Surface of Mercury
Written by Fraser Cain
If you looked at an image of Mercury's surface, and compared it to the Moon, you'd have a difficult time telling them apart. That's because both Mercury and the Moon are airless, meteorite-pounded expanses of rock and dust. But seen up close, with the new images coming back from NASA's MESSENGER spacecraft, and the surface of Mercury is far more interesting that you might have thought.
As with the Moon, Mercury has been geologically inactive for billions of years. But almost 4 billion years ago, the whole Solar System experienced a period called the late heavy bombardment. Mercury and the rest of the planets were pounded by many objects from space. Without any kind of atmosphere to protect it, Mercury had no way to slow down these space rocks.
At the same time, the surface of Mercury was volcanically active. As meteorites struck the surface of the planet, magma welled up to fill in the low-lying areas to produce smooth plains, which are similar to the maria on the Moon.
Some of the largest craters are Mercury are hundreds of kilometers across, and two of the largest are the Caloris Basin, with a diameter of 1,550 km, and the Skinakas Basin at 1,600 km across. It's thought that the impact from space rocks was so severe that waves traveled through the planet, causing high stresses on the opposite side of the impact.
One of the most unusual features uncovered by MESSENGER is an unusual crater with a series of trenches emanating away from it, which scientists have called "the spider".
Another interesting feature are compression folds that cross the planet. It's thought that these formed as the planet cooled and contracted. The surface of Mercury then folded and buckled.
Mercury also experiences intense tides from the Sun, which raise and lower its surface.
Filed under: Astronomy
