Jeffrey Andrews-Hanna

And this is, in fact, the area on the moon that you're most familiar with.

So when you look up at the moon and see the man on the moon, rabbit on the moon is what the Chinese say, which I think is a lot more accurate.

I can't see a man, but I can see a rabbit.

But all these dark spots make an area that is somewhat roundish in pattern.

So early workers noted this and said, well, you know, this looks a lot like it could be a giant impact basin.

Just like we see lava ponded within these smaller basins, like Imbrium and Serenitatis and Crisium, well, maybe this big concentration of lava here is ponded within one single giant basin.

So this was named the Procellarum Basin, an enormous basin encompassing much of the near side.

but a very controversial basin, because unlike these younger basins, a lot of the telltale signs of an impact crater really weren't there.

So this has been a matter of debate in the field for some time.

As you can imagine, if we could look into the subsurface to see the subsurface structure of Procellarum, maybe we could say something more about this.

So here, I'm showing a topography map of the moon.

And this is a funny projection, but centered on that prosolarum basin.

And you see, well, the near side of the moon has all this low topography in this area.

You can imagine how you could trace a circle in this area and make that the rim of the basin, and make this look like other basins like Imbrium, like Oriental.

And so, to first order, the idea of a prosolar impact basin seems reasonable.

But now, let's look in the gravity data.

Let's look beneath the surface and see what we see.

This is a gravity gradient map of the same region, and we do see structures.

Something very dramatic is happening in this region

but it looks kind of square.