In 2004, Cassini, the largest interplanetary spacecraft ever launched by NASA, arrived in orbit around Saturn. Since then, it's sent back oodles of information about the planet and some of its attendant moons. Now, thanks to the spacecraft, scientists believe that Saturn's moon Enceladus might have never-before-confirmed thermal activity on its ocean floor which could make the conditions right for life.
"Enceladus may even represent a very common habitat in the galaxy: icy moons around giant gas planets, located well beyond the 'habitable zone' of a star, but still able to maintain liquid water below their icy surface," said Nicolas Altobelli, in a statement. Altobelli is the Cassini project scientist from the European Space Agency.
By studying four years of data from Cassini's Cosmic Dust Analyzer, along with lab experiments and computer simulations, researchers found supersmall dust grains in orbit around Saturn that measure 4-16 nanometers in diameter. (To put that in perspective, 1 million nanometers could fit on the head of a pin.)
The dust particles were rich in silicon, which provides a clue the researchers believe points to the hydrothermal activity.
On Earth, small specks of silica -- the oxidized form of the element silicon (PDF) -- are most commonly formed through hydrothermal activity, says the statement. So the researchers who examined Cassini's data believe the particles swirling around Saturn formed the same way -- by hydrothermal vents on the bottom of the ice-covered ocean on Enceladus, the planet's nearby moon.
Their thinking is that beneath the icy crust and ocean that covers Enceladus, there is hydrothermal activity creating water with temperatures of at least 90 degrees Celsius (194 degrees Fahrenheit). This activity dissolves the minerals from the moon's interior -- maybe even from deep in its core. As the minerals rise on the hot water jets, most of them condense out as the water cools, leaving the nano-size particles of silica floating around. Those particles are then embedded in ice beneath the moon's icy crust and when they're ejected into space by the at least 101 geysers on the moon, the ice erodes and the particles float over to orbit Saturn.
While that might seem like a lot of leaps for the researchers to make, they feel pretty confident in their findings.
"We methodically searched for alternative explanations for the nano silica grains, but every new result pointed to a single, most likely origin," said Frank Postberg in a statement. Postberg is a Cassini Cosmic Dust Analyzer scientist at the University of Heidelberg in Germany, and a co-author on the paper published today in the journal Nature that details the findings.
"These findings add to the possibility that Enceladus, which contains a subsurface ocean and displays remarkable geologic activity, could contain environments suitable for living organisms," said John Grunsfeld in a separate statement. Grunsfeld is an astronaut and associate administrator of NASA's Science Mission Directorate in Washington. "The locations in our solar system where extreme environments occur in which life might exist may bring us closer to answering the question: are we alone in the universe."