Planets: Surface of Mercury

by Jeanette Cain

The planet Mercury was formed around 4.6 billion years ago, and during the next 700 million years, its surface was bombarded by space rocks causing craters. The planet surface had cooled and shrunk to the current size around 500 million years. Seventeenth century observations showed Mercury as having phases, but it was in 1965 that the rotation period of Mercury was confirmed by the bouncing of radar waves from the surface. Mariner 10 sent the first images of any detail of the surface in 1974, and in 1991, radar was the method used to study the unseen areas of the planet Mercury.

Although Mercury is not too far away from Earth, it poses a difficult problem for observation. The Hubble Space Telescope has been unable to provide images of the Mercurian surface, because of the possibility of Sun ray damage to Hubble's sensitive instruments. Mariner 10 was protected with sunshields for its trip to Mercury, but the flight path provided only one part of the Mercurian surface for photographing. There is still over half of the surface of Mercury that has yet to be explored.

Mercury's Caloris Basin is a 1,300 kilometer wide crater, which was created around 3.6 billion years ago as the result of an asteroid impact. Science has estimated the size of the asteroid as about 100 km across, but the Caloris Basin center and crater floor have not been photographed.

When a space rock formed the Caloris Basin on Mercury, it was still in an infancy stage. Its mantle and upper crust were still unstable, and continuing to cool and compress. Impact shock waves from the collision vibrated through the planet causing the surface to form mountains and hills. Mercury's surface has many craters from an impact of thousands of meteorites. The Caloris Montes surround the Caloris Basin, but beyond, the surface is covered in rock and lava-flooded plains. As the young planet formed, wrinkles and ridges were created across the surface.

Beethoven is the second largest Mercurian surface feature. Its floor is 643 km wide, and was flooded from volcanic materials and latter meteorite impacts. Mercury has craters that are named for the women and men within the arts, such as, Ludwig van Beethoven, the German composer. Beethoven's neighbor is the flooded crater called Tolstoj. A more recent crater is named Petrarch. The Discovery Rupes is about 2 km high and stretches for about 500 km across the surface. Scientists have found 16 similar features across the Mercurian surface.

Mercury's polar regions are always shaded from the heat of the Sun, so scientists study the polar regions by reflecting radar off the poles. It is believed that Mercury's polar regions hold water, but these findings have not been confirmed, plus, sulphur could cause the same results.

Mercury's path takes place just below, or above the Sun, but every few years, a transit will occur by the aligning of Mercury, the Sun, and the Earth. When this happens, Mercury will travel the face of the Sun, and can be viewed as a black dot. It may take several hours for Mercury to cross from one side of the Sun to the other.

Sources:

1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999