Caloris Basin | Universe Today

Written by Fraser Cain

The Caloris Basin is one of the largest impact craters on Mercury, and even one of the largest impact sites in the entire Solar System. It measures 1,550 km in diameter, and was discovered by NASA's Mariner 10 probe during its flyby in 1974.

It's believed that the Caloris Basin was created billions of years ago during a period in the Solar System's history called the Late Heavy Bombardment Period. This was a time when there was still a lot of debris left over from the formation of the Solar System. We can see the scars from this period on Mercury and the Moon, but it's hidden here on Earth because plate tectonics have continued to resurface our planet.

When Mariner 10 first imaged the Caloris Basin (or Caloris Planitia), the crater was half hidden in shadow, so the spacecraft could only reveal half of it. Fortunately, NASA's MESSENGER spacecraft made another flyby in January, 2008 and was able to reveal the missing half. The full crater measures 1,550 km in diameter, and it ringed by mountains up to 2 km high. The floor of the crater is filled in with lava plains, and material has been ejected out of the crater for another 1,000 km.

Astronomers think that the collision that created the Caloris Basin had so much energy that shockwave ripples traveled around the planet and met at the opposite side of the planet causing an ejection of lava from inside Mercury. There is a region on the antipode of the planet that is relatively smooth with few craters. It's referred to as the Chaotic Terrain (aka Weird Terrain).

We have written many stories about Mercury here on Universe Today. Here's an article about a the discovery that Mercury's core is liquid. And how Mercury is actually less like the Moon than previously believed.

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