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Hubble: Possible Water Plumes on Jupiter's Moon Europa
Jet Propulsion Laboratory
September 26, 2016

Astronomers using NASA's Hubble Space Telescope have imaged what may be
water vapor plumes erupting off the surface of Jupiter's moon Europa.
This finding bolsters other Hubble observations suggesting the icy moon
erupts with high altitude water vapor plumes.

The observation increases the possibility that missions to Europa may
be able to sample Europa's ocean without having to drill through miles
of ice.

"Europa's ocean is considered to be one of the most promising places that could potentially harbor life in the solar system," said Geoff Yoder,
acting associate administrator for NASA's Science Mission Directorate
in Washington. "These plumes, if they do indeed exist, may provide another
way to sample Europa's subsurface."

The plumes are estimated to rise about 125 miles (200 kilometers) before, presumably, raining material back down onto Europa's surface. Europa has
a huge global ocean containing twice as much water as Earth's oceans,
but it is protected by a layer of extremely cold and hard ice of unknown thickness. The plumes provide a tantalizing opportunity to gather samples originating from under the surface without having to land or drill through
the ice.

The team, led by William Sparks of the Space Telescope Science Institute
in Baltimore observed these finger-like projections while viewing Europa's limb as the moon passed in front of Jupiter.

The original goal of the team's observing proposal was to determine whether Europa has a thin, extended atmosphere, or exosphere. Using the same observing method that detects atmospheres around planets orbiting other stars, the
team realized if there was water vapor venting from Europa's surface,
this observation would be an excellent way to see it.

"The atmosphere of an extrasolar planet blocks some of the starlight that
is behind it," Sparks explained. "If there is a thin atmosphere around
Europa, it has the potential to block some of the light of Jupiter, and
we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."

In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They saw what could be plumes erupting on
three of these occasions.

This work provides supporting evidence for water plumes on Europa. In
2012, a team led by Lorenz Roth of Southwest Research Institute in San
Antonio detected evidence of water vapor erupting from the frigid south
polar region of Europa and reaching more than100 miles (160 kilometers)
into space. Although both teams used Hubble's Space Telescope Imaging Spectrograph instrument, each used a totally independent method to arrive
at the same conclusion.

"When we calculate in a completely different way the amount of material
that would be needed to create these absorption features, it's pretty
similar to what Roth and his team found," Sparks said. "The estimates
for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds
to their earlier work."

But as of yet, the two teams have not simultaneously detected the plumes
using their independent techniques. Observations thus far have suggested
the plumes could be highly variable, meaning that they may sporadically
erupt for some time and then die down. For example, observations by Roth's team within a week of one of the detections by Sparks' team failed to
detect any plumes.

If confirmed, Europa would be the second moon in the solar system known
to have water vapor plumes. In 2005, NASA's Cassini orbiter detected jets
of water vapor and dust spewing off the surface of Saturn's moon Enceladus.

Scientists may use the infrared vision of NASA's James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity
on Europa. NASA also is formulating a mission to Europa with a payload
that could confirm the presence of plumes and study them from close range during multiple flybys.

"Hubble's unique capabilities enabled it to capture these plumes, once
again demonstrating Hubble's ability to make observations it was never designed to make," said Paul Hertz, director of the Astrophysics Division
at NASA Headquarters in Washington. "This observation opens up a world
of possibilities, and we look forward to future missions -- such as the
James Webb Space Telescope -- to follow-up on this exciting discovery."

The work by Sparks and his colleagues is published in the Sept. 29 issue
of the Astrophysical Journal.

Planetary scientist Kevin Hand of NASA's Jet Propulsion Laboratory, Pasadena, California, co-authored the new paper.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (the European Space Agency.) NASA's Goddard Space Flight
Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute, which is operated for NASA by the Association of Universities
for Research in Astronomy in Washington, conducts Hubble science operations.

For images and more information about Europa and Hubble, visit:

http://www.nasa.gov/hubble

http://hubblesite.org/news/2016/33

News Media Contact
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches@jpl.nasa.gov

Sean Potter / Laurie Cantillo
Headquarters, Washington
202-358-1536 / 202-358-1077
sean.potter@nasa.gov / laura.l.cantillo@nasa.gov

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

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