Mimas
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| Mimas | |
|---|---|
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| Mimas, with crater Herschel, taken by Cassini | |
| Date of discovery | July 18, 178918 July 1789 24 Tammuz 5549 H 26 Tammuz 5947 AM[1] |
| Name of discoverer | William Herschel[1][2] |
| Name origin | A giant killed in action by Hephaestus in the Titan-Olympian War |
| Orbital characteristics | |
| Celestial class | Moon |
| Primary | Saturn |
| Order from primary | 8 |
| Perikrone | 181,772 km0.00122 AU 112,947.884 mi[3] |
| Apokrone | 189,268 km0.00127 AU 117,605.683 mi[3] |
| Semi-major axis | 185,520 km0.00124 AU 115,276.784 mi[4][5] |
| Orbital eccentricity | 0.0202[4] |
| Sidereal month | 0.9424218 da0.00258 a[4] |
| Avg. orbital speed | 14.32 km/s51,552 km/h 8.898 mi/s 32,032.928 mph[2] |
| Inclination | 1.53°0.0267 rad 1.7 grad to Saturn's equator[4] |
| Rotational characteristics | |
| Sidereal day | 0.9424218 da22.618 h[4] |
| Rotation speed | 0.01534 km/s55.224 km/h 0.00953 mi/s 34.315 mph[3] |
| Axial tilt | 0°0 rad 0 grad[4] |
| Physical characteristics | |
| Mass | 3.79 * 1019 kg5.15766e-4 M☾ 6.34205e-6 M⊕[4][6] |
| Mean density | 1150 kg/m³1.15 g/ml 71.792 lb/ft³[4] |
| Mean radius | 198.8 km123.529 mi[7] |
| Surface gravity | 0.06402 m/s²0.21 ft/s² 0.00653 g[3] |
| Escape speed | 0.1595 km/s574.2 km/h 0.0991 mi/s 356.791 mph[3] |
| Surface area | 496,641 km²191,754.162 mi² 0.0131 A☾ 9.73668e-4 A⊕[3] |
| Mean temperature | 73 K-200.15 °C -328.27 °F 131.4 °R[2] |
| Composition | Water ice[2] |
| Color | #999999 |
| Albedo | 0.6[4] |
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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.[8] It is also the smallest known body in the solar system that maintains a hydrostatic equilibrium shape.
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Discovery and naming
William Herschel discovered Mimas on July 18, 1789.[9]
Sir John Herschel, his son, suggested the current names of the seven largest satellites of Saturn, including Mimas. 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.[10]
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.[11]
Physical characteristics
Mimas is slightly more dense than water, and thus is probably composed mostly of water ice.[2][11][12] The tidal interaction between it and Saturn causes it to assume an ellipsoidal shape. Its radial semi-axis is 209 km.[4]
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.[13]
The largest and most prominent impact crater is named Herschel, after the discoverer.[8] 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.[11][2][12] 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.[2][12] 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.[12]
The remaining craters vary in diameter from 20 km to 40 km.[2] Curiously, the south pole region has few craters larger than 20 km in diameter.[2]
Observation and Exploration
Voyager 1 was the first to visit and photograph Mimas. In the process, Voyager 1 discovered the Herschel crater.
The 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
 Mimas, looking directly at Herschel by Cassini |
 Mimas, with Herschel at upper right, in false colors, showing surface constituent variation |
 Mimas against Saturn's northern hemisphere. The lines are the shadows of Saturn's rings. |
References
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Related Links
Categories: Astronomy | Solar system | Moon | Saturn
