Astrochemistry: Discoveries to Inform the Chemical Sciences and Engineering Communities Proceedings of a Workshop–in Brief (2019) / Chapter Skim
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Astrochemistry: Discoveries to Inform the Chemical Sciences and Engineering Communities: Proceedings of a Workshop - in Brief
Astrochemistry: Discoveries to Inform the Chemical Sciences and Engineering Communities: Proceedings of a Workshop - in Brief
Pages 1-12
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Caselli described dark clouds in which the temperature is so low (6 K) that molecules freeze out onto dust particles and form thick icy mantles, which are composed primarily of water, carbon monoxide, and other molecules and represent the precursors of planets.
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SESSION 1: THE CHEMISTRY OF SPACE: NOVEL CHEMICALS AND REACTION MECHANISMS Eric Herbst, Commonwealth Professor of Chemistry at the University of Virginia, provided a few introductory remarks to begin Session 1. He reviewed the types of molecules that have been identified in space -- simple species, carbon chains, complex organic molecules (COMs)
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Mapping the molecular structure of disks provides insight into the material available for building planetary or cometary systems; the relative ratios of dominant volatile chemicals will dictate the compositions of planetary atmospheres. Walsh stated that the chemical structure of protoplanetary disks is set by the complex interplay between gas-phase chemistry, surface chemistry, radiation, and dynamics.
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Laboratory experiments support that hypothesis, but mechanisms of PAH evolution in circumstellar environments are unclear. One challenge today is that the data have low spectral resolution and that researchers therefore cannot define PAH molecular structures or features, Peeters said.
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It is on the basis of rotational transitions that most molecules in space have been positively identified. Table 1 Physical Environment of Various Interstellar Regions with Earth as a Reference Point Molecular Density, Environment Temperature, K molecules/cm3 Earth at sea level ~1019 ~300 Diffuse interstellar medium ~10 ~50 Dense interstellar clouds ~103 ~10 Star-forming regions ~107 ~100–300 Widicus Weaver stated that observatories today are providing complex spectral data to analyze, but the challenge is to assign and analyze all the information.
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Cleeves described the disk chemical composition (see Figure 3) and noted that various physical factors can change the composition of protoplanetary disks.
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The Cassini mission also showed that O+ flows into Titan's atmosphere; this finally explained why carbon monoxide was present in the atmosphere. Hörst emphasized that scientists would never have been able to explain that conundrum without the data from Cassini and that the data led to predictions of various organic compounds, such as amino acids, in Titan's atmosphere.
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SESSION 3: DISCOVERIES FROM SPACECRAFT MISSIONS IN THE SOLAR SYSTEM AND FROM LABORATORY STUDIES OF EXTRATERRESTRIAL SAMPLES Stefanie Milam, a research physical scientist in the Astrochemistry Laboratory of the NASA Goddard Space Flight Center, introduced the third session by emphasizing the importance of planetary missions and analysis of extraterrestrial samples. Those activities provide insight into interstellar chemistry and the formation of planetary systems.
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Scientists believe that the Gale Crater is a lakebed and that sampling of this area could provide a history of Mars -- its transformation from a warm wet environment to a cold dry one. Glavin said that the Curiosity rover contains a complex suite of instruments, including a quadrupole mass spectrometer and gas chromatograph.
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Stockton stated that scientists also use the terrestrial analogues to plan sample collection so that biosignatures will not be missed. She described work that was conducted in the Atacama Desert and emphasized the importance of both depth sampling, given the surface sterilization caused by UV radiation, and the taking of multiple samples, given the expected low biomass.
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Panel Discussion Several questions posed by workshop participants centered on sample analysis. One participant asked about advances in developing highly sensitive analytic techniques, such as position-specific isotopic analysis.
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The statements recorded here are those of the individual workshop participants and do not necessarily represent the views of all participants, the planning committee, the Chemical Sciences Roundtable, or the National Academies. To ensure that this proceedings meets institutional standards of quality and objectivity, it was reviewed in draft form by William Latter, NASA; Stefanie Milam, NASA; and Susanna Widicus Weaver, Emory University.
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