Asteroid Ryugu samples contain organic matter older than Solar System

The uppermost surface grains of Ryugu can protect organic molecules

The asteroid sample contained many organics in liquid water, including aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-containing heterocyclic compounds.

"The presence of prebiotic molecules on the asteroid surface despite its harsh environment caused by solar heating and ultraviolet irradiation, as well as cosmic-ray irradiation under high-vacuum conditions, suggests that the uppermost surface grains of Ryugu have the potential to protect organic molecules," Hiroshi Naraoka of Kyushu University, Fukuoka, Japan, said in a statement.

Naraoka is the lead author of a paper about this research published online on February 23 in Science. His team investigated soluble organic molecules.

Though the amino acid results from Ryugu are primarily consistent with what has been seen earlier, not everything has been examined.

"Sugars and nucleobases (components of DNA and RNA), which have been discovered in some carbon-rich meteorites, have not yet been identified in samples returned from Ryugu," said Daniel Glavin of NASA Goddard, a co-author of the paper. "It is possible these compounds are present in asteroid Ryugu but are below our analytical detection limits given the relatively small sample mass available for study."

The isotopes found in Asteroid Ryugu contained anomalies

The second research team, led by Hikaru Yabuta, examined macromolecular matter's distribution and chemical composition around the asteroid.

Macromolecules on Ryugu include ketones, aromatic and aliphatic carbon, and carboxyl functional groups. This was another indication that Ryugu's parent body had liquid water that later changed its mineral composition.

The researchers also found anomalies in the isotopes present in the sample - the ratio of elements detected in the isotope suggests that some organic matter is even older than the Sun. "The organic matter in Ryugu probably consists of primordial materials that formed during (or before) the early stages of the Solar System’s formation, which were later modified by heterogeneous aqueous alteration on Ryugu’s parent body asteroid," the study says. 

The matter came from a cold protosolar cloud kept safe for more than five billion years.

Study Abstract 1:

The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The models were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

Study Abstract 2:

Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugu’s parent body.