Europa Transiting Geometry
This diagram shows how the plumes on Europa are seen in silhouette as
the moon moves across the face of Jupiter. Europa makes a complete orbit
of Jupiter in just 3.5 Earth days. Credit: NASA, ESA, and A. Feild (STScI). Release imagesAstronomers 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, D.C.. "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 (STScI) in Baltimore, Maryland, 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 also 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, Texas, detected evidence for water vapor erupting from the frigid south polar region of Europa and reaching more than 100 miles (160 kilometers) into space. Although both teams used Hubble's Space Telescope Imaging Spectrograph (STIS) 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 the 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, D.C. "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 will be published in the Sept. 29 issue of The Astrophysical Journal.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Maryland, conducts
Hubble science operations. STScI is operated for NASA by the
Association of Universities for Research in Astronomy in Washington,
D.C.
Contact:
NASA Headquarters, Washington, D.C.
202-358-1536 / 202-358-1077
sean.potter@nasa.gov / laura.l.cantillo@nasa.gov
Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu
William Sparks
Space Telescope Science Institute, Baltimore, Maryland
410-338-4843
sparks@stsci.edu
Source: HubbleSite
