Thematic Articles

Advances in analytical techniques are essential for understanding the nature, formation, and evolutionary history of extraterrestrial organic matter. In this chapter, we briefly review analytical techniques used to detect and characterize organic matter in extraterrestrial materials. Mass spectrometry is often coupled with gas chromatography or liquid chromatography for elemental and isotopic analysis, and for identifying specific organic compounds. Spectroscopy involves interaction of molecules with electromagnetic radiation at various wavelengths. Almost every wavelength—from X-rays to radio waves—can be used for spectroscopic measurements. The most major microscopic and nanoscopic techniques are scanning and/or transmission electron microscopy. Spectroscopy and mass spectrometry can also be coupled with microscopic analysis for detailed compositional investigations.

The C-type asteroid Ryugu samples returned by the Hayabusa2 spacecraft are the chemically most pristine material in the Solar System, as they have not been exposed to terrestrial environments. The organic matter in Ryugu records the molecular evolution from the Sun’s parent molecular cloud chemistry to asteroidal aqueous alteration. In this article, we review the results of Ryugu sample analysis and discuss the evolution of organic matter in the early Solar System by comparing these results with recent radio and infrared observations of protostars and protoplanetary disks.

Complex organic matter is present in many extraterrestrial materials such as chondrite meteorites, micrometeorites, and interplanetary dust. The observed complexity of this organic matter is due to the combination of diversity of primitive organic materials that accreted onto asteroids and the subsequent effect of hydrothermal and/or metamorphic alteration that took place after accretion. These processes resulted in a variety of carbonaceous grain morphologies, elemental abundances, and organic functional group compositions. Some carbonaceous dust grains and micrometeorites have cometary origins and provide insights into the unique processing histories on those outer Solar System bodies. Isotopic analyses can help distinguish carbonaceous grains that retain their pre-accretion heritage, while advanced microscopy techniques reveal the interplay of complex organic matter with surrounding mineral.

The inner Solar System—including the planet Earth—was heavily bombarded by comets, asteroids, and their fragments (i.e., meteorites, micrometeorites, and interplanetary dust particles) from 4.56 to about 3.5 billion years ago. This bombardment resulted in a rich assortment of organics delivered to the Earth, as comets and many asteroids contain carbonaceous material. These organic compounds were likely further processed on the early Earth (e.g., by impact-shock reactions), providing a feedstock of prebiotic molecules to the crust and oceans. In this chapter, we review the mechanisms of organic matter delivery to the primitive Earth, further reactions and processing, and the importance of exogenous material in the evolution of our planet and life.

Organic compounds are a major component of dust in molecular clouds, alongside silicates and water ice, due to the high abundances of elements that make up these compounds in the Galaxy. The initial molecular inventory of the Solar System, inherited from the molecular cloud, was modified and new complex molecules were formed in the protoplanetary disk and planetesimals. Because astronomical observations mainly target gas, while cosmochemical evidence deals with solid phases, it is crucial to link discrepant knowledge on organic species through state-of-the-art modeling. This chapter reviews the latest understanding of surface reactions on inter- stellar dusts, gas–dust reactions in the protoplanetary disk, and alteration processes on planetesimals in the early Solar System.

Extraterrestrial organic matter forms in a variety of locations in space through different mechanisms. Its nature, distribution, formation mechanisms and locations are of particular interest. Some organic molecules can even be considered as key players for the emergence of life. Although new organic species are continuously detected in the interstellar media, Solar System bodies, and extraterrestrial materials, their formation and evolution are still not fully understood. Ground-based and space observations can detect organic matter in different objects with a range of complexity and diversity, while laboratory investigations of astromaterials allow detailed characterization of extraterrestrial organic matter with high precision. This issue reviews different aspects of extraterrestrial organic matter, including its origin, evolution, diversity, and delivery.