# astro: the turbulent history of Ryugu

<< The asteroid Ryugu may look like a solid piece of rock, but it's more accurate to liken it to an orbiting pile of rubble. >>

<< Ryugu is considered a C-type, or carbonaceous, asteroid, meaning it's primarily composed of rock that contains a lot of carbon and water (..) As expected, most of the surface boulders are also C-type; however, there are a large number of S-type, or siliceous, rocks as well. These are silicate-rich, lack water-rich minerals and are more often found in the inner, rather than outer, solar system. Given the presence of S- as well as C-type rocks on Ryugu, researchers are led to believe the little rubble-pile asteroid likely formed from the collision between a small S-type asteroid and Ryugu's larger C-type parent asteroid.  If the nature of this collision had been the other way around, the ratio of C- to S-type material in Ryugu would also be reversed. >>

Rock types on Ryugu provide clues to the asteroid's turbulent history. University of Tokyo. Sep 21, 2020. 

https://phys.org/news/2020-09-ryugu-clues-asteroid-turbulent-history.html

Tatsumi E., Sugimoto C., et al. Collisional history of Ryugu’s parent body from bright surface boulders. Nat Astron. doi: 10.1038/ s41550-020-1179-z. Sep 21, 2020.

https://www.nature.com/articles/s41550-020-1179-z   

Also

How small particles could reshape an asteroid. FonT. Sep 26, 2020.

https://flashontrack.blogspot.com/2020/09/gst-how-small-particles-could-reshape.html

# gst: how small particles could reshape an asteroid

<< In January 2019, NASA's OSIRIS-REx spacecraft was orbiting asteroid Bennu when the spacecraft's cameras caught something unexpected: Thousands of tiny bits of material, some just the size of marbles, began to bounce off the surface of the asteroid—like a game of ping-pong in space. Since then, many such particle ejection events have been observed at Bennu's surface. >>

AA have been studying << asteroids for a long time, and no one had ever seen this phenomenon before—these little particles getting shot off of the surface  (..) such seemingly small occurrences may add up over time—perhaps even helping to give the asteroid its telltale shape, which is often compared to a spinning top. >>

<< basic orbital calculations suggest that all of these particles should do one of two things: Jump off the surface and fall right back down or escape from Bennu's gravity and never come back. >>

<< When particles eventually land on Bennu's surface, many appear to disproportionately fall near its equator where the asteroid has a distinct bulge. As a result, these events could be reshaping the asteroid over thousands or millions of years by moving mass from its north and south to its middle. >>

Daniel Strain. How small particles could reshape Bennu and other asteroids. University of Colorado at Boulder. Sep 9, 2020.

https://phys.org/news/2020-09-small-particles-reshape-bennu-asteroids.html 

McMahon Jay W, Scheeres Daniel J, et al. Dynamical Evolution of Simulated Particles Ejected From Asteroid Bennu. J Geophys Res: Planets. 125 (8). doi: 10.1029/ 2019JE006229. May 18, 2020.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JE006229 

Scheeres Daniel J, McMahon Jay W, et al. Particle Ejection Contributions to the Rotational Acceleration and Orbit Evolution of Asteroid (101955) Bennu. 

J Geophys Res: Planets. 125 (3). doi: 10.1029/ 2019JE006284. March 11, 2020. 

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006284