Intriguing new close-ups of Jupiter's icy companion Europa sent back by the Galileo spacecraft suggest that a huge watery underworld may lie beneath the moon's frozen crust, offering a possible habitat for life, researchers at NASA's Jet Propulsion Laboratory in Pasadena said Tuesday.
In the wake of last week's dramatic discovery of possible ancient life on Mars, NASA chief Dan Goldin warned against jumping the gun. But the prime question on the minds of planetary scientists seemed to be: Could there be life?
Goldin said in an interview that the space agency has shifted its focus toward missions designed to answer specific questions about the origins of the universe and the existence of extraterrestrial life.
Huge chunks of ice resembling arctic ice floes appear to have shifted about on Europa's surface like pieces of a puzzle, suggesting that a lubricating layer of water or mushy ice lies underneath. Water, along with carbon compounds and heat, are considered the necessary ingredients for life.
Researchers have long wondered about possible life on Europa, where thousand-mile-long rift lines crisscross the moon like an interstate highway system that would impress any Angeleno. "I wish we had lanes like these in Southern California," said Ronald Greeley, a geologist at Arizona State University, who said the distinctive black and white striped lanes were five or six miles wide.
The lanes suggest ancient--and possibly current--geological activity. As the huge mass of Jupiter tugs on Europa's thin ice crust, slabs of the crust break off and slide around on the surface, much like continental plates on Earth, researchers believe.
The outer edges of the lanes are dark and diffuse, like shadows, perhaps laid down when dirty ice erupted through fractures in Europa's frozen surface, Greeley speculated. The white center divider might have been laid down later, after the crack "clears its throat," he said, sending up clean, white ice or snow. New lanes are piled on top of older ones like pickup sticks, allowing researchers to reconstruct their history.
Although the images of Europa sent back by Galileo are 100 times better than those taken by the Voyager missions of the 1970s, they are still relative long-shots, snapped while the spacecraft was 96,000 miles out.
On its closest approach next year, Galileo will come within 370 miles of Europa's surface, and Greeley is hoping to see evidence of ice geysers. "But we'll have to be in the right place at the right time," he said.
Galileo's cameras also caught Jupiter's sulfurous moon Io in the act of spewing out a 60-mile-high bluish plume, probably glowing sulfur dioxide gas. The outburst rises from an area called Ra Patera--the size of New Jersey--that has been completely resurfaced by volcanic eruptions since the Voyager fly-by 17 years ago.
In contrast to our own inert moon, which barely feels the tug of distant Earth, Europa and Io are continually pulled and squeezed by the immense gravity of nearby Jupiter, and also by each other. Although Io's volcanic activity can change in a matter of hours, researchers aren't certain whether Europa is still geologically active, or whether they are seeing scars created in the moon's distant past.
On the giant planet itself, Caltech's Andrew Ingersoll said Jupiter's great red spot appeared much as it did when the first telescopes spied it 300 years ago--except for the first time, researchers found towering 30 mile high clouds that might be evidence of long-suspected thunderstorms.
The tornado-like red spot, which could swallow three Earths, sits like a stone in a raging stream, turning sedately counterclockwise while 250-mph jet streams flow by in opposite directions on either side.
The persistence of the spot and the high winds are a mystery that researchers hope to unravel as the craft gets closer. However, thunderstorms in the vicinity of the spot have been anticipated for some time. "There's definitely rain," said Ingersoll, who showed a brief two-frame "movie" of the spot turning around its axis.
Because of the loss of Galileo's high-gain antenna during the craft's journey through space, the film is not the continuous Technicolor feature researchers had hoped for. The small, secondary antenna sends back data at a painfully slow rate, about the same as a standard computer modem. It has to store images on a tape recorder to be played back at a later date, drastically restricting the number of images transmitted.
"We could have made movies lasting three days," Ingersoll said. "We could have been playing it back in real time."
Asked about the potential for life on Jupiter, Ingersoll said speculation about floating life forms on Jupiter has been popular ever since Carl Sagan suggested the idea at the time of the Voyager missions. Jupiter, he noted, has all the necessary ingredients: water in the form of rain, organic (carbon-based) molecules and a moderate temperature.
"What you don't have is peace and quiet," he said. Jupiter's turbulent winds would quickly carry any life form up to the surface where it would get fried by ultraviolet radiation from the sun, or down into the planet's interior, where it would get cooked by the heat.
"Personally, I can't imagine life evolving in such a zone," he said.
Researchers agreed, however, that looking for life beyond Earth has become a new focus for NASA.
"It's clear that Dan Goldin is very interested in the biological aspects of space exploration and the origin of life," said UCLA paleobiologist William Schopf.
Goldin enthusiastically concurred:
"I'd be happy with a singled-celled [organism]," he said.