Extraterrestrial ice shower as Cassini zips past Enceladus

Enceladus ("en-SELL-a-duss") is one of Saturn's 62 moons. That plume ejecting from its southern pole is made of ice and organic molecules, and it's where the Cassini space probe is heading today. The probe passed through the ice shower just after 4 p.m. (1700 UCT) on October 28.

By capturing some of the moon's ejected ice crystals, scientists hope to get clues about the watery ocean beneath the layers of ice. Is geothermal activity keeping it warm? And could that warmth potentially sustain life? The depth of the ocean is estimated at 10 kilometers (six miles). One key to potential life: molecular hydrogen that could be found in the ice crystals.

Flying so close to Enceladus (within 30 miles, or 48 km) means that the Cassini probe can capture heavier molecules - which would typically fall back to the moon first due to gravity - as well as lighter ones. Previous flybys through the plume have occurred at much higher altitudes. The south pole, by the way, is Enceladus' only "hot spot."

This is not Cassini's first Enceladus flyby. It's number 21, or E-21 in NASA jargon. This image, taken from E-20 two weeks ago, did not take the space probe to the warm, geothermally active south pole, but to the moon's northern pole.

Up north, there are no ice plumes - just ice. Craters are not erased as quickly there due to slower ice tectonics; in this photo, the craters featured center are part of three that NASA calls "snowman." The pocked northern landscape is currently bathed in sunlight, which was great for the photos taken two weeks ago, but it doesn't bode well for E-21's "deep dive" to the south pole...

...and that's because the southern pole will have no direct sunlight on it on October 28. That doesn't mean it will be pitch black as Cassini passes through it, though. In the same way that a full moon allows for a midnight stroll, Enceladus will be lit by sunlight reflecting off Saturn - what NASA scientists call "Saturnshine." It will provide enough light for Cassini to take photographs.

Further complicating matters for Cassini's inboard cameras is that zipped past the moon at 30,000 kilometers per hour. The probe had just a few tenths of a second to snap photos and grab ice before it exited the plume. It then took 26 minutes to beam new information back to earth at light speed. Photos "smeared" by the probe's velocity will be cleaned and compiled by NASA computers.

The Cassini spacecraft is the little robot that could. We have images of Titan's liquid methane lakes and beautiful shots of Dione - to name just a few achievements - thanks to this plutonium-powered probe. Its extended, 20-year voyage will end September 15, 2017, when it will be flown intentionally into Saturn's rings, so as not to biologically contaminate the planet's moons.