NASA’s Hubble Space Telescope has directly imaged what may be
plumes of water vapor on Jupiter’s icy moon Europa.
Europa has long been thought to harbor a global ocean of water
beneath its surface of ice, making it a prime target of
study for anyone interested in searching for alien life.
Eventually our search for life will take us into that ocean,
but until then, the existence of a water vapor plume would
provide an early glimpse into the ocean’s conditions. In 2012,
a team of astronomers used the Hubble Space Telescope to
observe a faint aurora from the interaction of Europa and
Jupiter’s magnetic field. They detected emissions in
wavelengths characteristic of the breakup of water molecules,
and after considering a wide variety of causes, the team
concluded that the most plausible explanation for these
spectroscopic measurements was the existence of plumes of water
vapor erupting from the surface of Europa. Now a different team
of astronomers has used a different method with similar
results - they used Hubble to image Europa in ultraviolet
light as the moon transited across the disk of Jupiter and
were actually able to take direct images of what appear to
be the silhouettes of plumes rising about 125 miles above the
surface of Europa. If these observations are indeed of water
vapor plumes, then they approximately match the 2012
observation estimates for the plumes’ mass, height, and
location. Also, these plumes are transient, meaning they come and
they go - out of ten observations of Europa
transiting across Jupiter, the team saw possible plumes on just
three of the transits. Both the recent observations and the 2012
observations provide evidence, not proof, of water vapor plumes
on Europa. Science is a process; it’s not always cut-and-dried.
But future observations by Hubble, and infrared
observations by the James Webb Space Telescope, could continue
to build a case for the existence of these plumes on
Europa. And then NASA’s future Europa flyby mission would
continue the search for the plumes and visit them to look
for evidence of a habitable underwater world.
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