In the Cold: The Future of Astromaterials Curation?
Christopher D. K. Herd1
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada

1

Introduction: Astromaterials, including meteorites, lunar samples, solar wind, cometary dust, asteroidal regolith andinterplanetary dust, provide a unique record of the conditions that prevailed during the formation of our solar system, and thesubsequent processes involved in the evolution of a variety of planetary bodies. However, the majority of astromaterials
formed in environments not found at the Earth’s surface [1]. Therefore, curation is a critical component in the planning ofsample return missions [1] (and can be captured in the question: Why spend billions to bring samples back if they becomecontaminated during sample handling and curation?).
Modern curation facilities have as their primary goal the isolation of astromaterials from the terrestrial environment [1].
Airborne particulate contaminants are mitigated using HEPA filtration systems, as well as recognized clean room practices(e.g., use of gloves, gowns, boots, etc.). Due to the relative abundance of organic compounds at the Earth’s surface, organic
contamination is particularly problematic, and may be mitigated by specialized handling practices to limit the transfer ofterrestrial organics to the samples, and cleaning procedures and methods for identifying and monitoring contaminants [e.g., 2].
However, astromaterials can be compromised in ways other than simple sorption of non-indigenous compounds on exposed
surfaces, or via mixture with airborne dust. Oxidation and hydrolysis are a type of invasive contamination as both processes
permanently chemically alter the intrinsic compounds and minerals in the sample; for this reason, inert atmospheres are
utilized in curation to limit reaction of the indigenous organics and minerals with atmospheric water and molecular oxygen gas.
However, the recognition of volatile and/or reactive organic species in carbonaceous chondrites [e.g., 3] necessitatesconsiderations of curation at low temperature, in order to prevent the loss of intrinsic volatile species.
Insights from Tagish Lake: The Tagish Lake meteorite fell January 18 2000 onto a frozen lake surface in northern British
Columbia, Canada. Samples of the meteorite were recovered within a week of the fall and kept frozen and untouched by hand(the so-called “pristine specimens”). Studies of the Tagish Lake meteorite demonstrate that it is an ungrouped Type 2
carbonaceous chondrite with affinities to CI and CM chondrites [4]. Tagish Lake is among the most enriched in carbon of allchondrites, containing up to ~6 wt% total C, of which approximately half is organic [5]. The soluble organic component, while
relatively small (~2 % of organic C), contains several classes of compounds of prebiotic interest, including some which areparticularly volatile (e.g., formic acid) [6-8]. Systematic study of different lithologies within Tagish Lake demonstratevariation in organic matter characteristics that correlate with mineralogy and petrology [9]; these variations are thought torepresent a record of the effect of parent body alteration on the structure and composition of the organic matter [10]. Further
details on intrinsic and contaminant organic species found in the Tagish Lake meteorite are summarized by [11].
Cold curation in practice: The pristine specimens of Tagish Lake necessitated the development of a facility that would enable
the documentation, processing and storage of astromaterials under cold, inert conditions. The Subzero Curation Facility for
Astromaterials at the University of Alberta is designed with these considerations in mind, within the limitations of funding
available. At the heart of the facility is an Ar gas glove box (MBraun, Inc.), housed within a controlled environment chambercapable of maintaining temperatures between -30 and -10 °C (Fig. 1). The glove box consists of a single user station made ofbrushed 304 stainless steel with radius corners, with a polycarbonate window with chemical and scratch resistant coating (Fig.
1c). Integrated into the window is a binocular microscope (Leica, Inc.), fitted with a camera adapter (Fig. 1c). An adjustablestage sits beneath the microscope, within the glove box. On the right side of the main box is a secondary, storage box made of
the same materials as the main box (Figure 1c); separated from the main box by a sealable door, this box allows for temporarystorage of samples while experiments (e.g., involving solvents) are being carried out in the main box. The atmosphere within
the glove box is maintained using an MB 20 G gas purifier (MBraun, Inc.); once charged with high-purity oxygen-free(99.998%) argon, the system continuously recirculates the argon through a purification system, which removes airborne
contaminants and maintains O2 and H2O to < 1 ppm. HEPA filters on gas inlets also reduce any particulate matter that may beotherwise be circulated into the glove box. An activated carbon filter unit on the gas outlet for the main glove box removes any
volatile organic compounds that might contaminate the materials used within the purifier; this feature also allows for organic
solvents (e.g., chlorinated solvents such as dichloromethane) to be used within the glove box, either for cleaning purposes or tocarry out organic extractions on samples within a purified inert atmosphere at low temperature. A Class 1000 clean room
(Lasco Services, Inc.) serves as a room temperature anteroom to the freezer chamber (Fig. 1a). This anteroom was establishedto provide a source of clean air for the freezer chamber, since HEPA filtering of the freezer chamber air was not practicable.
The anteroom also provides improved storage for the University of Alberta Meteorite Collection. Further details are provided
in [11], including methods and results pertaining to commissioning of the facility.

Figure 1. The Subzero Curation Facility at the University of Alberta, consisting of a Class 1000 room temperature anteroom (A), and a walkin freezer (B) in which an Ar glove box is housed (C).

Insights into cold curation for future sample return: Processing of Tagish Lake specimens now occurs on a routine basis
within the Subzero Curation Facility for Astromaterials. To date, no significant levels of organic contaminants have beenobserved in any meteorite samples, although the use of witness plates is planned but not yet implemented. In practicality, thefacility accomplishes the purpose for which it was built, i.e., to enable the processing of Tagish Lake specimens under clean,cold conditions in an inert atmosphere (although Tagish Lake specimens remain in storage in air, [11]). The two main
limitations encountered thus far in the use of the facility include mitigation of a glove box leak and user comfort – the lowtemperature of the freezer chamber compounds the challenges associated with glove box work. As with any cold environment
work, standard operation involves donning insulated clothing (under the clean room smocks), working with a partner, andlimiting exposure to the cold – typically 15-20 minutes at a time. The main advantage of the facility is the reduced risk tospecimens once they are transferred into the glove box, allowing for frequent user breaks (to warm up). However, in the caseof a sudden leak or atmospheric contamination event, rapid mitigation of the problem can be hampered by the cold, especially
if the user has already been working in that environment before the problem is noticed.
Conclusions: In spite of the challenges, cold curation provides significant advantages over room-temperature curation,
including: the retention of intrinsic volatiles; the suspension or inhibition of microbial activity; the minimization of outgassingof glovebox components; and the reduction in reaction rates of oxidation and hydrolysis of intrinsic organic compounds andminerals. Therefore cold curation is recommended for future sample return from any parent body in which volatile components
are anticipated (e.g., organic-rich asteroids, cometary nuclei, Mars). The optimal design of a cold curation facility will need tobalance the parent-body-specific conditions required to preserve the sample with those which maintain user comfort. In
practice, this will most likely require the ultra-cold (~ -80°C) storage of specimens and the handling and processing ofspecimens under cold (~ -15°C) conditions. Notably, micromanipulation of small samples under cold conditions has yet to betested, and is an important consideration for future sample return mission planning.
References[1] Allen C. et al. 2011. Chemie der Erde - Geochemistry 71:1-20. [2] Calaway M.J. et al. 2014. Organic Contamination
Baseline Study in NASA Johnson Space Center Astromaterials Curation Laboratories, Report S-1159. [3] Botta O. and J.L.
Bada 2002. Surveys in Geophysics 23:411-467. [4] Zolensky M.E. et al. 2002. Meteoritics & Planetary Science 37:737-761.
[5] Grady M.M. et al. 2002. Meteoritics & Planetary Science 37:713-735. [6] Pizzarello S. et al. 2001. Science 293:2236-2239.
[7] Hilts R.W. et al. 2014. Meteoritics & Planetary Science 49:526-549. [8] Glavin D.P. et al. 2012. Meteoritics & Planetary
Science 47:1347-1364. [9] Blinova A.I. et al. 2014. Meteoritics & Planetary Science 49:473-502. [10] Herd C.D.K. et al. 2011.
Science 332: 1304-1307. [11] Herd C.D.K. et al. 2016. Meteoritics & Planetary Science 51:499-519.