Photomosaic of Cassini images taken Dec. 31, 2004, showing the dark Cassini Regio, large craters, and the newly discovered equatorial ridge
Cassini Regio is the enigmatic dark area that covers half of Saturn's moon Iapetus. It is named after Giovanni Cassini, the discoverer of Iapetus.
The nature of the material that caused the extensive discoloration of Cassini Regio is not known, but it appears to be thick, and may be the result of a form of cryo-vulcanism. It is hoped that the NASACassini probe, newly arrived at Saturn, will clarify the nature of Cassini Regio during its forthcoming close approaches of Iapetus.
In 2004, it was discovered that a 1,300 km long ridge of 12km high mountains runs down the centre of Cassini Regio, almost perfectly following Iapetus's equator. The origin of this extremely unusual feature is as yet unknown.
For more details, see the main article on Iapetus.
Cassini was born in Perinaldo, Imperia, at that time in the Republic of Genoa.
Cassini was the first to make successful measurements of longitude by the method suggested by Galileo, using eclipses of the satellites of Jupiter as a clock.
Cassini was employed by Pope Clement IX in regard to fortifications, river management, and flooding of the Po.
The uniform appearance of the dark materials at the equator, the apparent thinning and spottiness of the dark materials at progressively higher latitudes and dark wispy streaks near the distal margin of CassiniRegio strongly suggest that dark material was emplaced as a coating.
Thus, CassiniRegio may have had its origin in plume-style eruptions in which dark particulate materials accumulated on the surface as fallout, perhaps in conjunction with the creation of the equatorial ridge.
Cassini acquired the images in this mosaic with its narrow angle camera on Dec. 31, 2004, at a distance of about 172,400 kilometers (107,124 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 50 degrees.
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