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NASA/JPL
The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 to 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Europa is nearly the same size as Earth’s Moon, but much smoother, showing few highlands or large impact craters.
Clues are building toward the possibility of life on Jupiter’s moon Europa, which has a liquid water ocean under its icy crust.
Observations from the Keck Observatory on Mauna Kea show that the moon’s surface has diluted but abundant hydrogen peroxide, a common cleaning agent that could be an important energy supply for simple forms of life.
“Life as we know it needs liquid water, elements like carbon, nitrogen, phosphorus and sulfur, and it needs some form of chemical or light energy to get the business of life done,” said Kevin Hand of the NASA Jet Propulsion Laboratory, Pasadena, Calif., in a statement Thursday. “Europa has the liquid water and elements, and we think that compounds like peroxide might be an important part of the energy requirement. The availability of oxidants like peroxide on Earth was a critical part of the rise of complex, multicellular life.”
Hand was the lead author of a research paper published online in Astrophysical Journal Letters.
More than five times farther than Earth from the sun, Europa has a frigid exterior, with a temperature of minus 260 degrees Fahrenheit at the equator and minus 370 at the poles.
Its interior salty ocean is kept liquid by heat from tectonic forces generated by the huge gravitational tug of Jupiter. But the ocean is dark so any life would likely be supported by chemosynthesis rather than photosynthesis.
That likelihood increases with the presence of hydrogen peroxide, which decays to oxygen when mixed with liquid water, scientists say.
“At Europa, abundant compounds like peroxide could help to satisfy the chemical energy requirement needed for life within the ocean, if the peroxide is mixed into the ocean,” said Hand.
Cracks in the ice and other evidence suggest that mixing does take place.
Hydrogen peroxide was first detected on Europa by NASA’s Galileo mission, which explored the Jupiter system from 1995 to 2003, but Galileo observations were of a limited region. The near-infrared data from Keck, taken over four nights in September 2011, show that peroxide is widespread across much of the surface.
“The Galileo measurements gave us tantalizing hints of what might be happening all over the surface of Europa, and we’ve now been able to quantify that with our Keck telescope observations,” said Caltech astronomer Mike Brown, a co-author of the study. “What we still don’t know is how the surface and the ocean mix, which would provide a mechanism for any life to use the peroxide.”
The study was funded in part by the NASA Astrobiology Institute through the Icy Worlds team based at the Jet Propulsion Laboratory, a division of Caltech.
