Mercury is the solar system's smallest and innermost world. It was an enigmatic planet for years. NASA's MESSENGER ended its mission in April this year by crashing into Mercury's surface. Images that MESSENGER collected during its more than four years in orbit revealed a vast array of large fault scarps, or cliffs, on Mercury. These scarps resemble giant stair steps in the landscape — the largest are more than 1,000 kilometers long and more than 3 km high.
Mercury is a relatively recent arrival (in Cosmic terms) in its present orbit around the Sun. Its incline and elliptical orbit, as well as its surface, show that it is related to our Moon. Mercury went into orbit around the Sun while the Moon went into orbit around the Earth. They are both from the same source and placed in their positions by design.
For more on this, read: http://m.space.com/29623-mercury-mystery-huge-cliff-patterns.html
Both images below are sourced from this site.