In 2013, NASA's Hubble Space Telescope saw columns of water vapor shooting 120 miles into space from the south pole of Jupiter's moon, Europa. Scientists were excited at the prospect of testing Europa's ocean and potential for life without having to land a probe on the moon's surface, but recent Hubble attempts at detecting the geysers have failed, according to Scientific American.
"We have not yet found any signals of water vapor in the new images so far," said Lorenz Roth of the Southwest Research Institute in San Antonio.
It isn't just Hubble that hasn't seen the plumes. Images from 1995 through 2003 taken by NASA's Galileo probe haven't proven the existence of the geysers, said Cynthia Phillips of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, according to Scientific American.
"I find it hard to believe that if a plume that was similar to the plumes we see on Enceladus had been going off on Europa during the Galileo era - I find it really unlikely that we would have missed it," Phillips said. "I think we would have seen that thing."
Enceladus is the icy moon of Saturn that shoots liquid water through the ice of its south pole. Both moons' subterranean water is thought to be heated by tidal forces, according to Scientific American.
NASA's Cassini spacecraft also passed by Jupiter in 2001 en route to Saturn without observing any water vapor geysers.
"We found no evidence for water near Europa, even though we have readily detected it as it erupts in the plumes of Enceladus," Larry Esposito, University of Colorado at Boulder and team leader for Cassini's ultraviolet imaging spectrograph instrument (UVIS), said in a NASA statement.
"It is certainly still possible that plume activity occurs, but that it is infrequent or the plumes are smaller than we see at Enceladus," said Amanda Hendrix of the Planetary Science Institute in Tucson, Ariz. and Cassini UVIS team member. "If eruptive activity was occurring at the time of Cassini's flyby, it was at a level too low to be detectable by UVIS."
Roth said that Hubble had not seen the geysers in October 1999 or November 2012, so constant activity was never an expectation.
"It was clear from the beginning that this is a transient phenomenon. The end result here is, stay tuned."
