Just in time for Halloween, NASA has released ghostly images of the icy geysers shooting out of Saturn's moon Enceladus. More data taken during the Cassini spacecraft's deepest-ever dive through the plume will be released in coming days as scientists use the spacecraft's data to answer questions about whether, and to what extent, Enceladus is friendly to life.
The dive through the plume of water particles, organic molecules and other chemicals may have been deep, but it didn't last very long. Researchers estimated before the flyby that the spacecraft would whiz through the plume at about 19,000 miles per hour, and that this pass would last only tens of seconds.
The images aren't all that Cassini's sending back. Before passing through the plume, the spacecraft was reoriented so that its gas and dust analyzing instruments would be able to capture as much data as possible. Those measurements should give researchers an even better look at what lies within the icy moon – and whether it's a habitable environment.
Linda Spilker, Cassini's project scientist at NASA's Jet Propulsion Laboratory, ticked off the objectives of this deep dive during a briefing earlier this week. First, the researchers want to confirm the presence of molecular hydrogen in the plume, because that would serve as freestanding evidence that there's hydrothermal activity going on beneath Enceladus, perhaps akin to the hydrothermal vents on Earth that host deepwater microbial life. The more hydrogen they find, the more hydrothermal activity (and thus, available energy for those hypothetical microbes) there is.
This flyby wasn't Cassini's closest to the surface, but it was the deepest dive through the plume. Scientists have already spotted organic molecules like methane in the geyser, but this plunge – coming within 30 miles of the moon's surface – allowed them to sample a denser part of the plume. It could also allow them to see more complex organic molecules, since heavier chemicals in the plume wouldn't float up as high as their lighter peers.
"We might find new organics that we haven't seen previously that are just at the limits of our detection," Spilker said at the NASA briefing.
The scientists also want to find out whether the plumes of gas coming out from four "tiger stripe" slits around the south pole are shooting out like jets or erupting continuously along the length of each stripe like a "curtain" of material. Solving that mystery could offer insight into how long Enceladus has been active, she added.
Compared to Jupiter's moon Europa, which also hosts an ocean, Enceladus is a tiny moon, only about 300 miles across. And yet this water world could potentially help answer some profound questions about our place in the universe.
"If [life] arose twice in one solar system, the implications for how probable and how frequent it arises in the universe as a whole are profound," Curt Niebur, Cassini's program scientist at NASA in Washington, D.C., said during the briefing.
But don't go packing for a trip just yet; like NASA's Curiosity rover on Mars, Cassini doesn't have the instruments to look for living things – just for the signs of a habitable environment. Searching for biosignatures and other hints of life would be up to a future mission.