Several sulphur-bearing species have already been observed in different families of comets. However, the knowledge on the minor sulphur species is still limited. The comet's sulphur inventory is closely linked to the pre-solar cloud and holds important clues to the degree of reprocessing of the material in the solar nebula and during comet accretion. Sulphur in pre-solar clouds is highly depleted, which is quite puzzling as the S/O ratio in the diffuse interstellar medium is cosmic. This work focuses on the abundance of the previously known species H 2 S, OCS, SO, S 2 , SO 2 and CS 2 in the coma of comet 67P/Churyumov–Gerasimenko measured by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Double Focusing Mass Spectrometer between equinox and perihelion 2015. Furthermore, we present the first detection of S 3 , S 4 , CH 3 SH and C 2 H 6 S in a comet, and we determine the elemental abundance of S/O in the bulk ice of (1.47 ± 0.05) × 10 −2 . We show that SO is present in the coma originating from the nucleus, but not CS in the case of 67P, and for the first time establish that S 2 is present in a volatile and a refractory phase. The derived total elemental sulphur abundance of 67P is in agreement with solar photospheric elemental abundances and shows no sulphur depletion as reported for dense interstellar clouds. Also the presence of S 2 at heliocentric distances larger than 3 au indicates that sulphur-bearing species have been processed by radiolysis in the pre-solar cloud and that at least some of the ice from this cloud has survived in comets up the present.

/pdf/sulphur-bearing-species-in-the-coma-of-comet-67p-churyumov-146b2sl01a.pdf

Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko

1.1. What is astrobiology?
Astrobiology is the science that seeks to understand the story of life in our universe. Astrobiology includes investigation of the conditions that are necessary for life to emerge and flourish, the origin of life, the ways that life has evolved and adapted to the wide range of environmental conditions here on Earth, the search for life beyond Earth, the habitability of extraterrestrial environments, and consideration of the future of life here on Earth and elsewhere. It therefore requires knowledge of physics, chemistry, biology, and many more specialized scientific areas including astronomy, geology, planetary science, microbiology, atmospheric science, and oceanography.

However, astrobiology is more than just a collection of different disciplines. In seeking to understand the full story of life in the Universe in a holistic way, astrobiology asks questions that transcend all these individual scientific subjects.

Astrobiological research potentially has much broader consequences than simply scientific discovery, as it includes questions that have been of great interest to human beings for millennia (e.g., are we alone?) and raises issues that could affect the way the human race views and conducts itself as a species (e.g., what are our ethical responsibilities to any life discovered beyond Earth?).

/pdf/the-astrobiology-primer-v2-0-1ehl8m0f6x.pdf

The Astrobiology Primer v2.0

The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley1, 2. Such matter is generally thought to have originated in the interstellar medium3, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed4. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization5. Many gaseous organic molecules, however, have been observed6, 7, 8, 9; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei8. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula10. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites11, 12. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies11. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.

High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko

The search for evidence of extraterrestrial life in our Solar System is currently guided by our understanding of terrestrial biology and its associated biosignatures. The observed homochirality in all life on Earth, that is, the predominance of "left-handed" or l-amino acids and "right-handed" or d-sugars, is a unique property of life that is crucial for molecular recognition, enzymatic function, information storage and structure and is thought to be a prerequisite for the origin or early evolution of life. Therefore, the detection of l- or d-enantiomeric excesses (ee) of chiral amino acids and sugars could be a powerful indicator for extant or extinct life on another world. However, studies of primitive meteorites have revealed they contain extraterrestrial amino acids and sugar acids (aldonic acids) with large enantiomeric excesses of the same chirality as terrestrial biology resulting from nonbiological processes, complicating the use of chiral asymmetry by itself as a definitive biosignature. Here we review our current knowledge of the distributions and enantiomeric and isotopic compositions of amino acids and polyols found in meteorites compared to terrestrial biology and propose a set of criteria for future life detection missions that can be used to help establish the origin of chiral asymmetry.

The Search for Chiral Asymmetry as a Potential Biosignature in our Solar System.

Complex organic molecules have been observed for decades in the interstellar medium. Some of them might be considered as small bricks of the macromolecules at the base of terrestrial life. It is hence particularly important to understand organic chemistry in Solar-like star-forming regions. In this article, we present a new observational project: Seeds Of Life In Space (SOLIS). This is a Large Project using the IRAM-NOEMA interferometer, and its scope is to image the emission of several crucial organic molecules in a sample of Solar-like star-forming regions in different evolutionary stages and environments. Here we report the first SOLIS results, obtained from analyzing the spectra of different regions of the Class 0 source NGC 1333-IRAS4A, the protocluster OMC-2 FIR4, and the shock site L1157-B1. The different regions were identified based on the images of formamide (NH2CHO) and cyanodiacetylene (HC5N) lines. We discuss the observed large diversity in the molecular and organic content, both on large (3000–10,000 au) and relatively small (300–1000 au) scales. Finally, we derive upper limits to the methoxy fractional abundance in the three observed regions of the same order of magnitude of that measured in a few cold prestellar objects, namely ~10-12-10-11 with respect to H2 molecules.

/pdf/seeds-of-life-in-space-solis-the-organic-composition-3iurj60dfm.pdf

Seeds Of Life In Space (SOLIS): The Organic Composition Diversity at 300–1000 au Scale in Solar-type Star-forming Regions*

The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples, a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result demonstrates that comets could have played a crucial role in the emergence of life on Earth.

https://advances.sciencemag.org/content/advances/2/5/e1600285.full.pdf

Prebiotic chemicals—amino acid and phosphorus—in the coma of comet 67P/Churyumov-Gerasimenko

The thermal structure of planetary atmospheres is an essential input for predicting and retrieving the distribution of gases and aerosols, as well as the bulk chemical abundances. In the case of Jupiter, the temperature at a reference level—generally taken at 1 bar—serves as the anchor in models used to derive the planet’s interior structure and composition. Most models assume the temperature measured by the Galileo probe. However, those data correspond to a single location, an unusually clear, dry region, affected by local atmospheric dynamics. On the other hand, the Voyager radio occultation observations cover a wider range of latitudes, longitudes, and times. The Voyager retrievals were based on atmospheric composition and radio refractivity data that require updating and were never properly tabulated; the few existing tabulations are incomplete and ambiguous. Here we present a systematic electronic digitization of all available temperature profiles from Voyager, followed by their reanalysis, employing currently accepted values of the abundances and radio refractivities of atmospheric species. We find the corrected temperature at the 1 bar level to be up to 4 K greater than the previously published values, i.e., 170.3 ± 3.8 K at 12°S (Voyager 1 ingress) and 167.3 ± 3.8 K at 0°N (Voyager 1 egress). This is to be compared with the Galileo probe value of 166.1 ± 0.8 K at the edge of an unusual feature at 6.°57N. Altogether, this suggests that Jupiter’s tropospheric temperatures may vary spatially by up to 7 K between 7°N and 12°S.

James Hunter Waite

Papers

Prebiotic chemicals—amino acid and phosphorus—in the coma of comet 67P/Churyumov-Gerasimenko

Jupiter's Temperature Structure: A Reassessment of the Voyager Radio Occultation Measurements