Prebiotic Organic Compounds in Asteroid Ryugu

A sample of dark pebbles and powder from asteroid Ryugu. Credit: Yada et al.

The Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission to asteroid Ryugu investigated its surface from 2018 to 2020 and successfully returned approximately 5.4 grams of Ryugu samples to Earth in December 2020. Initial analyses of the returned samples revealed that Ryugu is a primitive carbonaceous asteroid composed mainly of hydrous minerals and organic compounds. Carbonaceous asteroids are thought to be the parent bodies from which carbonaceous chondrite meteorites originate. One major hypothesis holds that such bodies delivered prebiotic organic molecules such as amino acids, which are essential for the emergence of life, to the primitive Earth. Organic matter in primitive asteroids such as Ryugu is some of the oldest material in the solar system. This material may preserve information from the protosolar nebula to early parent body processing to the evolution and distribution of organic compounds in the solar system. The returned samples from Hayabusa2 offer an unprecedented opportunity to study such materials in a pristine condition. ย 

The Hayabusa2-initial-analysis soluble organic matter team led by Hiroshi Naraoka of Kyushu University, Japan, examined the bulk and organic chemistry of the returned samples collected from the surface of asteroid Ruygu. They found that Ryugu samples contained more hydrogen, carbon, and nitrogen than known carbonaceous chondrites and showed similar isotopic signatures to the very primitive CI-type chondrites. The Ryugu grains were analyzed for amino acids using a combination of high-resolution mass spectrometry and high-precision liquid chromatography with high-sensitivity fluorescence detectors. More than 10 amino acids were identified, including glycine and L-alanine, which are building blocks of proteins for living organisms. The observation of chiral amino acids suggests extraterrestrial and non-biological origins. The results also showed that the organic matter has been affected by aqueous alteration but has not been significantly heated. This research provides the first direct observation of primitive organic compounds on a carbonaceous asteroid. READ MORE