On October 15, 1997, the spacecraft was launched atop a Titan IV rocket from the Kennedy Space Center in Florida. Over the next three years it received two gravity assists from Venus and one each from Earth and Jupiter. Cassini arrived at Saturn in July 2004, becoming the first spacecraft ever to orbit the planet.
The Cassini orbiter is equipped with twelve scientific instruments. It also carried the Huygens probe with six instruments of its own. (See Figure 8.7.) The probe, provided for the mission by the ESA, was released on December 25, 2004, and began its three-week journey to the surface of Titan. It penetrated the thick cloud cover that hides the moon and touched down on January 14, 2005. The probe sampled Titan's atmosphere and provided the first photographs ever of its surface. The orbiter continued to circle Saturn and conducted flybys of Titan and the smaller moons Enceladus, Hyperion, Dione, Rhea, Iapetus, and Phoebe.
In July 2005 NASA compiled a list of the top-ten science highlights of the first year of the Cassini-Huygens mission:
- Titan's surprise surface and organic atmosphere—The surface did not include global oceans as scientists expected, but was Earth-like in some ways. There is evidence of volcanoes, erosion, craters, dunes, and dry and wet lake beds. Titan's atmosphere contains organic chemicals, such as benzene and methane. Scientists believe the moon experiences methane showers from clouds sweeping overhead.
- Saturn's complex rings—The rings were found to have "straw-like clumps" several miles long and
FIGURE 8.7 Huygens probe
Linda J. Spilker, editor, "Probing Titan's Depths," in Passage to a Ringed World: The Cassini-Huygens Mission to Saturn and Titan, National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology, October 1997, http://saturn.jpl.nasa.gov/multimedia/products/pdfs/ptarw.pdf (accessed December 28, 2005) rotating ring particles. Cassini discovered an oxygen atmosphere exists just above the rings. - First detailed images of Phoebe—Cassini found this tiny moon battered and scarred by numerous large crater strikes. There was evidence of water ice and silicate and organic materials on the surface.
- Saturn's colorful and violent atmosphere—Scientists were surprised to find the northern hemisphere of the planet appeared deep blue, rather than hazy yellow like the rest of the world. Also, violent lightning was detected in enormous thunderstorms nearly the size of Earth.
- Enceladus may have an atmosphere—Magnetic field data suggest the tiny icy moon has an atmosphere around it.
- Saturn's inner radiation belt—Cassini discovered a previously unknown radiation belt circles the entire planet in between the cloud tops and the edge of the D-ring.
- Dynamic ring-moon relationships—Images revealed unexpected interactions between Saturn's rings and moons, such as particle stealing. Two previously unknown moons were also discovered.
- Saturn's rotational speed—Comparisons of Cassini measurements to those made by Voyager spacecraft during the early 1980s suggest that Saturn's internal rotation rate is slowing down.
- Massive mountains on Iapetus—Scientists learned that there is a massive mountain range on the dark side of the moon Iapetus. Some of the mountains exceed twelve miles in height. For comparison, Mount Everest on Earth is approximately 5.5 miles high.
- Cracks in Dione—Cassini images reveal that the moon's terrain is creased with giant fractures.
Later in 2005 Cassini captured dramatic new images during flybys of the moons Mimas, Tethys, Hyperion, and Dione. As of 2006 the orbiter continues its journey around Saturn conducting detailed studies of the planet, its rings, and moons.
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