Deimos
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| Deimos | |
|---|---|
| |
| Deimos by Viking Orbiter | |
| Date of discovery | August 12, 187712 August 1877 3 Elul 5637 He 2 Elul 5880 AM |
| Name of discoverer | Asaph Hall |
| Name origin | Greek deimos panic; attendant of Greek god of war |
| Orbital characteristics | |
| Celestial class | Moon |
| Primary | Mars |
| Order from primary | 2 |
| Periareion | 23,455 km1.56787e-4 AU 14,574.261 mi[1] |
| Apoareion | 23,465 km1.56854e-4 AU 14,580.475 mi[1] |
| Semi-major axis | 23,460 km1.5682e-4 AU 14,577.368 mi[2] |
| Orbital eccentricity | 0.0002[2] |
| Sidereal month | 1.262 da0.00346 a[2][3] |
| Avg. orbital speed | 1.36 km/s4,896 km/h 0.845 mi/s 3,042.233 mph[4] |
| Inclination | 1.8°0.0314 rad 2 grad to the ecliptic[2][4] |
| Rotational characteristics | |
| Sidereal day | 1.026 da24.624 h[3] |
| Rotation speed | 1.35 km/h3.75e-4 km/s 2.33014e-4 mi/s 0.839 mph |
| Axial tilt | 0°0 rad 0 grad |
| Physical characteristics | |
| Mass | 1.4 * 1015 kg1.9052e-8 M☾ 2.34271e-10 M⊕[1] |
| Mean density | 1,471 kg/m³1.471 g/ml 91.832 lb/ft³[5] |
| Mean radius | 6.2 km3.853 mi[5] |
| Surface gravity | 2.5e-3 m/s²0.082 ft/s² 0.00255 g[1] |
| Escape speed | 0.0056 km/s20.16 km/h 0.00348 mi/s 12.527 mph[1] |
| Surface area | 480 km²185.329 mi² 1.26586e-5 A☾ 9.41044e-7 A⊕[1] |
| Mean temperature | 233 K-40.15 °C -40.27 °F 419.4 °R |
| Composition | Rock and ice mix |
| Color | #999999 |
| Albedo | 0.068[5] |
Deimos (from the Greek δειμος or deimos panic) is the outer, and the smaller, of the two moons of Mars.
Contents |
Discovery
Deimos was discovered by the astronomer Asaph Hall on August 12, 1877, at the United States Naval Observatory in Washington, DC.[6][7][8] The astronomer V. Knorre named the satellite Deimos (and also provided the name Phobos for the other satellite that Hall discovered six days later), per a suggestion by Henry G. Madan of Eton, based on the names given in The Iliad for the two servants of Ares, the Greek god of war, named Fear (Phobos) and Panic (Deimos).[9]
Orbital and physical characteristics
Deimos orbits Mars at a distance slightly further away than the distance of a synchronous orbit. For that reason, Deimos rises in the east and sets in the west of the Martian sky, about 2.7 days after its rising.[10]
Deimos is not round, but is shaped like a potato, with dimensions 15 x 12.2 x 11 km. Its largest surface feature is a 2.3 km diameter crater.[10] Deimos is heavily cratered but has a smooth-appearing surface. Its surface gravity is very weak, perhaps too week to retain the ejecta from a crater impact. This ejecta is likely retained around Mars in a ring and redeposited as regolith on the surface of Deimos as it passes.[11]
Deimos' orbit is so little inclined with respect to the ecliptic that it makes daily transits across the Sun.[10]
Origin
The favored theory among conventional astronomers is that Deimos and its companion moon Phobos are captured C-type asteroids.[3][10] However, that theory is not universally accepted.[3]
Exploration
The NASA Viking 1 and Viking 2 orbiters both have taken close-up photographs of Deimos on the way to deliver their respective landing craft to the Martian surface. Since then, several missions have made flybys of Deimos, including the Mars Reconnaissance Orbiter. The two Mars Excursion Rovers have taken photographs of Deimos as seen from the surface of Mars.
Gallery
 Successive views of Phobos and Deimos photographed from "Husband Hill" by a Mars Excursion Rover |
 Animated image of Deimos making one of its daily transits of the Sun |
References
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