Yesterday, May 2, marked the last time for the next three years when the NASA Cassini spacecraft conducted a close flyby of Enceladus, one of Saturn's most interesting moons. During the same mission, the orbiter flew relatively close to another Saturnine moon, Dione.
The flight plan developed by mission controllers at the NASA Jet Propulsion Laboratory
(JPL), in Pasadena, California, took the satellite within 74 kilometers (46 miles) of Enceladus' surface yesterday.
This enabled the composite infrared spectrometer instrument aboard the spacecraft to observe a side of the moon that constantly points away from Saturn. Enceladus is tidally locked to the gas giant, meaning it always keeps the same face oriented towards it.
However, the spacecraft's main mission was to use its radio science experiment to establish a stable connection to the American space agency's Deep Space Network, back on Earth. All propulsion was then shut down aboard the vehicle.
The radio link was used to gage the path Cassini took with extreme precision. Even the slight deviations from the planned course can indicate areas of higher mass underneath the surface of the moon, and researchers are very interested in learning how Enceladus' interior looks like.
This is the third in a series of flybys dedicated specifically to understanding how mass is distributed under the thick ice sheet covering the Saturnine moon. The object is one of the most interesting in the solar system, and also one of the most likely to support basic lifeforms.
The first two flybys dedicated to gravitational studies were carried out on April 28, 2010, and November 30, 2010. Experts add that the south pole is the most interesting target of all, since this is where plumes of water-ice and organic molecules are being ejected.
Enceladus is famous for its tiger stripes, landscape features that include geysers, which spew out plumes of matter from within the moon's interior. These plumes contain water-ice and organic molecules, and indicate that an ocean of liquid water may exist under miles of ice.
During the flyby, Cassini used its spectrometer to image the plumes when they were lit by the Sun from behind. The photos were snapped from around 106,000 kilometers (66,000 miles) away.
“Cassini's visible light cameras rode along and captured several images of the moon's leading hemisphere at resolutions of about 1,500 feet (450 meters) per pixel,” the JPL team explains.
Cassini also conducted a flyby of the Saturnine moon Dione at the same time, from a distance of about 5,000 miles (8,000 kilometers). Its imaging cameras created several mosaic images of the icy moon, while the composite infrared spectrometer monitored its heat emissions.
After a flyby of Titan, scheduled for May 22, Cassini will move away from Saturn's equatorial plane, and into an inclined orbit around the gas giant. This will enable it to image the object's north and south poles with extreme accuracy.
The spacecraft will then fly by the moon Rhea, on March 9, 2013. This event will be followed by a long period of studying Saturn and its rings exclusively. Beyond 2013, the next flyby will take place around Dione, in June 2015. Enceladus will only come into view again on October 14, 2015.