Mars Phoenix to try shake-and-bake once more

The problem is, the opening to the oven is about the thickness of a pencil lead. The Martian soil is proving to be much clumpier -- cemented, in scientific terms -- than expected.

Late last week, the lander's nearly 8-foot-long robotic arm dumped a cup full of soil on top of oven No. 4. But none of the particles fell through the guard screen into the oven.

Over the weekend, the science team at the University of Arizona and the Jet Propulsion Laboratory in La Cañada Flintridge ordered the instrument containing the ovens, the Thermal Evolved-Gas Analyzer, to shake the soil in an attempt to break it up.

That didn't work either. Images beamed down from the site where Mars landed May 25 showed that the shaking had shifted the mound of soil. A few tiny particles fell into the oven, but the sample was too small to test, according to William Boynton, the lead scientist for the TEGA instrument.

"The soil appears to be quite cloddy," Boynton said.

The clumpiness could be caused by any of several factors, including the presence of water. Ice is thought to lie inches below the lander. Another condition that could cause soil adhesion is the presence of salts in the dirt, possibly laid down millions of years ago when liquid water flowed on the surface of Mars.

At a news briefing Monday at the University of Arizona, Boynton said it was too soon to start worrying that the instrument, one of the key elements of the $420-million mission, would not be able to do its job. The scientists now think the robotic arm simply delivered too much soil in too big a lump.

Boynton said the science team would try one more time to shake the soil into the oven before switching to a strategy of dribbling the soil out in a narrow stream.

The problem with the oven is the latest in a series of glitches to set back the mission's timeline. Ideally, Boynton said, they would by now have completed the first analysis of the Martian surface and would be well on the way to digging into the ice layer.

Unlike NASA's twin Mars rovers, Spirit and Opportunity, which are now in their fourth year of operation, Phoenix is designed to last only three months.

When winter arrives, the lander will be covered in carbon dioxide ice.

Without the sun to charge its batteries, the lander will expire before the next spring arrives.

The U.S. has been sending spacecraft to other planets for more than three decades, but Phoenix is the first to hunt for water, the foundation of life as we understand it.

The discovery of complex organic compounds could indicate that some rudimentary forms of life may once have existed, or might still exist, on Mars.

john.johnson@latimes.com