At about 10:31 p.m. Pacific time tonight, when most of the country is asleep, NASA Mars rover team leader Dawn Sumner will be experiencing long minutes of space program terror.

The terror comes from the uncertainty that faces NASA's Curiosity rover when it enters the thin Martian atmosphere at 1,000 mph.

The goal is for the Mini Cooper-sized craft to execute a highly complex and as yet unproven landing process that is designed to put it safely inside Mars' 96-mile-wide Gale crater.

Landing on Mars and then having a fruitful mission have never been a given. NASA's success rate for such missions is only 40 percent.

A lot is riding on this $2.5 billion mission – both for science, where the goal is to establish whether Mars could have supported life, and for NASA, which has seen its Mars explorations budgets cut drastically recently.

An epic failure would be catastrophic, said Sumner, who is on the geology faculty at the University of California, Davis, and co-investigator on the NASA rover team at the Jet Propulsion Laboratory in Pasadena.

"It will be an adrenaline rush, but I tend to be an optimist," Sumner said via phone from Pasadena.

The roughly 350 million miles that separate Earth from Mars mean there is a 14-minute delay in communication time. "By the time word gets to us about what has happened it will all be over already," Sumner said.

The Curiosity program is the most ambitious and scientifically thorough rover program ever attempted by NASA. Launched last November, Curiosity is the fourth NASA rover mission to Mars. It has been termed the "Hubble Telescope" of rover missions for its capacity to look deeply into areas that are currently unknown to planetary scientists.

The rover will offer NASA scientists nothing short of a traveling lab to work with. The plum would be finding evidence of organic material that could later support the development of life. NASA has not attempted to find that since the Viking landers of the 1970s.

The rover boasts a laser, dubbed ChemCam, that can vaporize rocks to study their chemical composition. Also included is a mini-lab that sports 74 cups for studying rocks the rover will pulverize.

The rover will also relay the first true color images of the planet. Prior rover missions shot in black and white; filters and color enhancers were added to photos.

As co-investigator, Sumner is in charge of culling information from data sent back from the rover. "We will be looking for rocks that are 3 billion years old," she said.

Old rocks, or "early Earth" rocks are something Sumner knows well. She has spent most of her professional life studying them and their significance. She has studied them in places as far-flung as South Africa, western Australia and Antarctica.

She said the Gale crater location is ideal in that it mirrors the timeline-like structure of rock formations found in the Grand Canyon – where tens of millions of years of rock and environmental change are arranged in strata, chronologically.

It has already been established that water – a major building block for the development of life – has flowed on the Martian surface.

Evidence of organics? So far that has gone wanting.

"We want to know how much water was present there. Were there lakes, or was it dry?" Sumner said.

A successful mission may go a long way to making any subsequent Mars rover exploration missions a reality, she said.

"Unfortunately, space exploration tends to be a fairly political issue and the funding for it changes a great deal," she said.

Last February, the Obama administration proposed a 2013 budget that included lopping off 40 percent of NASA's Mars exploration budget, said G. Scott Hubbard, former director of NASA's Mars exploration program and current aeronautics and astronautics professor at Stanford University.

"This mission is huge," said Hubbard. "It will play a critical role in attempting to convince Congress to restore funding for planetary science, and Mars in particular."

In 2000, Hubbard served as NASA's first Mars program director and was charged with refocusing the Mars exploration program in the wake of Mars Climate Observer and Mars Polar lander failures in 1999.

Hubbard feels that, as it stands, the Curiosity rover mission may be the last of its kind for a while.

In the near term, the goal in the planetary exploration community is to send a rover to Mars that is capable of sending samples back to Earth.

"This would offer us dozen of labs and hundreds of investigators to examine the samples," Hubbard said.

But current budget cuts make that a dim prospect. Such a mission was previously slated for 2016, but now won't happen until the 2020s, if at all.

"After all this effort, we are truly on the verge of understanding the habitability of life on Mars," said Hubbard. "To stop now would be a scientific tragedy.

Sumner concurs, and believes what is gleaned by Curiosity may deeply influence the way humanity sees itself.

"A question that has been central to all cultures on Earth is 'What is our purpose?' and 'Who are we?' " she said. "If there is evidence of life elsewhere then that fact will have a strong influence on how people think about themselves."

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