Craters on Mercury
Written by Fraser Cain
Compare photographs of the Moon and Mercury and it's actually pretty hard to tell them apart. Both are grey, lifeless worlds, pockmarked with craters and mountain ranges. Where did Mercury's craters come from, and how do they compare to other objects in the Solar System?
Just like the Moon and Mars, the craters on Mercury came from meteoroid impacts over billions of years. These objects smashed into the surface of Mercury, creating millions of craters ranging in size from 100 meters to over 1,300 km across. The largest crater on the surface of Mercury is the Caloris Basin.
The Caloris Basin is so large that Mariner 10 couldn't fully photograph it during its 1974 flyby. It wasn't until NASA's MESSENGER spacecraft made its flyby in 2008 that the full extent of the crater was visible. In fact, estimates for the size of the crater were increased after the more complete images from MESSENGER were returned to Earth. Astronomers theorize that the impact that formed the Caloris Basin was so big that it sent shock waves through the planet, raising up a mountain range on the opposite side of the planet.
All of the objects in the inner Solar System went through a period of heavy bombardment in the first billion years after they formed. There was still a lot of material left over from the formation of the Solar System, and it took that first billion years for them all get swept up.
Craters on Mercury appear to be in all states of decay, from fresh craters with full rays, to highly eroded crater remnants, where features of the crater are just barely recognizable. Mercury has a much higher surface gravity than the Moon, so material doesn't eject out as far and create the large ejecta blankets that we see on the Moon.
We have done several stories on Universe Today about the craters on Mercury. Here are some images of Mercury returned by NASA's MESSENGER spacecraft, and a side of Mercury that had never been seen until recently.
Want more information on Mercury? Here's a link to NASA's World Book on Mercury, and here's NASA's Solar System Exploration Guide to Mercury.
We have also recorded a whole episode of Astronomy Cast that's just about planet Mercury. Listen to it here, Episode 49: Mercury.
Filed under: Astronomy
