The provenance,formation, and implications of reduced carbon phases in Martian meteorites

This review is intended to summarize the current observations of reduced carbon in Martian meteorites, differentiating between terrestrial contamination and carbon that is indigenous to Mars. Indeed, the identification of Martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade, including the Mars Science Laboratory and Mars 2020. Organic carbon compounds are essential building blocks of terrestrial life, so the occurrence and origin (biotic or abiotic) of organic compounds on Mars is of great significance; however, not all forms of reduced carbon are conducive to biological systems. This paper discusses the significance of reduced organic carbon (including methane) in Martian geological and astrobiological systems. Specifically, it summarizes current thinking on the nature, sources, and sinks of Martian organic carbon, a key component to Martian habitability. Based on this compilation, reduced organic carbon on Mars, including detections of methane in the Martian atmosphere, is best described through a combination of abiotic organic synthesis on Mars and infall of extraterrestrial carbonaceous material. Although conclusive signs of Martian life have yet to be revealed, we have developed a strategy for life detection on Mars that can be utilized in future life‐detection studies.     

An alkaline spring system within the Del Puerto Ophiolite (California,USA): A Mars analog site

Mars appears to have experienced little compositional differentiation of primitive lithosphere, and thus much of the surface of Mars is covered by mafic lavas. On Earth, mafic and ultramafic rocks present in ophiolites, oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of cold-water alkaline springs associated with these mafic and ultramafic rocks represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene, yields fluids with unusual chemistry (Mg–OH and Ca–OH waters with pH values up to ～12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rock-hosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial alkaline springs associated with mafic and ultramafic rocks are particularly timely. This study focuses on the alkaline Adobe Springs, emanating from mafic and ultramafic rocks of the California Coast Range, where a community of novel bacteria is associated with the precipitation of Mg–Ca carbonate cements. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.     

Why exobiology on Mars?

Processing of organic molecules by liquid water was probably an essential requirement towards the emergence of terrestrial primitive life. According to Oparin's hypothesis, organic building blocks required for early life were produced from simple organic molecules formed in a primitive reducing atmosphere. Geochemists favour now a less reducing atmosphere dominated by carbon dioxide. In such an atmosphere, very few building blocks are formed. Import of extraterrestrial organic molecules may represent an alternative supply. Experimental support for such an alternative scenario is examined in comets, meteorites and micrometeorites. The early histories of Mars and Earth clearly show similarities. Liquid water was once stable on the surface of Mars attesting the presence of an atmosphere capable of decelerating C-rich micro-meteorites. Therefore, primitive life may have developed on Mars, as well. Liquid water disappeared from the surface of Mars very early, about 3.8 Ga ago. The Viking missions did not find, at the surface of the Martian soil, any organic molecules or clear-cut evidence for microbial activities such as photosynthesis, respiration or nutrition. The results can be explained referring to an active photochemistry of Martian soil driven by the high influx of solar UV. These experiments do not exclude the existence of organic molecules and fossils of micro-organisms which developed on early Mars until liquid water disappeared. Mars may store below its surface some well preserved clues of a still hypothetical primitive life.     

History of Martian volatiles: Implications for organic synthesis

A theoretical reconstruction of the history of Martian volatiles indicates that Mars probably possessed a substantial reducing atmosphere at the outset of its history and that its present tenous and more oxidized atmosphere is the result of extensive chemical evolution. As a consequence, it is probable that Martian atmospheric chemical conditions, now hostile with respect to abiotic organic synthesis in the gas phase, were initially favorable. Evidence indicating the chronology and degradational history of Martian surface features, surface mineralogy, bulk volatile content, internal mass distribution, and thermal history suggests that Mars catastrophically developed a substantial reducing atmosphere as the result of rapid accretion. This atmosphere probably persisted—despite the direct and indirect effects of hydrogen escape—for a geologically short time interval during, and immediately following, Martian accretion. That was the only portion of Martian history when the atmospheric environment could have been chemically suited for organic synthesis in the gas phase. Subsequent gradual degrassing of the Martian interior throughout Martian history could not sustain a reducing atmosphere due to the low intensity of planet-wide orogenic activity and the short atmospheric mean residence time of hydrogen on Mars. During the post-accretion history of Mars, the combined effects of planetary hydrogen escape, solar-wind sweeping, and reincorporation of volatiles into the Martian surface produced and maintained the present atmosphere.     

Determining the local abundance of Martian methane and its’ 13C/12C and D/H isotopic ratios for comparison with related gas and soil analysis on the 2011 Mars Science Laboratory (MSL) mission

Understanding the origin of Martian methane will require numerous complementary measurements from both in situ and remote sensing investigations and laboratory work to correlate planetary surface geophysics with atmospheric dynamics and chemistry. Three instruments (Quadrupole Mass Spectrometer (QMS), Gas Chromatograph (GC) and Tunable Laser Spectrometer (TLS)) with sophisticated sample handling and processing capability make up the Sample Analysis at Mars (SAM) analytical chemistry suite on NASA’s 2011 Mars Science Laboratory (MSL) Mission. Leveraging off the SAM sample and gas processing capability that includes methane enrichment, TLS has unprecedented sensitivity for measuring absolute methane (parts-per-trillion), water, and carbon dioxide abundances in both the Martian atmosphere and evolved from heated soil samples. In concert with a wide variety of associated trace gases (e.g. SO₂, H₂S, NH₃, higher hydrocarbons, organics, etc.) and other isotope ratios measured by SAM, TLS will focus on determining the absolute abundances of methane, water and carbon dioxide, and their isotope ratios: ¹³C/¹²C and D/H in methane; ¹³C/¹²C and ¹⁸O/¹⁷O/¹⁶O in carbon dioxide; and ¹⁸O/¹⁷O/¹⁶O and D/H in water. Measurements near the MSL landing site will be correlated with satellite (Mars Express, Mars 2016) and ground-based observations.     

An integrated laser anemometer and dust accumulator for studying wind-induced dust transport on Mars

Windborne dust is one of the most important and dynamic factors affecting the Martian surface and its atmosphere, yet there lacks a detailed physical understanding how it is transported. We present a miniature laser-based optoelectronic instrument for use on a Mars lander. It integrates sensors capable of quantifying important parameters needed for the understanding and modeling of dust transport on Mars, these include wind speed, wind direction, suspended dust concentration, dust deposition and removal rates as well as the electrification of the Martian dust. Dust electrification has been seen from experimental simulations to be of considerable importance to the processes of adhesion and cohesion, specifically prompting the formation of low mass density dust aggregates. Testing of this prototype instrument has been performed under simulated Martian conditions in a wind tunnel facility. The results and analysis of its functionality will be presented.     

AOST: Fourier spectrometer for studying mars and phobos

An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5?C25 ??m, the best spectral resolution (without apodization) is 0.6 cm^?1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.     

Can rapid loss and high variability of Martian methane be explained by surface H2O2?

It has been reported by several groups that methane in the Martian atmosphere is both spatially and temporally variable. Gough et al. (2010) suggested that temperature dependent, reversible physical adsorption of methane onto Martian soils could explain this variability. However, it is also useful to consider if there might be chemical destruction of methane (and compensating sources) operating on seasonal time scales. The lifetime of Martian methane due to known chemical loss processes is long (on the order of hundreds of years). However, observations constrain the lifetime to be 4 years or less, and general circulation models suggest methane destruction must occur even faster (<1 year) to cause the reported variability and rapid disappearance. The Martian surface is known to be highly oxidizing based on the Viking Labeled Release experiments in which organic compounds were quickly oxidized by samples of the regolith. Here we test if simulated Martian soil is also oxidizing towards methane to determine if this is a relevant loss pathway for Martian methane. We find that although two of the analog surfaces studied, TiO₂·H₂O₂ and JSC-Mars-1 with H₂O₂, were able to oxidize the complex organic compounds (sugars and amino acids) used in the Viking Labeled Release experiments, these analogs were unable to oxidize methane to carbon dioxide within a 72 h experiment. Sodium and magnesium perchlorate, salts that were recently discovered at the Phoenix landing site and are potential strong oxidants, were not observed to directly oxidize either the organic solution or methane. The upper limit reaction coefficient, α, was found to be <4×10^?17 for methane loss on TiO₂·H₂O₂ and <2×10^?17 for methane loss on JSC-Mars-1 with H₂O₂. Unless the depth of soil on Mars that contains H₂O₂ is very deep (thicker than 500 m), the lifetime of methane with respect to heterogeneous oxidation by H₂O₂ is probably greater than 4 years. Therefore, reaction of methane with H₂O₂ on Martian soils does not appear to be a significant methane sink, and would not destroy methane rapidly enough to cause the reported atmospheric methane variability.     

Oxygenic photosynthesis and the oxidation state of Mars

The oxidation state of the Earth's surface is one of the most obvious indications of the effect of life on this planet. The surface of Mars is highly oxidized, as evidenced by its red color, but the connection to life is less apparent. Two possibilities can be considered. First, the oxidant may be photochemically produced in the atmosphere. In this case the fundamental source of O2 is the loss of H2 to space and the oxidant produced is H2O2. This oxidant would accumulate on the surface and thereby destroy any organic material and other reductants to some depth. Recent models suggest that diffusion limits this depth to a few meters. An alternative source of oxygen is biological oxygen production followed by sequestration of organic material in sediments--as on the Earth. In this case, the net oxidation of the surface was determined billions of years ago when Mars was a more habitable planet and oxidative conditions could persist to great depths, over 100 m. Below this must be a compensating layer of biogenic organic material. Insight into the nature of past sources of oxidation on Mars will require searching for organics in the Martian subsurface and sediments.     

Fluid transport on Earth and aeolian transport on Mars

Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars—in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect.     

Methane emissions from Earth’s degassing: Implications for Mars

The presence of methane on Mars is of great interest, since one possibility for its origin is that it derives from living microbes. However, CH₄ in the martian atmosphere also could be attributable to geologic emissions released through pathways similar to those occurring on Earth. Using recent data on methane degassing of the Earth, we have estimated the relative terrestrial contributions of fossil geologic methane vs. modern methane from living methanogens, and have examined the significance that various geologic sources might have for Mars.Geologic degassing includes microbial methane (produced by ancient methanogens), thermogenic methane (from maturation of sedimentary organic matter), and subordinately geothermal and volcanic methane (mainly produced abiogenically). Our analysis suggests that ～80% of the “natural” emission to the terrestrial atmosphere originates from modern microbial activity and ～20% originates from geologic degassing, for a total CH₄ emission of ～28.0×10⁷ tonnes year^?1.Estimates of methane emission on Mars range from 12.6×10¹ to 57.0×10⁴ tonnes year^?1 and are 3–6 orders of magnitude lower than that estimated for Earth. Nevertheless, the recently detected martian, Northern-Summer-2003 CH₄ plume could be compared with methane expulsion from large mud volcanoes or from the integrated emission of a few hundred gas seeps, such as many of those located in Europe, USA, Mid-East or Asia. Methane could also be released by diffuse microseepage from martian soil, even if macro-seeps or mud volcanoes were lacking or inactive. We calculated that a weak microseepage spread over a few tens of km², as frequently occurs on Earth, may be sufficient to generate the lower estimate of methane emission in the martian atmosphere.At least 65% of Earth’s degassing is provided by kerogen thermogenesis. A similar process may exist on Mars, where kerogen might include abiogenic organics (delivered by meteorites and comets) and remnants of possible, past martian life. The remainder of terrestrial degassed methane is attributed to fossil microbial gas (～25%) and geothermal-volcanic emissions (～10%). Global abiogenic emissions from serpentinization are negligible on Earth, but, on Mars, individual seeps from serpentinization could be significant. Gas discharge from clathrate-permafrost destabilization should also be considered.Finally, we have shown examples of potential degassing pathways on Mars, including mud volcano-like structures, fault and fracture systems, and major volcanic edifices. All these types of structures could provide avenues for extensive gas expulsion, as on Earth. Future investigations of martian methane should be focused on such potential pathways.     

The effects of Martian near surface conditions on the photochemistry of amino acids

In order to understand the complex multi-parameter system of destruction of organic material on the surface of Mars, step-by-step laboratory simulations of processes occurring on the surface of Mars are necessary. This paper describes the measured effects of two parameters, a CO₂ atmosphere and low temperature, on the destruction rate of amino acids when irradiated with Mars-like ultraviolet light (UV). The results show that the presence of a 7 mbar CO₂ atmosphere does not affect the destruction rate of glycine, and that cooling the sample to 210 K (average Mars temperature) lowers the destruction rate by a factor of 7. The decrease in the destruction rate of glycine by cooling the sample is thought to be predominantly caused by the slower reaction kinetics. When these results are scaled to Martian lighting conditions, cold thin films of glycine are assumed to have half-lives of 250 h under noontime peak illumination. It has been hypothesised that the absence of detectable native organic material in the Martian regolith points to the presence of oxidising agents. Some of these agents might form via the interaction of UV with compounds in the atmosphere. Water, although a trace component of Mars’ atmosphere, is suggested to be a significant source of oxidising species. However, gaseous CO₂ or adsorbed H₂O layers do not influence the photodestruction of amino acids significantly in the absence of reactive soil. Other mechanisms such as chemical processes in the Martian regolith need to be effective for rapid organic destruction.     

Early Mars serpentinization‐derived CH4 reservoirs,H2‐induced warming and paleopressure evolution

CH₄ has been observed on Mars both by remote sensing and in situ during the past 15 yr. It could have been produced by early Mars serpentinization processes that could also explain the observed Martian remanent magnetic field. Assuming a cold early Mars, a cryosphere could trap such CH₄ as clathrates in stable form at depth. The maximum storage capacity of such a clathrate cryosphere has been recently estimated to be 2 × 10¹⁹ to 2 × 10²⁰ moles of methane. We estimate how large amounts of serpentinization‐derived CH₄ stored in the cryosphere have been released into the atmosphere during the Noachian and the early Hesperian. Due to rapid clathrate dissociation and photochemical conversion of CH₄ to H₂, these episodes of massive CH₄ release may have resulted in transient H₂‐rich atmospheres, at typical levels of 10–20% in a background 1–2 bar CO₂ atmosphere. The collision‐induced heating effect of H₂ present in such an atmosphere has been shown to raise the surface temperature above the water freezing point. We show how local and rapid destabilization of the cryosphere can be induced by large events (such as the Hellas Basin or Tharsis bulge formation) and lead to such releases. Our results show that the early Mars cryosphere had a sufficient CH₄ storage capacity to have maintained H₂‐rich transient atmospheres during a total time period up to several million years or tens of million years, having potentially contributed to the formation of valley networks during the Noachian/early Hesperian.     

Simulation of the Martian spectral radiance in the presence of atmospheric dust

The interest towards Mars is nowadays renewed as various satellites, already launched or foreseen for the future, will visit this planet, providing a new wealth of data. In particular, infrared spectroscopic observations need a parallel modelling effort for a proper interpretation of observations. The goal of our modelling is to evaluate the influence of a non negligible fraction of dust particles on intensity and profile of atmospheric Martian spectra. The joint effects of the atmosphere and the surface materials have been also accounted for. For the modelling, a version of the MODTRAN code, expressly modified for application to the Mars environment, has been used. As an example of the materials forming dust dispersed in the atmosphere and on the surface, we have considered andesite. Indices of refraction (n and k) of this material have been derived from laboratory measurements. The obtained results can have an important impact on the interpretation of infrared spectra that instruments such as TES (Thermal Emission Spectrometer), on board the Mars Global Surveyor, and PFS, in the Mars Express mission, will provide.     

Analysis and survival of amino acids in Martian regolith analogs

Abstract— We have investigated the native amino acid composition of two analogs of Martian soil, JSC Mars‐1 and Salten Skov. A Mars simulation chamber has been built and used to expose samples of these analogs to temperature and lighting conditions similar to those found at low latitudes on the Martian surface. The effects of the simulated conditions have been examined using high‐performance liquid chromatography (HPLC). Exposure to energetic ultraviolet (UV) light in vacuum appears to cause a modest increase in the concentration of certain amino acids within the materials, which is interpreted as resulting from the degradation of microorganisms. The influence of low temperatures shows that the accretion of condensed water on the soils leads to the destruction of amino acids, supporting the idea that reactive chemical processes involving H₂O are at work within the Martian soil. We discuss the influence of UV radiation, low temperatures, and gaseous CO₂ on the intrinsic amino acid composition of Martian soil analogs and describe, with the help of a simple model, how these studies fit within the framework of life detection on Mars and the practical tasks of choosing and using Martian regolith analogs in planetary research.     

The electrical properties of Mars analogue dust

Dust is a major environmental factor on the surface and in the atmosphere of Mars. Knowing the electrical charge state of this dust would be of both scientific interest and important for the safety of instruments on the Martian surface. In this study the first measurements have been performed of dust electrification using suspended Mars analogue material. This has been achieved by attracting suspended dust onto electrodes placed inside a Mars simulation wind tunnel. The Mars analogue used was from Salten Skov in Denmark, this contained a high concentration of ferric oxide precipitate. Once suspended, this dust was found to consist of almost equal quantities of negatively (46±6%) and positively (44±15%) charged grains.These grains were estimated to typically carry a net charge of around 10⁵e, this is sufficient to dominate the processes of adhesion and cohesion of this suspended dust. Evidence is presented for electrostatic aggregation of the dust while in suspension. Development of a simple instrument for measuring electrical charging of the suspended dust on Mars will be discussed.     

MEDUSA: The ExoMars experiment for in-situ monitoring of dust and water vapour

Dust and water vapour are fundamental components of the Martian atmosphere. In view of tracing the past environmental conditions on Mars, that possibly favoured the appearing of life forms, it is important to study the present climate and its evolution. Here dust and water vapour have (and have had) strong influence. Of major scientific interest is the quantity and physical, chemical and electrical properties of dust and the abundance of water vapour dispersed in the atmosphere and their exchange with the surface. Moreover, in view of the exploration of the planet with automated systems and in the future by manned missions, it is of primary importance to analyse the hazards linked to these environmental factors. The Martian Environmental Dust Systematic Analyser (MEDUSA) experiment, included in the scientific payload of the ESA ExoMars mission, accommodates a complement of sensors, based on optical detection and cumulative mass deposition, that aims to study dust and water vapour in the lower Martian atmosphere. The goals are to study, for the first time, in-situ and quantitatively, physical properties of the airborne dust, including the cumulative dust mass flux, the dust deposition rate, the physical and electrification properties, the size distribution of sampled particles and the atmospheric water vapour abundance versus time.     

Some problems related to the origin of methane on Mars

The following problems related to the origin of methane on Mars have been considered. (1) Laboratory simulations of the impact phenomena confirm effective heterogeneous chemistry between the products of the fireball. This chemistry lowers the fireball freezing temperature from 2000 to 750 K for methane and to 1100 K for CO/CO₂. Production of methane on Mars by cometary impacts is 0.8% of the total production. A probability that the observed methane on Mars came from impact of a single comet is 0.0011. (2) The PFS observations of variations of methane on Mars require a very effective heterogeneous loss of methane. Heterogeneous effect of dust is half that of the surface rocks. Thermochemical equilibrium requires production, not loss, of methane. Existing kinetic data show a very low efficiency of heterogeneous reactions of methane. Highly reactive superoxide ions generated by the solar UV photons on the martian rocks cannot remove methane. The required efficiency of heterogeneous loss of methane on Mars is higher than that on Earth by a factor of ?1000, although the expected efficiency on Earth is stronger than that on Mars because of the liquid ocean and the abundant oxygen. All these inconsistencies may be removed if variations of the rock reflectivity contribute to the PFS observations of methane on Mars. The PFS data on H₂CO, HCl, HF, and HBr also raise doubts. (3) Although geologic sources of methane are possible, the lack of current volcanism, hydrothermal activity, hot spots, and very low seepage of gases from the interior are not favorable for geologic methane. Any proposed geological source of methane on Mars should address these problems. Some weak points in the suggested geologic sources are discussed. (4) Measurements of ¹³C/¹²C and D/H in methane would be difficult because of the low methane abundance. These ratios are mostly sensitive to a temperature of methane formation and cannot distinguish between biogenic and low-temperature geologic sources. Their analysis requires the carbon isotope ratio in CO₂ on Mars, which is known with the insufficient accuracy, and D/H in water, which is different in the atmosphere, polar caps, regolith and interior. Therefore, the stable isotope ratios may not give a unique answer on the origin of methane. (5) Ethane and propane react with OH much faster than methane. If their production relative to methane is similar to that on Earth, then their expected abundances on Mars are of a few parts per trillion. (6) Loss of SO₂ in the reaction with peroxide on ice is smaller than its gas-phase loss by an order of magnitude. The overall results strengthen the biogenic origin of martian methane and its low variability.     

Microbial life in martian ice: A biotic origin of methane on Mars?

Despite the fact that microbial cells are unlikely to be found in the Martian soil in the near future, this paper is written on the assumption that some of the seasonally varying concentration of Martian methane is due to ongoing methanogenesis. It is first pointed out that life might have arisen on Mars first and been transported to Earth later. A case is made that an icy origin of life is more likely than a hot origin, especially if biomolecules take advantage of the high encounter rates and stability against hydrolysis, and that microorganisms feed on the ions that comprise eutectic solutions in ice. Although certain difficulties are avoided if RNA and DNA grow while adsorbed on clay grains, double strand-breaks of microbial DNA due to alpha radioactivity are a far greater threat to microbial survival on clay or other rock types than in ice. Developing a relation between the rate of microbial metabolism in ice and the experimentally determined rate of production of trapped gases of microbial origin, one can estimate the concentration of methanogens that could account for the methane production rate as a function of temperature of their habitat. The result, of order 1 cell cm⁻³ in the Martian subsurface, seems an attainable goal provided samples are taken from at least 1 or 2 m below the hostile surface of Mars. Instruments on NASA’s 2011 Mars Science Lab will measure stable isotopes for methane, water, and carbon dioxide, which on Earth served to distinguish abiotic, thermogenic, and microbial origins. Future measurements of chirality of biomolecules might also provide evidence for Martian life.     

Atmospheric entry heating of micrometeorites at Earth and Mars: Implications for the survival of organics

The atmospheric entry heating of micrometeorites (MMs) can significantly alter their pre‐existing mineralogy, texture, and organic material. The degree of heating depends predominantly on the gravity and atmospheric density of the planet on which they fall. For particles falling on Earth, the alteration can be significant, leading to the destruction of much of the pre‐entry organics; however, the weaker gravity and thinner atmosphere of Mars enhance the survival of MMs and increase the fraction of particles that preserve organic material. This paper investigates the entry heating of MMs on the Earth and Mars in order to examine the MM population on each planet and give insights into the survival of extraterrestrial organic material. The results show that particles reaching the surface of Mars experience a lower peak temperature compared to Earth and, therefore, experience less evaporative mass loss. Of the particles which reach the surface, 68.2% remain unmelted on Mars compared to only 22.8% on Earth. Due to evaporative mass loss, unmelted particles that reach the surface of Earth are restricted to sizes <70 μm whereas particles >475 μm survive unmelted on Mars. Approximately 10% of particles experience temperatures below ~800 K, that is, the sublimation temperature of refractory organics found in MMs. On Earth, this fraction is significantly lower with less than 1% expected to remain below this temperature. Lower peak temperatures coupled with the larger sizes of particles surviving without significant heating on Mars suggest a much higher fraction of organic material surviving to the Martian surface.