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Deimos (moon)

Deimos
Deimos
An enhanced-color image of Deimos (MRO, 21 February 2009).
Image: NASA/JPL-Caltech/University of Arizona
Discovery
Discovered by Asaph Hall
Discovery date 12 August 1877
Designations
Adjectives Deimosian
Orbital characteristics
Epoch 2012-Sep-21
(JD 2456191.5)
Periapsis 23455.5 km
Apoapsis 23470.9 km
23463.2 km (6.92 Mars radii)
Eccentricity 0.00033
1.263 d
(30.312 h)
Average orbital speed
1.3513 km/s
Inclination 0.93° (to Mars's equator)
1.791° (to the local Laplace plane)
27.58° (to the ecliptic)
Satellite of Mars
Physical characteristics
Dimensions 15 × 12.2 × 11 km
Mean radius
6.2 ± 0.18 km
(0.97316 mEarths)
495.1548 km2
(97.0755 µEarths)
Volume 999.78 km3
(92.2979 nEarths)
Mass 1.4762×1015 kg
(0.247179 nEarths)
Mean density
1.471±0.166 g/cm3
0.003 m/s2
(306 µg)
5.556 m/s
(20 km/h)
Synchronous
Albedo 0.068 ± 0.007
Temperature ≈ 233 K

Deimos (systematic designation: Mars II) is the smaller and outer of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. The name Deimos is pronounced /ˈdmɒs/ DY-mos, /'deɪmɒs/, or sometimes /ˈdməs/ DEE-məs or like the Greek Δεῖμος. In Greek mythology, Deimos was the twin brother of Phobos and personified terror.

Deimos is 23,460 km (14,580 mi) from Mars, much further than Mars's other moon, Phobos.

Deimos was discovered by Asaph Hall, Sr. at the United States Naval Observatory in Washington, D.C on 12 August 1877, at about 07:48 UTC (given in contemporary sources as "11 August 14:40" Washington mean time, using an astronomical convention of beginning a day at noon, so 12 hours must be added to get the actual local mean time). Hall also discovered Phobos on 18 August 1877, at about 09:14 GMT, after deliberately searching for Martian moons.


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