Looking Up – Bob Eklund

Astronomers Open a Window into Europa’s Ocean –Caltech astronomer Mike Brown and Kevin Hand from JPL have found the strongest evidence yet that salty water from the vast liquid ocean beneath Europa’s frozen exterior actually makes its way to the surface.

The data suggests there is a chemical exchange between the ocean and surface, making the ocean a richer chemical environment, and implies that learning more about the ocean could be as simple as analyzing the moon’s surface. The work is described in a paper that has been accepted for publication in the Astronomical Journal.

The findings were derived from spectroscopy delivered from the Keck Observatory in Hawaii.

“We now have the best spectrum of this thing in the world,” Brown says. “Nobody knew there was this little dip in the spectrum because no one had the resolution to zoom in on it before.”

The ten-meter Keck II telescope, fitted with Adaptive Optics (AO) to adjust for the blurring effect of Earth’s atmosphere as well as its OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS), produced details not capable of collection when NASA’s Galileo mission (1989-2003) was sent to study Jupiter and its moons.

“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface ‘talk’ to each other and exchange chemicals,” adds Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy at Caltech. “That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”

“The surface ice is providing us a window into that potentially habitable ocean below,” says Hand, deputy chief scientist for solar system exploration at JPL.

Since the days of the Galileo mission, when that spacecraft showed that Europa was covered with an icy shell, scientists have debated the composition of Europa’s surface. The infrared spectrometer aboard Galileo was not capable of providing the detail needed to definitively identify some of the materials present on the surface. Now, using current technology on ground-based telescopes, Brown and Hand have definitively identified a spectroscopic feature on Europa’s surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite (“Epsom salts”), which could only originate from the ocean below.

“Magnesium should not be on the surface of Europa unless it’s coming from the ocean,” Brown says. “So that means ocean water gets onto the surface, and stuff on the surface presumably gets into the ocean water.”

Other spectroscopic data suggest that ordinary table salt—sodium chloride—is also present. Brown and Hand believe the composition of Europa’s sea is likely to closely resemble the salty ocean of Earth. “If you could go swim down in the ocean of Europa and taste it, it would just taste like normal old salt,” Brown says.

Hand emphasizes that, from an astrobiology standpoint, Europa is considered a premier target in the search for life beyond Earth; a NASA-funded study team led by JPL and the Johns Hopkins University Applied Physics Laboratory has been working with the scientific community to identify options to explore Europa further. “If we’ve learned anything about life on Earth, it’s that where there’s liquid water, there’s generally life,” Hand says. “And of course our ocean is a nice salty ocean. Perhaps Europa’s salty ocean is also a wonderful place for life.”



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