I guess this is a good news hook to mention something cool about the surfaces of asteroids. They probably get “reset” about every 10 million years when they have a close encounter with a major planet, like Apophis is about to have. 1/N
2/ Asteroid surfaces undergo “space weathering” which includes radiation effects, thermal cracking, and bombardment. We don’t think the surfaces of asteroids undergo so much micrometeoroid bombardment like the Moon does due to the lower gravity, so it isn’t the dominant process. https://t.co/W47c2sw55M
3/ But as the asteroid turns in the sunlight, the rocks are slowly broken down by thermal cracking, creating dust that falls into the surface. This will build up until the asteroid passes a major planet like Earth. https://t.co/bZE8IxjZCZ
4/ The gravity pulls the asteroid and the tidal force stretches it out as shown in this simulation by Richardson & Walsh (Annual Review of Earth and Planetary Sciences, April 2006).
5/ The asteroid eventually pulls back together, but the space weathering of the surface has been reset. I don’t know if Apophis will pass close enough to Earth to have its regolith disrupted or not, but if so it will be an amazing opportunity for science…
6/ because calibrating the space weathering models is difficult yet vital. We mostly know the composition of asteroids by comparing to meteorites that have fallen on Earth. But it is hard to compare because the meteorites have had the space weathering burned off so… https://t.co/ffqn81x0Ng
7/ they look different, spectroscopically, than the asteroids in the sky that are covered with a space weathered surface. In fact, one of the reasons to visit Phobos and Deimos in Mars orbit is because they are probably captured asteroids undergoing space weathering near Mars, https://t.co/0JbIxurO3x
8/ …so looking at their weathered surface and unweathered subsurface will calibrate how much space weathering occurs at that distance from the Sun. I wonder if Apophis will provide another great opportunity! If we can see any tidal disruption at all it would be amazing.
9/ Once we calibrate the space weathering models we can learn much more about the asteroids that we haven’t visited yet. We will be better able to tell their composition, formation history, and dynamical evolution, helping unravel the history of our corner of the cosmos. /end🧵 https://t.co/d3WtFKHtsW