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All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Conditions on Early Mars Might Have Fostered Rapid and Early Development of Life

The exploration of Mars during the past decades has begun to unveil the history of the planet. The combinations of remote sensing, in situ geochemical compositional measurements and photographic observations from both above and on the surface have shown Mars to have a dynamic and active geologic evolution. Mars geologic evolution clearly had conditions that were suitable for supporting life. For a planet to be able to be habitable, it must have water, carbon sources, energy sources and a dynamic geologic past. Mars meets all of these requirements. The first 600 My of Martian history were ripe for life to develop because of the abundance of (i) Water-carved canyons and oceans or lakes with the early presence of near surface water shown by precipitated carbonates in ALH84001 well-dated at approx.3.9 Gy., (ii) Energy from the original accretional processes, a molten core which generated a strong magnetic field leaving a permanent record in the early crust, early active volcanism continuing throughout Martian history, and, and continuing impact processes, (iii) Carbon and water from possibly extensive volcanic outgassing (i.e. H2O, CO2, CH4, CO, O2, N2, H2S, SO2, etc.) and (iv) some crustal tectonics as revealed by faulting and possible plate movement reflected by the magnetic pattern in the crust. The question arises: "Why would life not evolve from these favorable conditions on early Mars in its first 600 My?" During this period, it seems likely that environmental near-surface conditions on Mars were more favorable to life than at any later time. Standing bodies of water, precipitation and flowing surface water, and possibly abundant hydrothermal energy would all favor the formation of early life. Even if life developed elsewhere (on Earth, Venus, or on other solar systems) and was transported to Mars, the surface conditions were likely very hospitable for that introduced life to multiply and evolve.

Gibson, Everett K.↗
NASA NTRS2011

The Formation of Fe/Mg Smectite Under Mildly Acidic Conditions on Early Mars

The detection of Fe/Mg smectites and carbonate in Noachian and early Hesperian terrain of Mars has been used to suggest that neutral to mildly alkaline conditions prevailed during the early history of Mars. However, if early Mars was neutral to moderately alkaline with a denser CO2 atmosphere than today, then large carbonates deposits should be more widely detected in Noachian terrain. The critical question is: Why have so few carbonate deposits been detected compared to Fe/Mg smectites? We suggest that Fe/Mg smectites on early Mars formed under mildly acidic conditions, which would inhibit the extensive formation of carbonate deposits. The goal of this work is to evaluate the formation of Fe/Mg smectites under mildly acidic conditions. The stability of smectites under mildly acidic conditions is attributed to elevated Fe/Mg activities that inhibit smectite dissolution. Beidelite and saponite have been shown to form from hydrothermal alteration of basaltic glass at pH 3.5-4.0 in seawater solutions. Nontronite is also known to be stable in mildly acidic systems associated with mafic and ultramafic rock. Nontronite was shown to form in acid sulfate soils in the Bangkok Plain, Thailand due to oxidation of Fe-sulfides that transformed saponite to nontronite. Smectite is known to transform to kaolinite in naturally acid soils due to selective leaching of Mg. However, if Mg removal is limited, then based on equilibrium relationships, the dissolution of smectite should be minimized. If Fe and Mg solution activities are sufficiently high, such as might be found in a low water/rock ratio system that is poorly drained, smectite could form and remain stable under mildly acidic conditions on Mars. The sources of mild acidity on early Mars includes elevated atmospheric CO2 levels, Fe-hydrolysis reactions, and the presence of volcanic SO2 aerosols. Equilibrium calculations dictate that water equilibrated with an early Mars CO2 atmosphere at 1 to 4 bar yields a pH of 3.6 to 3.9. Fe hydrolysis reactions on Mars is another source of protons that would have contributed to acidity. The presence of SO2 from volcanic processes could also have contributed to geochemical acidification. These sources of acidity competed with base-forming cations that resulted in mildly acidic solutions that were not favorable for carbonate formation but may have allowed for Fe/Mg smectite formation. Noachian to early Hesperian Mars could have been mildly acidic, allowing Fe/Mg smectite formation but preventing widespread carbonate deposition. This paradigm shift from an early Mars that was neutral-alkaline to mildly acidic may possibly explain why there is a disparity between the occurrence of carbonate and Fe/Mg smectites. Potential microbiological activity would not be eliminated under a mildly acidic Mars; however, there could be tighter constraints as to the type and species of microbiology that could exist.

Sutter, Brad↗
NASA NTRS2015

Strategic Map for Exploring the Ocean-World Enceladus

Among the many "ocean worlds" of our solar system, Enceladus appears unique in its combination of astrobiologically relevant, exploration-worthy attributes: extensive liquid-water ocean with high-temperature hydrothermal activity, containing salts and organics expressed predictably into space. The Enceladus south polar plume allows direct access to telltale molecules, ions, isotopes, and potential cytofragments in space. Plume mass spectroscopy and sample return, in situ investigation of surface fallback deposits, direct vent exploration, and eventually oceanographic exploration can all be envisioned. However, building consensus to fund such ambitious exploration hinges on acquiring key new data. A roadmap is essential. It could start with cost-capped onramps: 1) flythrough analysis of the plume, following up on Cassini measurements with modern instruments; 2) sample return of plume material for analysis on Earth. A methodical mission sequence in which each step depends on emergent results from prior missions would push in situ oceanographic exploration into the second half of this century. Even for this scenario, prioritization by the next planetary Decadal Survey would be pivotal.

Cassini↗
NASA NTRS1997

Microbial Fossils from Terrestrial Subsurface Hydrothermal Environments: Examples and Implications for Mars

The recognition of biological signatures in ancient epithermal deposits has special relevance for studies of early blaspheme evolution and in exploring for past life on Mars. Recently, proposals for the existence of an extensive subsurface blaspheme on Earth, dominated by chemoautotrophic microbial life, has gained prominence. However, reports of fossilized microbial remains, or biosedimentary structures (e.g. stromatolites) from the deposits of ancient subsurface systems, are rare. Microbial preservation is favoured where high population densities co-exist with rapid mineral precipitation. Near-surface epithetical systems with strong gradients in temperature and redox are good candidates for the abundant growth and fossilization of microorganisms, and are also favorable environments for the precipitation of ore minerals. Therefore, we might expect microbial remain, to be particularly well preserved in various kinds of hydrothermal and diagenetic mineral precipitates that formed below the upper temperature limit for life (approx. 120 C).

Hofmann, Beda A.↗
NASA NTRSDate not supplied

Worswick Hot Springs: A Radioactive Hydrothermal Field Site

We report on a systematic characterization of the radiation environment and water temperatures of Worswick Hot Springs, which is in support of companion biochemical and microbial investigations of iron respiration in the ‘extreme’ microbial systems found at the field site. We have discovered localized areas of elevated radioactivity that are approximately four to five times greater than background radiation. Additionally, we have observed that both the radiation environment and the temperature of the spring waters vary over time. Because localized “hot spots” of elevated radiation and biofilms are easily accessible, various biological studies of radiation resistance and biosignature formation are possible, making this field site relevant for analog field studies that consider microbiology, geochemistry, and ionizing radiation. In addition to Worswick being a natural radiation biology laboratory that may also be relevant for space biology applications, we assert that these unusual environmental conditions may inform us about locations on Mars that are also enriched in radioactive elements and their potential for hosting biosignatures.

Jon C. Rask↗
NASA NTRS2004

Medusa Sea Floor Monitoring System

The objective of the research described in this poster presentation is to develop technologies to enable fundamental research into understanding the potential for and limits to chemolithoautotrophic life. The Medusa Isosampler (isobaric sampler), for sampling fluids eminating from deep sea hydrothermal vents and cold seep sites analogous to extraterrestrial environments, is described by the presentation. The following instruments are integrated with the isosampler, and also described: in situ flow-through chemical sensor, intrinsic fluorescent-based microbial detector, isotope ratio spectral detector.

Flynn, Michael↗
NASA NTRS2016

A Fly-Through Mission Strategy Targeting Peptide as a Signature of Chemical Evolution and Possible Life in Enceladus Plumes

In situ detection of organic molecules in the extraterrestrial environment provides a key step towards better understanding the variety and the distribution of building blocks of life and it may ultimately lead to finding extraterrestrial life within the Solar System. Here we present combined results of two separate experiments that enable us to realize such in situ life signature detection from the deep habitats of the "Ocean World": a hydrothermal reactor experiment simulating complex organic synthesis and a simulated fly-through capture experiment of organic-bearing microparticles using silica aerogels, followed by subsequent analysis. Both experiments employ peptide as a plausible organics existing in Encleadus plume particles produced in its subsurface ocean. Recent laboratory hydrothermal experiments and a theoretical model on silica saturation indicated an on going hydrothermal reactions in subsurface Enceladus ocean. Given the porous chondritic origin of the core, it is likely that organic compounds originated by radiation chemistry such as amino acid precursors could have been provided, leached, and altered through widespread water-rock interactions. By using the same laboratory experimental setup from the latest water-rock interaction study, we performed amino acid polymerization experiments for 144 days and monitored the organic complexity changing over time. So far over 3,000 peaks up to the size of greater than 600 MW were observed through the analysis of capillary electrophoresis time-of-flight mass spectrometry (CE-TOF-MS) with an indication of amino acid derivatives and short peptides. Generally abiotic polymerization of enantiomeric amino acids results in forming stereoisomeric peptides with identical molecular weight and formula as opposed to homochiral biopolymers. Assuming Enceladus plume particles may contain a mixture of stereoisomeric peptides, we were able to distinguish 16 of the 17 stereoisomeric tripeptides as a test sample using capillary electrophoresis (CE) under optimized conditions. We further conducted Enceladus plume fly-through capture experiment by accelerating peptides soaked in rock particles up to a speed of 5.7 km/s and capturing with originally developed hydrophobic silica aerogels. Direct peptide extraction with acetonitrile-water followed by CE analysis led to detection of only but two stereoisomeric acidic peptide peaks, presenting the first run-through hypervelocuty impact sample analysis targeting peptides as key molecule to to understand the ongoing astrobiology on Enceladus.

organic molecules↗
NASA NTRSDate not supplied

Phosphate Textural Diversity in CI Chondrites and C-Type Asteroids

Introduction: Apatite, Ca 5 (PO 4 ) 3 (CL/F/OH-), is a ubiquitous phosphate found throughout the solar system, including the most primitive solids, CI-chondrites [1,2] and related samples of carbonaceous asteroids Ryugu [3] and Bennu [4], returned by JAXA’s Hayabusa2 and NASA’s OSIRIS-REx missions, respectively. Apatite in these primitive solids is found as individual grains or mineral clusters and has been inferred to form from the hydrothermal sequence during cooling of their respective parent body or bodies. To better understand the formation history and reworking of these early phosphates we have undertaken a highly coordinated study of phosphate microstructures, geochemistry and U/Pb geochronology from a suite of CI meteorites and carbonaceous asteroid samples. These data have identified novel phosphate microstructures and complex relationships across a suite of apatite grains from the early solar system, indicating multiple episodes of growth and modification on the CI parent body(ies). Methods: Samples of CI chondrites, Alais, Ivuna, Orgueil, Oued Chebeika 002, Yamato (Y) 82162, Y980115, Y980134, and two chips of Hayabusa2 Ryugu particles (A0262 and C0263) have been acquired for analysis. The bulk texture of the samples were first scanned by X-ray Computed Tomography (XCT) using the Nikon XT H 320 within the XFACT facility at NASA JSC or the Xradia 620 Versa at the UTCT facility. Based on the identification of petrofabrics or features of interest from the XCT data, samples were chipped, oriented, potted in epoxy and thick sections were prepared. After anhydrously polishing the samples with silicon carbide and dry diamond powder down to 1 µm, the samples were ion polished using a Hitachi ArBlade. Energy dispersive Xray spectrometry (EDS) maps were collected to ID phosphates of interest using a JEOL 7900F SEM. The internal microstructures of identified phosphates were then mapped by electron backscatter diffraction (EBSD) using the JEOL 7900F. Based on the EDS and EBSD data, domains of interest were targeted for quantitative chemical analyses using a JEOL 8530 EPMA. Subsequently, in situ U-Pb and 207 Pb/ 206 Pb ages will be collected using a Cameca ims1290 secondary ion mass spectrometer at UCLA across a range of microstructures. Results: Apatite grains are ubiquitous throughout the CI chondrites and carbonaceous asteroid materials, found as individual grains, disseminated clusters or grain aggregates. Apatite grains are associated with serpentine, magnet-ite, and/or carbonate. Of particular interest, we have identified individual and aggregate polycrystalline grains ex-hibiting an internal ‘honeycomb’ texture (Fig. 1). Some of these grains appear overprinted by subsequent alteration while others remain unaltered. Apatite halogen sites are dominated by the missing component, assumed to be OH, and F, comparable to published values from Bennu, Ryugu and CM-chondrites [3-5]. However, the Yamato CI-like meteorites show a broader range of Cl values, and one grain from Alais is dominated by CL. Summary: Apatite growth features indicate a protracted and complex growth history, consistent with precipitation from an evolving fluid system. The ‘honeycomb’ texture identified in some CI meteorites is, to the best of our knowledge, the first report of such a microstructure in meteoritic phosphate. The microtextures and zoning will guide subsequent age analyses, to better constrain the formation and reworking of phosphate in CI(-like) materials. Acknowledgments: We thank the National Institute of Polar Research, Japan for samples of Y82162, 980115 and 980134 meteorites, ASU’s Buseck Center for Meteorite Studies for samples of Ivuna and Alais meteorites, and JAXA curation for chips of Ryugu material. This work was funded by NASA ROSES LARS grant 24-LARS24-0014. References: [1] Morlok et al., 2016, GCA 70:5371-5394. [2] Alfin g et al., 2019, Geochemistry 79:125532. [3] Nakamura et al. (2022) Science 379:1-15. [4] Seifert et al. (2026) MAPS 61:504-521. [5] Piralla et al. (2021) MAPS 56:809-828.

CI chondrites↗
NASA NTRS2001

Catalysis in the 3rd Dimension: How Organic Molecules May be Formed

Catalysis is often little more than a word to phenomenologically describe the fact that a reaction follows a pat1 that leads to products of an unexpected kind or of unexpected yield. Low activation energy barriers for intermediates are recognized as the most likely cause why a system deviates from the thermodynamic pull towards minimizing its free energy and ends up in a metastable state. Seldom is the mechanism known. This i: particularly true for heterogeneous catalysis under hydrothermal conditions with minerals as catalysts. It is commonly assumed that catalytic action takes place across solid-fluid interfaces and that, on the atomic level, interfaces are just 2-dimensional contacts. This makes it difficult to understand, for instance, the assembly of long-chain carboxylic (fatty) acids. 3y studying single crystals that grew from a melt in the presence of H2O and CO2, we can show: (1) that numerals take up the fluid components into solid solution, (2) that some-thing happens converting them to -educedH and C, (3) that C atoms segregate into dislocations and tie C-C bonds. The products are medium-to-long chain Cn protomolecules, with some C-H attached, pre-assembled in the dislocations. Upon solvent extraction, these proto-molecules turn into carboxylic and dicarboxylic acids. This observation suggests that, in a very elementary step, catalysis under hydrothermal conditions leading to fatty acids involves the pre-assembly of Cn entities in the interface that is not 2-D but extends into the 3rd dimension, with dislocations as synthesis sites.

Freund, Friedemann↗
NASA NTRS2008

Coordinated Chemical and Isotopic Studies of GEMS in IDPS

Cometary IDPs contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula [1]. Following their accretion, these materials have remained relatively unaltered because of the lack of parent body hydrothermal alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these IDPs because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars [e.g. 2]. Amorphous silicates (in the form of GEMS grains) are a major component of cometary IDPs and so a major objective of this work is to elucidate their origins. In rare cases, GEMS grains have highly anomalous O isotopic compositions that establish their origins as circumstellar condensates [3]. Here we present data on a systematic study of the silicate components within a primitive IDP.

Keller, L. P.↗
NASA NTRS2003

Two Strategies for Microbial Production of an Industrial Enzyme-Alpha-Amylase

Extremophiles are microorganisms that thrive in, from an anthropocentric view, extreme environments including hot springs, soda lakes and arctic water. This ability of survival at extreme conditions has rendered extremophiles to be of interest in astrobiology, evolutionary biology as well as in industrial applications. Of particular interest to the biotechnology industry are the biological catalysts of the extremophiles, the extremozymes, whose unique stabilities at extreme conditions make them potential sources of novel enzymes in industrial applications. There are two major approaches to microbial enzyme production. This entails enzyme isolation directly from the natural host or creating a recombinant expression system whereby the targeted enzyme can be overexpressed in a mesophilic host. We are employing both methods in the effort to produce alpha-amylases from a hyperthermophilic archaeon (Thermococcus) isolated from a hydrothermal vent in the Atlantic Ocean, as well as from alkaliphilic bacteria (Bacillus) isolated from a soda lake in Tanzania. Alpha-amylases catalyze the hydrolysis of internal alpha-1,4-glycosidic linkages in starch to produce smaller sugars. Thermostable alpha-amylases are used in the liquefaction of starch for production of fructose and glucose syrups, whereas alpha-amylases stable at high pH have potential as detergent additives. The alpha-amylase encoding gene from Thermococcus was PCR amplified using carefully designed primers and analyzed using bioinformatics tools such as BLAST and Multiple Sequence Alignment for cloning and expression in E.coli. Four strains of Bacillus were grown in alkaline starch-enriched medium of which the culture supernatant was used as enzyme source. Amylolytic activity was detected using the starch-iodine method.

Bernhardsdotter, Eva C. M. J.↗
NASA NTRS2001

Noachian Faulting: What Do Faults Tell Us About the Tectonic History of Tharsis?

The western hemisphere of Mars is dominated by the formation of Tharsis, which is an enormous high-standing region (roughly 25% of the surface area of the planet) capped by volcanics, including the solar system's largest shield volcanoes. Tharsis is surrounded by an enormous radiating system of grabens and a circumferential system of wrinkle ridges that extends over the entire western hemisphere of Mars. This region is perhaps the largest and most long lived tectonic and volcanic province of any of the terrestrial planets with a well-preserved history of magmatic-driven activity that began in the Noachian and has lasted throughout Martian geologic time. Tharsis and the surrounding regions comprise numerous components, including volcanic constructs of varying sizes and extensive lava flow fields, large igneous plateaus, fault and ridge systems of varying extent and relative age of formation, gigantic outflow channel systems, vast system of canyons, and local and regional centers of tectonic activity. Many of these centers are interpreted to be the result of magmatic-related activity, including uplift, faulting, dike emplacement, volcanism, and local hydrothermal activity. Below we present a summary of our work for Tharsis focusing primarily on the earliest stage of development, the Noachian period. Here we hone in on the early centers and how they relate to the early development of the Tharsis Magmatic Complex (TMC).

Anderson, R. C.↗
NASA NTRS1983

Evaluation of radiometric and geometric characteristics of LANDSAT-D imaging system

With vegetation masked and noise sources eliminated or minimized, different carbonate facies could be discriminated in a south Florida scene. Laboratory spectra of grab samples indicate that a 20% change in depth of the carbonate absorption band was detected despite the effects of atmospheric absorption. Both bright and dark hydrothermally altered volcanic rocks can be discriminated from their unaltered equivalents. A previously unrecognized altered area was identified on the basis of the TM images. The ability to map desert varnish in semi-arid terrains has economic significance as it defines areas that are less susceptible desert erosional process and suitable for construction development.

Salisbury, J. W.↗
NASA NTRS1992

On the possibility of chemosynthetic ecosystems in subsurface habitats on Mars

Recent discoveries of nonphotosynthetic microbial ecosystems on earth have prompted the present reexamination of the prospects for microbial life on Mars, where well-protected subsurface niches associated with hydrothermal activity could have furnished a refuge after surface conditions became inhospitable. It is noted that extensive geological features attest to widespread ground ice-volcanism interactions. Attention is given to the possibility of anaerobic systems employing CO2 as the primary source of carbon, and liquid water furnished by melted subsurface permafrost. Gases from deep volcanic activity could effect reduction, thereby establishing a chemolithoautotrophic basis for a methanogenic or acetogenic and sulfur-based ecology microbial community.

Boston, Penelope J.↗
NASA NTRS1993

The RNA World: Life Before DNA and Protein

All of the life that is known, all organisms that exist on Earth today or are known to have existed on Earth in the past, are of the same life form: a life form based on DNA and protein. It does not necessarily have to be that way. Why not have two competing life forms on this planet? Why not have biology as we know it and some other biology that occupies its own distinct niche? Yet that is not how evolution has played out. From microbes living on the surface of antarctic ice to tube worms lying near the deep-sea hydrothermal vents, all known organisms on this planet are of the same biology. Looking at the single known biology on Earth, it is clear that this biology could not have simply sprung forth from the primordial soup. The biological system that is the basis for all known. life is far too complicated to have arisen spontaneously. This brings us to the notion that something else something simpler, must have preceded life based on DNA and protein. One suggestion that has gained considerable acceptance over the past decade is that DNA and protein-based life was preceded by RNA-based life in a period referred to as the 'RNA world'. Even an RNA-based life form would have been fairly complicated - not as complicated as our own DNA- and protein-based life form - but far too complicated, according to prevailing scientific thinking, to have arisen spontaneously from the primordial soup. Thus, it has been argued that something else must have preceded RNA-based life, or even that there was a succession of life forms leading from the primordial soup to RNA-based life. The experimental evidence to support this conjecture is not strong because, after all, the origin of life was a historical event that left no direct physical record. However, based on indirect evidence in both the geological record and the phylogenetic record of evolutionary history on earth, it is possible to reconstruct a rough picture of what life was like before DNA and protein.

Joyce, Gerald F.↗
NASA NTRS2017

Interstellar and Solar Nebula Materials in Cometary Dust

Laboratory studies of cometary dust collected in the stratosphere and returned from comet 81P/Wild 2 by the Stardust spacecraft have revealed ancient interstellar grains and molecular cloud organic matter that record a range of astrophysical processes and the first steps of planetary formation. Presolar materials are rarer meteorites owing to high temperature processing in the solar nebula and hydrothermal alteration on their asteroidal parent bodies. The greater preservation of presolar materials in comets is attributed to their low accretion temperatures and limited planetary processing. Yet, comets also contain a large complement of high temperature materials from the inner Solar System. Owing to the limited and biased sampling of comets to date, the proportions of interstellar and Solar System materials within them remains highly uncertain. Interstellar materials are identified by coordinated isotopic, mineralogical, and chemical measurements at the scale of individual grains. Chondritic porous interplanetary dust particles (CP IDPs) that likely derive from comets are made up of 0.1 - 10 micron-sized silicates, Fe-Ni-sulfides, oxides, and other phases bound by organic material. As much as 1% of the silicates are interstellar grains that have exotic isotopic compositions imparted by nucleosynthetic processes in their parent stars. Crystalline silicates in CP IDPs dominantly have normal isotopic compositions and probably formed in the Solar System. 81P samples include isotopically normal refractory minerals that resemble Ca-Al rich inclusions and chondrules common in meteorites. The origins of sub-micron amorphous silicates in IDPs are not certain, but at least a few % of them are interstellar grains. The remainder have isotopic compositions consistent with Solar System origins and elemental compositions that are inconsistent with interstellar grain properties, thus favoring formation in the solar nebula [4]. The organic component in comets and primitive meteorites has large enrichments in D/H and N-15/N-14 relative to terrestrial materials. These isotopic signatures are probably due to low temperature chemical processes in cold molecular clouds or the outermost reaches of the protoplanetary disk. The greatest isotopic anomalies are found in sub-micron organic nanoglobules that show chemical signatures of interstellar chemistry. The observation that cometary dust is mostly composed of isotopically normal minerals within isotopically anomalous organic matter is difficult to reconcile with the formation models of each component. The mineral component likely formed in high temperature processes in the inner Solar System, while the organic fraction shows isotopic and chemical signatures of formation near 10 K. Studying more primitive remnants of the Solar System starting materials would help in resolving this paradox. Comets formed across a vast expanse of the outer disk under differing thermal and collisional regimes, and some are likely to be better preserved than others. Finding truly pristine aggregates of presolar materials may require return of a pristine sample of comet nucleus material.

Messenger, Scott↗
NASA NTRS1990

Earth analogs for Martian life - Microbes in evaporites, a new model system for life on Mars

It is suggested that 'oases' in which life forms may persist on Mars could occur, by analogy with terrestrial cases, in (1) rocks, as known in endolithic microorganisms, (2) polar ice caps, as seen in snow and ice algae, and (3) volcanic regions, as witnessed in the chemoautotrophs which live in ocean-floor hydrothermal vents. Microorganisms, moreover, have been known to survive in salt crystals, and it has even been shown that organisms can metabolize while encrusted in evaporites. Evaporites which may occur on Mars would be able to attenuate UV light, while remaining more transparent to the 400-700 nm radiation useful in photosynthesis. Suggestions are made for the selection of Martian exobiological investigation sites.

Rothschild, Lynn J.↗