Feb. 27, 2007 — It's been seven years since the Galileo space probe last flew by Jupiter's mysterious moon Europa, but what scientists learned still has them pining for more.
Beneath the moon's icy, flat and relatively crater-free surface lurks what is believed to be an enormous ocean, filled with more water than twice the amount on Earth.
Dedicated missions to Europa so far have been confined to PowerPoint presentations, but there is something in the offing that should temporarily appease researchers' appetites for more information.
On Wednesday, a Pluto-bound spacecraft will fly by Jupiter to slingshot itself off the giant planet's enormous gravity field, picking up an extra 9,000 mph of speed.
The flyby will position the half-ton probe to reach Pluto in another eight years — three years sooner than it could get there on its own. The spacecraft, called New Horizons, began its 3-billion-mile journey in January 2006.
Liquid or Ice?
During the Jupiter encounter, all the probe's science instruments will be collecting data, including possibly some details about suspected upwellings on Europa's frozen surface made by its hidden, subterranean sea.
"We know there's water there," Arizona State University planetary scientist Ronald Greeley said at the American Association for the Advancement of Science conference in San Francisco last week. "The question is, 'Is it liquid or not and where does it reside beneath the surface?'"
Scientists believe tidal flexing — a process triggered by the gravitational tug of Jupiter and neighboring moons — keeps Europa's interior far warmer than its frozen surface. The phenomenon is apparent on sister moon Io, which has active volcanoes.
On Europa, the process is more subtle, but there is ample evidence the moon's inner layers are liquid.
With liquid water, organic molecules and energy sources from tidal flexing and the Sun, Europa may be the most likely place in the solar system to find life beyond Earth, scientists say.
"If there is life, it probably evolved independent of life on Earth and it's probably carbon-based, but it may not be anything like what we have here," said Jere Lipps, a professor of integrative biology at the University of California at Berkeley.
