In a just published paper scientists reveal how they think they have identified the oldest rocks on the rubble pile asteroid Ryugu, and found them to be distributed across the entire face of the asteroid.
These boulders are light enough that they would float on water.
Ryugu is thought to have initially formed as a fluffy planetesimal that coalesced from accumulated dust in the early Solar System, and subsequently underwent processes such as thermal evolution and compression. This parent body was then later destroyed in a collision and fragments of this reaccumulated into the asteroid. However, planetesimals have never been seen, so whether they really existed or what they may have looked like is one of the biggest challenges in understanding the planet formation process. The boulders discovered in this research are thought to be a material that most strongly retains the appearance of the fluffy planetesimals that triggered the birth of the planets in the Solar System.
Additionally, the data from all the scientific instruments onboard Hayabusa2 that were used to examine the surface of Ryugu revealed that fragments of material similar to those of the ultra-high porosity boulders are globally distributed over the asteroid surface, and may have been collected in the sample taken by Hayabusa2. If highly primitive material with the ultra-high porosity discovered here is also found in the collected samples, it will both clarify the formation and evolutional history of Ryugu’s parent body, and also provide evidence of planetesimal formation in the early stage of the Solar System formation process.
There is no word yet from the scientists studying the Hayabusa-2 samples on what they have found. This paper gives them an idea of what could be the most important type of rock to look for.
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