Iapetus, moon of Saturn, discovered 1671

Iapetus, the third largest moon of Saturn, was discovered by Giovanni Cassini, October 25, 1671.  It is unique for several reasons.  First, it has a dark region, known as Cassini Regio, which is contrasted with the brightness from ice on the rest of the moon.  Ice covers most of the moon.

Second, Iapetus has an inclined orbit, more than any of the regular, i.e. largest, moons.  The rings of Saturn would be clearly visible because of its inclined orbit.  

Third, it has an equatorial ridge that runs through the center of  Cassini Regio.  Mountains in this ridge rise over 12 miles of the surrounding plains, making them among the tallest mountains in the solar system.  Mons Olympus on Mars is the tallest in the solar system. 

The source of the dark material and why the equatorial ridge exists only in Cassini Regio are unknown.

The spacecraft Cassini passed by at a range of 1,227 km (762 miles) on September 10, 2007. 

Farewell, Cassini, the little probe that could!

Just before 8am EDT today, Cassini, the spacecraft sent to study Saturn and her moons, sent her last signal.  She plunged into the Saturnian atmosphere to end a massively successful mission.  Launched October 15, 1997, she spent Cassini spent 7 years en route and arrived at Saturn in 2004.  For 13 years, she has explored the gas giant and released the Huygens probe from the ESA to land on Titan, a first for a celestial body in the outer solar system.

Cassini did flybys of Jupiter, our moon and Asteroid 2685 Masursky.  She discovered new moons Methone, Pallene, Polydeucesin, Daphnis, Anthe, Aegaeon and S/2009 S 1.  I'm sure they will find a better name for the last one.

She also performed flybys of moons Titan, Phoebe, Enceladus, Iapetus, Rhea, Hyperion and Dione.

Seventeen countries joined together in this effort.

Cassini-Hugyens spacecraft launched in 1997

The Cassini-Huygens space probe, now circling Saturn and her moons and sending back tons of data, started its seven year trek on October 15, 1997.  It arrived at the planet in June 2004 for a four year mission, which it completed in 2008 however it is still going strong.  It has sent back hundreds of gigabytes of data on Saturn, Titan, Enceladus, Iapetus, Dione, Hyperion, Tethys and other moons.

Starting this week, Cassini will make three close encounters with Enceladus.  She will fly through the icy material continually erupting from the moon's surface.  A tricky maneuver, given the speed of the probe and what damage even a small particle can do.

Part of the mission was to deploy the Huygens lander on the surface of Titan.  It landed with little difficulty and transmitted about 90 minutes after touchdown.  Images show an orange surface covered with hydrocarbon-coated water ice pebbles.  The temperature was a balmy -179.35 °C!  It's the farthest surface landing from Earth.