By Dave Paiz
Arizona Daily Wildcat
March 5, 1998

Images from Europa suggest water or slush below surface

Nearly 400 years after Galileo first peeked at Jupiter's moons through a homemade telescope, the spacecraft named in his honor is now giving UA scientists their best look ever at the planet's icy satellite, Europa.

Dramatic high-resolution images released this week from the Galileo spacecraft suggest the existence of slush or possibly liquid water under the bright moon's glacial outer crust.

The images were obtained during Galileo's 12th orbit around Jupiter Dec. 16. About 124 miles above the surface, it was the closest Europa fly-by ever.

The December images had been delayed by the sun's passage between Earth and Jupiter and were received last week.

In an area called the "chaos" region, the new images show colossal chunks of Europa's crust the size of entire city blocks, which seem to "float" in a sea of of rough, swirled material.

"When you look at the surface, it looks like a portion has melted and then refrozen," said University of Arizona planetary sciences professor Richard Greenberg, a member of Galileo's imaging team and director of the UA Lunar and Planetary Laboratory's Galileo Home Institution Image Processing System.

Greenberg, along with UA senior research scientist Paul Geissler and graduate students Randy Tufts and Gregory Hoppa, are developing a model to explain how Europa's unique surface may have formed.

"There are tides on Europa that would cause cracking of the ice - creating ridges," Greenberg said.

He said that over the course of an 80-hour Europan day, tides caused by Jupiter's gravitational pull cause these surface cracks to spread apart and slam back together.

"Just like the moon raises tides on Earth, Jupiter - which is really big - raises tides on Europa," Greenberg said.

According to the model, slush beneath the surface is forced up between the cracks, freezing, and thus creating the long ridges that crisscross over Europa's surface.

"The way the ridges look is pretty consistent with squeezing an Eegee's up through the cracks," said Greenberg.

"One of these ridges going through (the UA) would just cover it up - they're really huge," said 49-year-old Tufts who, after a career as a community organizer, came back to school specifically to study Europa.

Similar to Earth's plate tectonics and continental drift, Europa's glacial outer crust appears to be sliding around on top of a much warmer interior.

"It's tectonics, but it's completely different," Greenberg said.

Tufts said the new images pose many challenges for scientists attempting to understand what it is they are looking at.

"It is almost a spiritual process in some ways - you have to leave behind your previous impressions," he said.

For Tufts, the possibility that life may exist on Europa is tantalizing enough to warrant its continued investigation.

"It (The Europa mission) is worth the trip - it (the possibility of life) is worth checking out," Tufts said.

Galileo made another pass over Europa's surface Feb. 10 - this time at an altitude of about 2,200 miles.

Another fly-by is scheduled for Mar. 29 - the third of eight such "close encounters" expected to last over a year as part of the Galileo Europa Mission.

"I think the next two years will be really exciting," Greenberg said.

These new pictures have sparked NASA's interest in future missions to Europa to include plans for a possible Europa Orbiter Mission sometime in 2003.