Phobos is the innermost and larger of the two natural satellites of Mars. It was discovered in 1877 by American astronomer Asaph Hall at the US Naval Observatory in Washington, D.C. Phobos is a small, irregularly shaped object with a mean radius of 11 km and is seven times as massive as the outer moon, Deimos. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite (Venus) and the personification of fear.
Deimos is the smaller and outermost of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a mean radius of 6.2 km and takes 30.3 hours to orbit Mars. Deimos is 23,460 km from Mars, much further than Mars's other moon, Phobos. It is named for Deimos who in Greek mythology is the twin brother of Phobos, and personifies terror. Deimos is composed of rock rich in carbonaceous material, much like C-type asteroids and carbonaceous chondrite meteorites. It is cratered, but the surface is noticeably smoother than that of Phobos, caused by the partial filling of craters with regolith. Deimos's orbit is slowly getting larger, because it is far enough away from Mars and because of tidal acceleration. It is expected to eventually escape Mars's gravity.
Landed on July 4, 1997 at Ares Vallis
It drove around the lander and traveled just over 100m driven
Sojourner is the first wheeled vehicle to rove another planet
Landed on January 4, 2004 at Gusev Crater
Spirit went on to function over twenty times longer than NASA expected
The spirit and opportunity rovers are siblings and based on the same design
Landed on January 25, 2004 at Meridiani Planum
Opportunity exceeded its operating plan by 14 years, driving 45.16km
Opportunity landed three weeks after its sister rover spirit
Landed on November 26, 2011 at Aeolis Palus
It drove more than 20km by now and is still operational
In December 2012, Curiosity's two-year mission was extended indefinitely
