Update 19.10.2015: The first images of the north pole of Saturn’s icy moon, Enceladus, provided by the Cassini mission following the 14 October 2015 flyby are available here.
The Cassini mission begins today a series of three close encounters with Saturn’s moon Enceladus with first images expected within the next days. From more than a billion kilometers away on Earth, the Cassini team is able to send the spacecraft hurtling past Saturn’s moons at closest approach distances as small as 25 kilometers to perform flybys, which are are a critical part of the Cassini mission, for both science and navigation purposes. When Cassini last approached Enceladus the north of the moon was shrouded in darkness during its winter but now that it is summer there, the Sun is shining on the high northern latitudes.
Flybys are a major element of Cassini’s tour. The spacecraft’s looping, elliptical path around Saturn is carefully designed to enable occasional visits to the many moons in the system. All flybys provide an opportunity to learn more about Saturn’s icy satellites, and encounters with giant Titan are actually used to navigate the spacecraft, changing its orbit or setting up future flybys.
Many of the most exciting encounters are “targeted” flybys, for which Cassini’s flight path is steered so the spacecraft will pass by a specific moon at a predetermined distance, referred to as “closest approach”. Cassini’s targeted flybys have yielded incredible close-up views and many groundbreaking science results. Visits to Dione and Hyperion, for example, as well as the daring Oct. 2008 dives through the Enceladus plume, have provided some of the great highlights of the mission.
During a flyby Cassini approaches the target moon at great speed. The spacecraft keeps its instruments precisely pointed toward a target using either its reaction wheels or thrusters, which spin the spacecraft in order to track the moon as it passes by. Thrusters are also used to keep Cassini from tumbling when it experiences drag while passing through Titan’s upper atmosphere during close flybys and during the deepest plunges through the icy plume of Enceladus.
During the next couple of months the Cassini missions will perform flybys on:
14 October 2015 – ‘E-20′ Flyby: Enceladus’ North Pole Revealed
During this flyby, Cassini will image the north polar regions of Enceladus – something not possible in the first years of the mission, when the moon’s north pole was in darkness. Scientists are eager to search for indications of whether the north polar region might have been geophysically active at some time in the past. There are also two plume observations designed to allow scientists to better understand the connection of specific jets to surface hot spots, and to search for variability in the plumes.
28 October 2015 – Enceladus Flyby ‘E-21’
This daring flyby will bring the spacecraft within 30 miles (48 kilometers) of Enceladus’ south pole. The flyby is timed to occur when the moon’s plumes are at their maximum output — a first for the mission. This will allow Cassini to obtain the most accurate measurements yet of the plume’s composition.
19 December 2015 – Enceladus Flyby ‘E-22’
This will be the last targeted Enceladus flyby of the mission. The CIRS instrument will observe the moon’s south polar terrain. By the time the mission concludes on 2017, Cassini will have obtained observations over six years of winter darkness in the moon’s southern hemisphere. These are ideal conditions for improving measurements of heat flow from the interior to the surface. Understanding heat flow is important because it provides key information on what is driving the geysers.
“We’ve been following a trail of clues on Enceladus for 10 years now”, said Bonnie Buratti, a Cassini science team member and icy moons expert at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
“The amount of activity on and beneath this moon’s surface has been a huge surprise to us. We’re still trying to figure out what its history has been, and how it came to be this way”, he added.
About the Cassini-Huygens mission
The Cassini-Huygens mission is a mutual project of NASA, ESA and the Italian Space Agency.
Cassini was launched in October 1997 with the European Space Agency’s Huygens probe. The probe was equipped with six instruments to study Titan, Saturn’s largest moon. It landed on Titan’s surface on 14 January 2005 and returned spectacular results.
Cassini completed its initial four-year mission to explore the Saturn System in June 2008 and the first extended mission, called the Cassini Equinox Mission, in September 2010.
Now, the healthy spacecraft is seeking to make exciting new discoveries in a second extended mission called the Cassini Solstice Mission.
Further information about the Cassini mission are available here.