Deimos is the smaller and outer of Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

's two moons

Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

 (the other being Phobos

Phobos (moon)

Phobos is the larger and closer of the two natural satellites of Mars. Both moons were discovered in 1877. With a mean radius of , Phobos is 7.24 times as massive as Deimos...

). It is named after Deimos

Deimos (mythology)

In Greek mythology, Deimos was the personification of terror.He was the son of Ares and Aphrodite. He is the twin brother of Phobos and the goddess Enyo who accompanied Ares into battle, as well as his father's attendants, Trembling, Fear, Dread, and Panic...

, a figure representing dread

Fear

Fear is a distressing negative sensation induced by a perceived threat. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of danger...

 in Greek Mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

. Its systematic designation is .
Deimos was discovered by Asaph Hall, Sr.

Asaph Hall

Asaph Hall III was an American astronomer who is most famous for having discovered the moons of Mars in 1877...

 at the US Naval Observatory in Washington, D.C on August 12, 1877, at about 07:48 UTC

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

 (given in contemporary sources as "August 11 14:40" Washington mean time

Washington mean time

Washington mean time was the time at the meridian through the center of the old dome atop the main building at the old US Naval Observatory at Washington, D.C. This Washington meridian was defined on 28 September 1850 by the United States Congress...

, using an astronomical convention of beginning a day at noon, so 12 hours must be added to get the actual local mean time).