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| − | {{Planet
| + | I have Phobos Phobia! AHAHAHa... Oh, well |
| − | | name=Phobos
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| − | | image=Phobos vik1 big.jpg
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| − | | caption=Phobos by [[Viking Orbiter]]
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| − | | date=August 18, 1877
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| − | | discname=[[Asaph Hall]]
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| − | | origname=Greek ''phobos'' fear; attendant of Greek god of war
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| − | | primary=Mars
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| − | | order=1
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| − | | periapsis=9236.39 km<ref name=calc>Calculated</ref>
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| − | | apoapsis=9519.61 km<ref name=calc/>
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| − | | semimajor=9,378 km<ref name=ssdelem>"[http://ssd.jpl.nasa.gov/?sat_elem Planetary Satellite Mean Orbital Parameters]," Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 11, 2008.</ref>
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| − | | eccentricity=0.0151<ref name=ssdelem/>
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| − | | sidereal=0.3189 da<ref name=ssdelem/>
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| − | | synodic=0.3191 da
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| − | | orbitspeed=2.138 km/s
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| − | | inclination=1.093°
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| − | | siderealday=0.3189 da
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| − | | rotatespeed=11.0 km/h
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| − | | axialtilt=0°
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| − | | mass=1.073 * 10<sup>16</sup> kg (1.795 * 10<sup>-7</sup>% earth)<ref name=calc/>
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| − | | density=1,872 kg/m³<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 11, 2008.</ref>
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| − | | meanradius=11.1 km<ref name=ssdphys/>
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| − | | surfacegrav=5.81 * 10<sup>-3</sup> m/s² (5.92 * 10<sup>-4</sup> ''g'')<ref name=calc/>
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| − | | escapespeed=0.0114 km/s<ref name=calc/>
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| − | | surfacearea= 2997 km²<ref name=calc/>
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| − | | mintemp=161 K<ref name=nasa1>"[http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mar_Phobos Entry for Phobos]." Solar System Exploration, [[NASA]]. Accessed February 11, 2008.</ref>
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| − | | meantemp = 233 K
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| − | | maxtemp=269 K<ref name=nasa1/>
| + | |
| − | | composition=Rock and ice mix
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| − | | albedo=0.071<ref name=ssdphys/>
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| − | }}
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| − | '''Phobos''' (from the Greek φόβος or ''phobos'' fear) is the inner, and the larger, of the two [[satellite]]s of [[Mars]].
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| − | == Discovery ==
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| − | Phobos was discovered by the astronomer [[Asaph Hall]] on August 18, 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> Astronomers were especially excited by the very short sidereal month of Phobos--about one-third of a Martian sidereal day--a phenomenon without precedent at the time.
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| − | The astronomer V. Knorre named the satellite ''Phobos'' (and also provided the name ''Deimos'' for the other satellite that Hall had discovered six days earlier), 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>
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| − | == Orbital and physical characteristics ==
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| − | Phobos orbits Mars at a distance closer than the distance of a synchronous orbit. For that reason, Phobos actually rises in the ''west'' and sets in the ''east'' of the Martian sky.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/our_solar_system/mars/phobos.html Entry for Phobos]." The Planetary Society. Accessed February 11, 2008.</ref> Yet because Phobos orbits Mars so closely, it is not visible above the horizon at latitudes higher than 70° north or south.
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| − | Phobos is not round, but is shaped like a [[potato]], with dimensions 27 x 21.6 x 18.8 km. Its most remarkable surface feature is Creater Stickney, named for the family of Mrs. Asaph Hall. Stickney has a diameter of 10 km, and its outer rim has pronounced surface striations suggesting a tremendous impact.<ref name=nasa2>"[http://marsprogram.jpl.nasa.gov/facts/phobos.html Entry for Phobos]." Mars Exploration Program, [[NASA]]. Accessed February 11, 2008.</ref><ref name=planetsoc/>
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| − | Phobos is spiraling in toward Mars at a rate of 18 mm per year. At that rate, if it had 50 million years to wait, it would enter the Martian atmosphere and drop to the surface in a cataclysmic crash, or else disintegrate into a ring.<ref name=nasa1/>
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| − | == Origin ==
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| − | The favored theory among conventional [[astronomy|astronomers]] is that Phobos and its companion moon [[Deimos]] are captured [[C-type asteroids]].<ref name=nasa1/><ref name=planetsoc/> However, that theory is not universally accepted.<ref name=nasa1/>
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| − | The [[Union of Soviet Socialist Republics|Soviet]] spacecraft ''Phobos 2'' discovered that Phobos was venting something into space, but all its systems failed before its controllers could determine what that substance was--most commentators believe that it was water.
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| − | In the 1950's and 1960's, a number of American and Soviet astrophysicists actually speculated that Phobos was hollow, and even that it was an artificial construct.<ref>Öpik, E. J. "[http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1964IrAJ....6..281. Is Phobos Artificial]?" ''Irish Astronomical Journal'', 6:281, September 1964. Accessed February 11, 2008.</ref> This speculation had part of its basis on a lack of understanding of Phobos' density and a gross overestimation of the rate of Phobos' orbital decay--5 cm per year instead of the 1.8 cm per year that present observations have established.
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| − | == Exploration ==
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| − | The NASA probe ''Viking 1'' took the first close-up photographs of Phobos on its way to deliver a landing craft to the Martian surface. Since then, several missions have made flybys of Phobos, including the orbiter that services the Spirit and Opportunity rovers, and the [[European Space Agency]]'s ''Mars Express''.<ref name=esa1>"[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31031 Close Inspection for Phobos]." Mars Express, European Space Agency, February 11, 2008.</ref><ref>"[http://www.esa.int/SPECIALS/Mars_Express/SEM21TVJD1E_1.html Martian Moon Phobos in Detail.]" Mars Express, European Space Agency, November 11, 2004. Accessed February 11, 2008.</ref>
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| − | == Gallery ==
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| − | <gallery>
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| − | Image:Phobos_from_Mars.jpg|Successive views of Phobos photographed from the surface of Mars by the Spirit Mars rover
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| − | Image:Phobos_hires_MOC.jpg|High-resolution of Phobos from the camera in the Mars Orbiter now in orbit around [[Mars]]
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| − | </gallery>
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| − | == References ==
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| − | <references/>
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| − | {{Solarsystem}}
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I have Phobos Phobia! AHAHAHa... Oh, well
