According to observations by the Hubble Telescope from 1999 to 2015, the icy surface of Jupiter’s moon Europa seems to constantly feed its thin atmosphere with water vapor.
New research published in Geophysical Research Letters describes a stable aquatic atmosphere in Europe. Ironically, this visible water vapor was only detected in the tail hemisphere of the Moon, that is, on the side facing away from its orbital direction. The article was written by astronomer Lorenz Roth of the Royal Institute of Technology KTH in Sweden.
Europe is a vast global ocean completely covered in ice. Plumes of water are known to erupt from cracks in the surface, ejecting steam over 60 miles (100 kilometers). This results in scattered, temporary pockets of water vapor in the painfully thin atmosphere of Europe.
But the water vapor described in the new study doesn’t come from these geysers. Rather, it comes straight from the surface as solid ice turns directly into gas. It appears to be a continuous process leading to a constant replenishment of water vapor in the atmosphere of Europe.
A paper earlier this year, co-authored with Roth, discovered similar traces of water vapor in the atmosphere of Jupiter’s moon Ganymede. Using the same observational technique, Roth has now shown that a similar process appears to be taking place in Europa, but on only one side. In both cases, the astronomer found traces of oxygen seen in the ultraviolet rays of the Hubble Space Telescope. In the case of Europa, Roth found these characteristic spectral signatures in archived datasets that were collected with the Hubble Imaging Spectrograph (STIS) in 1999, 2012, 2014, and 2015. Ultraviolet observations were made when Europa appeared at various points in its orbit. around Jupiter.
Hubble telescope data showed an abundance of oxygen, the main component of water. Roth studied the strength of these emissions at various wavelengths to infer the presence of water vapor in Europa’s atmosphere. Roth considered other possibilities, such as single molecules of oxygen, hydroxide, and even carbon dioxide, as all of these can produce oxygen signatures. But, as Roth explained in an email, only water “really matches the data, and so we conclude that [water] must be present, “adding that” it remains an indirect detection. “
This potential discovery of stable water vapor on Europa came as a surprise given the temperature difference between it and Ganymede; Europe, because it has a highly reflective surface, does not get hotter than -265 degrees Fahrenheit. This is about 60 degrees Fahrenheit colder than the surface temperature on Ganymede. But even at low temperatures in Europa, water ice on the surface can sublimate, passing directly from a solid state to a gas.
The question of why water vapor appears only over one of the hemispheres of Europe remains open. All sides of Europe are exposed to sunlight during its 42-hour day, and Hubble always watched the side that was lit by sunlight. This is an odd observation, but Roth has several theories.
“The posterior hemisphere is darker and therefore probably warmer, because“ dark ”means more light is being absorbed, which leads to heating. This means that water molecules can be more easily released from sublimation on the warmer side, ”explained Roth. “The back hemisphere is also the side from where charged particles rush to Europa. More charged particles can hit the surface from this side, but this is unclear because charged particles have complex trajectories. “
Further work will be required to confirm Roth’s discovery of persistent water vapor in Europa’s atmosphere and to solve this final celestial mystery. A couple of upcoming NASA missions Europa Clipper and ESA Jupiter’s Ice Moons Explorer, can greatly contribute to our understanding of Jupiter and its intriguing, water-rich moons.
More: Evidence of life may have existed right under Europa’s icy surface…