(CNN) -- Chains of scalloped lines running for hundreds of miles across the surface of Jupiter's moon Europa are the result of the ebb and flow of Jupiter's gravitational tug on the satellite, scientists say.

The lines, called flexi or cycloids, were first photographed by Voyager in 1979. Later, NASA's Galileo orbiter showed the cracks and ridges of the flexi covered Europa, but their origin remained a mystery.

Now, planetary scientists at the University of Arizona in Tucson have modeled how the flexi formed, a result that bolsters the theory that the 100-mile thick frozen surface covers a global ocean. Some scientists also think there could be life in the water.

The result was reported in the latest issue of Science magazine.

Gregory V. Hoppa and his colleagues at the UA Lunar and Planetary Laboratory think the cracks form with the daily rise and fall of tides in the subsurface ocean, each taking under four days to form -- or how long it takes Europa to circle Jupiter.

They modeled and scrutinized images of Europa taken by NASA's Galileo spacecraft between 1996 and 1999.

Europa's ocean tides rise and fall a distance of 30 meters. By comparison, tides at most ocean beaches on Earth rise and fall 1 to 2 meters, or 4 to 6 feet.

"Sometimes Europa is a little closer, other times a little farther from Jupiter," Hoppa said. "When Europa is closer to Jupiter, the tides are higher because Jupiter is pulling on it more. When Europa is farther, the tides fall because Jupiter's force falls. This causes Europa's ice shell to flex."

The UA model shows that when tidal stress reaches the tensile strength of ice, the ice begins to crack like a saltine cracker.

The crack then creeps slowly across the surface, following a curving path until stress drops beneath the strength of the ice and it halts.

A few hours later, when tidal stress again exceeds the ice's strength, the crack begins anew in another direction.

The cycloids faithfully record the 85-hour daily flexing of Europa's ice shell just as trees faithfully record each growing season in annual rings.

Related site: FORMATION OF CYCLOIDAL FEATURES

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Air Force launch a success at Alaska site

(CNN) -- An Air Force, Navy and industry team at the Kodiak Launch Complex in Alaska launched a rocket carrying science instruments Wednesday.

Initial radio signals indicated the launch was a success and the rocket, a commercially made Thikiol Castor IVB topped by a government second stage, released its scientific payloads, called atmospheric interceptor technology or ait.

The ait program is developing and demonstrating lightweight launch vehicle technology within Earth's atmosphere to support ballistic missile technology.

Spectators were able to watch the rocket as far up as its second-stage ignition at about 33 miles above Earth. That burn took place 64 seconds after launch from the pad which is on the Narrow Cape peninsula of Kodiak Island.

A plume of smoke from the rocket motor hung in the air for several minutes after launch, tracing the rocket's path into space.

This was the second Air Force atmospheric interceptor technology launch from the Kodiak complex, said Lt. Col. Bob Kelsey, mission director for ait.

The Air Force launched the first ait rocket from Kodiak a year ago from the site owned and operated by the Alaska Aerospace Development Corp.

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