Amino Acids in Returned Samples and other Solar System Materials
Jamie E. Elsila
NASA Goddard Space Flight Center, Greenbelt, MD USA

1Introduction:
The organic contents of asteroids and comets reflect early solar system chemistry, as well as the physical and chemical
processes that have occurred in the past 4.5 billion years. Both returned samples and meteorites present an opportunity tounderstand these organic contents. Meteorites provide samples from a diverse selection of solar system bodies, while returned
samples have the advantage of context, known parent bodies, and minimal contamination.
Among the most well-studied of the organic compounds present in these extraterrestrial materials are amino acids. Aminoacids are of particular interest to astrobiology and astrochemistry research for several reasons: (1) they are essential to life on
Earth; (2) they are a structurally diverse group of compounds; and (3) some of them possess large enantiomeric excesses ofextraterrestrial origin. Amino acids have been detected in a variety of meteorites, as well as in materials collected fromNASA’s Stardust mission to Comet Wild-2 and in lunar samples returned by NASA’s Apollo missions. Observations by theROSINA mass spectrometer also identified glycine in the coma of 67P/Churyumov-Gerasimenko. The abundances, relative
distributions, enantiomeric ratios, and stable isotopic composition of amino acids in extraterrestrial materials can be used tounderstand formation histories and contamination of these materials.
Amino acids in meteorites:
We have examined the abundances, structural distributions, stable isotopic ratios, and enantiomeric compositions of aminoacids in meteorites from all eight carbonaceous chondrite groups (CI, CM, CR, CO, CV, CK, CH, and CB), as well asrepresentatives of other meteorite classes[1]. Analytical techniques include liquid chromatography coupled with fluorescence
detection and time-of-flight mass spectrometry (LC-FD/ToF-MS) to sensitively measure abundances, and gas chromatography
coupled with mass spectrometry and isotope-ratio mass spectrometry (GC-MS/IRMS) to measure compound-specific isotopic
ratios. These studies show a wide diversity in the amino acids present across these samples. This diversity highlights thepotential roles of parent body processes and composition on the organic content of these bodies, as well as the potential for avariety of formation mechanisms and organic reservoirs in the solar system. In addition, the observed large L-enantiomeric
excesses of some proteinogenic amino acids in certain meteorites (up to ~60%) may be relevant to understanding the origin ofhomochirality in life on Earth, although the potential mechanisms leading to these enantiomeric excesses are currently poorly
understood.
Amino acids in returned samples:
Analysis of bulk comet-exposed materials from the Stardust collector by LC-FD/ToF-MS revealed several amines and aminoacids, including glycine, methylamine and ethylamine [2]. The origin of these compounds could not be firmly established by
LC-FD/ToF-MS data alone, although the distinctive 1:1 ratio of methylamine to ethylamine suggested a cometary origin for
those compounds. Subsequent GC-MS/IRMS analyses measured the stable carbon isotopic ratios of glycine and determined
its likely extraterrestrial origin for glycine, representing the first detection of a cometary amino acid [3]. The in-situ
measurements of glycine in the coma of 67P/Churyumov-Gerasimenko supported the presence of cometary amino acids [4].
Lunar regolith samples returned by NASA’s Apollo missions were investigated almost immediately after their return, but thesestudies yielded inconclusive identifications about the origins of detected amino acids (e.g. [5,6]), in part due to analyticallimitations. It was not possible to determine if the detected amino acids were indigenous to the lunar samples or the result ofterrestrial contamination. More recently, we applied modern analytical techniques to determine the abundances, distributions,and carbon isotopic ratios of amino acids in lunar regolith from the Apollo 16 and 17 missions. We observed amino acids inlow concentrations in all samples. Isotopic and abundance data suggested that terrestrial biological contamination was a
primary source of the observed amino acids, but that some contribution from meteoritic infall was also present [7].
The material returned by JAXA’s Hayabusa mission from asteroid Itokawa was examined for organic materials, including
amino acids. Five individual particles were extracted with organic solvents, but analyses of these extracts showed amino acids

present only at levels below those seen in a procedural blank [8]. Future studies with hot-water extraction may be possible, but
the small sample sizes available from this returned material may preclude any compound-specific amino acid identification.
Future plans for amino acid studies of returned samples:
Both the samples to be returned by NASA’s OSIRIS-REx mission to asteroid Bennu and JAXA’s Hayabusa2 mission toasteroid Ryugu are expected to be analyzed for amino acids and other organic materials. Asteroid Bennu is a B-type
carbonaceous asteroid whose spectra most closely match those of CI and CM chondrites. A comparison of the amino acidcontent of the Bennu regolith with previous carbonaceous chondrite studies will help in understanding the potential
relationship of these meteorites to asteroid parent bodies. Asteroid Ryugu is a Cg-type asteroid that may preserve some of themost pristine material in the solar system and studies of its organic content and amino acid inventory will add to ourknowledge of extraterrestrial organic formation, distribution, and preservation.
References[1] Elsila J. E. et al. (2016) ACS Central Science, 2, 370-379. [2] Glavin D. P. et al. (2008) Meteorit Planet Sci, 43, 399-413.
[3] Elsila J. E. et al. (2009) Meteorit. Planet. Sci., 44, 1323-1330. [4] Altwegg K. et al. (2016) Science Advances, 2. [5] HaradaK. et al. (1971) Science, 173, 433-435. [6] Hare P. E. et al. (1970) Proc. Apollo 11 Lunar Sci. Conf.; Geochim. Cosmochim.
Acta, Suppl. 4, Vol. 2, 1799-1803. [7] Elsila J. E. et al. (2016) Geochim. Cosmochim. Acta, 172, 357-369. [8] Naraoka H. et al.
(2012) Geochem J, 46, 61-72.