Changes

== Orbital characteristics ==

== 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.

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 ==

== Rotational characteristics ==

== Physical characteristics ==

== 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/>

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&nbsp;km.<ref name=saturnsatfact/>

=== Surface ===

=== 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 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 largest and most prominent impact crater is named Herschel, after the discoverer.<ref name=planetsoc/> It measures 130&nbsp;km in diameter and 10&nbsp;km deep. Its walls rise 5&nbsp;km high, and its central mountain rises 6&nbsp;km above the floor.<ref name=Hamilton/><ref name=Britannica/><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/>

The remaining craters vary in diameter from 20&nbsp;km to 40&nbsp;km.<ref name=Hamilton/> Curiously, the south pole region has few craters larger than 20&nbsp;km in diameter.<ref name=Hamilton/>

== Observation and Exploration ==

== Observation and Exploration ==