The history of one of the oldest objects in the Solar system unveiled

An international team of scientists have unveiled details of the history of the asteroid Ryugu, a truly ancient object in the Solar system, after the Hayabusa2 mission brought samples from this asteroid back to Earth. The ESRF was one of the institutes involved in sample characterization, on ID15A. The results are published in Science.

The asteroid Ryugu, located at 200 million kilometres from the Earth, is one of the most primitive objects of the solar system. The Japanese spacecraft Hayabusa2 explored it from 2018 until it came back to Earth two years later with minuscule multiple samples from the asteroid.

Two years later, and thanks to the international collaboration of institutes led by the Japan Aerospace Exploration Agency (JAXA), the first results on the analysis of the samples shed light on the history of Ryugu, from its formation to its collisional destruction.

Researchers used cosmochemical and physical methods at universities and institutes, including the ESRF and four other synchrotron radiation facilities in Japan, United States, and Europe.

The results combined with computer simulation have allowed scientists to picture the origins of Ryugu:  the Ryugu parent body accumulated about 2 million years after the formation of the solar system, and then heated up to about 50°C over the next 3 million years, resulting in chemical reactions between water and rock. The size of the impactor that destroyed the Ryugu parent body, which is about 100 km in diameter, is at most 10 km in diameter, and that the present-day Ryugu is composed of material from a region far from the impact point.

What the data explain

In particular, the seventeen Ryugu samples analysed contain particles (such as Ca- and Al-rich inclusions) that were formed in high-temperature environments (>1000°C). These high-temperature particles are thought to have formed near the Sun and then migrated to the outer solar system, where Ryugu was formed. This indicates that large-scale mixing of materials occurred between the inner and outer solar system at the time of its birth.

Based on the detection of the magnetic field left in the Ryugu samples, it is highly likely that the original asteroid from which the current Ryugu descended (Ryugu’s parent body) was born in the darkness of nebular gas, far from the Sun, where sunlight cannot reach.

The scientists also discovered liquid water trapped in a crystal in a sample. This water was carbonated water containing salts and organic matter, which was once present in the Ryugu parent body. Crystals shaped as coral reefs grew from the liquid water that existed inside Ryugu’s parent body. Rocks that were deeper underground contained more water than those in the surface.

Read more on the ESRF website

Image: A coloured view of the C-type asteroid 162173 Ryugu, seen by the ONC-T camera on board of Hayabusa2.

Credit: JAXA Hayabusa 2

From Antarctica to the beamline, #weekendusers

A Belgian team is trying to find out about the origin of the Solar System by studying micrometeorites from Antarctica on the Dutch-Belgian beamline (DUBBLE).

Sør Rondane Mountains, Antarctica, 2013. Steven Goderis, from the Analytical Environmental and Geochemistry (AMGC) research group in the Vrije Universiteit Brussel (Belgium), is part of a Japanese-Belgian expedition looking for meteorites preserved in the cold and dry environment of the South Pole. And they hit the jackpot: they found 635 fragments of micrometeorites. After coming back with the precious load, similar meteorite recovery expeditions and field campaigns focusing on micrometeorites continued in the following years, all equally successful. To date, they have found hundreds of pieces of meteorites and thousands of pieces of micrometeorites.

So what is the point of micrometeorites? Of all the material reaching Earth from space only a small part will survive the heating and shock experienced upon entry in the atmosphere. The large majority of this material, the micrometeorites, will rain on Earth as extraterrestrial particles of less than 2mm in size. Although meteorites in general provide us with essential information on the origin and evolution of the planets and the Solar System, micrometeorites, mostly originating from the most primitive objects still remaining in the Solar System, raise an even higher scientific interest. “Any information we can get from micrometeorites will complement the knowledge we have of meteorites, so it is really important to study them. We have a wide array of samples so that we can get the best possible picture of these materials”, explains Bastien Soens, who is doing his PhD on this subject.

>Read more on the European Synchrotron website

Image: The team on the beamline. From left to right: Niels de Winter, Bastien Soens, Dip Banerjee, Stephen Bauers and Niels Collyns.
Credits: C. Argoud.