These days, it seems like we’re finding water all over the solar system.

Still, it takes a lot more than a little H2O to support life. The environment also needs a source of energy and the perfect cocktail of elements, and that’s been a lot harder to find.

But last week, in a paper in the journal Science, researchers announced that we might have found that mix on Saturn’s moon Enceladus, which has a huge ocean underneath its icy surface. Back in 2005, when the Cassini spacecraft was still young and full of energy, it observed plumes of water ice and other vapor spraying out of cracks in the surface of Enceladus. We had no idea those plumes existed before we got there, but thankfully Cassini was already equipped with an instrument to identify their composition.

The instrument, called the Ion and Neutral Mass Spectrometer, or INMS for short, was originally designed to sample the atmosphere of Titan, another one of Saturn’s moons, but it was perfect for Enceladus, too. And now, 12 years and 22 Enceladus flybys later, researchers have identified the gas in the plumes: It’s almost 98% water, about 1% hydrogen, and a combination of other molecules like carbon dioxide, methane, and ammonia. We’ve known about most of those components for a while, but that hydrogen gas — which might be coming from chemical reactions near hydrothermal vents on the ocean floor — is big news!

That’s because, here on Earth, we’ve seen microorganisms combine hydrogen and carbon dioxide to create energy in a reaction called methanogenesis. Like the name suggests, the reaction also produces methane, which we’ve also seen in Enceladus’ plumes. Now, even though Enceladus has the right ingredients for some methanogenic microbes to survive, it doesn’t mean there /has to be/ life there.

We just know it’s possible, since life on Earth can make do with some hydrogen and CO2. We don’t have any more missions to Enceladus on the calendar just yet, but maybe we’ll go get a closer look someday. So if any microbes are out there, listening to this YouTube video, just hang in there for a while!

Meanwhile, next door at Jupiter, NASA also announced that the Hubble Space Telescope spotted more evidence for water plumes on Europa. Because apparently all the cool moons have water plumes these days. We /think/ we’ve seen them before — once in 2012 and again in 2014.

And, as published last week in The Astrophysical Journal Letters, in 2016 the Hubble telescope spotted what looks like another plume in the same spot as the 2014 one, shooting water 100 kilometers into the air! -and by air, I mean space... That might sound like pretty clear evidence, but because of how we’ve been looking at them, it’s still hard to say for sure what these plumes are or if they even exist. Like with Enceladus, NASA is especially interested in Europa because it most likely has an enormous, liquid water ocean under its icy crust — in fact, Europa probably has twice as much water as all the oceans on Earth combined!

For years, scientists have been hoping to take samples of Europa’s ocean, but there hasn’t been clear evidence for easily-accessible water plumes like on Enceladus. Scientists can only see these plumes when one erupts just as Europa is passing in front of Jupiter, from Hubble’s perspective. Then, the plume blocks out some of the ultraviolet radiation from the planet behind it, which we can see as a silhouette with the Hubble’s Space Telescope Imaging Spectrograph, or STIS.

The possible 2014 and 2016 plumes came from the same place on Europa’s surface, which, according to data from NASA’s Galileo spacecraft, seems to be a slightly cracked warm spot. This could mean that there’s a place on Europa with consistent plumes that are somehow heating up the nearby surface. But there’s always a chance that we’re misinterpreting something about all these results, because the Hubble telescope wasn’t designed to make these specific observations.

So we’ll keep using Hubble to monitor Europa for more evidence, but in the meantime, NASA is working on other projects! Next fall, the James Webb Space Telescope will launch, and it will have an infrared camera that could help confirm if the plumes are really there. And the Europa Clipper Mission, which is scheduled to launch in the 2020s, will have a powerful ultraviolet camera on board.

This spacecraft will get a closer look at Europa than Hubble ever could. So hopefully in a few years, we’ll be able to tell you if plumes on Europa exist and what their composition is, just like we can with Enceladus! But even now, some of the water worlds of the solar system are looking a lot more interesting and promising in our search for life off-Earth.

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