Hints about “surprising activity” on Europa have been circulating for a week, and we finally know what the big news is. NASA officials announced today that Hubble found new evidence of water plumes jetting off of the icy Jovian moon.

Scientists are almost positive that below Europa’s icy exterior, there’s about 3 billion cubic kilometers of water sloshing around in a subsurface ocean. That’s more water than we have here on Earth. And because life on Earth requires water, the Jovian moon is one of the top spots in our solar system where scientists would like to search for alien life.

The trouble is, Europa’s ocean is thought to be buried under about 62 miles of solid ice. Which is why it was so exciting, in 2013, when Hubble spied water vapor above Europa. This water vapor may be erupting in plumes from Europa’s surface, and if those plumes are shooting up from the inner ocean, a spacecraft could potentially sample the ocean simply by swooping through the plumes–no drilling rig required.

For the new observations, scientists watched Europa pass in front of Jupiter. As light bounces off the planet, it illuminates the gases in Europa’s thin atmosphere and produces an ultraviolet signature of the molecules there, which the telescope read as H2O. (Whether it’s water vapor or water ice is still unknown.)

europa plumes
New data detected evidence of water plumes on Europa on three different occasions in 2014. NASA, ESA, W. Sparks (STScI)

Scientists still aren’t 100 percent sure the plumes are real–there’s a small chance that the ‘water’ may actually be an instrument error.

Hubble watched Europa through 10 transits, and found evidence for the plumes, which shoot out of the south end and maybe the equator, in three of the passes. This indicates that the plumes aren’t always “on”, which could be valuable information for planning the Europa flyby mission that NASA may launch in the 2020s. That mission will be able to confirm without a doubt the presence or absence of the plumes, as well as what they contain.

water plumes on europa
Hubble’s view of huge plumes of water vapor in 2013, data shown superimposed on a photo of Europa NASA/ESA/L. Roth/SWRI/University of Cologne
Planet material


At its heart, this large Jovian satellite (at 1,940 miles wide, a smidge smaller than our own) has an extensive ocean and possible undersea volcanoes. A proposed mission would investigate whether its conditions are conducive to life.