Ocean spray: Europa plumes seem to be showering its surface with water
Of all the bodies in our solar system, none arouse the interest of life-seeking astronomers in quite the way Europa does. As one of Jupiter's four largest moons, the satellite has drawn the interest of scientists for decades not because of its frosty, inhospitable surface, but the salty global ocean thought to be hidden within. But how can a water of body be examined for signs of life when packed away under miles of solid ice? New evidence revealed by NASA today suggests Europa might just offer us a helping hand, by ejecting water plumes out into space and spraying its surface with more easily sampled material in the process.
Among the discoveries gleaned by the Galileo spacecraft as it inspected Jupiter's moons throughout the 90s and early 2000s was a disruption in the planet's magnetic field around one satellite in particular, Europa. This suggested that the moon itself was creating a magnetic field through the presence of some kind of electrically conductive liquid. And given its icy makeup, scientists concluded that a huge saltwater ocean was the most likely explanation.
The intrigue surrounding Europa went up a notch in 2012, when the Hubble Space Telescope detected evidence of water vapor over the south pole, something scientists believed to be the result of plumes erupting from the presumed subsurface ocean. These findings were produced by two independent science teams using the telescope's Imaging Spectrograph instrument and described water vapor shooting 100 m (160 km) out into space.
Today's announcement throws more weight behind this theory, and that's a good sign because studying liquid water is easier when you don't have to drill through miles of ice to get it. In making the discovery, a team at the Space Telescope Science Institute in Baltimore borrowed a trick used in exoplanet hunting circles to directly image what may well be plumes shooting from the surface.
Space telescopes like Kepler detect exoplanets by searching for changes in brightness when a candidate passes in front of its star and blocks the light. The team used this approach to observe Europa as it transited Jupiter, watching its silhouette against the backdrop of the gas giant across 10 separate passes through a 15-month period.
And on three of these passes, the team spotted what could be plumes shooting from the surface. This indicates that if the plumes do indeed exist, they are only firing sporadically, because in seven of the 10 images no plumes were sighted at all. But promisingly, the suspected plumes are estimated to have the same mass and originate from the same latitude as those spotted in 2012. The estimates around height are also similar, but have been revised to around 125 mi (200 km).
While all this sounds exciting and like another step forward in our search for extraterrestrial life, the scientists emphasized the need for caution, noting that in producing the direct ultraviolet images of Europa that form the basis of the research, Hubble is operating at the very edge of its capabilities.
But the good news is that when the James Webb Space Telescope launches in 2018, it may be possible to use its infrared capabilities to confirm or disprove the existence of these water vapor plumes once and for all. And failing that, there is NASA's planned Europa mission, slated for liftoff sometime in the 2020s, that would send a solar-powered spacecraft off to conduct 45 close flybys of Europa, getting as close as 16 mi (25 kms) to the surface.
The research will be published this week in The Astrophysical Journal, and you can check out the accompanying video below.