The site for NASAs next Mars landing appears to be more hilly and hazardous than mission planners initially had thought, but for now there is no plan to steer the Mars Polar Lander to a backup touchdown site, a scientist said Friday.

Scientists and engineers used preliminary mapping data in August from the Mars Global Surveyor -- a spacecraft already orbiting Mars -- to choose what they thought was a smooth landing site for the lander, now just six weeks from arriving at a site close to the Red Planets south pole.

"We do see more structure in the site, but we still believe the spacecraft can land safely in the error ellipse," Zurek said. "Right now, Id say were sticking with the primary site."

Up to one or two percent of the swath chosen for the landing the error ellipse may pose a danger to the three-legged craft, were it to set down there, he said.

There would be no way for the spacecraft to navigate around such hazards just before it set down on December 3, but scientists and engineers now have a week to go before a maneuver during which they could keep the craft pointed at a primary landing site or slow it down to set down at a back-up landing site 200 kilometers away. The mission team will use the latest data on the landing site to decide which of the two selected sites is safest, Zurek said. Both are on layered terrain, which intrigues scientists.

Mission planners overseeing planetary landings and space destinations routinely must balance the wishes of scientists for complex, data-rich sites with the more conservative tack of flight engineers, hoping to preserve spacecraft.

A final decision for Polar Lander will be made in the next week to give flight engineers enough time to prepare for a thruster firing on October 30 the last opportunity to steer the craft toward one of the two landing sites.

Carbon dioxide frost covering both sites complicates the choice, Zurek said.

"Its difficult to see whats a shadow and whats a change in surface frost coverage," he said.

However, the mission team found no evidence of extreme hazards and there is no sense of panic with the new data from Mars Global Surveyor, he said.

"Its not like, Oh my word, the whole site is filled with giant rocks," Zurek said. "Its more a matter of, there is risk in going to any site on layered terrain because we dont know what this material is like when youre really on the surface. Thats why we want to go there."