Bad Astronomy

Spiders on Mercury!

OK, not really. But the folks from MESSENGER, the probe that passed Mercury recently, have released lots of images and made some scientific announcements, too. The image that really struck me was this one:

This is near the center of a vast region on Mercury called Caloris Basin. The radial cracks – called The Spider by the MESSENGER team – are very cool, and nothing like them has ever been seen before. Caloris Basin is an impact feature. Something very large hit Mercury a long time ago, carving out a major hole, which filled with molten rock (or whatever Mercury is made of). Over time, the floor of the basin cracked…

There are many cliffs on Mercury due to the shrinkage of the planet (the pool water was cold!). As the planet cooled and solidified, the crust settled, creating the network of scarps and cliffs. I wonder if the Spider is something along those lines. I’m sure Emily is feverishly writing even as I type this. (Update: Indeed she was!)

The impact crater in the middle of the lines is weird too. The odd shape must be due to the cracks themselves; clearly the crater formed after the cracks (it overlays them). The surface around there must be a total mess. I’ll be very curious to see the high-res images once MESSENGER settles into orbit in a few years. Many of the craters on the planet have odd shapes, and I just bet that’s due to the surface being cracked everywhere. That would play havoc with what would ordinarily be nice, round craters.

Besides that image there was lots of science released; they measured Mercury’s magnetic field, took ground altimetry data, and even observed a giant cloud of sodium blowing off the planet (it was known before from ground-based data, but this is much better resolution – there’s nothing like being there).

Once MESSENGER becomes a moon of Mercury, expect to see lots of very cool stuff from a very hot planet.