The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.

The recognition of past habitable environments on Mars has increased the urgency to understand biosignature preservation in and characterize analogues of these environments on Earth. In this Review, we examine the detection and interpretation of potential biosignatures preserved in deposits rich in carbonates, silica and clay. Many of the earliest chemical, textural and morphological evidence of life on Earth are found in carbonates and carbonate-hosted phases. Early diagenetic chert within carbonate deposits can exceptionally preserve microbial body fossils, and clay minerals that form in ult

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we

verance Mars rover from an ancient dry riverbed in Jezero Crater could preserve evidence of ancient microbial life. Taken from a rock named “Cheyava Falls” last year, the sample, called “Sapphire Canyon,” contains potential biosignatures, according to a paper published Wednesday in the journal Nature. A potential biosignature is a substance or structure that might have a biological origin but requires more data or further study before a conclusion can be reached about the absence or presence of life. “This finding by Perseverance, launched under President Trump in his first term, is the closest we have ever come to discovering life on Mars. The identification of a potential biosignature on the Red Planet is a groundbreaking discovery, and one that will advance our understanding of Mars,” said acting NASA Administrator Sean Duffy. “NASA’s commitment to conducting Gold Standard Science will continue as we pursue our goal of putting American boots on Mars’ rocky soil.” NASA’s Perseverance rover discovered leopard spots on a reddish rock nicknamed “Cheyava Falls” in Mars’ Jezero Crater in July 2024. Scientists think the spots may indicate that, billions of years ago, the chemical reactions in this rock could have supported microbial life; other explanations are being considered. Credit: NASA/JPL-Caltech/MSSS NASA’s Perseverance Mars rover took this selfie, made up of 62 individual images, on July 23, 2024. A rock nicknamed “Cheyava Falls,” which has features that may bear on the question of whether the Red Planet was long ago home to microscopic life, is to the left of the rover near the center of the image. Credit: NASA/JPL-Caltech/MSSS Perseverance came upon Cheyava Falls in July 2024 while exploring the “Bright Angel” formation, a set of rocky outcrops on the northern and southern edges of Neretva Vallis, an ancient river valley measuring a quarter-mile (400 meters) wide that was carved by water rushing into Jezero Crater long ago. “This finding is the direct result

—early in the history of Mars (pre-Noachian to Noachian periods)—and the rapid discontinuity of habitable surface conditions ( cf. Cockell et al. , 2012 ) imply that, if life appeared on the Red Planet, it probably remained in a very primitive state of evolution, in most cases probably not achieving (anaerobic) photosynthesis. [We note that Noffke ( 2015 ) hypothesized the existence of phototrophic microbial mats from observation of photographs from Gale Crater, but based on the lack of direct evidence and on our considerations above, we think that phototrophy at the surface of Mars is very unlikely]. The nature and preservation of biosignatures for both Earth and Mars have been reviewed by Farmer and Des Marais ( 1999 ), Westall and Cavalazzi ( 2011 ), and Summons et al. ( 2011 ). Our objectives in this contribution are to place biosignature preservation in the context of the “punctuated” habitability of Mars and to consider the impact on missions, such as Mars Science Laboratory, ExoMars, and Mars 2020, whose objectives are to search for life at any chosen location on the planet. We use as examples preserved biosignature analogues of the kinds of anaerobic microorganisms that could have lived on, or may still live in the subsurface of, Mars, highlighting the spatial distribution of the biosignatures on the microbial scale within their host sedimentary habitat. 2. Habitability and Life on Mars 2.1. Abiotic/prebiotic carbon on Mars Given the emphasis on in situ measurements in the search for organic traces of life ( e.g. , MSL, Mahaffy et al. , 2015 ; ExoMars, http://exploration.esa.int/mars/45103-rover-instruments/?fbodylongid=2132 ), in this section we examine the possible sources of the kinds of organic molecules that might be preserved on Mars. Whether or not life arose on Mars, it is to be expected that abiotic organic molecules of endogenous and/or exogenous origin could be preserved in rock formations that predate the oxidation of the surface. These molecules • Biosignature identification needs to take into account a broad variety of morphological, geochemical, and organic characteristics. • Searching for signs of past life on Mars will be challenging because the most detectable in situ biosignatures will be organic molecules. 1. , 2010 ). Nevertheless, the paucity of natural ingredients necessarily would have placed difficult-to-overcome limits on the existence of life at the surface of Mars, especially after the Noachian/Early Hesperian period [although there has been a suggestion that its surface may have been oxidizing, Tuff et al. ( 2013 )]. These possible energy limitations would have had important consequences for the nature of martian life-forms and their preservation and therefore also for present and future missions dedicated to astrobiology. Thus environments on Mars that could have hosted already-established life would have been more common than those in which life could have feasibly appeared. Moreover, it is possible that life could have emerged (or could reemerge) in one environment on Mars at the same time as it flourished in another because of the relative lack of spatial connectivity of the habitats. Figure 1 illustrates the temporal and spatial variability of habitable environments on Mars, excluding possible present-day habitats at the poles. We term this situation “punctuated” habitability. In oxidizing environments, for example at the surface of present Earth, the OM may be completely oxidized and only the mineral cast of the microorganism may remain, for example, in hot springs ( cf. Cady and Farmer, 1996 ). FIG. 2. Fossilization of microorganisms by mineral replacement. ( a ) Schematic view of chemical bonding of minerals in solution to functional groups on the organic surface (microbial cell wall, EPS, etc.). ( b ) Scanning electron microscope and ( c ) transmission electron microscope view of an artificially fossilized, modern, chemolithotrophic microorganism, Pyrococcus abyssi , an analogue for early life on Earth and possible life on Mars (Orange et al. , 2009 ). Nonetheless, as demonstrated above, documentation of the distribution of carbon with respect to specific structural or textural features of the rock at the Impact ejecta or fluvial detritus may also have deposited fragments of rock containing fossil traces of life, or detrital organic carbon in the case of aqueous transport, to a location that was never habitable. All these scenarios must be considered when looking for life at any particular location (landing site) on Mars. Moreover, as noted above in Section 3 (and in Summons et al. , 2011 ), when looking for past traces of life, the possibilities for, or lack of, fossilization and preservation need to be taken into account. For example, observation of active and dormant life may be due to contamination by living organisms from Earth and/or to the presence of dormant martian cells. This figure highlights the difficulty in detecting and demonstrating the existence of potential past or present microbial life on Mars. FIG. 13. Demonstration of the possibilities for interpreting the presence or absence of biosignatures at a particular landing site on Mars. (Color graphics available at www.liebertonline.com/ast ) 5. Conclusions 5.1. What? The lack of continuously hospitable conditions on Mars would have inhibited the evolution of potential microorganisms. However, the detection and identification of organic compounds on Mars is complicated by the presence of perchlorates, which can be activated and degrade organics depending on the method used for extracting and delivering the compounds to the detector (Glavin et al. , 2013 ). Our future missions need to be robust against the possible presence of perchlorates in the deposits and rocks to be studied. The identification of potential organic biosignatures in a bulk sample will be of the greatest importance. At a minimum, such a finding will indicate that life could have existed on the planet.

Iron (oxyhydr)oxide microbial mats in modern to ∼100 ka tufa terraces are present in a cold spring system along Ten Mile Graben, southeastern Utah, USA. Mats exhibit morphological, chemical, and textural biosignatures and show diagenetic changes that occur over millennial scales. The Jurassic Brushy Basin Member of the Morrison Formation in the Four Corners region of the USA also exhibits comparable microbial fossils and iron (oxyhydr)oxide biosignatures in the lacustrine unit. Both the modern spring system and Brushy Basin Member represent alkaline, saline, groundwater-fed systems and preserve diatoms and other similar algal forms with cellular elaboration. Two distinct suites of elements (1. C, Fe, As and 2. C, S, Se, P) are associated with microbial fossils in modern and ancient iron (oxyhydr)oxides and may be potential markers for biosignatures. The presence of ferrihydrite in ∼100 ka fossil microbial mats and Jurassic rocks suggests that this thermodynamically unstable mineral may also be a potential biomarker. One of the most extensive sedimentary records on Mars is exposed in Gale Crater and consists of non-acidic clays and sulfates possibly of lacustrine origin. These terrestrial iron (oxyhydr)oxide examples are a valuable analogue because of similar iron- and clay-rich host rock compositions and will help (1) understand diagenetic processes in a non-acidic, saline lacustrine environment such as the sedimentary rocks in Gale Crater, (2) document specific biomediated t

Sedimentary rocks exposed in the Meridiani Planum region of Mars record aqueous and eolian deposition in ancient dune and interdune playa-like environments that were arid, acidic, and oxidizing. On Earth, microbial populations have repeatedly adapted to low pH and both episodic and chronic water limitation, suggesting that, to a first approximation, the Meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place. On the other hand, the environmental conditions inferred for Meridiani deposition would have posed a challenge for pre

search for biomolecules or biosignatures from past life. Its core task is to determine whether life ever existed on Mars, or still does today. As of 2026 Rosalind Franklin, previously known as the ExoMars rover, is a planned European robotic Mars rover, part of the international astrobiology programme ExoMars led by the European Space Agency (ESA). The rover is named after Rosalind Franklin, a British chemist and DNA research pioneer. Rosalind Franklin will be the first Mars rover to drill into a depth of up to two metres below the planet's surface Mi… Mars X-Ray Diffractometer (Mars-XRD) - Powder diffraction of X-rays would have determined the composition of crystalline minerals. This instrument includes also an X-ray fluorescence capability that can provide useful atomic composition information. The identification of concentrations of carbonates, sulphides or other aqueous minerals may be indicative of a Martian [hydrothermal] system capable of preserving traces of life. In other words, it would have examined the past Martian environmental conditions, and more specifically the identification of conditions related to life. The Urey instrument was planned to search for organic compounds in Martian rocks and soils as evidence for past life…