Cassini Flyby – Rhea

Cassini flew by Rhea yesterday in an effort to better understand the heavily cratered world with wispy terrain similar to the ice cliffs and fractures of Dione.

The image above shows the planned image coverage as Cassini passed only 500 kilometers (310 miles) above Rhea on Saturday. When Cassini was still 76,689 kilometers (47,652 miles) away from Rhea it captured the raw image on the right with Saturn’s rings in the background. The image data is still streaming back to earth and should appear on the public Cassini-Huygens mission website in the raw images section sometime today or tomorrow.

From NASA’s mission description document (PDF link):

“November of 2005 includes the final flyby of an amazing string of close icy satellite encounters. As September included the closest-ever encounters with Tethys and Hyperion, October contained the single targeted encounter at Dione . November brings the only targeted encounter at Rhea. Rhea was discovered by Jean-Domnique Cassini (after whom our orbiter is named) in 1672. . In Greek mythology, Rhea is known as the mother of the gods. She is the mother of Demeter, Hades, Hera, Hestia, Poseidon and Zeus.

“The closest approach to Rhea occurs on Saturday, November 26th, at 22:37 spacecraft time (4:49 PM Pacific Time) at an altitude of 500 km (310 miles) above the surface and at a speed of 7.3 kilometers per second (16,330 mph). Rhea has a diameter of 1528 km (949 miles), making it the largest icy satellite. Rhea is spherical in shape. The next-closest encounter with Rhea occurs in 2007 on orbit 49, at a distance of 5000 km.

“This encounter is set up with two maneuvers: an apoapsis maneuver scheduled for November 13, and an approach maneuver, scheduled for November 23. The encounter itself occurs approximately 12 hours prior to periapsis to Saturn. The cleanup maneuver for the flyby occurs just a day after the encounter.

“Occurring on orbit 18, Rhea will be the eighth close encounter with icy satellites, after Phoebe, Enceladus (orbit 3, non-targeted), Enceladus (orbit 4), Enceladus again (orbit 11), Tethys (orbit 15, non-targeted), Hyperion (also orbit 15) and Dione (orbt 16). (It could be argued that the study of Iapetus on orbit C was intense enough even at 120,000 km to merit inclusion in this list, making this encounter the ninth.)”

In one month, Cassini will return to Titan. The spacecraft’s closest approach will be 10,400 kilometers (6,500 miles).

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Richard Leis

Richard Leis is a writer and poet living in Tucson, Arizona. His poetry has been published in Impossible Archetype. His essays about fairy tales and technology have been published on Tiny Donkey and Fairy Tale Review’s “Fairy-Tale Files“.