Jeffrey Andrews-Hanna

It's not quite like that, but very much size depends.

So I was a late addition to the GRAIL team, which meant I did none of the hard work to develop the mission and make it fly, and got to have all of the fun with playing with the data.

So we get gravity from both.

With GRAIL, the key things about GRAIL being lower to the surface and also that having two spacecraft really helps you get the precision you need.

But Dawn has given us some really impressive gravity data, lower in resolution, and yet at the same time, that's the first gravity data we've got from Vesta and so on.

That's most of it.

Actually, one of the things we can do with GRAIL that Alex, who I work with, has been doing is actually, you can take a crater and fill it in with lava so you can't see it anymore.

It's harder to hide it from gravity.

And so he's using the GRAIL to actually see those craters buried beneath those volcanic planes.

Many are there.

Not quite as many as you'd expect.

And that's interesting.

I wish I knew.

We really don't have an answer.

What Alex has been doing is just going through every possible energy source to drive it, combination of adding different elements to the core to increase that density contrast, adding more heat, doing whatever he can, really going beyond the bounds of plausibility and still not able to reproduce it.

So we're still looking for an answer on that one.

Yeah, so the Moon, and like I said, the Moon-forming impact is the biggest thing that happened to the Earth, and we absolutely would not be here without the Moon.

One good point of comparison is Mars.

The Earth has a really big Moon, which really stabilizes our spin axis.

So the spin axis of the Earth, it wiggles a little bit.