NASA's big announcement was worth the wait: confirmed cryovolcanoes on Europa

After much anticipation, NASA held a press conference(Opens in a new window) on Monday to detail new findings(Opens in a new window) from images of Jupiter's moon Europa. The agency was clear from the beginning that its announcement would not be signs of life -- but, as it turns out, life was still the main topic of discussion. NASA announced more evidence for the existence of subsurface oceans on Europa -- and, more excitingly, that the moon may host "plumes" of water ice ejected from those oceans. This means both that alien life not only is very much on the table for the nearby moon, but that some of its ocean water may be relatively easy to obtain.

Europa has long been thought, and more recently known, to have subsurface oceans. The tidal forces between layers of the moon's crust create enough heat to keep the water in a liquid form. This can be seen in the gravitational impact of the moon. Its density in these subsurface areas is 1 -- that is, the density of liquid water. Now, thanks to new observations by the Hubble Space Telescope, NASA believes that the intense pressure of kilometers of ice above these oceans is forcing small fingers of liquid water all the way up to the surface and beyond. These plumes of water ice, sometimes referred to as "cryovolcanoes," are exciting targets for further scientific study.

If confirmed, these would be broadly similar to the famous cryovolcanoes of Enceladus, which so captured people's imaginations when they were first unveiled. The detections on Europa are notable for a couple of reasons, not the least that they were made by the Hubble Space Telescope working all the way back at Earth, while plumes at Enceladus had to be confirmed by a Voyager flyby. Scientists at the press event said that Hubble is the only instrument capable of making this detection, and that even NASA's venerable workhorse was stretched to the absolute limit in ultra-violet light.

The detections themselves took the form of 10 "transits" collected over 15 months -- that is, 10 snapshots of Europa passing between Jupiter and the Earth. The goal was originally to look for evidence of a thin atmosphere around the moon, evidenced by distortions in the image of the planet behind. What they found instead was a much stronger distortion at the 7-o'clock angle in the image above. That's what a cryovolcano looks like, when seen from Earth.

The technique is broadly similar to that used to spy distant planets against the backdrop of their host stars, offering a stark silhouette of the smaller object that can be more easily studied. Collected with the Space Telescope Imaging Spectrograph (STIS), this is the same instrument that has previously provided a wealth of information on Europa. It's also the crucial component famously repaired(Opens in a new window) by EVA in 2009 -- without such heroics, we wouldn't have this observation today.

Why care about cryovolcanoes? Because we care about the makeup of Europa's subsurface oceans, and these little planetary pimples offer a means to get at their water directly. Missions to Europa's oceans have been proposed since time immemorial. But the big problem has always been the prospect of drilling down from the surface of the moon to the surface of the ocean -- it took years to drill down to Lake Vostok in Earth's Arctic. All Armageddon references aside, it's probably not going to happen in the near future. (Incidentally, consider checking out the surprisingly well-made film about drilling on the surface of Europa, Europa Report(Opens in a new window).)

With volcanoes bringing that water to the surface for us, however, it becomes a whole lot easier to imagine testing an alien ocean directly. The Cassini probe was able to actually fly right through a thin portion of the plumes coming from Enceladus, collecting some material for analysis. These samples not only confirmed the makeup of the plumes, they also confirmed Enceladus as the source of material for Saturn's "E Ring." By looking at these ejected bits of water and nitrogen-based compounds, scientists were able to learn a lot about oceans they could never get to themselves.

Thankfully, NASA is working on a concept called the Europa Multiple Flyby Mission, which could include an orbiter and a lander. This mission would of course give a lot of attention to the composition of water below the surface. If these plumes are real, then any future mission to Europa can safely leave the drilling equipment at home.

But, strong though this evidence is, it is not detailed enough to motivate a multi-billion dollar lander project just yet. NASA has two ways forward already in the works. First, there are two more transits observed by Hubble still to be analyzed and integrated into this dataset. This will likely confirm the detections made at Europa.

More to the point, Hubble's anointed successor, the James Webb Space Telescope, is nearing its 2018 debut, and it will greatly increase mankind's ability to see into the UV portion of the spectrum. With this in hand, NASA will be able to not just further confirm these findings, but discern the detail needed to assay the makeup of the plumes from a distance. It could also provide the basis for a more realistic physical mission to Europa, one that specifically plans to find and study these plumes.