and understanding how
threshold requirements for complexity and information processing place
upper and lower bounds on the biological utilization of energy. (ii)
Mechanistic - elucidating mechanisms by which the principal elements of
energy transduction - capture of environmental energy, storage by
membrane-based or molecular means, and coupling to key energy-requiring
processes - may have functioned in primordial environments and combined
into dedicated energy-transducing systems. (iii) Evolutionary -
understanding how the energy capture and utilization systems evolved
from a complete lack of energy transduction, through a partially
developed state, to fully elaborated and dedicated systems for
collecting and directing energy, and to examine how they co-evolved with
the capabilities for fuctionality, information processing and
replication.

**Origins of cellularity and protobiological systems.** For life to
begin in a natural setting such as a planetary surface, mechanisms must
exist that concentrate and maintain interacting molecular species in a
microenvironment. A bounded system of replicating and catalytic
molecules capable of undergoing Darwinian evolution is by definition a
cell. At some point life on Earth became cellular, either from its
inception or soon thereafter. Boundary membranes divide complex
molecular mixtures into large numbers of individual structures that can
undergo selective processes required for biological evolution. They also
have the capacity to develop substantial ion gradients that represent a
central energy source for virtually all life today. A primary objective
of research is to understand self-organizing and evolutionary processes
that lead to the emergence of cellular structures and test this
understanding by creating laboratory models of primitive cells. These
are systems of interacting molecules within bounded environments capable
of working in concert to capture energy and nutrients from the
surroundings, transduce environmental signals, form metabolic networks
that allow for growth through polymerization, and reproduce some of
their polymeric components. Approaching this challenging problem will
lead to a more refined definition of the living state, and will clarify
the hurdles faced by self-assembled systems of organic molecules as they
evolved toward life.

**Objective 3.1 - Sources of prebiotic materials and catalysts.**
Characterize the exogenous and endogenous sources of matter (organic and
inorganic) for potentially habitable environments in the Solar System
and in other planetary and protoplanetary systems.

***Example investigations***

Emphasizing important prebiotic species, trace the formation, chemical
evolution and processing of interstellar molecules and solids into more
complex compounds.

Conduct laboratory experiments and simulations to provide a framework
for analyzing meteorites, samples returned from comets and asteroids,
and for interpreting spectra of interstellar clouds. Analyze meteorites
and returned samples to understand the nature of extraterrestrial
organic compounds.

Identify the organic compounds and complexes produced under primordial
planetary conditions through laboratory simulation experiments.

**Objective 3.2 - Origins and evolution of functional biomolecules.**
Identify plausible pathways for the synthesis of prebiotic monomers and
their condensation into polymers. Identify the potential for creating
catalytic and genetic functions, investigate their protobiological
evolution and explore primitive mechanisms for linking these two
functions.

***Example investigations***

Investigate polymers other than nucleic acids that have the potential to
have been precursor molecules capable of containing genetic information.

Conduct laboratory experiments and computational studies on the
emergence of functional proteins. Investigate mechanisms by which
primordial proteins evolved towards increased efficiency and
selectivity, and acquired new structures and functions.

Investigate ancestral translation mechanisms and the emergence of the
genetic code using laboratory experiments and clues from structural
biology and bioinformatics.

**Objective 3.3 - Origins of energy transduction.** Investigate,
conceptually and quantitatively, the relationship between energy,
complexity, and information as applied to the origin of biological
systems. Understand how the evolution of molecules, metabolic cycles,
linked systems, and organisms is enabled and constrained by the
development of energy transduction. Identify prebiotic mechanisms by
which energy can be captured, stored, and coupled to energy-requiring
processes.

***Example investigations***

Quantify the theoretical amount of energy required to specify the
sequence of amino or nucleic acid polymers as a function of chain
length; compare to the actual energy input required based on known
biological mechanisms.

Identify the classes of reactions available for prebiotic synthesis
under a range of plausible Solar System environmental conditions, based
on single-random inputs of energy or no inputs of energy.

Investigate mechanisms by which the energy available in ion gradients
across boundary membranes could couple to the synthesis of high-energy
compounds such as pyrophosphate.

**Objective 3.4 - Origins of cellularity and protobiological systems.**
Investigate both the origins of membranous boundaries on the early Earth
and the associated properties of energy transduction, transport of
nutrients, growth, and division. Investigate the origins and early
coordination of key cellular processes such as metabolism, energy
transduction, translation and transcription. Without regard to how life
actually emerged on Earth, create in the laboratory and study artificial
chemical systems that undergo mutation and natural selection.

***Example investigations***

Determine how ionic and polar nutrients could permeate membrane
boundaries to supply monomers and energy for intracellular metabolism
and biosynthesis.

Investigate polymerase reactions that can take place in membrane-bounded
microenvironments using external sources of monomers and chemical
energy, and determine self-replication capabilitlies of such simple
systems.

Considering clues from prebiotic chemistry and contemporary
biochemistry, investigate the organization of chemical reactions into a
primitive cellular metabolism and establish properties of the emerging
metabolic networks.

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**GOAL 4 - Understand how life on Earth and its planetary environment
have co-evolved through geological time.** Investigate the evolving
relationships between Earth and its biota by integrating evidence from
the geosciences and biosciences that shows how life evolved, responded
to environmental change, and modified environmental conditions on a
planetary scale.

Understand how extraterrestrial processes and the planetary environment
have influenced the evolution of life and how biological processes have
transformed conditions on local to planetary scales. An improved
knowledge of how life operated under diverse and extreme conditions will
improve our ability to define, detect and interpret biosignatures of
living and extinct organisms, here and elsewhere. Studies of key steps
in the development of life will enable a deeper understanding of the
pathways leading to biological complexity and thus inform the search for
living systems on distant worlds.

***Background***

As in other areas of astrobiology, integration of knowledge from many
fields of science is needed to understand the evolution of life in a
planetary context. Earth system models that relate processes operating
on vastly different temporal and spatial scales, from the core of the
Earth to the atmosphere and beyond, are an integral part of this
endeavor. Comparative genomic studies, often based on environmental
samples, including those from subsurface habitats, will provide a fuller
understanding of microbial biodiversity within communities that control
biogeochemical cycles, such as those involving the use of carbon,
sulfur, iron, and nitrogen compounds. Studies of the metabolic
requirements for life, the geochemical effects of those metabolic
activities in the form of proxy records, and the preserved biomolecular
signatures of ancient organisms will provide a deep time dimension to
the evolution of life in a global context and show how Earth's planetary
profile, as observed remotely, has changed throughout time.
Investigations that explore the response of life to environmental
perturbations on ecological to geological timescales will enhance our
understanding of planetary habitability and contribute to the search for
life beyond the Solar System. And research based on the fossil record of
life and its activities, coupled with knowledge gained from living
organisms, will enable key steps in the pathways to biological
complexity to serve as guideposts in the search for life beyond the
Solar System.

Using these tools and methods, astrobiologists can study the reciprocal
interactions between organisms and their planetary environment and
address the following questions: What microbial metabolisms existed at
the time of the oldest sedimentary rocks and what were their
environmental effects? What might we learn about the earlier history of
life on Earth if even older sedimentary samples can be found on the
Moon? What can we learn from the early history of life on Earth that
will inform the search for biosignatures on ancient Mars? How was the
evolution of Earth's atmosphere and oceans during the first half of
Earth history related to the development of life? How have life's course
and Earth's habitability been changed by major environmental
perturbations such as those resulting from extraterrestrial impacts, the
eruption of large igneous complexes, the oxygenation of the atmosphere,
global glaciations, and significant biological innovations? How does
biological complexity arise and what are its effects on planetary-scale
environments? Is there a predictable series of biological innovations
that will inform searches for life on planets orbiting other stars?
These and other questions are tied to this goal that seeks to understand
the historical interconnections between Earth and its biota to help
guide our search for life elsewhere. All of this research requires a
deeper understanding of evolutionary mechanisms at the levels of
molecules, cells, organisms, and ecosystems (Goal 5). The results
contribute directly to the identification of biosignatures (Goal 7).

**Objective 4.1 - Earth\'s early biosphere.** Investigate the
development of key biological processes and their environmental
consequences during the early history of Earth through biogeochemical,
paleobiological, geological, and genomic studies.

***Example investigations***

Explore the earliest sedimentary rock records for evidence of microbial
metabolic activities using biogeochemistry, isotope geochemistry, and
paleobiological methods.

Study the evolution of ancient environments across space and time using
high-resolution biogeochemical proxies from surface and subsurface
stratigraphic sections.

Use information obtained from microbial genomes to understand the
evolution of key metabolic pathways, such as methanogenesis, and search
for biogeochemical evidence for the existence of these pathways in
Archean sedimentary sequences.

Develop complex numerical models for the behavior of biogeochemical
cycles under the conditions that existed on the early Earth and apply
such knowledge to the interpretation of early Mars.

**Objective 4.2 -- Production of complex life.** Investigate the
pathways and mechanisms that increased the complexity of life from
microbial communities through successive levels of multicellularity.

***Example investigations***

Study detailed records of biogeochemical proxies to determine if global
environmental events were driven by biological innovation.

Use comparative genomics in conjunction with the fossil and biomolecular
fossil records to better understand key steps in the evolution of
eukaryotes and sources of their genomes.

Apply knowledge gained from studies of the evolution of development to
understand the sudden evolution of complex animals during the
Neoproterozoic and early Cambrian.

**Objective 4.3 -- Effects of extraterrestrial events upon the
biosphere.** Study the short and long-term effects of extraterrestrial
phenomena such as secular changes in the magnitude and quality of solar
and cosmic radiation, the evolution of the Earth-Moon system, nearby
supernovae, and infalling comets and asteroids on life and the
environments in which it exists.

***Example investigations***

Use data obtained from the geological record to understand the coupling
between extraterrestrial environmental perturbations that might have
influenced the sustainability of life.

Investigate the mechanisms that enable small changes in the amount and
quality of solar radiation received by the Earth to influence global
climate and biological productivity.

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**Goal 5 - Understand the evolutionary mechanisms and environmental
limits of life.** Determine the molecular, genetic, and biochemical
mechanisms that control and limit evolution, metabolic diversity, and
acclimatization of life.

The diversity of life on Earth today is a result of the dynamic
interplay between genetic opportunity, metabolic capability and
environmental change. For most of its existence, our habitable
environment has been dominated by microorganisms and subjected to their
metabolism and evolution. As a consequence of such microbial activities
on a geological time scale, the physical-chemical environment on Earth
has been changing, thereby determining the path of evolution of
subsequent life. For example, the release of molecular oxygen by
cyanobacteria as a by-product of photosynthesis as well as the
colonization of the Earth\'s surface by metazoan life resulted in
fundamental, global changes in the Earth\'s environment. The altered
environment, in turn, posed novel evolutionary opportunities to the
organisms present, which ultimately led to the formation of our
planet\'s major animal and plant species. Therefore, this
\'co-evolution\' between organisms and their environment is an intrinsic
feature of living systems.

Life survives and sometimes thrives under what seem to be harsh
conditions on Earth. For example, some microbes thrive at temperatures
of 113˚C. Others exist only in highly acidic environments or survive
exposures to intense radiation. While all organisms are composed of
nearly identical macromolecules, evolution has enabled such microbes to
cope with this wide range of physical and chemical conditions. What are
the features that enable one microbe to thrive under extreme conditions
that are lethal to many others? An understanding of the tenacity and
versatility of life on Earth, as well as an understanding of the
molecular systems that some organisms utilize to survive such extremes,
will provide a critical foundation for the search for life beyond Earth.
These insights will help us to understand the molecular adaptations that
define the physical and chemical limits for life on Earth. They will
provide a baseline for developing predictions and hypotheses about life
on other worlds.

**Background**

The evolution of biogeochemical processes, genomes, and microbial
communities has resulted in the complexity and robustness of the modern
biosphere. However, we lack an understanding of how mutational events
one the single gene level scale to altered macroscopic ecological
performances of entire populations. We can examine the reciprocal
interactions between biosphere and geosphere that can shape genes,
genomes, organisms, and species interactions. Accordingly, we will begin
to develop an understanding of the evolution of biochemical and
metabolic machinery that drives the global cycles of the elements, as
well as the potential and limits of such evolution. Furthermore, we must
observe their coordination into genetic circuitries, and their
integration into more complex biological entities, such as whole cells
and microbial communities.

While co-evolution of the Earth\'s physical-chemical environment and its
living world is dynamic and proceeds at all organismic levels,
prokaryotic microorganisms have played a critical role in shaping our
planet. Microbes can serve as highly advanced experimental systems for
biochemical, genetic, and genomic studies. To date, over 500 microbial
genomes have been sequenced. This unprecedented wealth of information,
together with the experimental tools now available for single cell
studies, provides a tremendous opportunity for experimental studies to
be conducted on the evolution of microbial genes, genomes, and microbial
communities. Such studies will uncover fundamental principles of
molecular, cellular and community level evolution with relevance to
Earth and other planets. Of specific interest is observing or simulating
the evolution of those molecular properties that facilitate the
metabolic coupling of the oxidation/reduction cycles of elements and the
adaptation to novel environments, especially extreme environments,
created by simulated perturbations. Hypothesis-driven experimentation on
microbial ecosystems using single species with known genome sequences
can be employed to predict environmental changes and evolutionary
solutions. Such studies can be extended to defined mixed communities to
study the plasticity and adaptation of the \"metagenome,\" comprising
the genomes of all members of a microbial community, when subjected to
environmental changes and genetic flux. The evolved genotypes and
phenotypes should be correlated to the specific changes they induce in
the physical-chemical environment.

Our ongoing exploration of the Earth has led to continued discoveries of
life in environments that have been previously considered uninhabitable.
For example, we find thriving communities in the boiling hot springs of
Yellowstone, the frozen deserts of Antarctica, the concentrated sulfuric
acid in acid-mine drainages, and the ionizing radiation fields in
nuclear reactors. We find some microbes that grow only in brine and
require saturated salts to live and we find others that grow in the
deepest parts of the oceans and require 500 to 1000 bars of hydrostatic
pressure. Life has evolved strategies that allow it to survive even
beyond the daunting physical and chemical limits to which it has adapted
to grow. To survive, organisms can assume forms that enable them to
withstand freezing, complete desiccation, starvation, high-levels of
radiation exposure, and other physical or chemical challenges.
Furthermore, they can survive exposure to such conditions for weeks,
months, years, or even centuries. We need to identify the limits for
growth and survival, and to understand the molecular mechanisms that
define these limits. Biochemical studies will also reveal inherent
features of biomolecules and biopolymers that define the
physical-chemical limits of life under extreme conditions. Broadening
our knowledge both of the range of environments on Earth that are
inhabitable by microbes and of their adaptation to these habitats will
be critical for understanding how life might have established itself and
survived in habitats beyond Earth.

**Objective 5.1 Environment-dependent, molecular evolution in
microorganisms.** Experimentally investigate and observe the evolution
of genes, metabolic pathways, genomes, and microbial species.
Experimentally investigate the forces and mechanisms that shape the
structure, organization, and plasticity of microbial genomes. Examine
how these forces control the genotype-to-phenotype relationship. Conduct
environmental perturbation experiments on single microbial species to
observe and quantify adaptive evolution to astrobiologically relevant
environments.

*Example investigations*

Experimentally observe the expansion and contraction of microbial
genomes within the context of different environments and selective
forces.

Examine the molecular basis of the robustness and resilience of
metabolic pathways in response to environmental changes.

Develop an understanding of the link between single gene evolution and
the ecological consequences on the level of microbial populations.

**Objective 5.2**. **Co-evolution of microbial communities**.
Experimentally examine the metabolic and genetic interactions in
microbial communities that have determined major geochemical processes
and changes on Earth. Investigate how these interactions shape the
evolution and maintenance of metabolic diversity in microbial
communities. Investigate how novel microbial species establish and adapt
into existing communities.

*Example investigations*

Investigate small molecule interactions and their role in coordinating
energy flow in mixed phototrophic/chemotrophic microbial communities.

Examine the molecular basis of speciation, e.g., the evolution of a
generalist to a specialist, and, conversely, of a specialist a to
generalist.

Examine the deterministic and stochastic processes leading to the
resilience of established microbial communities.

**Objective 5.3**. **Biochemical adaptation to extreme environments.**
Document life that survives or thrives under the most extreme conditions
on Earth. Characterize and elucidate the biochemical capabilities that
define the limits for cellular life. Explore the biochemical and
evolutionary strategies that push the physical-chemical limits of life
by reinforcing, replacing, or repairing critical biomolecules (e.g.,
spore formation, resting stages, protein replacement rates, or DNA
repair). Characterize the structure and metabolic diversity of microbial
communities in such extreme environments.

*Example investigations*

Investigate the physiological and molecular basis of the ability of
microorganisms to persist at low water activity.

Biochemically characterize the diversity of DNA-repair mechanisms that
allow microorganisms to recover from radiation damage.

Study microbial strategies that permit life in stationary phase.

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**Goal 6: Understand the principles that will shape the future of life,
both on Earth and beyond.** Elucidate the drivers and effects of
microbial ecosystem change as a basis for forecasting future changes on
time scales ranging from decades to millions of years, and explore the
potential for microbial life to survive and evolve in environments
beyond Earth, especially regarding aspects relevant to the President's
Vision for Space Exploration.

Life on Earth depends upon networks of biogeochemical reactions that
interact with the crust, oceans and atmosphere to maintain a biosphere
that has been remarkably resilient to environmental challenges. These
reaction networks developed within self-organized microbial ecosystems
that collectively responded to environmental conditions and changes.
Evolutionary biologists are working to understand how such biological
and environmental processes have shaped specific ecosystems in Earth\'s
history. It is highly challenging yet critically important to employ
such principles to formulate accurate predictions about the state of
future ecosystems, especially when environments change faster than the
tempo of biological evolution. Predictions of this nature will require
improved models of the biogeochemical cycling of critical elements that
links biological processes with the surrounding physical world.

Viewing Earth\'s ecosystems in the context of astrobiology challenges us
to consider how \"resilient\" life really is on a planetary scale, to
develop mathematical representations of stabilizing feedbacks that
permit the continuity of ecosystems in the face of rapidly changing
physical conditions, and to understand the limits of these stabilizing
feedbacks. Ideally this consideration will provide insight into the
potential effects of environmental changes that are abrupt as well as
those changes that unfold over time scales ranging from seasonal cycles
to millions of years.

The ability of life to move beyond Earth will depend upon the potential
for microorganisms to utilize resources and to adapt and evolve in
extraterrestrial environments. Viable microorganisms [might]{.underline}
be transported by natural events such as impacts or by robotic
spacecraft, but they most certainly [will]{.underline} accompany human
missions. Life forms will be challenged by extremes in temperature,
pressure, radiation and the availability of nutrients. Studies of
adaptation and survival will indicate not only whether microbial life
can expand its evolutionary trajectories beyond Earth but also how it
can play key supporting roles in human exploration.

*Background*

Humans are increasingly perturbing Earth\'s biogeochemical cycles. In
addition to impacting the carbon cycle, humans have doubled the natural
global sulfur emissions to the atmosphere, doubled the global rate of
nitrogen fixation, enhanced levels of phosphorus loading to the ocean,
altered the silica cycle, and perhaps, most critically, altered the
hydrological cycle. When compared to many natural perturbations, the
effects of human activities have been extremely rapid. Understanding how
these changes will affect planetary climate, ecosystem structure, and
human habitats is an urgent research priority in which astrobiology can
play an important role.

A conceptual continuum embraces the development of biogeochemical
cycles, the evolution to the modern biosphere and ongoing human effects.
Studies of processes over long time scales (millenia to millions of
years) offer an observational context that extends and strengthens the
interpretation of shorter time scale (annual to century) phenomena.
While longer-term changes in Earth\'s ecosystems are strongly affected
by processes such as tectonics and evolution, the relatively rapid rates
of recent change, influenced by anthropogenic forcing, may only have
analogues in previous important events such as major extinctions.

A key objective for elucidating the sign of the feedbacks in
biogeochemical cycles and for understanding how the cycles respond to
perturbations is to develop quantitative models that incorporate the
interactions between metabolic and geochemical processes. For example,
how are the key biogeochemical cycles of the light elements (e.g., C, N,
O, S, P, etc.) related? What constrains these cycles on time scales of
years to millions of years? How are these cycles altered by rapid
changes in climate? Does functional redundancy, as indicated by a great
diversity within microbial ecosystems, ensure ecosystem resilience? Are
specific metabolic pathways more sensitive to perturbations than others?
How have the biogeochemical cycles co-evolved with terrestrial
environments on time scales of millions of years? Our vision of the
future will be sharpened by a retrospective view offered by a
biogeochemical model that is verified by preserved records. This effort
is needed in order to expand the current focus on short-term changes and
\"what is happening\" in order to perform more hypothesis-testing and
thus address \"why is this happening.\"

Life forms that are transported beyond their planet of origin will
probably experience conditions more extreme than those in the most
extreme habitats on Earth. Such conditions will challenge their very
existence in most, if not all, cases. Understanding survival and
evolution beyond the planet of origin is essential for evaluating the
potential for the interplanetary transfer of viable organisms and thus
the potential that life elsewhere in the Solar System might share a
common origin with life on Earth. Survivorship beyond Earth is an
ultimate test of the resilience of terrestrial life and thus of its
potential to diversify far beyond the limits of our current
understanding. Microbes and other organisms are destined ultimately to
play critical roles in life support during extended human missions.
Their study should be an integral component of the expansion of mankind
throughout the solar system as NASA carries out the Vision for Space
Exploration over the next century.

**Objective 6.1*.* Effects of environmental changes on microbial
ecosystems.** Conduct remote sensing, laboratory and field studies that
relate the effects of present-day environmental changes to the
biogeochemical cycling of key elements by microorganisms. Relate changes
in elemental cycling to effects on the structure and functioning of
microorganisms, their ecosystems, and the surrounding environment.
Develop predictive models that integrate biogeochemical cycles with
adaptation by microbial ecosystems and with environmental change (both
those driven by anthropogenic and non-anthropogenic forces, including
extraterrestrial events \[see Objective 4.3).

*Example investigations*

Construct biogeochemical models of ecosystems and test the models with
biogeochemical assays and functional genomic analyses of the constituent
parts of the ecosystems.

Document the ecological impact of changes in climate, habitat complexity
and nutrient availability upon the structure and function of a selected
ecosystem, as a guide to understanding changes that might occur over
time scales ranging from abrupt events (a few years or less) to millions
of years.

**Objective 6.2*.* Adaptation and evolution of life beyond Earth.**
Explore the adaptation, survival and evolution of microbial and other
organisms under environmental conditions that simulate conditions in
space or on other potentially habitable planets. Identify survival
strategies to evaluate the potential for interplanetary transfer of
viable organisms and to establish requirements for effective planetary
protection. Identify and validate roles that microorganisms might play
in life support and resource acquisition during human missions
envisioned by the Vision for Space Exploration. Develop tools to track
the function and adaptation of microbes and other organisms to
extraterrestrial environments during mankind's exploration efforts.

*Example investigations*

Document the effects of the space environment upon microbial ecosystems.

Examine the survival, genomic alteration, and adaptation of microbial
ecosystems in a wide range of simulated Martian environments. Interpret
the significance of these experiments regarding the potential for the
forward biological contamination of Mars and for utilizing
microorganisms to support the needs of human exploration.

Examine the effects of the space environment upon the biosynthesis and
utilization of biomolecules that play key roles in biogeochemical
processes and also upon the viability of microbes that might be
transferred between planets by natural processes (e.g., impact
ejection).

Develop automated assay tools to monitor the adaptation of organisms in
lunar and Martian environments, especially those areas most likely to be
visited by human explorers over the next century.

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**Goal 7: Determine how to recognize signatures of life on other worlds
and on early Earth.** Identify biosignatures that can reveal and
characterize past or present life in ancient samples from Earth,
extraterrestrial samples measured *in situ*, samples returned to Earth,
remotely measured planetary atmospheres, surfaces and technologies.

Our concepts of life and biosignatures are inextricably linked. To be
useful for exploration, biosignatures must be defined in terms that can
be measured and quantified. Measurable attributes of life include its
complex physical and chemical structures and also its utilization of
free energy and the production of biomass and wastes; phenomena that can
be sustained through self-replication and evolution. Habitable planets
might create nonbiological features that mimic biosignatures and
therefore must be understood in order to clarify our interpretations. We
must create a library of biosignatures and their nonbiological mimics of
life as we know it. A strategy is needed for recognizing novel
biosignatures. This strategy ultimately should accommodate a diversity
of habitable conditions, biota and technologies in the universe that
probably exceeds the diversity observed on Earth.

***Background***

Astrobiological exploration is founded upon the premise that signatures
of life (biosignatures) will be recognizable in the context of their
environments. A biosignature is an object, substance and/or pattern
whose origin specifically requires a biological agent. The usefulness of
a biosignature is determined, not only by the probability of life
creating it, but also by the improbability of nonbiological processes
producing it. An example of such a biosignature might be complex organic
molecules and/or structures whose formation is virtually unachievable in
the absence of life. A potential biosignature is a feature that is
consistent with biological processes and that, when it is encountered,
challenges the researcher to attribute it either to inanimate or to
biological processes. Such detection might compel investigators to
gather more data before reaching a conclusion as to the presence or
absence of life.

Catalogs of biosignatures must be developed that reflect fundamental and
universal characteristics of life, and thus are not restricted solely to
those attributes that represent local solutions to the challenges of
survival. For example, certain examples of our biosphere\'s specific
molecular machinery, e.g., DNA and proteins, might not necessarily be
mimicked by other examples of life elsewhere in the cosmos. On the other
hand, basic

principles of biological evolution might indeed be universal.

However, not all of the universal attributes of life will be expressed
in ancient planetary materials or detectable remotely (e.g., by
astronomical methods). For example, the processes of biological
evolution are highly diagnostic for life, but evidence of biological
evolution might not be readily detected as such in a sample returned
from Mars. However, better-preserved evidence of life might include
complex structures that are often retained in aquatic sediments or can
be preserved in large quantities in the environment. Thus, for example,
categories of biosignatures can include the following: cellular and
extracellular morphologies, biogenic fabrics in rocks, bio-organic
molecular structures, chirality, biogenic minerals, biogenic stable
isotope patterns in minerals and organic compounds, atmospheric gases,
remotely detectable features on planetary surfaces (photosynthetic
pigments, etc.) and characteristic temporal changes in global planetary
properties (e.g. seasonally-mediated respiration and biomass cycles). On
Earth, biosignatures also include those key minerals, atmospheric gases
and crustal reservoirs of carbon, sulfur and other elements that
collectively have recorded the enduring global impact of the utilization
of free energy and the production of biomass and wastes.
Oxygen-producing photosynthesis has simultaneously created large
reservoirs of atmospheric oxygen, marine sulfates and sedimentary ferric
iron and sulfates (its oxidized products), as well as large sedimentary
reservoirs of biogenic organic matter and sulfides (its corresponding
reduced products). Again, in order to be biosignatures such features
must be sufficiently complex and/or abundant so that they retain a
diagnostic expression of some of life\'s universal attributes. Also,
their formation by nonbiological processes should be highly improbable.

All biosignatures are characteristic of the modification of a local or
planetary environment by life. Human technology and its resultant
products and outputs can therefore also be considered as a biosignature,
with the added benefit that it might be detected remotely. Thus,
although technology is probably much rarer than life in the universe,
its associated biosignatures perhaps enjoy much higher
\"signal-to-noise\" ratios. Accordingly, current methods should be
further developed and novel methods should be identified for detecting
electromagnetic radiation or other diagnostic artifacts that indicate
remote technological civilizations.

**Objective 7.1. Biosignatures to be sought in Solar System materials.**
Learn how to recognize and interpret biosignatures that, if identified
in samples from ancient rocks on Earth or in rocks and atmospheres on
other Solar System planets, can help to detect and/or characterize
ancient and/or present-day life.

***Example Investigations***

Determine additional organic biomarkers that will help to chart the
presence and development of photosynthetic microbiota in Precambrian
rocks.

Determine the features of sedimentary laminated textures that uniquely
require biological processes.

Identify examples of chemical, mineralogical and stable isotopic
biosignatures that can indicate the presence of subsurface biota (e.g.,
microbes living in aquifers), and that can be preserved in ancient
rocks.

Understand the potential sources and any diagnostic characteristics
(e.g. isotopic signatures) of methane in the Martian atmosphere, and
determine how these might be measured and discriminated between
spectroscopically via orbiting spacecraft or ground-based observatories.

**Objective 7.2. Biosignatures to be sought in nearby planetary
systems.** Learn how to identify and measure biosignatures that can
reveal the existence of life or technology through remote observations.

***Example Investigations***

Determine the nature and fate of reduced gases that are produced by
specific microbial ecosystems in an anoxic (\"pre-oxygenated\")
biosphere.

Carry out laboratory, observational and modeling studies to separate
false from true biosignatures (e.g., atmospheric O~2~ in a range of
planetary environments \[see Objective 1.2\]).

Develop novel approaches to detect evidence of distant technologies.