As astronomers look for signs of possible life elsewhere in our solar system, an intriguing possibility is the liquid ocean under the icy surface of Europa.
Europa, one of the four moons of Jupiter discovered by Galileo in 1610, has a surface temperature of 260 degrees below zero Fahrenheit.
That keeps its surface frozen, but the water below remains liquid because of the gravitational tug of giant Jupiter. There also may be underwater volcanoes similar to Hawaii’s Loihi, southeast of Hawaii island, and those at seafloor spreading zones.
On Earth, submarine volcanism spews chemicals that can feed a range of species, from crabs to huge exotic worms.
In theory, the same could be happening on Europa.
Now scientists using the Keck Observatory on Mauna Kea have found the strongest evidence yet that salty water from the vast liquid ocean beneath Europa’s frozen exterior makes its way to the surface. That makes sense, since the surface has lines that look like cracks.
"We now have evidence that Europa’s ocean is not isolated — that the ocean and the surface talk to each other and exchange chemicals," Mike Brown, a professor at Caltech, said in a statement Tuesday. "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."
Added Kevin Hand, a collaborator at the Jet Propulsion Laboratory in Pasadena, Calif., "The surface ice is providing us a window into that potentially habitable ocean below."
Their work is described in a paper that has been accepted for publication in The Astronomical Journal.
The Keck II telescope, fitted with adaptive optics to adjust for the blurring effect of Earth’s atmosphere, used an instrument called an OH-Suppressing Infrared Integral Field Spectrograph, or OSIRIS, to find the chemical signature of magnesium sulfate salt, a mineral called epsomite, which could only originate from the ocean below.
That kind of study was impossible when NASA’s Galileo mission was sent to study Jupiter and its moons from 1989 to 2003, Keck officials said.
Europa is a bit smaller than Earth’s moon, but its ocean is about 60 miles deep, as opposed to 7 miles for Earth’s ocean.
The two researchers hypothesize that the ocean is chlorine-rich and that the sodium and potassium must be present as chlorides. Sodium chloride is table salt.
That means the composition of Europa’s sea could 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 said.
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 ways 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."
