It is the closest planet to the Sun , and second smallest planet in the solar system . It is even smaller than Jupiter's moon Ganymede and Saturn's moon Titan . If an explorer were to step onto the surface of Mercury, he would discover a world resembling lunar terrain. Mercury's rolling, dust-covered hills have been eroded from the constant bombardment of meteorites . Fault-cliffs rise for several kilometers in height and extend for hundreds of kilometers.
Craters dot the surface.
As the explorer gazes out into space, he might see two bright stars. One appearing as cream colored Venus and the other as blue colored Earth . At maximum elongation it is only 28 degrees from the Sun as seen from Earth. Because of this, it can only be viewed during daylight hours or just prior to sunrise or after sunset. When observed at dawn or dusk, Mercury is so low on the horizon that the light must pass through 10 times the amount of Earth's atmosphere than it would if Mercury was directly overhead.