From all the Galileo flybys, this appears to be the only one where it flew through a plume. Another, E26 on January 3, 2000 at a height of 400 kilometers (250 miles), did also see a spike. But it lasted just seconds, with the team suggesting this was probably not the result of a plume.
One of the most intriguing things about the E12 flyby is the location of the suspected plume. The team thinks it was coming from a region near a big crater on Europa called Pwyll Crater, which is just south of the moon’s equator. And this is a similar region to where Hubble saw its plumes before.
This suggests there is some sort of “thermal anomaly” in this area, notes Jia, from which Europa is emitting plumes. It’s unclear at the moment how continuous this process is, though, and that could be vital to scientists on two upcoming missions.
Some see Enceladus as a better bet for the search for life, as its plumes from its south pole appear to be continuous. While that case can be argued, the fact remains there are two upcoming missions planned for Europa, and none for Enceladus.
In the early 2020s, NASA is planning to send a mission to Europa called the Europa Clipper. This will perform 45 flybys of the moon, many of which will be below that of Galileo’s E12 pass. If there are plumes there, and with its instrumentation on board, Clipper could directly sample them.
An ESA mission, too, is heading to Europa. Called the Jupiter Icy Moons Explorer (JUICE), it’s intended to launch in 2022. Again, it has the instruments necessary to directly sample any plumes that are present on Europa.
We do of course already have a spacecraft in orbit around Jupiter, NASA's Juno spacecraft, but that mission is currently orbiting over the poles of the gas giant and can't study Europa. It's unclear at the moment if that could change in future.
“We have looked at having Juno search for plumes on Europa during our baseline mission,” Scott Bolton from the Southwest Research Institute in Texas, who was not involved in this paper but was on the original Galileo team and is now Principal Investigator on Juno, told IFLScience. “We have not yet investigated changing the orbit during an extended mission. An extended mission on Juno would not start until 2022”
Europa’s ocean beneath its surface is thought to be vast, with perhaps more water than there is on Earth. Accessing it is difficult, however, as the moon is encased in an icy crust that’s tens of kilometers thick.
These plumes provide a way to directly sample the ocean beneath without burying beneath the surface. Although their exact process of formation is unclear, it’s thought cracks in the surface can open up and release bursts of water into space.
And that has all kinds of crazy implications. Because the interior of Europa, and other icy moons like it, may contain the necessary ingredients for life, including water and energy in the form of heat. If they have hydrothermal vents at their ocean floor, as some suggest, then these could be prime locations for life to arise.
“The obvious science you can do is you have a way of measuring the composition in that plume, because that certainly is going to be interesting to know whether the ingredients for life are in the water that’s coming out from those plumes,” said Kurth.
“Europa could be sending samples of what’s in its ocean right out to [space].”