Could Jupiter Moon Harbor Fish-Size Life?
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(Click to enlarge image) It may look like a giant ball of scuffed ice, but between its frigid shell and rocky center, Europa (pictured) is likely all ocean, scientists say. Research presented in October 2009 suggests the Jupiter moon's oceans may harbor complex life—perhaps not unlike fish—thanks to a drastic upward revision of the seas' expected oxygen content. (Image courtesy NASA/JPL/DLR)
In the oceans of a moon hundreds of millions of miles from the sun, something fishy may be alive—right now.
(From National Geographic / by Victoria Jaggard) — Below its icy crust Jupiter’s moon Europa is believed to host a global ocean up to a hundred miles (160 kilometers) deep, with no land to speak of at the surface.
And the extraterrestrial ocean is currently being fed more than a hundred times more oxygen than previous models had suggested, according to provocative new research.
That amount of oxygen would be enough to support more than just microscopic life-forms: At least three tons of fishlike creatures could theoretically live and breathe on Europa, said study author Richard Greenberg of the University of Arizona in Tucson.
“There’s nothing saying there is life there now,” said Greenberg, who presented his work last month at a meeting of the American Astronomical Society’s Division for Planetary Sciences. “But we do know there are the physical conditions to support it.”
In fact, based on what we know about the Jovian moon, parts of Europa’s seafloor should greatly resemble the environments around Earth’s deep-ocean hydrothermal vents, said deep-sea molecular ecologist Timothy Shank.
“I’d be shocked if no life existed on Europa,” said Shank, of the Woods Hole Oceanographic Institution, who was not involved in the new study.
Video: Hydrothermal Vents on Earth
Despite the promising new estimates, it’s too early to do more than speculate about how Europan life might have evolved. A closer look—perhaps by a NASA orbiter now in development—will be needed to tell exactly how chemicals are distributed on Europa and how the moon’s geologic history might have contributed to life’s chances.
Europa’s Shiny New Coat
Italian astronomer Galileo Galilei discovered Europa in 1610. But it wasn’t until Galileo, the NASA spacecraft, reached the Jupiter system in 1995 that scientists were able to study the moon in detail.
What the Galileo probe found was so exciting that NASA deliberately crashed the spacecraft into Jupiter in 2003 to prevent the craft from contaminating one of its own discoveries: the salty, subsurface ocean on Europa. Although the probe didn’t see the ocean directly, scientists are pretty sure it’s there, based on the age, composition, and structure of the moon’s icy surface.
For instance, pictures of the moon’s bright surface suggest it’s relatively young, said the University of Arizona’s Greenberg, author of Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon.
Europa, like the other planets and moons in our solar system, is more than four billion years old. But a relative lack of impact craters implies that the icy crust is just 50 million years old. “It’s an entirely different surface now than it was at the time the dinosaurs went extinct on Earth,” Greenberg said.
“Repaving” Sends Oxygen Steadily Downward?
Europa’s smooth surface is marred only by dark, crisscrossing ridges that suggest the icy shell is being stretched and compressed by tidal forces.
“We’re used to thinking of tides on Earth as something seen on the shore,” Greenberg explained. But on a larger scale, gravity from the sun and moon constantly squishes and stretches Earth as a whole.
Europa, which is about as big as our moon, also gets tidally stretched, not by the sun but by the gravity of massive Jupiter.
The friction from all this tidal stretching probably heats Europa enough to maintain liquid water, Greenberg said—even though the Jovian moon is 483 million miles (778 million kilometers) from the sun.
The warmer ocean material may be oozing up through cracks in the ice and freezing on the surface at the same rate that older ice sinks and melts into the liquid interior.
This cycle of “repaving” would explain the young look of the surface ice—and would open the door for oxygen at the surface to permeate the subsurface ocean.
Oxygen is created when charged particles from Jupiter’s magnetic field hit the ice. Given his estimates for the moon’s rate of repaving, Greenberg thinks it would have taken one to two billion years for the first surface oxygen to reach the ocean below.
