Space Station Info :: Mars Moons

Mars Moons

Mythology Mars

The Phobos and Deimos are the two moons of Mars and their orbits are seen from above Mars' North Pole. Both Phobos and Deimos are tidally locked with Mars, always pointing the same face towards it. Since Phobos orbits around Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future Phobos will be broken up by gravitational forces. Deimos, on the other hand, is distant enough that its orbit is being gradually boosted instead.

Both satellites were discovered in 1877 by Asaph Hall, and are named after the characters Phobos (panic/fear) and Deimos (terror/dread) who, in Greek mythology, accompanied their father the Greek god Ares into battle. Ares was known to the Romans as Mars, the god of war.

Mars' Natural Satellites:


Diameter (km)

Mass (kg)

Mean orbital radius (km)

Orbital period (h)



(27 21.6 18.8)


9378 7.66



(10 12 16)



Phobos 22.2 (27 21.6 18.8) 1.081016 93787.66
Deimos 12.6 (10 12 16) 21015 23,40030.35

As seen from Mars, Phobos has an angular diameter of between 8' (rising) and 12' (overhead), while Deimos has an angular diameter of about 2'. The Sun's angular diameter, by contrast, is about 21'.

Mythology Mars

In ancient times Mars has certainly been seen by skygazers. It was well-known by the Egyptians as "Her Deschel" or "the Red One." Amid the Babylonians Mars was known as "Nirgal" or "the Star of Death". The Romans were the ones to give Mars its modern name, after the God of War.

Physical Characteristics of Mars

Mars has iron oxide (rust) on its surface which gives it a red and flaming appearance. Mars has only a quarter the surface area of the Earth and only one-tenth the mass (The solar day on Mars is about the same length as it is on Earth: 24 hours, 39 minutes, and 35.244 seconds.

Atmosphere of Mars

The atmosphere of Mars is comparatively thin and the air pressure on the surface is only 750 Pascal, about 0.75 percent of the average on Earth. Though, the scale height of the atmosphere is about 11 km, fairly higher than Earth's 6 km.

The constituents of Mars include 95 percent carbon dioxide, 3 percent nitrogen, 1.6 percent argon, and traces of oxygen and water. Methane was apparently discovered in the atmosphere by Earth-based telescopes In 2003, and perhaps confirmed in March 2004 by the Mars Express Orbiter, present measurements state an average methane concentration of about 114 ppb by). The thin atmosphere cannot embrace heat and is the cause of the lower temperatures on Mars. The presence of methane on Mars would be very fascinating, since as an unstable gas it indicates that there must be a source of the gas on the planet.

Volcanic activity, comet impacts and the existence of life in the form of microorganisms such as methanogens are among possible however as yet unconfirmed sources.

The methane appears to occur in patches, which suggests that it is being hastily broken down before it has time to become uniformly distributed in the atmosphere.

Geology Mars

Mars is mainly composed of basalt and andesite rock on its surface, covered in many places by meters or more of a dust as fine as talcum powder. Mars Global Surveyor spacecraft observations says that the magnetic fields on Mars exposed that parts of the planet's crust has been magnetized in alternating bands, usually measuring 100 miles wide by 600 miles long (160 km by 1000 km), in a similar pattern to those found on the ocean floors of Earth.

In 1999 one fascinating theory, published saying that these bands could be evidence of the past operation of plate tectonics on Mars, although this has yet to be confirmed. New findings, published in October 2005 support this theory, and seem to indicate an early era of tectonic activity similar to that found on Earth due to sea-floor spreading .If true, the processes involved may have helped to sustain an Earth-like atmosphere by transporting carbon rich rocks to the surface, while the presence of a magnetic field would have helped to protect the planet from cosmic radiation.

Topography of Mars

The feature of Martian topography is striking, northern plains trampled by lava flows disparity with the southern highlands, bumpy and cratered by ancient impacts. The surface of Mars as seen from Earth, is divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra (land of Arabia) or Amazonis Planitia (Amazonian plain).

Mars has polar ice caps that contain frozen water and carbon dioxide that vary with the Martian seasons - the carbon dioxide ice sublimates in summer, revealing a surface of layered rocks, and forms again in winter. An extinct shield volcano, Olympus Mons (Mount Olympus), is at 27 km the highest mountain in the solar system. It is in a vast upland region called Tharsis, containing several large volcanos.

Canals of Mars

Mars plays a vital place in human imagination due to the faith that life exists on Mars. These beliefs are primarily owing to observations by many in the 19th century popularized by.

Percival Lowell and Giovanni Schiaparelli. Schiaparelli called these observed features canali, meaning channels in Italian. This was usually mistranslated as 'canals', and the myth of the Martian canals began.

They were apparently artificial linear features on the surface that were asserted to be canals, and due to seasonal changes in the brightness of some areas that were thought to be caused by vegetation growth. This gave rise to many stories regarding Martians.

The linear features are now known to be typically non-existent or, in some cases, dry ancient watercourses.