Windows Into Europa's Icy Interior
April 15, 2013

NASA Scientists Pinpoint Ideal Regions For Study Of Europa’s Interior

redOrbit Staff & Wire Reports - Your Universe Online

By taking a second look at observations made more than a decade ago, NASA scientists have discovered regions that might give them the best look at the deep saltwater ocean beneath the icy shell of Jupiter´s moon Europa.

The surface of this natural satellite exposes material originating both from the inside of the moon and from matter and energy coming from above, the US space agency explained in a statement on Friday.

In order to best investigate Europa´s surface, the organization said that it is best to focus on regions that have more “stuff” from the inside and less of the “stuff” originating from above — and they have located those areas courtesy of observations from NASA´s Galileo mission to Jupiter back in 2003.

“We have found the regions where charged electrons and ions striking the surface would have done the most, and the least, chemical processing of materials emplaced at the surface from the interior ocean,” said J. Brad Dalton of NASA's Jet Propulsion Laboratory (JPL), lead author of a recently published report describing NASA´s findings.

“That tells us where to look for materials representing the most pristine ocean composition, which would be the best places to target with a lander or study with an orbiter,” he added. A paper from Dalton and co-authors from both JPL and the Johns Hopkins University Applied Physics Laboratory in Maryland detailing their findings appears in the journal Planetary and Space Science.

Europa, which is approximately the same size as Earth´s moon, is filled with charged, energetic particles linked to Jupiter´s powerful magnetic field, the US space agency explained. In addition to electrons, those particles include sulfur and oxygen ions that originate from volcanic eruptions on another of Jupiter´s moons, Io.

“The magnetic field carrying these energetic particles sweeps around Jupiter faster than Europa orbits Jupiter, in the same direction: about 10 hours per circuit for the magnetic field versus about 3.6 days for Europa's orbit,” NASA said. “So, instead of our mountain-circling car getting bugs on the front windshield, the bugs are plastered on the back of the car by a ℠wind´ from behind going nearly nine times faster than the car. Europa has a ℠leading hemisphere´ in front and a ℠trailing hemisphere´ in back.”

Previous research had discovered that more sulfuric acid was produced towards the center of the trailing hemisphere than anywhere else on Europa´s surface. It is believed that is the result of chemistry driven by sulfur ions bombarding the icy surface of the satellite. Dalton and his colleagues looked at data collected from observations with Galileo's near infrared mapping spectrometer of five different regions of the moon´s surface.

“The spectra of reflected light from frozen material on the surface enabled them to distinguish between relatively pristine water and sulfate hydrates,” the space agency said. “These included magnesium and sodium sulfate salt hydrates, and hydrated sulfuric acid. They compared the distributions of these substances with models of how the influxes of energetic electrons and of sulfur and oxygen ions are distributed around the surface of Europa.”

They found that there was a lot of variation in the concentration of frozen sulfuric acid on Europa´s surface. Near the center of the leading hemisphere, the levels were nearly undetectable, while near the center of the heavily-bombarded trailing hemisphere, it made up more than half of the surface materials. The concentration was said to be closely related to the amount of electrons and sulfur ions impacting with the surface.

“The close correlation of electron and ion fluxes with the sulfuric acid hydrate concentrations indicates that the surface chemistry is affected by these charged particles,” Dalton said. “If you are interested in the composition and habitability of the interior ocean, the best places to study would be the parts of the leading hemisphere we have identified as receiving the fewest electrons and having the lowest sulfuric acid concentrations.”

The surface deposits in those areas are extremely likely to have preserved the original chemical compounds from within the interior, the researchers said. As a result, they suggest that future missions to Europa should consider focusing on those areas for research from an orbital position, or even as potential landing sites.

“The darkest material, on the trailing hemisphere, is probably the result of externally-driven chemical processing, with little of the original oceanic material intact,” Dalton said. “While investigating the products of surface chemistry driven by charged particles is still interesting from a scientific standpoint, there is a strong push within the community to characterize the contents of the ocean and determine whether it could support life. These kinds of places just might be the windows that allow us to do that.”