Ryugu probably came from one of these two other asteroids

LES BOIS, Texas – The Ryugu asteroid is a fragment of the old block. The planetary scientists of the Japanese spacecraft team Hayabusa2 have reduced the parent body of the near-Earth asteroid to one of two larger and more distant asteroids: Polana and Eulalia.

"Based on links to these specific asteroids, we can talk about Ryugu's long history," said global scientist Seiji Sugita of the University of Tokyo at a press conference held on March 19 at the Lunar and Planetary Science.

The small size of Ryugu, about 900 meters wide, and its nature of pile of rubble make scientists think that the asteroid was formed after the destruction of a larger body, there are about 700 million of them. years. According to Ryugu 's orbit, which takes space rock within 95 400 kilometers of the Earth, astronomers believe that the asteroid probably comes from the inner part of the belt. main asteroids of the solar system, between Mars and Jupiter. But it was difficult to further reduce Ryugu's origins before the Hayabusa2 shuttle arrived on the asteroid in June 2018 (SN online: 6/27/18).

Hayabusa2 showed that Ryugu is uniformly dark, one of the darkest objects known to the solar system. Its color best corresponds to that of the asteroids of the main belt Polana, which is about 55 kilometers wide, and the Eulalia, 37 kilometers wide, said Sugita. He estimated the probability that Ryugu comes from one of these two bodies between 80 and 90%.

Ryugu's chemistry suggests that his asteroid had water in his rocks early on, but that he lost much of it before the dissolution that led to Ryugu. Determining the timing of Ryugu's water history could help scientists understand how asteroids could have supplied water to the Earth in the early solar system.

The true test of Ryugu's origins will come when Hayabusa2 will return a sample of the asteroid to Earth by the end of 2020, and scientists will be able to measure the age of the rock (SN: 1/19/19, p. 20). An older Ryugu would suggest that Polana, the oldest, is the parent, while a younger sample would indicate Eulalia.