The planet Mars is the only terrestrial planet that has more than one moon. Deimos is the smaller of its two moons and if you look at both moons, they have a lumpy appearance of an asteroid. The appearance and the almost perfectly circular orbit around Mars has led scientists to question where and how Deimos showed up as a moon.

Deimos Introduction

Both Deimos and Phobos are part of the smallest moons in our solar system and their dark color and close proximity to the Mars surface made them almost impossible to see. Deimos only has a radius of 3.9 mi/6.2 km and is shaped kind of like a potato. It takes Deimos only around 30 hours, just a bit over a Martian day to complete its orbit around Mars.

Astronomers continue to be in debate as to whether Deimos was part of the asteroid belt and was drawn in by the gravity of Jupiter and then pushed towards Mars or is the remains of an impact into Mars that created a ring that eventually stuck together and became the moons.

Deimos, like Phobos, is made up of the same kind of material that make up dwarf planets and asteroids, called Type I or II carbonaceous chondrite.

Deimos is at a further distance from Mars than its brother, Phobos. In fact, Phobos is so close to Mars that it is slowly moving inwards, causing a decayed orbit. In around 50 million years, Phobos will either completely break up and create a ring around Mars or crash into Mars. Scientists think that the end of Phobos will actually push Deimos into outer space.

If you were standing on Mars, little Diemos would look like it was more of a star than a moon. At full moon, the light from Deimos shines as bright as the planet Venus. However, when Deimos eclipses the sun it’s only a tiny dot crossing the surface view.

Both moons only show one side towards the planet Mars. This is referred to as being “tidal-locked.”

Deimos Statistics:

  • Orbits: Mars
  • Discovered By: Asaph Hall
  • Discovery Date: August 12, 1877
  • Diameter: 12.4 km
  • Mass: 1.48 × 10^15 kg (0.000002% Moon)
  • Orbital Period: 1.3 days
  • Orbit Distance: 23,458 km
  • Surface Temperature: – 40 degrees C


Johannes Kepler was a German astronomer in the early 17th century. He based a proposal about the moons of Mars on the fact that it was positioned between Jupiter and Earth and they were known to have from 1-4 satellites.

His theory was that Mars had two moons. During that time no evidence could be presented to prove Kepler’s theory and some astronomers thought that Mars didn’t have any moons at all.

Deimos History

American Asaph Hall, an American astronomer had been searching for moons around Mars at the U.S. Naval Observatory in Washington, D.C. He had become very frustrated and was talking about completely giving up, but his wife Angelina kept offering encouragement and convinced him to continue. Hall used a 26” refractor on the telescope and was methodical about searching all of the areas around the Red Planet.

On August 12, 1877 he discovered the moon Deimos, and then only six days later he discovered Mars’ second moon, Phobos. He realized that one of the reasons that previous astronomers couldn’t find either moon was due to being so close to Mars and having the Mars light block them out.

Both of the moons of Mars are named after the twin sons of the mythological Greek god of war. Deimos means to flee or to escape in flight, and Phobos means to fear.

Formation, Structure and Surface:

Scientists are still trying to study and solve the question as to where both Deimos and Phobos originated from. Both small moons present a true riddle because they are made up of the kind of materials of asteroids and dwarf planets, yet if they had been pulled out of the asteroid belt by Jupiter’s gravity and pushed in Mars’ orbit, the orbits would not be as circular as they are today.

The materials that make up the two moons have made them some of the darkest in the solar system and another reason that they were so difficult to locate.

The surface of Deimos is covered in craters that have been impacting the little moon for thousands of years. Due to the small size of Deimos the craters look completely different than those found on other objects in space.

When an object collides with another object in space, the impact material is flung outwards and then falls back to the surface, creating what are known as “ejecta deposits.” Deimos is so small and has such low gravity that the debris only travels 13 mph/20 km/h and it’s lost in space away from the moon and there aren’t any ejecta deposits on the surface.

Deimos is covered in a fine dust called “regolith” that is believed to be around 328 ft/100 m thick. The dust has been created over thousands of years from the castoff materials from the various impacts.

Deimos and Phobos are both heavily cratered, and the craters on Deimos are somewhat smaller than those on Phobos. The craters on Deimos are around 1.6 mi/2.5 km in diameter and unlike Phobos, there aren’t any ridges or grooves that appear on the surface.

Atmosphere and Magnetosphere:

Deimos doesn’t have any atmosphere or magnetosphere.

Could Life Exist?

Deimos doesn’t have any of the defined requirements for life to start, continue, and thrive.

Interesting Information:

  • Deimos is named for one of the mythological twin sons of the Greek god of war. While the standard translation for the name Deimos usually includes fleeing, another translation means terror.
  • Deimos has two large impact craters named after the authors Jonathan Swift and Voltaire. Both authors included information about a moon around the planet Mars before any astronomer or scientist even thought that they existed.
  • Mars may have a thin atmosphere but it isn’t strong enough to assist an oncoming asteroid to maintain the circular orbit that both Deimos and Phobos have.
  • The moon Phobos travels around Mars at such a speed that it orbits the planet twice in a day. Deimos, however, takes 30.3 hours to complete an orbit around Mars, which is just a bit over a Martian day of 24.7 hours.
  • Deimos is moving farther away from the planet Mars.
  • Both Deimos and Phobos have similar temperatures ranging from 25 degrees F/-4 degrees C on the side that is sunlit and -170 degrees F/-112 degrees C on the dark side.


There have been a number of spacecraft sent to Mars by quite a few countries. A visit to Mars usually includes investigating the moons of Mars.

The 1971 Mariner 9 was the first spacecraft to ever orbit a planet and it explored both Deimos and Phobos. The images taken on this mission showed that the moons had the appearance of lumpy potatoes. They spacecraft could only take pictures of one side since the moons are tidal-locked, showing only one face towards the planet.

The Viking Orbiters and the Soviet Phobos 2, NASA’s Mars Global Surveyor, and the European Mars Express have visited the moons.

The Mars rovers, Spirit, Opportunity, and Curiosity have taken images of both Deimos and Phobos from the surface of Mars.

Facts about Deimos Moon for Kids:

  • There is no atmosphere on either Deimos or Phobos. They don’t have any activity to create an atmosphere and too low of a gravity to retain any atmosphere.
  • Deimos and Phobos are closer to a C-type asteroid than a moon. Most moons are spherical in shape, whereas, Deimos and Phobos are oddly lumpy.
  • Deimos does have some craters on its surface but it’s a lot smoother than the surface of Phobos.
  • All of the information and data that we have received from spacecraft for Deimos and Phobos have been images taken as they mapped Mars.
  • Scientists still haven’t figured out if Deimos and Phobos originated in the asteroid belt and were caught by Jupiter’s gravity and then thrown into the gravity of Mars.
  • When an asteroid is thrown into the gravity of a planet it doesn’t usually have the kind of circular orbit that both Deimos and Phobos exhibit.
  • Astronomers continue to have a debate if Deimos and Phobos were the result of debris caused by an impact on Mars that turned into a ring that eventually clumped together to create the moons.
  • An additional theory about the creation of Deimos and Phobos is that they are the result of a collision of planetesimals outside of Mars that eventually clung together to form the two moons.
  • There haven’t been any space missions specifically focused on the study of the two moons of Mars.
  • Future space missions are being considered to study both Phobos and Deimos. One mission is called PADME (Phobos and Deimos and Mars Environment). An additional mission is called OSIRIS-Rex 2, which is a follow up to the OSIRIS-RE-x mission.

Pop Culture:

There are only two craters on Deimos that have been named. The English author, Jonathan Swift, made note of Kepler when he referred to the two moons around Mars in his novel, Gulliver’s Travels. A few years later, French writer François-Marie Arouet (pen name Voltaire) mentioned the moons in one of his short stories. One crater on Deimos is named Swift, the other is named Voltaire.

Many creative individuals have included the moon Deimos as part of their stories in novels, games, television shows, and film.

Edgar Rice Burroughs wrote the Barsroom novels in which the moon Deimos is called Cluros. In The Chessmen of Mars that moon is described as “stately, majestic, almost stationary, shedding his steady light upon the world below.”

In the 2003 version of the Astro Boy series, the episode of Destination Deimos has a character visiting the moon.

Alastair Reynolds’ Great Wall of Mars has Deimos making an appearance as the base that they use to observe Conjoiners.

The 2010 Douglas Preston Novel, Impact, has the crater named Volataire as the location of an ancient extraterrestrial civilization machine.

Rhea Culture color

The Unreal Tournament 3 story line includes a map of a satellite base around Deimos.

The Eighth Doctor & Tamsin Drew in the Doctor Who television series land on Deimos in the 23rd century where Mars and both moons are tourist destinations. It’s here that they meet the Ice Warriors, the original Mars inhabitants.

The television series, The Expanse, has Deimos as a radar base for the Martian Congressional Republic Navy. The base is destroyed by the United Nations Navy of Earth as a warning after the MCRN destroys Phoebe, the moon of Saturn as an act to keep the UNN from reaching an abandoned laboratory located on Phoebe. The situations almost change a cold war that exists between the two planets into an all-out armed conflict.

In the Noon Universe, Deimos is discovered to be an artificial satellite, just like Phobos, that was constructed by the Wanderers.

In the universe of the Warhammer 40,000, in the world of the Grey Knights chapter, Deimos has been moved out of its orbit to a new orbit around Titan so that it can be their Forge World.

In Sailor Moon, Deimos is a crow and both Deimos and Phobos are guardians of Rei Hino, Sailor Mars. It’s revealed that they were originally in human form and came from the Coronis Planet.

The 1993 Green Mars by Kim Stanley Robinson has a detailed description of a manned landing craft on Deimos. Later in the story, Deimos is taken out of orbit and sent into the asteroid belt.