Today marks the end of this year’s Lunar and Planetary Science Conference, but many of us are already looking forward to meetings in the future. This is because we know our colleagues have cool new rocks to study, and the best is, in some ways, yet to come.

A lot of geologists get their start as rock collecting kids. The biggest change from those kids to the researchers I get to work with is the power of the microscopes they now get to use looking at their rocks. Oh, and some of their rocks now come from outer space.

Right now, three nations, in particular, are going all out on bringing rocks back to Earth. The Chang’e series of missions to the Moon sent Chang’e 5 up in December, and this mission brought back the first lunar samples collected from young lava deposits – called mare basalts – on the moon. Ahead of the mission, it was estimated these deposits are just 1.2 billion years old, and now everyone is holding their breath while we wait for actual rock ages to be measured. In combination with the Apollo and Luna rock samples, this will allow us to better calibrate the impact history on the Moon and the actual ages of the different features we, and our spacecraft, can see.

This Chinese mission made going to the moon look easy. For those of us in Gen X and younger, we don’t remember the scary moments of humanity’s first attempts at landing on the Moon. One of the oft-forgotten concerns was that the Moon’s surface would be centimeters to meters deep in dust, and the spacecraft would simply sink like Luke’s X-wing in the swamps of Dagobah.

This concern was so well forgotten that it wasn’t brought up with the sample collection missions to Ryugu or Bennu. And here we have a fascinating tale of two worlds that look really alike and really are not.

The Japanese Hayabusa2 team bombed their asteroid, and it just made a crater. They dropped a bunch of tiny robots, and they all bounced around happily. Ryugu, which is a pile of rocks, is a pretty solid object, and the sample collection process went off without a problem, with multiple samples being successfully grabbed and returned to Earth. Now those rocks are getting divided up as agreed and analyzed by researchers around the world. Soon, or at least by the next LPSC, we’ll have analysis showing compositions, ages, and more. The samples are here! And they are awesome.

But, as I mentioned yesterday, the situation for little OSIRIS-REx is a bit different. This US-based mission found the asteroid Bennu to have a surface consistency like that of a ball pit. A very, very deep ball pit. The mission punched roughly 0.5 meters into Bennu and had to fire thrusters to stop its downward plunge. I mentioned this part yesterday. What I learned later is that it’s estimated the spacecraft would have descended many meters into Bennu; this means it could have submerged itself, folks. 

At a certain point, this is unsurprising. This is a tiny object and its gravitational pull on a human would be about the same as the Earth’s pull on a piece of paper. If it is rubble all the way through, and not just on the surface, it is the consistency of a ball pit. To get a better understanding of this weird reality, the team is planning to fly OSIRIS-REx over its sample site before the mission heads home in May, and they’re going to take high-resolution images of their encounter site. We’ll get to see for ourselves: did OSIRIS-REx make a crater like Hayabusa2 did, or did the hole fill itself in like would happen at a ball pit?

More Information

The Scientific Achievements by Chang’E-4 and the New Lunar Samples Returned by Chang’E-5 (LPSC abstract)

Handling and Description of C-Type Asteroid Ryugu Samples Returned by Hayabusa2 (LPSC abstract)

The OSIRIS-REx Touch-and-Go Sample Acquisition Event and Implications for the Nature of the Returned Sample (LPSC abstract)