|
 If confirmed, the discovery could affect scientists' assessments
of whether the moon has the right conditions for life, planetary
scientist Kurt Retherford, with the Southwest Research Institute in
San Antonio, Texas, told reporters at the American Geophysical Union
conference in San Francisco.
"We've only seen this at one location right now, so to try to infer
that there's a global effect as a result of this is a little
difficult at this time," Retherford said.
Researchers using the Hubble Space Telescope found 125-mile-high
(200-km-high) plumes of water vapor shooting off from Europa's south
polar region in December 2012.
The jets were not seen during Hubble observations of the same region
in October 1999 and November 2012. The now-defunct Galileo
spacecraft, which made nine passes by Europa in the late 1990s,
likewise did not detect any plumes.
Scientists believe the water vapor may be escaping from cracks in
Europa's southern polar ice that open due to gravitational stresses
when the moon is farthest from Jupiter.
"When Europa is close to Jupiter, it gets stressed and the poles get
squished and the cracks close up. Then, as it moves further away
from Jupiter, it becomes un-squished, the pole moves outward and
that's when the cracks open," said planetary scientist Francis
Nimmo, with the University of California in Santa Cruz.
The plumes also could be the result of frictional heating from
rubbing ice blocks or a fortuitously timed comet impact, scientists
said.
[to top of second column] |
Similar jets have been detected on Saturn's moon Enceladus, which
because it has 12 times less gravity than Europa, can shoot its
plumes much farther into space.
Scientists find it interesting that both Europa and Enceladus, which
is being studied by the Saturn-orbiting Cassini spacecraft, are
pumping out about the same amount of water vapor, roughly seven tons
per second.
"We were really kind of surprised by the number ... and we're
grasping what that means," Retherford said.
Additional Hubble observations are planned, as well as a review of
archived Galileo data taken when Europa was farthest away from
Jupiter.
"Now that we know where (the plumes) are, that narrows the window
that we have in comparison to the passes that we've made," said
NASA's planetary sciences chief, Jim Green.
"I think we'll have some other great results, or another
controversy," he said.
(Reporting by Irene Klotz; editing by Jane Sutton and Cynthia Osterman)
[© 2013 Thomson Reuters. All rights
reserved.] Copyright 2013 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
 |
