Organic molecules in the early Solar System are one of important building blocks of planets, as their elements (C, H, O, N, and S) are very abundant in space. The first organic molecules were synthesized in inter­stellar clouds through photochemical reactions in the gas phase and on dust surfaces. The interstellar molecules were then involved in further synthesis and decomposition through various processes in the protoplanetary disk and planetesimals, which resulted in diversity in chemical compositions of asteroids (meteorites) and comets. These small bodies are thought to have supplied organics as life's building blocks to the early Earth during the Late Heavy Bombardment. Therefore, organic compounds in the primitive small bodies are 4.5 billion-year-old “fossils” to record the Solar System history.

The most primitive meteorites are classified as carbonaceous chondrites. Carbonaceous chondrites contain 2 wt% total organic carbon that contains insoluble macromolecules (IOM) (> 1%) and soluble organic molecules (SOM). The chemical structure of IOM is complex and its exact compositions are still unknown, but a number of previous studies have suggested that it is composed of aromatic network crosslinking with short-branched aliphatic chains and various oxygen functional groups. The IOM in the primitive carbonaceous chondrites show variable D and 15N enrichments, indicating that precursor molecules of IOM were formed in extreme cold environments such as interstellar cloud or outer solar nebula. SOM has been historically well studied represented by a variety of compounds of biochemical interest, such as amino acids, carboxylic acids, hydrocarbons, etc., although there still exist more than 10000 unidentified molecules.

Classification of meteorites is based on different asteroidal parent body and/or solar nebula histories, which include processes such as aqueous alteration, thermal metamorphism, and impact-induced dehydration. These chemical histories are recorded in the variations of elemental, molecular, and isotopic compositions of organic molecules in meteorites. Assuming that all the chondritic IOM had a common origin, any variations in the IOM composition within and across chondrite classes are reflected by the conditions of parent body and/or nebular processes.

The advantages of small body exploration missions compared to the meteoritic studies are to link chemical compositions with the geology of the target bodies and to understand the intact compositions without terrestrial contamination. To date, there have been several successful missions, NASA's cometary dust sample return mission, Stardust; JAXA's stony asteroid sample return mission, Hayabusa; and ESA's comet rendezvous mission, Rosetta. Japanese carbonaceous asteroid sample return mission, Hayabusa2, will explore the near-Earth asteroid Ryugu. The primary scientific goal of Hayabusa2 is to investigate the interaction of organic molecules, water, and minerals on the primitive asteroid. The spacecraft will arrive at Ryugu around July 2018. During its 18-month stay, remote-sensing and lander observations will be carried out. Hayabusa2 is planned to collect asteroid samples from up to three sites. The third sampling site will be around the artificial crater created by the small carry-on impactor, which enables sampling of the asteroid interior. The collected samples will be returned to the Earth in the end of 2020.