080812 Cassini swoops past Enceladus

Top Stories

		Hubble celebrates 100,000 trips around the Earth ...Hubble is today celebrating its 100,000th orbit around the Earth with the release of a spectacular image of a fantasy-like landscape embellished with scenes of stellar birth and renewal... read more Computer simulations put Solar System in its place ...traditional theories of Solar System formation assume our neighbourhood to be pretty run of the mill, but in a new study using data from 300 exoplanets discovered orbiting other stars, our planetary haven turns out to be one of a kind... read more Dark matter clumps and streams in Milky Way ...researchers have reason to believe that dense clumps and streams of dark matter lurk in the inner regions of the Milky Way’s galactic halo... read more

Spaceflight Now +

		Subscribe to Spaceflight Now Plus for access to our extensive video collections! How do I sign up? Video archive STS-120 day 2 highlights Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights. Play STS-120 day 1 highlights The highlights from shuttle Discovery's launch day are packaged into this movie. Play STS-118: Highlights The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation. Full presentation Mission film STS-120: Rollout to pad Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission. Play Dawn leaves Earth NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt. Full coverage Dawn: Launch preview These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter. Launch \| Science Become a subscriber More video

Cassini swoops past Enceladus
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: August 12, 2008

The Cassini spacecraft flew by Saturn’s enigmatic moon Enceladus on Monday to get a closer look at the ‘tiger stripe’ features and associated icy jets that emanate from the fractures, and has begun sending data back to Earth.

"We are happy to report that Cassini's begun sending data home," says Julie Webster, Cassini team chief at NASA’s Jet Propulsion Laboratory. "The downlink will continue through the night and into tomorrow [Tuesday] morning.”

"There is a lot of anticipation and excitement about what the flyby might reveal," adds Bob Pappalardo, Cassini project scientist. "Over the next few days and weeks, the Cassini teams will be analysing the photos and other data to tease out new clues about this tiny, active world."

Artist impression of Cassini flying by Enceladus. The enigmatic tiger stripes have been enhanced in this illustration and were the focus of yesterday’s flyby. Image: NASA/JPL.

Cassini zoomed past the tiny moon at a mere distance of 50 kilometres from its surface, and all of the spacecraft's cameras –covering infrared, visible and ultraviolet wavelengths – turned towards the fissures running along the moon's south pole. The image resolution at this locality will be as fine as seven metres per pixel and will cover known active spots on three of the prominent tiger stripe fractures.

"Our main goal is to get the most detailed images and remote sensing data ever of the geologically active features on Enceladus," says Paul Helfenstein, a Cassini imaging team associate. "From this data we may learn more about how eruptions, tectonics, and seismic activity alter the moon's surface."

A close up view of just one of the fissures, and perhaps even the chance to see inside it, may provide more information on the terrain and depth of the fractures, as well as the size and composition of the ice grains inside, which will provide insight into the processes that operate at the heart of the moon. And by measuring the temperatures along the fractures, the mission scientists may be able to determine if water – in vapour or liquid form – lies close to the surface, helping to build and refine theories on what powers the jets.

Heat radiating from the entire length of the 150 kilometre long fractures is seen in this heat map of Saturn’s icy moon Enceladus, derived from data obtained in Cassini’s last flyby in March of this year. Temperatures as high as 180 Kelvin were recorded along the brightest fracture, compared with 72 Kelvin elsewhere in the south pole. The latest flyby will hopefully add further detail to this temperature map. Image:NASA/JPL/GSFC/SwRI/ SSI.

"We'd like to refine our numbers and see which fracture or stripe is hotter than the rest because these results can offer evidence, one way or the other, for the existence of liquid water as the engine that powers the plumes," says Bonnie Buratti of JPL, team member on Cassini's visual and infrared mapping spectrometer.

The flyby opens the extended Cassini mission named ‘The Saturn Equinox Mission’, which will see seven Enceladus flybys in total, along with 26 Titan flybys and one flyby each of icy moons Dione, Rhea and Helene over the next two years. The first Enceladus flyby enabled Cassini to taste organic material thrown out by the geysers (see our reports Cassini flyby success and Cassini tastes organic material at Enceladus), and two more flybys are planned for 2008. The October 9 flyby will slash yesterday’s record close approach in half, bringing the spacecraft to just 25 kilometres from the surface in order to sample more of the plume ingredients, and the October 31 flyby is optimised for the optical remote sensing instruments.