Asteroid Ryugu may be a leftover from the Sun's formation

In 2018, a spacecraft called Hayabusa2 landed on a moving asteroid named Ryugu and collected particles from above and below its surface. One and a half years later, it returned to Earth with a sealed capsule containing five grams of dust and rock from this asteroid. Analyses of this sample have now revealed that the asteroid may be part of the matter that coalesced into our Sun four and a half billion years ago.

“We previously only had a handful of these rocks to study, and all of them were meteorites that fell to Earth and were stored in museums for decades to centuries, which changed their compositions,” said study co-author Nicolas Dauphas, a geochemist at the University of Chicago. “Having pristine samples from outer space is simply incredible. They are witnesses from parts of the solar system that we have not otherwise explored.”

By studying the chemical and isotopic composition of this sample, the scientists found that Ryugu is similar to a class of meteorites known as “Ivuna-type carbonaceous chondrites,” which have a similar chemical composition to the Sun and date back to the very beginnings of our solar system, before the formation of the Sun and planets. At the beginning, all that existed was a gigantic, rotating cloud of gas, which was later on pulled into the center, forming the star we know as the Sun. The remnants of the gas cooled down and transformed into rocks, which still float around our solar system. According to the scientists, Ryugu appears to be one of them.

Although today the asteroid is relatively dry, the fragments showed evidence of having been soaked in water about five million years after the solar system formed. “One must picture an aggregate of ice and dust floating in space, that turned into a giant mudball when ice was melted by nuclear energy from the decay of radioactive elements that were present in the asteroid when it formed,” Dr. Dauphas explained. 

These findings may hint at similar formation conditions among comets and other asteroids, and can be used to clarify conditions under which such astronomical objects formed and changed over vast expanses of time.

The Hayabusa2 space mission is the first of several international missions that aim to bring back to Earth samples of other asteroids, as well as from unexplored areas of the Moon, Mars, and other planets.

“It has been very much under the radar for the public and some decision makers, but we are entering a new era of planetary exploration that is unprecedented in history. Our children and grandchildren will see returned fragments of asteroids, Mars, and hopefully other planets when they visit museums,” concluded Dr. Dauphas.

The study is published in the journal Science.

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By Andrei Ionescu, Earth.com Staff Writer