Exploration of Saturn

The exploration of Saturn has been solely through unmanned spacecraft. Like all gas giants, there is no solid surface for a solid probe to land on. Most missions therefore have been flybys, although the "Cassini–Huygens" spacecraft is currently in orbit.

Flybys

Pioneer 11 flyby

Saturn was first visited by Pioneer 11 in September 1979. It flew within 20,000 km of the top of the planet's cloud layer. Low-resolution images were acquired of the planet and a few of its moons; the resolution of the images was not good enough to discern surface features. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. Pioneer 11 also measured the temperature of Titan which is 250 degrees K. [http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PN10&11.html]

Voyager flybys

elected for Voyager 1 to make a close approach of Titan. This greatly increased our knowledge of the atmosphere of the moon, but also proved that Titan's atmosphere is impenetrable in visible wavelengths, so no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.

Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. More close-up images of Saturn's moons were acquired, as well as evidence of changes in the rings. Voyager 2 probed Saturn's upper atmosphere with its radar, to measure temperature and density profiles. Voyager 2 found that at the highest levels (7 kilopascals pressure) Saturn's temperature was 70 kelvins (−203 °C) (i.e. 70 degrees above absolute zero), while at the deepest levels measured (120 kilopascals) the temperature increased to 143 kelvins (−130 °C). The north pole was found to be 10 kelvins cooler, although this may be seasonal. Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.

The probes discovered and confirmed several new satellites orbiting near or within the planet's rings. They also discovered the small Maxwell and Keeler gaps in the rings.

Cassini orbiter

On July 1 2004, the Cassini-Huygens spacecraft performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of Phoebe, sending back high-resolution images and data.

The orbiter completed two Titan flybys before releasing the Huygens probe on December 25 2004. Huygens descended onto the surface of Titan on January 14 2005, sending a flood of data during the atmospheric descent and after the landing. During 2005 Cassini conducted multiple flybys of Titan and icy satellites.

On March 10 2006, NASA reported that the Cassini probe found evidence of liquid water reservoirs that erupt in geysers on Saturn's moon Enceladus. [ [http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=639 Cassini-Huygens: News ] ]

On September 20 2006, a Cassini probe photograph revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. [ [http://www.cnn.com/2006/TECH/space/09/20/saturn.ring.reut/index.html New Ring Spotted Around Saturn] – Article on CNN.com.]

In July 2006, Cassini saw the first proof of hydrocarbon lakes near Titan's north pole, which was confirmed in January 2007. In March 2007, additional images near Titan's north pole discovered hydrocarbon "seas", the largest of which is almost the size of the Caspian Sea.

As of 2006 the probe has discovered and confirmed 4 new satellites. Its primary mission will end in 2008 when the spacecraft will be expected to have completed 74 orbits around the planet. The probe, however, is expected to have at least one mission extension.

:"For the latest information and news releases, see [http://saturn.jpl.nasa.gov Cassini website] ."

References

* H. Karttunen, P. Kröger, et al., "Fundamental Astronomy", Springer, 3th Ed., Helsinki, 2000.
*cite web | title=Saturn Science Results | work=Voyager Science Results at Saturn | url=http://voyager.jpl.nasa.gov/science/saturn.html | accessdate=February 8 | accessyear=2005

External links

* [http://saturn.jpl.nasa.gov/home/index.cfm NASA's Cassini mission to Saturn]