December 12, 2013
Hubble Spots Water Vapor Over Jupiter’s Moon Europa
[ Watch the Video: Europa Shows Evidence Of Liquid Water ]
Brett Smith for redOrbit.com - Your Universe Online
The space agency is looking to observations from other sources to confirm Hubble’s initial finding.
"By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa," said study author Lorenz Roth of Southwest Research Institute in San Antonio. "If those plumes are connected with the subsurface water ocean we are confident exists under Europa's crust, then this means that future investigations can directly investigate the chemical makeup of Europa's potentially habitable environment without drilling through layers of ice. And that is tremendously exciting."
If confirmed, Europa would be the second moon in the solar system known to vent liquid water from its surface. In 2005, mists of water vapor and dust were detected above Saturn’s moon Enceladus.
Evidence of the Europa plumes was first detected in December, 2012 when Hubble's imaging spectrograph picked up faint ultraviolet light from an aurora, caused by Jupiter's strong magnetic field, near the moon's south pole. Electrons along Jupiter’s magnetic field lines move so quickly, they break apart water molecules into excited oxygen and hydrogen atoms – resulting in a variable auroral glow.
NASA scientists said time samples from an imaging spectrograph allowed them to eliminate phenomena created by charged particles from Jupiter, as well as more exotic explanations such as the remnants of a rare meteorite impact.
"We pushed Hubble to its limits to see this very faint emission. These could be stealth plumes, because they might be tenuous and difficult to observe in the visible light," said study author Joachim Saur of the University of Cologne, Germany.
According to Roth, long fissures on Europa's surface, known as lineae, might be releasing water vapor into space as similar cracks have been observed releasing the Enceladus jets. The NASA team also found the strength of the Europa plumes, like those at Enceladus, change with Europa's position around Jupiter. Active jets have only been observed when the moon is at its most distant from Jupiter.
The researchers said the variability could be caused by lineae undergoing more stress as gravitational tidal forces affect the moon and open the vents at larger distances from Jupiter. These forces would presumably narrow or close lineae when the moon is closest to Jupiter.
"The apparent plume variability supports a key prediction that Europa should tidally flex by a significant amount if it has a subsurface ocean," said study author Kurt Retherford, also of Southwest Research Institute.
"If confirmed, this new observation once again shows the power of the Hubble Space Telescope to explore and opens a new chapter in our search for potentially habitable environments in our solar system," added John Grunsfeld, an associate administrator for science at NASA who was not directly involved in the research. "The effort and risk we took to upgrade and repair Hubble becomes all the more worthwhile when we learn about exciting discoveries like this one from Europa."
Earlier this week, it was reported Europa appears to have clay-type minerals on its surface, according to new data from NASA’s Galileo mission. This finding could also imply that Europa carries organic materials.
Image 2 (below): This artist's impression shows Jupiter and its moon Europa using actual Jupiter and Europa images in visible light. The Hubble ultraviolet images showing the faint emission from the water vapour plumes have been superimposed, respecting the size but not the brightness of the plumes. Credit: NASA, ESA, and M. Kornmesser.