Saturn’s moon Enceladus is famous for spewing tall jets of mineral-rich water several kilometres into the vacuum of space. But a new study suggests that those infamous jets, or geysers, spotted first by the Voyager mission and later by Cassini, may have been an optical illusion.
Fortunately, for Enceladus fans, the reality may be even cooler.
In a paper published May 6 in Nature, astronomers say that most of the material coming off Enceladus is erupting not in discrete geysers, but rather in long “curtains” that run the length of 120km-long cracks in the moon’s south polar region.
The astronomers came to this conclusion after examining higher resolution images of the eruptions than had previously been available.
Joseph Spitale, lead author of the study and astronomer at the Planetary Science Institute in Tuscon, Arizona, explains that in early images taken by the Cassini spacecraft, it looked like someone was firing a hose off the surface of Enceladus. However, in more recent pictures taken when Cassini was closer to the ice moon, the individual jets seemed less distinct.
“It looked like a lot of fine jets,” Spitale said.
He tried to triangulate the small jets in the new pictures just like he did in the old pictures, but he couldn’t.
“They all slid around; I couldn’t get a grip on them,” he said. “And there were a lot of places where we saw a broad glow – that’s when we started to model these things as curtains.”
The curtain modelling explained what they were seeing in the new images, and it could even be used to explain some, but not all, of the individual jets they saw in the old pictures.
In the paper, Spitale and his colleagues explain that the long cracks – known as “tiger stripes” – from which the curtains of material shoot out are not perfectly straight. There are times when the viewer is looking through the equivalent of a fold in a curtain, and these folds can look like distinct jets, even if that’s not actually the case.
“It is just like if you have sheer curtains in your windows,” Spitale said. “Sometimes you are looking through more curtain and sometimes you are looking through less, so the curtains can look darker and lighter.
The researchers add that there to do appear to be some intermittent prominent jets superimposed on the curtain structure. In general, the amount of material coming off Enceladus is so small that if you waved your hand over the cracks, you wouldn’t feel it.
“It’s a very diffuse spray of very fine particles,” Spitale said. “Unless you were looking right into the Sun, you probably wouldn’t even know anything was there.”
Still, these light sprays may hold the clues for what lies beneath Enceladus’ icy surface, and modelling them correctly will make sure scientists get to the right answer. “The ultimate goal would be to see if there is a body of water beneath the surface,” he said. – Los Angeles Times/Tribune News Service