NASA on Monday chose a University of Colorado proposal for a $485- million US mission to Mars, nine months after a conflict of interest derailed the original selection process.

NASA chose the University of Colorado's proposal to study the Martian atmosphere from 20 other ideas to study Mars that were trimmed to just two before a conflict of interest was declared.

The delay raised price of the probe by $10 million US, postponed the launch by two years and cut the science-gathering portion of the mission in half to one year, a NASA official said.

NASA has not disclosed what the conflict of interest was or who it involved, other than to say last year that it was not created by NASA but by one of the two groups. The space agency said last December that a "serious" conflict of interest in one of two proposals forced it to disband the board formed to pick the winner, and create a new panel to award the contract.

NASA on Monday said there is no more conflict of interest because the two finalists submitted new proposals and "the conflict in the original reports was irrelevant to the evaluation and the selection decision."

Officials maintained they still cannot disclose details because it involved "proprietary information." That information has been destroyed, NASA said.

Bruce Jakosky, associate director for the Colorado lab and principal investigator for the mission, said the conflict was not with the Colorado proposal.

The other finalist was the Southwest Research Institute in San Antonio. In December, a Southwest spokesman declined to comment on the delay or questions about the conflict; that group could not be reached for comment after business hours on Monday.

The Mars Scout program had originally been scheduled for 2011 launch. But since Mars only comes close enough to Earth to launch probes every 26 months, NASA had to postpone the mission to 2013.

The mission will focus on the Martian atmosphere, how it evolved and lost its water, becoming the desolate place it is now.

Because of the delay, the science mission will be cut from two years to one, Jakosky told the Associated Press. That's because the probe will be launched later in the solar cycle and after one year in orbit there will be considerably fewer solar events to study. But the science will still get done, he said.

"We're trying to learn the history of the atmosphere and the history of the water," Jakosky said. And that is done by studying how the sun and Martian atmosphere interact now.

The probe will carry instruments to measure characteristics of Mars' atmospheric gases, upper atmosphere, solar wind, and ionosphere — a layer of charged particles high in the Martian atmosphere.