Cassini to make final close pass of Enceladus
NASA’s Cassini spacecraft will soon make its final close approach of Saturn’s ocean-bearing moon Enceladus. Cassini will fly past Enceladus at a distance of 3,106 miles on Saturday, Dec. 19, at 12:49 p.m. EST (17:49 GMT).
Although Cassini will continue to observe Enceladus during the remainder of its mission, it will be from much further away – over four times the distance of its approach on December 19. Cassini’s mission will continue through September 2017.
The December 19 flyby will focus on measuring the amount of heat coming through the ice from the moon’s interior. This data will be crucial for understanding what causes the plume of gas and icy particles that sprays from an ocean beneath the surface of Enceladus.
“Understanding how much warmth Enceladus has in its heart provides insight into its remarkable geologic activity, and that makes this last close flyby a fantastic scientific opportunity,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.
The upcoming flyby will be at an opportune time for Cassini to observe the south polar region of Enceladus, which is currently in the darkness of the years-long Saturnian winter. The lack of heat from the Sun will make it easier for Cassini’s instruments to measure warmth coming from Enceladus itself.
As predetermined, this will not be Cassini‘s closest encounter with Enceladus. The purpose of this flyby is to allow Cassini’s Composite Infrared Spectrometer (CIRS) apparatus to discern heat flow across Enceladus’ south polar region.
“The distance of this flyby is in the sweet spot for us to map the heat coming from within Enceladus – not too close, and not too far away. It allows us to map a good portion of the intriguing south polar region at [a] good resolution,” said Mike Flasar, CIRS team lead at NASA’s Goddard Space Flight Center, Greenbelt, Maryland.
This fairly close flyby will be Cassini’s 22nd in its long mission. The spacecraft made its unexpected discovery of geologic activity on Enceladus in early 2005, after arriving at the Saturnian system in July 2004, which prompted modification to the spacecraft’s flight plan so that the number and quality of encounters with the icy moon could be maximized. The closest encounter of Enceladus by Cassini was accomplished on Oct. 9, 2008, at an altitude of 16 miles (25 kilometers).
On October 28, Cassini made a dive through Enceladus’ erupting plume, passing just 30 miles (49 kilometers) above the moon’s surface. Researchers are still analyzing data during that flyby to better understand the nature of the plume, its particles, and whether hydrogen gas is present. The data could provide further evidence of the existence of active hydrothermal systems in the seafloor.
In 2014, Cassini mission scientists had announced strong evidence of the existence of a regional subterranean sea near Enceladus’ south pole. That was revised in 2015 to confirm that the moon hosts a global ocean beneath its icy crust. This discovery has been one of the great achievements of the historic mission at the Saturnian system.
“Cassini’s legacy of discoveries in the Saturn system is profound,” said Spilker. “We won’t get this close to Enceladus again with Cassini, but our travels have opened a path to the exploration of this and other ocean worlds.”
Video courtesy of NASA/JPL
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.