Cassini studies activity on Enceladus in three separate flybys
NASA’s Cassini orbiter is conducting three separate flybys of Saturn’s icy moon Enceladus to further study the surprising levels of activity occurring on and below its surface and to obtain images and data that could help scientists determine whether the Saturnian moon could be habitable for microbial life.
The first flyby will provide an opportunity to closely observe Enceladus’ north polar region, now illuminated by summer Sun. Earlier approaches to the icy moon during Cassini‘s 11-year mission could conduct only limited observations of this area, which was long shrouded in winter darkness.
That encounter (E-20) took place on Wednesday, October 14, and is considered a moderately close approach. Cassini observed the moon from an altitude of 1,142 miles (1,839 km) and searched for signs of ancient geological activity similar to that known to have occurred on the icy moon’s south pole.
Earlier in its mission, Cassini discovered the south polar region spewing geysers and covered with “tiger stripes” fractures produced by hydrothermal activity beneath Enceladus’ frozen surface.
On Wednesday, October 28, the spacecraft will make its closest approach (E-21) to Enceladus, a daring flight just 20 miles (49 km) above its south polar region. That trajectory will plunge Cassini through the moon’s icy plumes, where data will be collected and images taken.
Mission scientists hope the close-up data and images will reveal the level of hydrothermal activity occurring in Enceladus’ subsurface ocean as well as ways that activity affects the ocean’s potential habitability for microbial life.
The spacecraft’s final encounter (E-22) with Enceladus will take place on Saturday, December 19, from an altitude of 3,106 miles (4,999 km), with the primary goal of determining the amount of heat coming from the icy moon’s interior.
Beginning in November, the Cassini team plans to slowly raise the spacecraft’s orbit, moving it out of Saturn’s equatorial region, where flybys of the large moons have taken place, and head for the smaller moons, located near the planet’s famous rings.
Enceladus has proven to be one of Cassini’s most notable successes in terms of discoveries. Its icy plumes were first spotted by the spacecraft in 2005, and subsequent flybys yielded more insight into the material being spewed out of warm fractures in its south polar region.
Within just the last year, mission scientists determined the geologically active moon hosts a global ocean beneath its icy crust and found evidence that hydrothermal activity could be occurring on the ocean floor.
Discovering that Enceladus wobbles slightly as it orbits Saturn led scientists to conclude the underground ocean is a global one. Such wobbling can occur only if the moon’s icy outer shell is not frozen solid through its interior.
“If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,” said Cassini scientist Matthew Tiscareno of the SETI Institute.
“This proves that there must be a global layer of liquid separating the surface from the core.”
The plumes emitted from fractured areas near Enceladus’ south pole, made up of water vapor, icy particles, and simple organic molecules, are likely supplied by the vast reservoir beneath the surface, mission team members stated in an article published in the journal Icarus last month.
The discoveries have propelled Enceladus to a top destination for future space missions.
Bonnie Buratti, a specialist in icy moons at NASA’s Jet Propulsion Laboratory (JPL) and a member of the Cassini team, said, “We’ve been following a trail of clues on Enceladus for 10 years now. 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.”
With a global underground ocean and possibly hydrothermal activity on the ocean’s floor, Enceladus’ subsurface environment could be similar to ocean floors on Earth, said Cassini mission scientist Jonathan Lunine of Cornell University.
“It is therefore very tempting to imagine that life could exist in such a habitable realm, a billion miles from our home,” he emphasized.
Video Courtesy of NASA Solar System
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.