A few years back, scientists saw plumes of water vapor shooting out of the ice-covered surface of Saturn's moon Enceladus. They determined that these plumes are signs of a liquid ocean trapped under the ice, raising hopes that the small moon might be home to life.
Now new research suggests we've actually underestimated the extent of water erupting from Enceladus. A analysis of photos taken by NASA's Cassini probe indicates there are actually long curtains of material shooting out of cracks in the ice — some up to 75 miles long.
The curtains of water vapor leaking from Enceladus
The researchers, led by Joseph Spitale of the Planetary Science Institute, looked at new, high-resolution images of Enceladus taken by Cassini. They noted that what had previously appeared as about 100 distinct, isolated plumes in previous photos seemed to be surrounded by hazy, smaller jets of material.
Enceladus's icy surface has four long cracks called "tiger stripes" — and the scientists suspected that traces of water might actually be leaking out of the entire length of them.
To test the idea, they modeled what faint curtains of vapor might look like to Cassini, and found that they'd mostly be difficult to spot — except in a few spots where the cracks bend, where they'd appear as a dense plume. These spots line up exactly with where Cassini has seen the more prominent plumes.
This makes it seem very likely that long curtains of water are shooting out of Enceladus's surface, rather than a hundred or so individual jets. If we ever send a spacecraft there to Enceladus look for signs of life, this could make it much easier to collect water samples.
Why Enceladus might be the best place to search for life
Scientists generally believe three key ingredients are necessary for life as we know it: liquid water, organic chemicals (the compounds that serve as the building blocks of all life on Earth), and an energy source.
We've spotted liquid oceans in several places in the solar system, including Jupiter's moons Europa and Ganymede (both of which also have oceans trapped under ice). But Enceladus is the only place where we have clear evidence for the other two ingredients, too.
Previous analysis of Enceladus's plumes by Cassini showed the water vapor contains abundant organic chemicals, and that it emanates from a six-mile-thick ocean present at the moon's south pole — an ocean could have about as much water as Lake Superior.
Then, a few months ago, scientists discovered something pretty exciting: evidence of hydrothermal vents on Enceladus's ocean floor, which might serve as the energy source for life.
The researchers looked at tiny grains of dust that were shot out of Enceladus's geysers and found that they likely formed as a result of interactions between hot rock and water. "The most clear indication of this is that [the particles are] mostly made of silica," Hsiang-Wen Hsu, the lead author, told me at the time. On Earth, silica forms at undersea hydrothermal vents, where chemicals dissolved in hot water crystallize as the water is suddenly cooled when it meets the ocean.
What's more, on Earth all sorts of life forms have sprung up around these hydrothermal vents, feeding off the chemical energy. Some researchers have even speculated that these could be the sites where life originally evolved billions of years ago.
To know for sure if there's life on Enceladus, we'll have to send another spacecraft — one that's capable of looking for direct evidence of life in the plumes of water vapor (Cassini can't) and perhaps even returning a sample of it to Earth. Right now, NASA is focusing on an upcoming mission to Europa, but if a probe is ever sent to Enceladus, the fact that water vapor is shooting out in these long curtains could make it a bit easier to sample.