The term MARS' TWO refers to the two moons of Mars, Phobos and Deimos. These moons were discovered in 1877 by astronomer Asaph Hall and are named after characters from Greek mythology. Phobos is the larger of the two moons and orbits closer to Mars, while Deimos is smaller and orbits further away. Both moons are irregularly shaped and have a low density, suggesting that they are composed of porous rock and ice.