Windows Into Jupiter's moon Europa's Interior

This graphic of Jupiter's moon Europa maps a relationship between the amount of energy deposited onto the moon from charged-particle bombardment and the chemical contents of ice deposits on the surface in five areas of the moon (labeled A through E). 

Credit: NASA/JPL-Caltech/Univ. of Ariz./JHUAPL/Univ. of Colo.

The surface of Jupiter's moon Europa exposes material churned up from inside the moon and also material resulting from matter and energy coming from above.

If you want to learn about the deep saltwater ocean beneath this unusual world's icy shell -- as many people do, certainly those who are interested in possible extraterrestrial life -- you might target your investigation of the surface.

New analysis of observations made more than a decade ago by NASA's Galileo mission to Jupiter helps identify the deposits that have emanated from 'below' the surface rather than those deposited 'on' the surface.

In particular the report examines Sulphuric Acid Hydrate production on Europa's surface.

J. Brad Dalton

"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, Pasadena, Calif., lead author of the report published recently in the journal Planetary and Space Science.

"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."

Europa is about the size of Earth's moon and, like our moon, keeps the same side toward the planet it orbits.

Picture a car driving in circles around a mountain with its left-side windows always facing the mountain.

Europa's orbit around Jupiter is filled with charged, energetic particles tied to Jupiter's powerful magnetic field.

Jupiter's Moon Io

Besides electrons, these particles include ions of sulphur and oxygen originating from volcanic eruptions on Io, a neighbouring Jupiter moon.

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.

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.

NASA's Galileo Satellite

Earlier studies had found more sulphuric acid hydrate being produced towards the center of the trailing hemisphere than elsewhere on Europa's surface, interpreted as resulting from chemistry driven by sulphur ions bombarding the icy surface.

Surface deposits in these areas are most likely to preserve the original chemical compounds that erupted from the interior.

Dalton suggests that any future spacecraft missions to Europa should target these deposits for study from orbit, or even attempt to land there.

Dalton stated "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."