By Ron Cowen, Science News
FAJARDO, Puerto Rico—If there are any fish on Jupiter’s moon Europa, they can breathe easy.
Researchers hunting for signs of life beyond Earth have long been drawn to Europa because several features of the moon’s icy surface—including its bright color, networks of long fractures and crater-free terrain—suggest that the moon contains a vast ocean buried under the ice. Now one researcher has calculated that the proposed ocean may receive about 100 times more oxygen than previous models indicated—enough to support respiration by 3 million tons of fish or their Europan equivalent.
Oxygen, generated by charged particles striking water molecules on the moon’s surface, would take 1 to 2 billion years to begin seeping into the ocean, calculated Richard Greenberg of the University of Arizona in Tucson. That delay would have been critical for supporting life because it would have allowed time for primitive organisms to develop the ability to use oxygen. If oxygen instead had been immediately released into the ocean, it would have destroyed fledgling life through the well-known process oxidation, commented Jonathan Lunine, also of the University of Arizona, who was not part of the study.
Greenberg reported the findings October 9 at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences.
Theorists had previously calculated that the charged particles striking Europa would produce oxygen within the top few centimeters of the moon’s crust. Small impacts from space debris would then kick up material that would bury this oxygenated layer to a depth of a few meters. The new part of the story, said Greenberg, came when he considered Europa’s youthful, nearly crater-free appearance. The paucity of craters indicates that the crust is continually resurfaced. Today’s crust is only 50 million years old, even though the moon formed soon after the solar system’s birth 4.56 billion years ago.
Over a period of about 50 million years, a layer of ice 300 meters thick slowly rose from below, eventually covering the moon’s surface and erasing old craters, Greenberg suggested. As a result of this facelift, Europa’s oxygenated layer grew increasingly thick, until after about 1 to 2 billion years the entire ice layer was oxygen-rich, Greenberg said. At that point, ice melting at the bottom of the frozen layer began delivering oxygen into the proposed buried ocean at a faster rate than previously estimated, resulting in about 100 times more oxygen in the ocean.