The Solar System Wiki
Deimos spacepedia.png

Planet of Origin



Asaph Hall

Date of Discovery

August 12, 1877

Surface Color

Brownish tan

Named Geographical Features

Swift and Voltaire craters

Deimos, also known as Mars I, is the smallest, and closest satellite in orbit, of Mars. It is one of the two Martian moons, the other one being its neighboring moon, Phobos. Deimos is smaller than its neighboring moon, Phobos, but they both appear to be asteroids, thus proving they were loose asteroids in space that were pulled in by Mars' gravitational pull. Deimos was discovered on August 12, 1877 by Asaph Hall, Sr. In fact, just six days later, he discovered the other Martian moon, Phobos.


The formation of Deimos is highly disputed and controversial.

Some astronomers go with the hypothesis that Deimos was created by Mars' bombardment period and left over debris from Phobos. Others side with the fact that Deimos was a meteor stray in space and was brought in by Mars' gravitational pull.

Proof supporting the first theory is that Deimos is smaller than Phobos, meaning that debris left over from Phobos was used for Deimos. Proof supporting the second theory is that the characteristics of Deimos match characteristics of Phobos and other asteroids.


Deimos is full of craters that were caused by relatively small impacts from meteors and asteroids. The surface is smoother and slicker than Phobos, however. The two major craters are Voltaire and Swift, named after Russian leader Voltaire and Jonathan Swift. They each measure around three kilometers in length.