Benou and Ryugu asteroids, two stacks of dark rubble in space

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The Japanese probes Hayabusa-2 and American Osiris-Rex have collected data that are the subject of ten simultaneous publications, Tuesday, March 19, in the scientific journals "Science" and "Nature".

By Pierre Barthélémy Published today at 18.38, updated at 18.38

Time to Reading 4 min.

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The shadow of the Hayabusa-2 probe on the surface of the Ryugu asteroid.
The shadow of the Hayabusa-2 probe on the surface of the Ryugu asteroid. TIP / AFP

This is called an editorial outbreak. Tuesday, March 19, the teams of two space missions – the Japanese Hayabusa-2, which has been monitoring the Ryugu asteroid since June 2018, and the American Osiris-Rex, who did the same with the Benou asteroid since December 2018 – have published the first results on these two small bodies in a total of ten studies. Three are dedicated to Ryugu and appear in science and the other seven describe Benou in nature and three of his daughter magazines, Nature Astronomy, Nature Geoscience is Communications of nature.

Indexes on the birth and evolution of the solar system

Ten simultaneous studies in some of the world's largest scientific journals, the case is not so common. For Patrick Michel, director of research at the CNRS at the Observatoire de la Côte d & # 39; Azur, which has the privilege of belonging to the teams of the two missions, this barrage is justified: "These are the first results ever obtained in situ on carbon asteroids", He explains. Astronomers are courting these objects because they are the remains of the materials that made up the planets just over 4.5 billion years ago. The authors of the study science dedicated to the surface of Benou they also underline that these asteroids are representative of the objects that could lead to the water of the primitive Earth and to the molecules favorable to the appearance of life. The information that can be drawn from it is therefore just as many clues about the birth and evolution of the solar system.

The Bénou asteroid seen from the Osiris-Rex probe.
The Bénou asteroid seen from the Osiris-Rex probe. NASA / Goddard / University of Arizona

Reading these articles, the similarity of the results is obvious: if we put aside the difference in size – less than 500 meters in diameter for Bénou, about twice that of Ryugu -, "These two asteroids are very similar, confirms Patrick Michel. They have an almost identical shape, globally spherical, with a bead at the equator. Both are very dark and very scattered. Another highlight, many rocks are present on their surface.

If you want to find a difference – the light – between the two bodies, you need to look for it in the composition of their rocks because, according to the spectroscopic analyzes that conducted Hayabusa-2 and Osiris-Rex, Ryugu counts less hydrated elements than its comparison. Two possible explanations for this, according to Patrick Michel: "O Ryugu saw less water, or it was warmer during his story, which dehydrated him."

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