The solar system formed approximately 4.5 billion years ago. Numerous fragments that bear witness to this early era orbit the sun as asteroids. Around three-quarters of these are carbon-rich C-type asteroids, such as 162173 Ryugu, which was the target of the Japanese Hayabusa2 mission in 2018 and 2019. The spacecraft is currently on its return flight to Earth. Many scientists, including planetary researchers from the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt; DLR), intensively studied this cosmic “rubble pile,” which is almost 1 kilometer in diameter and can come close to Earth. Infrared images acquired by Hayabusa2 have now been published in the scientific journal Nature. They show that the asteroid consists almost entirely of highly porous material. Ryugu was formed largely from fragments of a parent body that was shattered by impacts. The high porosity and the associated low mechanical strength of the rock fragments that make up Ryugu ensure that such bodies break apart into numerous fragments upon entering Earth’s atmosphere. For this reason, carbon-rich meteorites are very rarely found on Earth and the atmosphere tends to offer greater protection against them.
Source:
https://phys.org/news/2020-03-asteroid-ryugu-link-planetary-formation.html