Oliver Botta

Extraterrestrial Organic Compounds in Meteorites

Many organic compounds or their precursorsfound in meteorites originated in the interstellar or circumstellarmedium and were later incorporated intoplanetesimals during the formation of thesolar system. There they either survivedintact or underwent further processing tosynthesize secondary products on themeteorite parent body.The most distinct feature of CI and CM carbonaceouschondrites, two typesof stony meteorites, is their high carbon content(up to 3% of weight), either in theform of carbonates or of organic compounds. The bulkof the organic carbon consistsof an insoluble macromolecular material with a complexstructure. Also present is asoluble organic fraction, which has been analyzedby several separation and analyticalprocedures. Low detection limits can be achievedby derivatization of the organicmolecules with reagents that allow for analysisby gas chromatography/massspectroscopy and high performance liquidchromatography. The CM meteoriteMurchison has been found to contain more than70 extraterrestrial amino acids andseveral other classes of compounds includingcarboxylic acids, hydroxy carboxylicacids, sulphonic and phosphonic acids, aliphatic,aromatic and polar hydrocarbons,fullerenes, heterocycles as well as carbonylcompounds, alcohols, amines and amides.The organic matter was found to be enriched indeuterium, and distinct organiccompounds show isotopic enrichments of carbon andnitrogen relative to terrestrialmatter.

Extraterrestrial amino acids in Orgueil and Ivuna: Tracing the parent body of CI type carbonaceous chondrites

Amino acid analyses using HPLC of pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna have found that β-alanine, glycine, and γ-amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from ≈600 to 2,000 parts per billion (ppb). Other α-amino acids such as alanine, α-ABA, α-aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (<200 ppb). Carbon isotopic measurements of β-alanine and glycine and the presence of racemic (D/L ≈ 1) alanine and β-ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the CIs is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites.

Detecting Pyrolysis Products from Bacteria on Mars

A pyrolysis/sublimation technique was developed to isolate volatile amine compounds from a Mars soil analogue inoculated with ∼10 billion Escherichia coli cells. In this technique, the inoculated soil is heated to 500°C for several seconds at Martian ambient pressure and the sublimate, collected by a cold finger, then analyzed using high performance liquid chromatography. Methylamine and ethylamine, produced from glycine and alanine decarboxylation, were the most abundant amine compounds detected after pyrolysis of the cells. A heating cycle similar to that utilized in our experiment was also used to release organic compounds from the Martian soil in the 1976 Viking gas chromatography/mass spectrometry (GC/MS) pyrolysis experiment. The Viking GC/MS did not detect any organic compounds of Martian origin above a level of a few parts per billion in the Martian surface soil. Although the Viking GC/MS instruments were not specifically designed to search for the presence of living cells on Mars, our experimental results indicate that at the part per billion level, the degradation products generated from several million bacterial cells per gram of Martian soil would not have been detected.

Relative Amino Acid Concentrations as a Signature for Parent Body Processes of Carbonaceous Chondrites

Most meteorites are thought to have originated from objects in the asteroid belt. Carbonaceous chondrites, which contain significant amounts of organic carbon including complex organiccompounds, have also been suggested to be derived from comets. The current model for the synthesis of organic compounds found in carbonaceous chondrites includes the survival of interstellarorganic compounds and the processing of some of these compounds on the meteoritic parent body. The amino acid composition of fiveCM carbonaceous chondrites, two CIs, one CR, and one CV3 havebeen measured using hot water extraction-vapor hydrolysis,OPA/NAC derivatization and high-performance liquid chromatography(HPLC). Total amino acid abundances in the bulk meteorites as well as the amino acid concentrations relative to glycine = 1.0for β-alanine, α-aminoisobutyric acid and D-alaninewere determined. Additional data for three Antarctic CM meteorites were obtained from the literature. All CM meteoritesanalyzed in this study show a complex distribution of amino acidsand a high variability in total concentration ranging from ∼15 300 to ∼5800 parts per billion (ppb), while the CIs show a total amino acid abundance of ∼4300 ppb. The relatively(compared to glycine) high AIB content found in all the CMs is astrong indicator that Strecker-cyanohydrin synthesis is thedominant pathway for the formation of amino acids found inthese meteorites. The data from the Antarctic CM carbonaceous chondrites are inconsistent with the results from the other CMs,perhaps due to influences from the Antarctic ice that were effective during their residence time. In contrast to CMs, the data from the CI carbonaceous chondrites indicate that the Strecker synthesis was not active on their parent bodies.

The Astrobiology of Nucleobases

Nucleobases are nitrogen heterocycles (N-heterocycles) that are essential components of the genetic material in all living organisms. Extraterrestrial nucleobases have been found in several carbonaceous chondrites, but only in traces. No astronomical data on these complex molecules are currently available. A large fraction of the cosmic carbon is known to be incorporated into aromatic material, and given the relatively high abundance of cosmic nitrogen, the presence of N-heterocycles can be expected. We present infrared spectroscopic laboratory data of adenine and uracil under simulated space conditions. At the same time we tested the stability of these nucleobases against ultraviolet (UV) irradiation at 12 K. Our experimental results indicate that gas-phase adenine and uracil will be destroyed within hours in the Earths vicinity. In dense interstellar clouds exposed to UV radiation, only adenine could be expected to survive for a few million years. We discuss possible formation routes to purines and pyrimidines in circumstellar environments and in meteorite parent bodies.

Formation and photostability of N-heterocycles in space I. The effect of nitrogen on the photostability of small aromatic molecules

Nitrogen-containing cyclic organic molecules (N-heterocycles) play important roles in terrestrial biology, for exam- ple as the nucleobases in genetic material. It has previously been shown that nucleobases are unlikely to form and survive in interstellar and circumstellar environments. Also, they were found to be unstable against ultraviolet (UV) radiation. However, nucleobases were detected in carbonaceous meteorites, suggesting their formation and survival is possible outside the Earth. In this study, the nucleobase precursor pyrimidine and the related N-heterocycles pyridine and s-triazine were tested for UV stabil- ity. All three N-heterocycles were found to photolyse rapidly and their stability decreased with an increasing number of nitrogen atoms in the ring. The laboratory results were extrapolated to astronomically relevant environments. In the diffuse interstellar medium (ISM) these N-heterocycles in the gas phase would be destroyed in 10-100 years, while in the Solar System at 1 AU distance from the Sun their lifetime would not extend beyond several hours. The only environment where small N-heterocycles could survive, is in dense clouds. Pyridine and pyrimidine, but not s-triazine, could survive the average lifetime of such a cloud. The regions of circumstellar envelopes where dust attenuates the UV flux, may provide a source for the detection of N-heterocycles. We conclude that these results have important consequences for the detectability of N-heterocycles in astro- nomical environments.

Amino Acid Analyses of Desert Varnish from the Sonoran and Mojave Deserts

There has long been a debate as to whether desert varnish deposits are microbially mediated or are deposited by inorganic processes. Several researchers have cultured bacteria from the surface of desert varnish suggesting that bacteria are intimately associated with varnish coatings and may play a role in their formation. To test this hypothesis, we have collected scrapings of desert varnish from the Sonoran Desert in Arizona and the Mojave Desert in California and analyzed them for amino acids. Thirteen amino acids were found in desert varnish indicating a biogenic component of these varnishes. Two protein amino acids that were not detected in any of the varnishes are cysteine and tryptophan. Two nonprotein amino acids,β-alanine andγ-amino butyric acid, were found. These are known to be formed by enzymatic decarboxylation, thereby indicating possible organismal activity in varnish. Some D -enantiomers of the amino acids were also found. In addition to small amounts of the D -enantiomer of aspartic acid, which is rapidly formed by racemization and was present in most samples, D -alanine and D -glutamic acid were found. These latter two amino acids are components of the peptidoglycan cell wall material of bacteria. L -lysine was also detected, but not diaminopimelic acid. The combination of L -lysine, D -alanine, and D -glutamic acid is characteristic of the peptidoglycan from Gram-positive bacteria. Although the presence of these biomarkers does not prove that Gram-positive bacteria produce the coatings, finding them is consistent with the hypothesis that they may play a role in desert varnish formation.

Recognizing life in the Solar System: guidance from meteoritic organic matter

In the next decade, numerous space missions will attempt to detect organic matter on planets and other objects in the Solar System. Recognizing carbon-based life or its remains will be a fundamental goal of future missions. In preparation, studies of organic matter in meteorites are enabling scientists how to discriminate between biogenic and abiogenic materials. Received 27 October 2005, accepted 9 November 2005

MOD: an organic detector for the future robotic exploration of Mars

Abstract Searching for extinct or extant life on Mars is part of the future NASA surveyor class missions. Looking for key organic compounds that are essential for biochemistry as we know it or indicative of extraterrestrial organic influx is the primary goal of the Mars Organic Detector (MOD). MOD is able to detect amino acids, amines and PAHs with at least 100 times higher sensitivity than the Viking GCMS experiment. MOD is not capable of identifying specific organic molecules but can assess the organic inventory of amines and PAHs on the planet. MOD can also quantify adsorbed and chemisorbed water and evolved carbon dioxide in a stepped heating cycle to determine specific carbon-bearing minerals. All that comes with no sample preparation and no wet chemistry. The organics can be isolated from the carrier matrix by heating the sample and recovering the volatile organics on a cold finger. This sublimation technique can be used for extracting amino acids, amines and PAHs under Mars ambient conditions. The detection of amino acids, amines and PAHs is based on a fluorescence detection scheme. The MOD concept has functioned as a laboratory breadboard since 1998. A number of natural samples including shells, clays, bones, λ -DNA and E.-coli bacteria have been used and organic molecules have been extracted successfully in each case. The first prototype of MOD is operational as of early fall of 1999. MOD has been selected for the definition phase of the NASA-MSR 2003 mission.

Investigating complex organic compounds in a simulated Mars environment

The search for organic molecules and traces of life on Mars has been a major topic in planetary science for several decades. 26 years ago Viking, a mission dedicated to the search for life on Mars, detected no traces of life. The search for extinct or extant life on Mars is the future perspective of several missions to the red planet, for example Beagle 2, the lander of the Mars Express mission. In order to determine what those missions should be looking for, laboratory experiments under simulated Mars conditions are crucial. This review paper describes ongoing experiments that are being performed in support of future Mars spacecraft missions. Besides the description of the experiments, the experimental hardware and set-up, this paper also gives the scientific rationale behind those experiments. The historical background of the search for life on Mars is outlined, followed by a description of the Viking Lander biology and molecular analysis experiments and their results, as well as a summary of possible reasons why no organic compounds have been detected. A section concerning organic compounds in space and related experiments discusses the organic molecules we will use in simulation experiments. The set-up is discussed briefly in the following section. We conclude with an overview of future missions, stressing the relation between these missions and our laboratory experiments. The research described in this article has been developed as part of a Mars Express Recognized Cooperating Laboratory (RCL), and for planned future Mars missions such as the PASTEUR lander.