Deimos (moon)

Coordinates	19°46′12″N43°51′2″N
Name	Deimos
Adjectives	Deimosian
Caption	An enhanced-color image of Deimos taken by the Mars Reconnaissance Orbiter.
Discovery	yes
Bgcolour	#ffc0c0
Discoverer	Asaph Hall
Discovered	12 August 1877
Orbit ref
Semimajor
Eccentricity	0.000 2
Period	1.262 44 d (30.30 hours)
Avg speed	1.35 km/s
Inclination	0.93° (to Mars' equator)1.793° (to the local Laplace plane)27.58° (to the ecliptic)
Satellite of	Mars
Physical characteristics	yes
Mean radius
Mass	1.48 kg(0.25 nEarths)
Density	1.471 g/cm³
Surface grav	0.003 9 m/s² (3.9 mm/s²)0.000 40 g (400 µg)
Escape velocity	5.6 m/s (20 km/h)
Single temperature	≈233 K
Age	2 billion years

Deimos ( ; also ; ) is the smaller and outer of Mars's two moons (the other being Phobos). It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is . Hall also discovered Phobos at the same time, after deliberately searching for Martian moons.

The names, at first spelled Phobus and Deimus, were suggested by Henry Madan (1838–1901),

Characteristics

image of Deimos, October 5, 1977]]

Physical

Deimos, like Mars' other moon Phobos, has spectra, albedos and densities similar to those of a C- or D-type asteroid. Like most bodies of its size, Deimos is highly non-spherical with dimensions of 15 × 12.2 × 10.4 km. Deimos is composed of rock rich in carbonaceous material, much like C-type asteroids and carbonaceous chondrite meteorites. It is cratered, but the surface is noticeably smoother than that of Phobos, caused by the partial filling of craters with regolith. The regolith is highly porous and has a radar estimated density of only 1.1 g/cm³. The two largest craters, Swift and Voltaire, each measure about 3 kilometres across.

Orbital

Deimos' orbit is nearly circular and is close to Mars' equatorial plane. Mars' outer moon is possibly an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still controversial and disputed. although it is not clear that sufficient time is available for this to occur for Deimos. At its brightest ("full moon") it would be about as bright as Venus is from Earth; at the first- or third-quarter phase it would be about as bright as Vega. With a small telescope, a Martian observer could see Deimos' phases, which take 1.2648 days (Deimos' synodic period) to run their course. The main hypotheses are that they formed either by capture or by accretion. Because of the similarity to the composition of C- or D-type asteroids, one hypothesis is that the moons may be objects captured into Martian orbit from the asteroid belt, with orbits that have been circularized either by atmospheric drag or tidal forces. Capture also requires dissipation of energy. The current Mars atmosphere is too thin to capture a Phobos-sized object by atmospheric braking. The main alternative hypothesis is that the moons accreted in the present position. Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a planetesimal.

Named geological features

Only two geological features on Deimos have been given names. The craters Swift and Voltaire are named after writers who speculated on the existence of Martian moons before they were discovered.

{| class="wikitable sortable" |- ! Crater !! Named after !! Coordinates !! Diameter (m) |- | Swift || Jonathan Swift || || 1000 |- | Voltaire || Voltaire || || 1900 |}

See also

Transit of Deimos from Mars

Phobos and Deimos in fiction

References

External links

Deimos Profile by NASA's Solar System Exploration

Deimos rotation movie

Animation of Deimos

USGS Deimos nomenclature

Category:Moons of Mars