The evolution of asteroid Ryugu was recorded in its noble gases

In December 2020, the probe Hayabusa2 from the Japan Aerospace Exploration Agency (JAXA) launched in Australia a sealed container with samples, both solid and gaseous, collected in 2019 in Ryuguan asteroid that moves around the Sun in an orbit between Mars and Earth.

Ryugu has noble gas and nitrogen compositions similar to Ivuna-type carbonaceous chondrites, which are one of the most primitive meteorites and a possible source of volatile compounds on Earth.

Ryuji Okazaki (Kyushu University)

Since then, Japanese researchers have carried out several analyzes of the material collected and this week they present in the journal Science The valuable information that provide data from noble gases (stable isotopes of helium, neon, argon, krypton and xenon) and the nitrogen. Their concentrations were measured after performing a gradual heating of grains brought from Ryugu.

The isotopic compositions or proportions of this type of gas are closely related to the origins of the material that welcomed them, which was incorporated into the primitive bodies (asteroids and comets) of the solar system and eventually formed the planets.

Remnants of the early solar system

In the case of Ryugu, the results reveal the composition of its parent asteroid and its evolution. The current object was found to still retain noble gases from the early solar system, in greater abundance than found in any meteorite found to date, and it also preserves nitrogen isotopes from that remote period.

“Our finding is that Ryugu has similar noble gas and nitrogen compositions to Ivuna-like carbonaceous chondriteswhich are one of the most primitive meteorites and a possible source of volatile compounds on Earth”, explains the lead author to SINC, Ryūji Okazakifrom Kyushu University.

Above, illustration of the Hayabusa2 spacecraft collecting a sample of the asteroid Ryugu and real image captured just before landing. Central and below images, the capsule with the samples is recovered in Australia, from where they were taken to Japan to analyze their solid content (like the grains of black sand seen in the last image) and gaseous content. /JAXA et al./Akihiro Ikeshita

In addition to the primordial gas of the early solar system, the sample contained two additional types of noble gases: one caused by the incidence of solar wind and another produced by reactions triggered by the irradiation of galactic cosmic rays.

Their joint analysis reveals that Ryugu has moved in the past from the asteroid belt (located between the orbits of Mars and Jupiter) to the closest position to our planet, where it is today.

“These noble gas isotopes indicate that Ryugu migrated from asteroidal orbit to the current near-Earth orbit a few years ago. 5 million yearssays Okazaki.

Diagram of the evolution of asteroid Ryugu. / ©Okazaki et al., 2022a

Although Ryugu’s origin may be even further out in the solar system, according to iron isotopes of the asteroid analyzed by researchers at the University of Chicago (USA) and other international centers. Their study, published in the journal advances in scienceindicates that it could have formed beyond the orbits of Jupiter and Saturn.

“The growth and migration of the giant planets destabilized nearby planetesimals and expelled some inward to implant them in the main belt,” the authors note.

“And in this picture, most carbonaceous chondrites may have originated in regions close to the birthplaces of Jupiter and Saturn, while the different isotopic composition of CI and Ryugu chondrites may reflect their formation further out in the disk, due to their presence in the inner solar system for the excitation of Uranus and Neptune”.

Gas sample analysis

The researcher also led another studiopublished in the magazine advances in science, where the results of gas sample taken by the Hayabusas2 mission, “a treasure chest of Ryugu”, according to the authors.

“We measured that sample stored in the container and found that the gas is composed of solar wind heliumbut also from the Earth’s atmosphere, since the container was contaminated when passing through it”, says Okazaki, who recalls that “this is the first time that gas samples have been recovered from an asteroid”.

References:

Ryuji Okazaki et al. “Noble gases and nitrogen in samples from asteroid Ryugu record its volatile sources and recent surface evolution”. Science, 2022.

Ryuji Okazaki et al. “First sample of asteroid gas delivered by the quest Hayabusa2: A Ryugu Treasure Box”. advances in science2022

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