Europa's Elusive, Putative Plume

Categories: Europa News Brief

This graphic shows the location of water vapor detected over Europa's south pole in observations taken by NASA's Hubble Space Telescope in December 2012. Image Credit: NASA/ESA/L. Roth/SWRI/University of Cologne

This graphic shows the location of water vapor detected over Europa’s south pole in observations taken by NASA’s Hubble Space Telescope in December 2012. Image Credit: NASA/ESA/L. Roth/SWRI/University of Cologne

In 2001, while en route to the Saturn system, NASA’s Cassini mission performed a flyby of Jupiter’s moon Europa. Now, scientists have re-examined the data from Cassini’s brush with the jovian moon in order to better understand the potential for plumes on Europa.

In the spring of 2014, the Hubble Space Telescope made an intriguing observation of a possible plume of water vapor on Europa. The finding raised questions about whether or not Europa could have active plumes similar to those observed by Cassini on Saturn’s moon Enceladus. Unfortunately, a putative plume on Europa is much more difficult to spot than the geysers of tiny Enceladus.

Any water vapor ejected from Europa would be short-lived. Europa is larger than Enceladus and has a greater gravitational influence. This means that material ejected from Europa would be quickly pulled back down to the icy surface where it would be difficult to distinguish from the surrounding terrain.

By re-visiting the Cassini data, scientists have made some important new observations about Europa. Europa has a much thinner atmosphere than previously thought, and is surrounded by thin, hot gas. It also appears that this tenuous gas contained no evidence of an active plume on Europa at the time of Cassini’s flyby. In fact, the moon contributes less material to its surrounding environment than scientists once thought.

The new study of old data from Cassini shows that any plume activity on Europa would be intermittent, making it difficult to observe.

Fountains on Saturn's moon Enceladus backlit by the sun. The Cassini spacecraft image is greatly enhanced and colorized. Enceladus is among the locations in our solar system considered a candidate spot for life. Credit: NASA/JPL/Space Science Institute

Fountains on Saturn’s moon Enceladus backlit by the sun. The Cassini spacecraft image is greatly enhanced and colorized. Enceladus is among the locations in our solar system considered a candidate spot for life. Credit: NASA/JPL/Space Science Institute

Determining if and how a plume of material could erupt from Europa is extremely important to astrobiologists. Europa is one of the primary astrobiology targets in our solar system, and has recently been the focus of future mission plans at NASA. Beneath the icy crust of Europa is a cache of liquid water, and many scientists believe that this body of water could provide a habitat for life.

Unfortunately, accessing Europa’s subsurface ocean to search for signs of life might be extremely difficult. The water could be covered by very thick layers of ice, and gaining access might require a large mission to drill through the surface. However, if materials from Europa’s ocean erupt from below, they could provide an opportunity to easily capture samples of the ocean without having to break through Europa’s ice.

NASA is currently studying mission concepts for future Europa missions, and the presence of a plume could change the scientific motivation of such missions from ‘Is Europa habitable?” to “Is there life on Europa?”

An Expert Opinion

NASA’s Astrobiology Program is taking direct interest in new findings about Europa’s plumes, and will be hosting a workshop on February 18, 2015, to discuss the possibility of finding life in a putative Europa plume. The event is being convened by NASA’s Planetary Science Division and will be co-hosted by the NASA Astrobiology Institute (NAI) and the Solar System Exploration Research Virtual Institute (SSERVI) at NASA’s Ames Research Center.

The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in this newly-reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. Image credit: NASA/JPL-Caltech/SETI Institute

The puzzling, fascinating surface of Jupiter’s icy moon Europa looms large in this newly-reprocessed color view, made from images taken by NASA’s Galileo spacecraft in the late 1990s. Image credit: NASA/JPL-Caltech/SETI Institute

According to the NASA Astrobiology Program, an announcement will be made in early January 2015 with further details about the workshop and abstract submission instructions.

Check out this story from Astrobiology Magazine for further information about Europa’s putative plume and why it could be a very big deal for astrobiology: The Importance of Plumes

The new results were presented at the 2014 Fall Meeting of the American Geophysical Union (AGU).