Large impacts are fascinating. There’s the thriller-movie aspect of them, of course, spiced with enough reality to make them legitimately scary. But the physics of them is equally enthralling, and complex enough that it will be a rich field for scientists to study for years to come.
The good news for both these aspects is our Moon. Seriously! There are enough craters there for anyone to be happy studying them, and since the Moon is a giant lifeless chunk of rock, impacts there seem less urgently threatening.
I want to show you two craters on the Moon that are very different, and therefore very interesting.
First up, Copernicus. Or more accurately, a small part of this 90+ km (55 mile) wide impact feature: its central peaks.
[Click to enselenate.]
This image was taken by NASA’s wonderful Lunar Reconnassance Orbiter. Copernicus is a big crater, and easy to spot even with binoculars since it sits in a vast lava plain; the surrounding material is darkish grey, while the crater is far brighter. It’s also surrounded by a gorgeous system of rays: linear streaks caused by the collapsed plumes of material after the asteroid or comet smacked into the Moon to form the crater itself.
Copernicus has a series of mountains in its center, the tallest over a kilometer high. These weren’t created in tectonic events like on Earth, though! Giant impacts that cause big craters have weird physics. The pressure upon impact can be so high that the rock in the surface flows like a liquid. It splashes outward, then flows back in, surging upwards in the middle of the impact point. This video showing water dropping into various surfaces might help:
The Lunar Reconnaissance Orbiter takes amazing pictures of the Moon; I’ve posted dozens over the past couple of years. One of my favorite things is when the spacecraft snaps features I know: craters, mountains, winding valleys that I’ve seen myself behind the eyepiece. When I was younger I spent countless hours scouring the lunar surface with my telescope, and it’s still a fun target when I haul my ‘scope out to the end of the driveway.
And among the best of the best is the crater Tycho. You probably know it already; when the Moon is full the crater is bright, and the rays extending from it — plumes of material ejected radially during the impact that formed the crater — are extremely obvious. At 86 km (50 miles) across, it’s a decent-sized hole in the surface, with a beautifully-defined system of central mountain peaks 15 km (8 miles) across. So when LRO sets its sights on Tycho’s peaks, well… you get a gorgeous panorama like this:
You must click that to enlunenate it and see it in incredible detail. It’s truly spectacular!
That peak rises about 2 km (1.2 miles) about the crater floor. Look how steep it is! I was mentally comparing it to the local foothills of the Rockies near where I live in Boulder, and realized it’s not a bad analogy as far as size and shape go. In one way, hiking to the top of Tycho’s peak would be easier, since the gravity is only 1/6th of Earth’s… but while the air is thin here in Boulder, it’s literally nonexistent on the Moon. So I’m thinking hiking Tycho would be somewhat more taxing.
But what a sight when you reached the top! Sitting smack dab on that largest peak is a boulder I’d very much like to see up close: