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Expansion
{{Planet
|image=Mimas Herschel up close.jpg
|caption=Mimas, with crater Herschel, taken by Cassini
|date=July 18, 1789<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed April 17, 2008.</ref>
|discname=[[William Herschel]]<ref name=usgs/><ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/mimas.htm Entry for Mimas]." ''Views of the Solar System'', 2001. Accessed June 13, 2008.</ref>
|origname=A giant killed in action by Hephaestus in the Titan-Olympian War
|primary=Saturn
|order=8
|periapsis=181,772 km<ref name=calc>Calculated</ref>
|apoapsis=189,268 km<ref name=calc/>
|semimajor=185,520 km<ref name=saturnsatfact>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html Saturnian Satellite Fact Sheet]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], November 23, 2007. Accessed June 4, 2008.</ref><ref name=arval>"[http://www.oarval.org/ClasSaten.htm Classic Satellites of the Solar System]." ''Observatorio ARVAL'', April 15, 2007. Accessed June 12, 2008.</ref>
|eccentricity=0.0202<ref name=saturnsatfact/>
|sidereal=0.9424218 da<ref name=saturnsatfact/>
|orbitspeed=14.32 km/s<ref name=Hamilton/>
|inclination=1.53°<ref name=saturnsatfact/>
|siderealday=0.9424218 da<ref name=saturnsatfact/>
|rotatespeed=0.01534 km/s<ref name=calc/>
|axialtilt=0°<ref name=saturnsatfact/>
|mass=3.79 * 10<sup>19</sup> kg<ref name=saturnsatfact/><ref name=Jacobson>Jacobson, R.A., Spitale, J., Porco, C.C., and Owen, W.M., Jr. "[http://www.iop.org/EJ/abstract/1538-3881/132/2/711/ The GM Values of Mimas and Tethys and the Libration of Methone]." ''Astron. J.'' 132:711-713, 2006. {{doi|10.1086/505209}} Accessed June 13, 2008.</ref>
|density=1150 kg/m³<ref name=saturnsatfact/>
|meanradius=198.8 km<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." Solar System Dynamics, [[Jet Propulsion Laboratory|JPL]], [[National Aeronautics and Space Administration|NASA]]. Accessed June 14, 2008.</ref>
|surfacegrav=0.06402 m/s²<ref name=calc/>
|escapespeed=0.1595 km/s<ref name=calc/>
|surfacearea=496,641 km²<ref name=calc/>
|meantemp=73 K<ref name=Hamilton/>
|composition=Water ice<ref name=Hamilton/>
|color=Neutral gray
|albedo=0.6<ref name=saturnsatfact/>
}}'''Mimas''' or '''Saturn I''' is the eighth [[moon]] of [[Saturn]] in order of distance, the sixth moon of Saturn to be discovered, and the seventh heaviest.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/saturn/mimas.html Entry for Mimas]." ''The Planetary Society'', n.d. Accessed June 13, 2008.</ref> It is also the smallest known body in the [[solar system]] that maintains a hydrostatic equilibrium shape.
== Discovery and naming ==
[[William Herschel]] discovered Mimas on July 18, 1789.<ref name=Arrago>Arrago, M. "[http://laplaza.org/~tom/People/Herschel.htm Herschel]." Annual Report of the Board of Regents of the Smithsonian Institution, 1871, pp. 198-223</ref>
Sir [[John Herschel]], his son, suggested the current names of the seven largest satellites of Saturn, including Mimas. [[Titan (moon)|Titan]] received a generic name, and the other six received names of the Titans of mythology. Mimas was a giant who fell in battle against either Hephaestus or Ares in the Titan-Olympian War.<ref name=Lasell>Lassell, William. "[http://articles.adsabs.harvard.edu/full/seri/MNRAS/0008//0000042.000.html Satellites of Saturn]." ''Monthly Notices of the Royal Astronomical Society'', 8(3):42-43, January 14, 1848. Accessed June 4, 2008.</ref>
== Orbital characteristics ==
Mimas is in a somewhat eccentric orbit around [[Saturn]]. Its semimajor axis is 185,520 km, and thus it is outside the main body of the rings but within the E ring. Its sidereal day is about 22.5 hours.
== Rotational characteristics ==
Mimas is in [[tidal lock]] with Saturn.<ref name=Britannica>Hubbard, William B. "[http://www.britannica.com/eb/article-9052772 Mimas]." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 14 June 2008.</ref>
== Physical characteristics ==
Mimas is slightly more dense than [[water]], and thus is probably composed mostly of water ice.<ref name=Hamilton/><ref name=Britannica/><ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/mimas.html Entry for Mimas]." ''The <s>Nine</s> 8 Planets'', August 4, 2005. Accessed June 14, 2008.</ref> The tidal interaction between it and Saturn causes it to assume an ellipsoidal shape. Its radial semi-axis is 209 km.<ref name=saturnsatfact/>
=== Surface ===
The surface of Mimas is covered with multiple impact craters. Most of these are very deep, apparently because Mimas is not large enough for its self-gravity to relax the surface.<ref name=Thomas>Thomas, P.C., Veverka, J., Helfenstein, P., ''et al''. "[http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1639.pdf Shapes of the Saturnian Icy Satellites]." ''37th Annual Lunar and Planetary Science Conference'', 2006. Accessed June 13, 2008.</ref>
The largest and most prominent impact crater is named Herschel, after the discoverer.<ref name=planetsoc/> It measures 130 km in diameter and 10 km deep. Its walls rise 5 km high, and its central mountain rises 6 km above the floor.<ref name=Britannica/><ref name=Hamilton/><ref name=Arnett/> The Cassini orbiter has photographed apparent fracture marks on the side of Mimas opposite Herschel. This last has caused debate among astronomers as to how great an impact a body can suffer without shattering.<ref name=Hamilton/><ref name=Arnett/> In fact, some astronomers even speculate that a much larger body once occupied Mimas' place in the Saturnian system, and suffered a shattering impact. The fragments then reassembled themselves to form Mimas.<ref name=Arnett/>
The remaining craters vary in diameter from 20 km to 40 km.<ref name=Hamilton/> Curiously, the south pole region has few craters larger than 20 km in diameter.<ref name=Hamilton/>
== Observation and Exploration ==
[[Voyager 1]] was the first to visit and photograph Mimas. In the process, Voyager 1 discovered the Herschel crater.
The [[Cassini Huygens Mission|Cassini]] orbiter has taken many more images of much higher quality. Its closest rendezvous with Mimas took place on August 2, 2005. No further rendezvous are currently planned.
== Gallery ==
<gallery>
Image:Mimas Mercator.jpg|Mercator map of Mimas, annotated with plans for detailed coverage by Cassini
Image:Mimas Herschel dead-on.jpg|Mimas, looking directly at Herschel by Cassini
Image:Mimas Herschel false color.jpg|Mimas, with Herschel at upper right, in false colors, showing surface constituent variation
Image:Mimas Blues.jpg|Mimas against Saturn's northern hemisphere. The lines are the shadows of Saturn's rings.
</gallery>
== References ==
{{reflist|2}}
{{Solarsystem}}
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