Hayabusa 2 touchdown on asteroid Ryugu
Wow, wow, wow. What a great video. On February 21, Japan’s Haybusa 2 probe briefly touched down on the asteroid Ryugu, fired a bullet into the rocky rubble and collected a sample that will be returned to Earth in December 2020. You can see the collector horn at top center as the spacecraft descends to the surface.
The shadow cast by Hayabusa 2 grows, the rocks get closer and closer and finally, contact! You can’t see the tantalum bullet being fired, but it didn’t miss. Look at those rocks flying. Some hopefully made it into the horn where they were sealed for safekeeping in a canister. Ryugu is only about a half-mile across (0.8 km) and has so little gravitational pull that the remaining debris tumbled and floated above the asteroid before settling back on the surface.
Maybe not all of it. There’s a very good chance that some of those rocks gained enough speed to leave the asteroid altogether and take up their own orbits around the sun. “Rubble pile” asteroids like Ryugu are essentially mountains of debris that have accumulated during collisions with other asteroids over the history of the solar system. Rubble piles form when an asteroid is shattered in a collision with another asteroid. The material falls back together again under its own self-gravity to form an orbiting pile of boulders and smaller fragments. The process of coming together takes only days to weeks.
Looking at the video reminds me where meteorites come from, and how they get here. They originate with asteroids. While entire asteroids rarely strike Earth, fragments ejected by collisions with other asteroids can wend their way in Earth’s direction. If their paths cross Earth’s, they can slam into the atmosphere and sometimes survive the trip to the ground as meteorites. Here you can see that process on a small scale — human-made as it were — with your own eyes.
You can also use your own eyes to take in a beautiful, thin crescent lunar crescent at dusk this evening (March 7). The moon will be 1.3 days past new phase and appear low in the western sky starting about 25 minutes after sunset. Mercury lies about 8° to the moon’s upper right but will only shine at second magnitude. In a dark sky, seeing it would be easy but not so much in bright twilight near the horizon. Bring binoculars if you want to attempt this challenging observation.