Changes

== Discovery ==

== Discovery ==

Deimos was discovered by the astronomer [[Asaph Hall]] on August 12, 1877, at the [[United States Naval Observatory]] in [[Washington, DC]].<ref>Authors unknown. "[http://adsabs.harvard.edu//full/seri/Obs../0001//0000181.000.html Notes: The Satellites of Mars]." ''The Observatory'', 1:181-185, 1877. Accessed February 11, 2008, from the SAO/[[NASA]] Astrophysics Data System, [[Harvard University]].</ref><ref>Hall, A. "[http://adsabs.harvard.edu//full/seri/AN.../0091//0000013.000.html Observations of the Satellites of Mars]." ''Astronomische Nachrichten'', 91(2161):11-14, 1877. Accessed February 11, 2008.</ref><ref>Morley, TA. ''[http://adsabs.harvard.edu//full/seri/A+AS./0077//0000220.000.html A catalogue of ground-based astrometric observations of the Martian satellites], 1877-1982'', ''Astronomy and Astrophysics Supplement Series'' (ISSN 0365-0138), 77(2):209-226, February 1989. Accessed February 11, 2008.</ref> 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).<ref>Knorre, V. "[http://adsabs.harvard.edu//full/seri/AN.../0092//0000031.000.html Entdeckung zweier Planeten]." ''Astronomische Nachrichten'', 92(2187):47-48, March 14, 1878. Accessed February 11, 2008.</ref>

Deimos was discovered by the astronomer [[Asaph Hall]] on August 12, 1877, at the [[United States Naval Observatory]] in [[Washington, DC]].<ref>Authors unknown. "[http://adsabs.harvard.edu//full/seri/Obs../0001//0000181.000.html Notes: The Satellites of Mars]." ''The Observatory'', 1:181-185, 1877. Accessed February 11, 2008, from the SAO/NASA Astrophysics Data System, [[Harvard University]].</ref><ref>Hall, A. "[http://adsabs.harvard.edu//full/seri/AN.../0091//0000013.000.html Observations of the Satellites of Mars]." ''Astronomische Nachrichten'', 91(2161):11-14, 1877. Accessed February 11, 2008.</ref><ref>Morley, TA. ''[http://adsabs.harvard.edu//full/seri/A+AS./0077//0000220.000.html A catalogue of ground-based astrometric observations of the Martian satellites], 1877-1982'', ''Astronomy and Astrophysics Supplement Series'' (ISSN 0365-0138), 77(2):209-226, February 1989. Accessed February 11, 2008.</ref> 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).<ref>Knorre, V. "[http://adsabs.harvard.edu//full/seri/AN.../0092//0000031.000.html Entdeckung zweier Planeten]." ''Astronomische Nachrichten'', 92(2187):47-48, March 14, 1878. Accessed February 11, 2008.</ref>

== Orbital and physical characteristics ==

== 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.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/mars/deimos.html Entry for Deimos]." The Planetary Society. Accessed February 12, 2008.</ref>

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.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/mars/deimos.html Entry for Deimos]." The Planetary Society. Accessed February 12, 2008.</ref>

Deimos is not round, but is shaped like a [[potato]], with dimensions 15 x 12.2 x 11&nbsp;km. Its largest surface feature is a 2.3&nbsp;km diameter crater.<ref name=planetsoc/> 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.<ref name=nasa2>"[http://mars.jpl.nasa.gov/facts/deimos.html Mars: Extreme Planet: Deimos]." Mars Exploration Program, [[NASA]]. Accessed February 12, 2008.</ref>

Deimos is not round, but is shaped like a [[potato]], with dimensions 15 x 12.2 x 11&nbsp;km. Its largest surface feature is a 2.3&nbsp;km diameter crater.<ref name=planetsoc/> 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.<ref name=nasa2>"[http://mars.jpl.nasa.gov/facts/deimos.html Mars: Extreme Planet: Deimos]." Mars Exploration Program, NASA. Accessed February 12, 2008.</ref>

Deimos' orbit is so little inclined with respect to the [[ecliptic]] that it makes daily transits across the [[Sun]].<ref name=planetsoc/> These transits are not, strictly speaking, ''eclipses'' because Deimos does no more than cast a shadow over the Sun as it passes between the Sun and Mars.

Deimos' orbit is so little inclined with respect to the [[ecliptic]] that it makes daily transits across the [[Sun]].<ref name=planetsoc/> These transits are not, strictly speaking, ''eclipses'' because Deimos does no more than cast a shadow over the Sun as it passes between the Sun and Mars.