Asteroid samples could ‘rewrite the chemistry of the Solar System’

A fifth of an ounce of dark spots brought to Earth from an asteroid by a Japanese spacecraft are some of the most pristine bits of a baby solar system ever studied, scientists announced Thursday.

That fact should help planetary scientists refine their knowledge of the ingredients of the disk of dust and gas that circled the Sun about 4.6 billion years ago, before coalescing into planets and smaller bodies.

“We must rewrite the chemistry of the solar system,” said Hisayoshi Yurimoto, a professor of terrestrial and planetary science at Hokkaido University in Japan and head of the research analysis described in a paper published in the journal Science on Thursday.

The Hayabusa2 probe arrived at Ryugu, a carbon-rich asteroid, in 2018. The mission was operated by JAXA, the Japanese space agency, and spent more than a year studying Ryugu. This included briefly descending to the surface a few times to collect dirt samples from the asteroid and even using an explosive to blast a new crater on its surface.

In December 2020, Hayabusa2 passed by Earth again, leaving a small capsule containing the Ryugu pieces in the Australian outback.

Mission scientists have spent the past year studying what Hayabusa2 has brought back. “It’s a pile of rocks, pebbles and sand,” said Shogo Tachibana, a planetary scientist at the University of Tokyo and principal investigator responsible for analyzing the samples. The biggest piece was about a centimeter, about four-tenths of an inch, in size, he said. Many of the particles were about a millimeter wide.

The team of Dr. Yurimoto received just a tiny bit of the asteroid – less than 200 grams.

The biggest surprise from their analysis is that the Ryugu chunks look like a 1.5-pound meteorite that fell in Tanzania in 1938. The Ivuna meteorite, named after the region in which it fell, was of a very rare type. Of the more than 1,000 space rocks that have been found on the Earth’s surface, only five are of the type known as CI chondrite.

(OC stands for carbonaceous, which means it contains carbon compounds, and the I stands for Ivuna. A chondrite is a stony meteorite.)

“It’s super similar,” said Sara Russell, planetary materials group leader at the Natural History Museum in London, who was a member of the science team on the Hayabusa2 mission, as well as NASA’s OSIRIS-REX mission, which visited a rich asteroid. on different carbon, Bennu. She was an author for the journal Science.

OSIRIS-REX samples from Bennu will arrive on Earth next year.

The dating of the Ryugu samples indicated that the material formed about 5.2 million years after the birth of the solar system.

Dr. Russell said that carbonaceous chondrites were thought to form in the outer part of the solar system, farther away than the current orbits of most asteroids. She described them as “basically frozen relics of the early solar system”.

CI meteorites have a composition of heavier elements very similar to what is measured at the surface of the sun – such as the ratios of sodium and sulfur to calcium. So planetary scientists thought these were a good indication of the building blocks that filled the early solar system. This provides key parameters for computer models to understand how planets formed.

Analysis indicated that the material was heated early in its history, melting ice into water, which led to chemical reactions altering the minerals. But the relative amounts of various elements remained almost unchanged, the scientists said.

This fits with the image Ryugu formed from the debris that was knocked off a much larger asteroid, miles in diameter. (CI meteorites likely also came from the larger parent asteroid, not Ryugu.)

The results were “very important,” said Victoria Hamilton, a scientist at the Southwest Research Institute in Boulder, Colorado, who was not involved in the research. “While we’ve learned a lot about the early solar system from meteorites here on Earth, they don’t have any kind of context.”

In this case, planetary scientists know exactly where the samples came from.

The combination of Ryugu with CI meteorites was unexpected because CI meteorites contain a lot of water, and remote measurements from Hayabusa2 while at Ryugu indicated the presence of some water, but that the surface was almost dry. Laboratory measurements, however, revealed about 7 percent water, said Dr. Tachibana, co-author of the new Science study. That’s a significant amount for such a mineral.

Dr. Tachibana said scientists are working to understand the discrepancy.

Scientists also found some differences between samples from Ryugu and the Ivuna meteorite. The Ivuna meteorite included even greater amounts of water and contained minerals known as sulfates that were absent from Ryugu.

The differences could indicate how the meteorite’s mineralogy has changed over decades sitting on Earth, absorbing water from the atmosphere and undergoing chemical reactions. That, in turn, could help scientists figure out what formed as part of the solar system 4.6 billion years ago and what has recently changed in CI meteorites over the course of a few decades on Earth.

“It shows why it’s important to go and have space missions, to go out and explore and bring in material in a really controlled way,” said Dr. Russell.

This also raises expectations for OSIRIS-REX’s Bennu samples, which will land in the Utah desert on September 24, 2023. Dante Lauretta, the principal investigator for this mission, chose this asteroid in large part because it appeared to be similar to CI Meteorites. and OSIRIS-REX measurements at Bennu indicated more water than Hayabusa2 observed at Ryugu. But if Ryugu is already a match for a CI meteorite, that suggests Bennu might be made of something different.

“So now I’m asking myself, ‘What are we bringing back?'” said Dr. Lauretta, who also authored the Science article. “It’s kind of exciting, but it’s also intellectually challenging.”

Leave a Reply

%d bloggers like this: