Polycyclic aromatic hydrocarbons and amino acids in meteorites and ice samples from LaPaz Icefield,Antarctica

Abstract— –We have analyzed ice samples and meteorites from the LaPaz region of Antarctica to investigate the composition of polycyclic aromatic hydrocarbons (PAHs) and amino acids with the goal to understand whether or not there is a compositional relationship between the two reservoirs. Four LL5 ordinary chondrites (OCs) and one CK carbonaceous chondrite were collected as part of the 2003/2004 ANSMET season. Ice samples collected from directly underneath the meteorites were extracted. In addition, exhaust particles from the snowmobiles used during the expedition were collected to investigate possible contributions from this source. The meteorite samples, the particulate matter and solid‐state extracts of the ice samples and the exhaust filters were subjected to two‐step laser mass spectrometry (L2MS) to investigate the PAH composition. For amino acids analysis, the meteorites were extracted with water and acid hydrolyzed, and the extracts were analyzed with offline OPA/NAC derivatization combined with liquid chromatography with UV fluorescence detection and time of flight mass spectrometry (LC‐FD/ToF‐MS). PAHs in the particulate matter of the ice were found to be qualitatively similar to the meteorite samples, indicating that micron‐sized grains of the meteorite may be embedded in the ice samples. The concentration levels of dissolved PAHs in all the ice samples were found to be below the detection limit of the L2MS. The PAH composition of the snowmobile exhaust is significantly different to the one in particulate matter, making it an unlikely source of contamination for Antarctic meteorites. The amino acids glycine, β‐alanine and γ‐amino‐n‐butyric acid that were detected at concentrations of 3 to 19 parts per billion (ppb) are probably indigenous to the Antarctic meteorites. Some of the LaPaz ice samples were also found to contain amino acids at concentration levels of 1 to 33 parts per trillion (ppt), in particular α‐aminoisobutyric acid (AIB), an abundant non‐protein amino acid of extraterrestrial origin found in some carbonaceous chondrites. We hypothesize that this amino acid could have been extracted from Antarctic micrometeorites and the particulate matter of the meteorites during the concentration procedure of the ice samples.     

Amino acid analyses of Antarctic CM2 meteorites using liquid chromatography‐time of flight‐mass spectrometry

Abstract— Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β‐alanine, γ‐amino‐n‐butyric acid (γ‐ABA), and α‐aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440–3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α‐dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ?‐amino‐n‐caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon‐6 contamination from the Antarctic sample storage bags may have occurred during collection.     

Cometary glycine detected in samples returned by Stardust

Abstract— Our previous analysis of cometary samples returned to Earth by NASA's Stardust spacecraft showed several amines and amino acids, but the origin of these compounds could not be firmly established. Here, we present the stable carbon isotopic ratios of glycine and ε‐amino‐n‐caproic acid (EACA), the two most abundant amino acids identified in Stardust‐returned foil samples measured by gas chromatography‐mass spectrometry coupled with isotope ratio mass spectrometry. The δ¹³C value for glycine of +29 ± 6‰ strongly suggests an extraterrestrial origin for glycine, while the δ¹³C value for EACA of ?25 ± 2‰ indicates terrestrial contamination by Nylon‐6 during curation. This represents the first detection of a cometary amino acid.     

Amino acids in Antarctic CM1 meteorites and their relationship to other carbonaceous chondrites

Abstract— CM2 carbonaceous chondrites are the most primitive material present in the solar system, and some of their subtypes, the CM and CI chondrites, contain up to 2 wt% of organic carbon. The CM2 carbonaceous chondrites contain a wide variety of complex amino acids, while the CI1 meteorites Orgueil and Ivuna display a much simpler composition, with only glycine and β‐alanine present in significant abundances. CM1 carbonaceous chondrites show a higher degree of aqueous alteration than CM2 types and therefore provide an important link between the CM2 and CI1 carbonaceous chondrites. Relative amino acid concentrations have been shown to be indicative for parent body processes with respect to the formation of this class of compounds. In order to understand the relationship of the amino acid composition between these three types of meteorites, we have analyzed for the first time three Antarctic CM1 chondrites, Meteorite Hills (MET) 01070, Allan Hills (ALH) 88045, and LaPaz Icefield (LAP) 02277, using gas chromatography‐mass spectrometry (GC‐MS) and high performance liquid chromatography‐fluorescence detection (HPLC‐FD). The concentrations of the eight most abundant amino acids in these meteorites were compared to those of the CM2s Murchison, Murray, Mighei, Lewis Cliff (LEW) 90500, ALH 83100, as well as the CI1s Orgueil and Ivuna. The total amino acid concentration in CM1 carbonaceous chondrites was found to be much lower than the average of the CM2s. Relative amino acid abundances were compared in order to identify synthetic relationships between the amino acid compositions in these meteorite classes. Our data support the hypothesis that amino acids in CM‐ and CI‐type meteorites were synthesized under different physical and chemical conditions and may best be explained with differences in the abundances of precursor compounds in the source regions of their parent bodies in combination with the decomposition of amino acids during extended aqueous alteration.     

Laboratory simulations of prebiotic molecule stability in the jarosite mineral group; end member evaluation of detection and decomposition behavior related to Mars sample return

Recently, the prebiotic amino acid glycine has been found associated with natural jarosite samples from locations around the world. Since the discovery of jarosite on Mars, extensive research focuses on linking this mineral group with possible detection of biosignatures in the geologic record on Earth and Mars. Multiple analytical methods, including extraction and mass spectrometry techniques, have identified glycine and other biomolecules in jarosite samples. The jarosite end members jarosite (sensu stricto-potassium jarosite), natrojarosite (sodium jarosite), and ammoniojarosite (ammonium jarosite) have different thermodynamic stabilities, decompose at different rates, and have potentially different susceptibilities to substitution. The relationship between the thermodynamic stability of the jarosite end members and the effect that glycine has on the thermal decomposition behavior of each end member was investigated using thermal gravimetric analysis. Introducing glycine into the synthesis procedure (75 ppm) of the potassium, sodium, and ammonium jarosite end member has elucidated the effects that glycine has on the thermal stability of the mineral group. Potassium jarosite appears to be the least susceptible to the effects of glycine, with the sodium and ammonium end members showing marked changes in thermal decomposition behavior and decomposition rates. These results suggest that the sodium and ammonium jarosites are more suitable targets for identifying signs of prebiotic or biotic activity on Mars and Earth than the potassium jarosites. These results have implications for current in situ investigations of the martian surface and future sample return missions.     

Empirical constraints on the salinity of the europan ocean and implications for a thin ice shell

Induced electrical currents within Europa inferred from Galileo spacecraft magnetometer instrument data have been interpreted as due to a salty europan ocean. Published compositional models for Europa's ocean, based on aqueous leaching of carbonaceous chondrites, range over five orders of magnitude in predicted magnesium sulfate concentrations. We combine the Galileo spacecraft magnetometer-derived oceanic conductivities and radio Doppler data-derived interior models with laboratory conductivity vs concentration data for both magnesium sulfate solutions and terrestrial seawater to determine empirically the range of salt concentrations permitted for Europa's ocean. Solutions for both a three-layer spherical model, and a five-layer half-space model, that satisfy current preferred best fits to magnetometer data imply high, near-saturation salt concentrations and require a europan ice shell of less than 15 km thick, with a best fit at 4 km ice thickness. Adding a conductive core and mantle has a negligible effect on the amplitude when ocean conductivities are greater than a few Siemens per meter. Similarly, we find that including a realistic ionosphere has a negligible effect. We examine the implications of these results for the subsurface habitability of Europa.     

Principal component analysis and neural networks for detection of amino acid biosignatures

We examine the applicability of Principal Component Analysis (PCA) and Artificial Neural Network (ANN) methods of data analysis to biosignature detection. These techniques show promise in classifying and simplifying the representation of patterns of amino acids resulting from biological and non-biological syntheses. PCA correctly identifies glycine and alanine as the amino acids contributing the most information to the task of discriminating biotic and abiotic samples. Trained ANNs correctly classify between 86.1 and 99.5% of a large set of amino acid samples as biotic or abiotic. These and similar techniques are important in the design of automated data analysis systems for robotic missions to distant planetary bodies. Both techniques are robust with respect to noisy and incomplete data. Analysis of the performance of PCA and ANNs also lends insight into the localization of useful information within a particular data set, a feature that may be exploited in the selection of experiments for efficient mission design.     

Amino acids in the Tagish Lake meteorite

Abstract— High‐performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered 3 months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and CI carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 ppb), which is much lower than the total abundance of amino acids in the CI Orgueil (4100 ppb) and the CM Murchison (16 900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its 3 month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated from a different type of parent body than the CM and CI chondrites. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P‐ or D‐type asteroids. If the Tagish Lake meteorite was indeed derived from these types of parent bodies, our understanding of these primitive asteroids needs to be reevaluated with respect to their potential inventory of biologically important organic compounds.     

Indigenous amino acids in primitive CR meteorites

Abstract— –CR chondrites are among the most primitive meteorites. In this paper, we report the first measurements of amino acids in Antarctic CR meteorites. Three CRs, Elephant Moraine (EET) 92042, Graves Nunataks (GRA) 95229, and Grosvenor Mountains (GRO) 95577, were analyzed for their amino acid content using high‐performance liquid chromatography with UV fluorescence detection (HPLC‐FD) and gas chromatography–mass spectrometry (GC‐MS). Our data show that EET 92042 and GRA 95229 are the most amino acid–rich chondrites ever analyzed, with total amino acid concentrations ranging from 180 ppm to 249 ppm. The most abundant amino acids present in the EET 92042 and GRA 95229 meteorites are the α‐amino acids glycine, isovaline, α‐aminoisobutyric acid (α‐AIB), and alanine, with δ¹³C values ranging from +31.6‰ to +50.5‰. The carbon isotope results together with racemic enantiomeric ratios determined for most amino acids strongly indicate an extraterrestrial origin for these compounds. Compared to Elephant Moraine (EET) 92042 and GRA 95229, the more aqueously altered GRO 95577 is depleted in amino acids. In both CRs and CMs, the absolute amino acid abundances appear to be related to the degree of aqueous alteration in their parent bodies. In addition, the relative abundances of α‐AIB and β‐alanine in the Antarctic CRs also appear to depend on the degree of aqueous alteration.     

The amino acid composition of the Sutter's Mill CM2 carbonaceous chondrite

We determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25–26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low d/l ratios of several proteinogenic amino acids. The d/l ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional l‐ amino acid contaminants to SM12 and SM51. Higher percentages of glycine, β‐alanine, and γ‐amino‐n‐butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of d +l‐ β‐aminoisobutyric acid (β‐AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as β‐AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound‐specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20‐fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter's Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.     

Amino acid analyses of type 3 chondrites Colony,Ornans, Chainpur,and Bishunpur

Abstract– The CO3s Colony and Ornans and LL3s Chainpur and Bishunpur were analyzed for the first time for amino acids using gas chromatography–mass spectrometry (GC‐MS). Type 3 chondrites have relatively unaltered metamorphic and petrological histories. Chainpur was the most amino acid rich of the four type 3 chondrites with a total amino acid abundance of 3330 parts per billion (ppb). The other type 3 chondrites had total amino acid abundances that ranged from 660 to 1110 ppb. A d /l ratio of <0.7 for all proteic amino acids suggests at least some amino acid terrestrial contamination. However, a small fraction of indigenous extraterrestrial amino acids cannot be excluded because of the presence of the nonprotein amino acid α‐aminoisobutyric acid (α‐AIB), and unusually high relative abundances (to glycine) of β‐alanine and γ‐ABA. The comparisons between the free and total amino acid contents of the samples also indicate a low free/total amino acid ratio (ranging from about 1:4 in CO chondrites to about 1:50 in Chainpur), which indicate that amino acids are present mainly in the bound form and were made detectable after acid hydrolysis.     

Polymer amide in the Allende and Murchison meteorites

It has been proposed that exothermic gas phase polymerization of amino acids can occur in the conditions of a warm dense molecular cloud to form hydrophobic polymer amide (HPA) (McGeoch and McGeoch 2014). In a search for evidence of this presolar chemistry Allende and Murchison meteorites and a volcano control were diamond burr‐etched and Folch extracted for potential HPA yielding 85 unique peaks in the meteorite samples via matrix‐assisted laser desorption time‐of‐flight mass spectrometry (MALDI TOF/MS). The amino acids after acid hydrolysis in Allende were below the level of detection but many of the Allende peaks via the more sensitive MALDI/TOF analysis could be fitted to a polymer combination of glycine, alanine, and alpha‐hydroxyglycine with high statistical significance. A similar significant fit using these three amino acids could not be applied to the Murchison data indicating more complex polymer chemistry.     

Effect of polychromatic X‐ray microtomography imaging on the amino acid content of the Murchison CM chondrite

X‐ray microcomputed tomography (μCT) is a useful means of characterizing cosmochemical samples such as meteorites or robotically returned samples. However, there are occasional concerns that the use of μCT may be detrimental to the organic components of a chondrite. Small organic compounds such as amino acids comprise up to ~10% of the total solvent extractable carbon in CM carbonaceous chondrites. We irradiated three samples of the Murchison CM carbonaceous chondrite under conditions akin to and harsher than those typically used during typical benchtop X‐ray μCT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a nonexposed Murchison control sample occurred. After subjecting three meteorite samples to ionizing radiation dosages between ~300 Gray (Gy) and 3 kGy with bremstrahlung X‐rays, we analyzed the amino acid content of each sample. Within sampling and analytical errors, we cannot discern differences in the amino acid abundances and amino acid enantiomeric ratios when comparing the control samples (nonexposed Murchison) and the irradiated samples. We conclude that a polychromatic X‐ray μCT experiment does not alter the abundances of amino acids to a degree greater than how well those abundances are measured with our techniques and therefore any damage to amino acids is minimal.     

Do explosive ice ejections occur on Jupiter’s and Saturn’s satellites?

The possibility of an explosive mechanical instability of ice (the Bridgman effect) in the thick icy shells of Jupiter’s and Saturn’s satellites is discussed in principle. The Bridgman effect is an explosive instability of dielectric solid bodies, which disintegrate into microscopic fragments under a quasistatic uniaxial loading in open compression systems at high pressures. The explosive instabilities of ice recently discovered in laboratory experiments with the Bridgman effect are also expected to occur in the extensive deep layers of the shells of icy planetary satellites (for example, in the case of episodical formation of major cracks in their lithospheres due to tidal forces, nonsynchronous rotation of the satellites, or extremely powerful impacts). The depths of occurrence of mechanically unstable ice in the thick crusts of Ganymede, Europa, and Titan, taken as examples, are crudely estimated using a pure-ice model without a possible ammonia admixture. The estimated thickness of the explosive-instability zone in the icy crust of Ganymede (under the assumption that the crust is ～75 km thick) ranges from ～7 to ～27 km at depths from ～40 to ～67 km, depending on the scaling parameter E = 0.2–1. This parameter relates the experimentally determined thicknesses of the ice samples in which the Bridgman effect occurs under laboratory conditions to the expected thicknesses of the explosively unstable layers in the envelopes of the icy satellites. Explosive effects are possible not throughout the entire thickness of the unstableice layer but only within some part of it, several centimeters to several tens of meters in thickness. According to the estimated location of the unstable layer in the crust of Europa (for an assumed crust thickness of ～30 km), such a layer can exist only at scaling factors E < 0.6 at depths ranging from ～21 to ～28 km. For Titan, if its crust is ～100 km thick, the thickness of the unstable layer is similarly estimated to range from ～15 to ～55 km at depths from ～37 to ～92 km for a scaling parameter E lying within the range 0.2–1. At E 0.2, which is quite possible, explosive instabilities of ice could also be expected on the Earth, in the icy shells of Antarctica and Greenland at depths from ～1 to ～1.5 km.     

Concentration and variability of the AIB amino acid in polar micrometeorites: Implications for the exogenous delivery of amino acids to the primitive Earth

Abstract— Micrometeorites (MMs) are extraterrestrial particles ranging in size from 25 μm to 2 mm that survive atmospheric entry and are collected on the Earth's surface. They represent the largest mass flux (MF) of extraterrestrial material (30,000 ± 20,000 t/yr) to the present‐day Earth. Studies of large collections of MMs suggest that about 20% have not been heated to high temperatures and that they contain organic carbon. Since non‐protein amino acids have been found in some carbonaceous meteorites, they might also be found in unmelted MMs. However, previous searches for amino acids in MMs were inconclusive. We combined a new extraction method for amino acids with a highly sensitive analytical method to detect and quantitate amino acids in MMs collected at the South Pole. We found the non‐protein amino acid α‐amino isobutyric acid (AIB) in one of our samples. The non‐detection of this amino acid in the other samples analyzed suggests that there are amino acid‐containing and amino acid‐free MMs, with ?14% of the MMs containing AIB. Since the MF of MMs is much higher than that of carbonaceous chondrites (CMs), amino acids in these small particles would represent an important source of exogenous delivery of organic molecules. Therefore, the results are discussed on the basis of their implications for astrobiology.     

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.     

Thermal convection in ice-I shells of Titan and Enceladus

Cassini-Huygens observations have shown that Titan and Enceladus are geologically active icy satellites. Mitri and Showman [Mitri, G., Showman, A.P., 2005. Icarus 177, 447-460] and McKinnon [McKinnon, W.B., 2006. Icarus 183, 435-450] investigated the dynamics of an ice shell overlying a pure liquid-water ocean and showed that transitions from a conductive state to a convective state have major implications for the surface tectonics. We extend this analysis to the case of ice shells overlying ammonia-water oceans. We explore the thermal state of Titan and Enceladus ice-I shells, and also we investigate the consequences of the ice-I shell conductive-convective switch for the geology. We show that thermal convection can occur, under a range of conditions, in the ice-I shells of Titan and Enceladus. Because the Rayleigh number Ra scales with δ³/ηb, where δ is the thickness of the ice shell and ηb is the viscosity at the base of the ice-I shell, and because ammonia in the liquid layer (if any) strongly depresses the melting temperature of the water ice, Ra equals its critical value for two ice-I shell thicknesses: for relatively thin ice shell with warm, low-viscosity base (Onset I) and for thick ice shell with cold, high-viscosity base (Onset II). At Onset I, for a range of heat fluxes, two equilibrium states—corresponding to a thin, conductive shell and a thick, convective shell—exist for a given heat flux. Switches between these states can cause large, rapid changes in the ice-shell thickness. For Enceladus, we demonstrate that an Onset I transition can produce tectonic stress of ∼500 bars and fractures of several tens of km depth. At Onset II, in contrast, we demonstrate that zero equilibrium states exist for a range of heat fluxes. For a mean heat flux within this range, the satellite experiences oscillations in surface heat flux and satellite volume with periods of ∼50-800 Myr even when the interior heat production is constant or monotonically declining in time; these oscillations in the thermal state of the ice-I shell would cause repeated episodes of extensional and compressional tectonism.     

Convective-conductive transitions and sensitivity of a convecting ice shell to perturbations in heat flux and tidal-heating rate: Implications for Europa

We investigate the response of conductive and convective ice shells on Europa to variations of heat flux and interior tidal-heating rate. We present numerical simulations of convection in Europa's ice shell with Newtonian, temperature-dependent viscosity and tidal heating. Modest variations in the heat flux supplied to the base of a convective ice shell, ΔF, can cause large variations of the ice-shell thickness Δδ. In contrast, for a conductive ice shell, large ΔF involves relatively small Δδ. We demonstrate that, for a fluid with temperature-dependent viscosity, the heat flux undergoes a finite-amplitude jump at the critical Rayleigh number Racr. This jump implies that, for a range of heat fluxes relevant to Europa, two equilibrium states—corresponding to a thin, conductive shell and a thick, convective shell—exist for a given heat flux. We show that, as a result, modest variations in heat flux near the critical Rayleigh number can force the ice shell to switch between the thin, conductive and thick, convective configurations over a ∼10⁷-year interval, with thickness changes of up to ∼10-30 km. Depending on the orbital and thermal history, such switches might occur repeatedly. However, existing evolution models based on parameterized-convection schemes have to date not allowed these transitions to occur. Rapid thickening of the ice shell would cause radial expansion of Europa, which could produce extensional tectonic features such as fractures or bands. Furthermore, based on interpretations for how features such as chaos and ridges are formed, several authors have suggested that Europa's ice shell has recently undergone changes in thickness. Our model provides a mechanism for such changes to occur.     

A search for amino acids and nucleobases in the Martian meteorite Roberts Massif 04262 using liquid chromatography‐mass spectrometry

The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography‐mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot‐water extracts with high relative abundances of β‐alanine and γ‐amino‐n‐butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight‐chained amine‐terminal n‐ω‐amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites (Burton et al. 2012; Chan et al. 2012). A carbon isotope ratio of ?24‰ ± 6‰ for β‐alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of n‐ω‐amino acids may be due to a high temperature Fischer‐Tropsch‐type synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.