A fresh look at data collected by NASA's Cassini spacecraft during its 2001 flyby of Jupiter shows that its moon Europa's tenuous atmosphere is even thinner than previously thought.
The thin, hot gas around the moon does not show evidence of plume activity occurring at the time of Cassini flyby en route to Saturn in 2001, the US space agency said in a statement.
Members of Cassini's ultraviolet imaging spectrograph (UVIS) team analysed data collected by their instrument.
Europa contributes 40 times less oxygen than previously thought to its surrounding environment, calculated the study.
"Our work shows that researchers have been overestimating the density of Europa's atmosphere by quite a bit," said Don Shemansky, a Cassini UVIS team member with Space Environment Technologies in Pasadena, California and lead author.
"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, a Cassini UVIS team member with the Planetary Science Institute in Pasadena.
Europa is considered one of the exciting destinations in the solar system for future exploration due to strong indications of having an ocean beneath its icy crust.
Most of the hot, excited gas or plasma around Europa originates not from the moon itself but from volcanoes on the nearby moon Io.
The moon's tenuous atmosphere, which was already thought to be millions of times thinner than Earth's atmosphere, is actually about 100 times less dense than those previous estimates.
"We found no evidence for water near Europa, even though we have readily detected it as it erupts in the plumes of Enceladus," explained Larry Esposito from University of Colorado.
"Studies like this make the most of the data we have and help guide the kinds of of science investigations NASA should pursue in the future," concluded Curt Niebur, Outer Planets programme scientist at NASA headquarters in Washington.
The study appeared in the journal Astrophysical Journal.
