In June 2018, the Japanese Aviation Tracking Agency (JAXA) arrived at spacecraft and test exit mission Hayabsua-2 to the near-Earth asteroid 162173 Ryugu. The first scientific findings of the mission published this week in a trio of papers in the journal Science depict Ryugu as a porous "pile of rubble."
In one of the three studies, Dr. Sei-Ichiro Watanabe from JAXA and Nagoya University and co-authors presented the first up-close observations of Ryugu's mass, shape and density.
"The low density of the asteroid suggests that it has a very porous interior and is a" window pile "of loosely aggregated rocks, which formed into a spin-top shape for a period of rapid spin," they said.
"From the remote control of the asteroid, we identified potential landing sites for the spacecraft best suited for sample collection, which could further inform how Ryugu got its spinning-top shape."
In another study, the University of Aizu's Dr. Kohei Kitazato and colleagues Hayabusa-2's near-infrared spectrometer (NIRS3) to investigate the Ryugu surface composition.
They discovered that hydrated minerals are ubiquitous across the dark asteroid surface. The NIRS3 spectral data resembles known thermal and / or shock-metamorphosized carbonaceous chondrite meteorites.
"Just a few months after we received the first data, we have already made some exciting discoveries," says Dr. Seiji Sugita, a researcher at Tokyo University and Chiba Institute of Technology and co-author of the three studies.
"The primary is the amount of water, or lack of it, Ryugu seems to have. It is far drier than we had expected, and given that Ryugu is quite young – by asteroid standards – about 100 million years old , this suggests that the parent's body was also largely without water. "
Combining the results of the two previous studies as well as by observing the geological properties of Ryugu & # 39; dr. Sugita and colleagues – in a third study – tried to limit Ryugu's origin.
"Small asteroids, such as Ryugu, are estimated to have been born from very elderly parenting bodies through catastrophic disturbances and reconstruction of fragments during solar system development," the researchers said.
"Ryugu probably formed as ruins, ejected by an impact from a major parent asteroid."
"The overpowering of materials on the asteroid with small water signature suggests that a dominant part of its original maternal body was also" water-poor "
They think Ryugu is coming from a parent asteroid several tens of kilometers wide, probably in the asteroids families Polana or Eulalia.
"Thanks to the parallel missions of Ha yabusa-2 and OSIRIS-REX, we can finally address the question of how these two asteroids came to be," said Dr. Sugita.
"That Bennu and Ryugu may be siblings, yet show some strikingly different features, means that there must be many exciting and mysterious astronomical processes that we have not yet explored."
_____ [SWatanabe et al. . Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu – A spinning top-shaped brick. Science published online March 19, 2019; doi: 10.1126 / science.aav8032
K. Kitazato et al. . Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy. Science published online March 19, 2019; doi: 10.1126 / science.aav7432
S. Sugita et al. . Ryugu's geomorphology, color and thermal properties: Implications for maternal processes. Science published online March 19, 2019; doi: 10.1126 / science.aaw0422