TUCSON, Ariz. — Scientists for the Phoenix Mars Lander are wrestling with an intermittent short circuit on the spacecraft.

The problem is in a device that will analyze ice and soil dug from the planet's surface, the scientists said Friday. The short circuit was found during testing done before the mission's experiments get under way.

The short circuit isn't considered critical, said William Boyton of the University of Arizona's Lunar and Planetary Laboratory. Boynton is in charge of the device that will heat and analyze samples scooped up by the lander's robotic arm.

He said scientists know what is triggering the problem and what actions make it go away and are working on solutions.

Phoenix was designed to study whether the Martian north pole region could support primitive life forms and is to perform several experiments seeking traces of organic compounds.

Team members in charge of the robotic arm said new photos show the lander may be resting on splotches of ice. Washington University scientist Ray Arvidson said the spacecraft's thrusters may have uncovered the ice when the robot landed last Sunday. Mission planners aimed the craft to the red planet's northern regions hoping to find ice just under the surface.

"We're really pushing for ice, but we don't know if that's the case yet," Arvidson said.

The three-month mission is led by the University of Arizona, Tucson, and managed by NASA's Jet Propulsion Laboratory.

Meantime, in Cape Canaveral, Fla., managers at the Kennedy Space Center remained optimistic about this evening's launch of the space shuttle Discovery. There is an 80 percent chance that weather will be fine for the 3:02 p.m. MDT launch, said NASA weather officer Kathy Winters.

The shuttle will lift off with a large Japanese science module to be attached to the International Space Station.

Contributing: McClatchy Newspapers