NASA has revealed exciting new evidence that there is a vast ocean under the surface of Jupiter's moon Europa – and it may be even more accessible than we thought.
The evidence comes in the form of plumes of water vapor, seen by the Hubble Space Telescope in early 2014 and announced today. The plumes are mostly coming from Europa's south pole, which is the same location as some that were previously seen in 2012, raising the prospect they are a repeating occurrence.
A research paper describing the findings is to be published in the Astrophysical Journal this week.
“Today, we are presenting new Hubble evidence for water vapor plumes being expelled from the icy surface of Europa,” said William Sparks of the Space Telescope Science Institute (STScI), who led the team that made the finding, in a teleconference. “Observations indicate global saline liquid water engulfs the moon at the present time, hidden under miles of ice.”
A composite image showing the plumes at the 7 o'clock position. NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center
These plumes, thought to contain a few million kilograms of water, were found to be towering 200 kilometers (125 miles) above the surface, before raining back down. They were found using Hubble to image Europa as it moved in front of Jupiter. Examining the results of these images in detail, the team were able to spot plumes against the background of Jupiter using a similar way to how we find exoplanets around other stars – the transit method
In total, the team observed Europa 10 times, and saw the plumes on three occasions – in January, March, and April 2014. This means the plumes are repeating. More data from Hubble taken over the past two years is being analyzed at the moment to see if the plumes arise again.
That the plumes are repeating means an upcoming mission to Europa like NASA's Europa Multiple Flyby Mission, set to launch in the 2020s, could realistically fly through a plume and sample it, without having to land on the surface.
The plumes on three different days. The more red the plume, the more likely it is to be real. NASA, ESA, W. Sparks (STScI)
Some of the water may also be deposited on the surface, so if we were to send a lander in the future, it would not need to drill beneath the ice (thought to be several kilometers thick) to directly sample the ocean.
And one tantalizing reason to sample the ocean is that Europa looks like a good location for finding life off Earth.
“On Earth, life is found everywhere there is water, energy and nutrients,” said Paul Hertz, director of the Astrophysics Division at NASA, in the conference. “So there is special interest in any place that might possess those characteristics. And Europa might be such a place.”
Of course, that's very much speculation at the moment. But these results are certainly going to make Europa more enticing to visit.