CAPE CANAVERAL, Fla. -- NASA's Mars Science Laboratory is on track for an August arrival at the red planet and will land closer to prime scientific targets than previously expected, officials said Monday.

Consequently, its car-sized Curiosity rover won't have to travel as far -- and it won't take as long -- to get to a three-mile-high mountain in the middle of a giant gaping chasm known as Gale Crater.

And that's a big deal, scientifically. "The earlier we get there, the more time we have for science," said Pete Theisinger, the Mars Science Laboratory project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"It gets us closer to the base of Mount Sharp, where the primary science targets are," said John Grotzinger, MSL project scientist at the California Institute of Technology, also in Pasadena.

"So this is really an optimum outcome." Launched last November on an Atlas V rocket from Cape Canaveral Air Force Station, the lab and its rover are cruising toward a 1:31 a.m. EDT Aug. 6 landing in Gale Crater.

Almost 100 miles wide, the crater is located just south of the Martian equator on the eastern side of the planet. It's most impressive feature: a central mountain that rises higher than Mount Rainier looms above Seattle. Planetary geologists think the low-lying crater floor once was wet with water. The mountain's foundation is made up of sedimentary rocks.

That base is topped with layer after geological layer of material laid down in sequential stacks. Scientists think the strata will show the epoch-by-epoch geological evolution of the east-central region of Mars. The Curiosity rover is equipped with instruments that can determine whether Mars is, or ever could have been, a planetary home for primitive life.

It cannot detect life directly. But it can detect evidence of water and carbon compounds. Water, carbon compounds and energy, such as sunlight, are key to the formation of life.

Project officials say the laboratory's systems all are operating as expected, and an upgraded version of flight software was transmitted to the spacecraft two weeks ago. Two trajectory correction burns and new trajectory analyses enabled project officials to narrow a target ellipse inside the crater.

Project scientists still are investigating the potential effects of Teflon contamination created during the operations of a rover drill. Grotzinger said debris created by the drill would complicate -- but not prevent -- analyses of rock and soil samples that might contain carbon compounds.

NASA detected the problem prior to launch. But officials determined it was too late to replace the drill and still make a relatively short launch period in late November and early December. The mission would have had to be delayed two years until Earth and Mars once again aligned in a way to make the flight possible. The delay would have cost more than $560 million.

Curiosity will be traveling 13,200 mph when it reaches the top of the thin Martian atmosphere -- a point about 78 miles above the planet's surface. For the first time, a spacecraft will make a guided atmospheric entry.

The spacecraft will steer itself through the atmosphere -- rather than making a ballistic dive. A complicated, new "sky crane" that works like a heavy-lift cargo helicopter will be used in an attempt to place the rover on the ground.

Project officials are trying to downplay expectations for the $2.5 billion flagship mission. "We've done everything we can prudently to ensure the greatest probability of success. But the reality is that this is a very risky business," said Dave Lavery, the MSL program executive at NASA Headquarters in Washington, D.C.

Historically, only 40 percent of Mars missions have been successful, he said. "There is never a guarantee of success."

By TODD HALVORSON, Florida Today