CAPE CANAVERAL, Fla. — With the roar of an Atlas 5 engine, NASA on Saturday began its boldest venture yet to another planet — sending the Mars Science Laboratory on an eight-month journey expected to provide more detailed information about whether the red planet is, or ever has been, hospitable to life.

After a one-day delay to replace a faulty battery, the launch went off flawlessly at 10:02 a.m. EST, the rocket rising on a column of white smoke into a blue sky mottled with puffy cumulus clouds.

“Whew! That felt so good,” said Joy Crisp, a deputy project scientist with NASA’s Jet Propulsion Lab in La-Canada Flintridge, as the rocket trailed out of sight. “That was spectacular!”

Its payload was the rover Curiosity, the largest and most sophisticated in a series of robotic vehicles that NASA has sent to Mars. Built at the Jet Propulsion Laboratory, Curiosity is a six-wheeled, one-ton vehicle the size of a compact car that is bristling with an array of sophisticated scientific gadgets.

Its mission, NASA officials have stressed, is not to find life on Mars, but to find out whether life ever could have existed there in the form of microbes, tiny organisms that are abundant on Earth. It also will try to find further evidence to suggest whether astronauts could survive on Mars, part of NASA’s long-term plan to send a manned mission there.

“I like to say it’s extraterrestrial real estate appraisal,” Pan Conrad, a NASA astrobiologist, said at a pre-launch briefing earlier in the week.

Forty-three minutes after launch, a second stage rocket fell away, leaving the science lab capsule on its own. Control of the spaceship then shifted from the Kennedy Space Center to JPL, which will run the mission for its duration, expected to be a minimum of two years.

A group of JPL scientists and engineers at Kennedy burst into applause when the capsule separated from the rocket. Like most people associated with the mission, the successful launch left them excited and relieved. Many have worked on the Mars Science Laboratory for nearly a decade and had to endure a two-year delay when the project missed its original launch date.

Pete Theisinger, the project manager at JPL, couldn’t stop grinning when he got up to speak at a news conference after the launch. “Our spacecraft is in excellent health and it’s on its way to Mars,” he said. “Any questions?”

The lab faces a journey of 354 million miles. (Although Mars is less than half that distance from Earth, the fact that it is a moving target makes the trip longer.) It is due to land in spectacular fashion just after 1 a.m. EDT on Aug. 5.

Because of the size of the rover, NASA decided that its previous landing technique, in which vehicles were bounced onto the surface of the planet on air bags, would not work. So Curiosity, after being slowed in its descent by parachutes, will be lowered softly — NASA hopes — on long bridles using a sky crane technique modeled after those used by helicopters.

Once on the ground, NASA intends for the rover to spend one Martian year, or about two Earth years, exploring an area called Gale Crater, the site of a gently sloped, 3-mile-tall mountain made of sedimentary rock. As with prior missions, there is the likelihood that the rover will keep going after its two-year “warranty” expires.

Scientists hope that as the rover ascends the mountain, the rock will tell the geologic history of the area — and ideally suggest whether the planet could have supported life. That would require the presence of three things: water, energy and carbon. The first two have been established as existing on Mars, but previous missions have not allowed scientists to determine whether there is carbon.

“We’re basically reading the history of Mars’ environmental evolution,” John Grotzinger, the project’s chief scientist, said at one of the pre-launch briefings. However, he has been at pains to tamp down expectations.

“It’s like looking for a needle in a haystack,” he said, “and the haystack’s as big as a football field.”

Scientists believe it is more likely that Curiosity will find other indications of environmental conditions that point toward the possibility that life once existed on Mars, when it was warmer and wetter than it is today.

The researchers said they were excited by the opportunity to deploy some of Curiosity’s new technology. One gadget, called a “chem cam,” will use a laser to zap rocks, then analyze the resulting sparks with a spectrometer to identify the chemical elements in the material.

Curiosity also has a lab in its belly that will allow it to take soil and rock samples, analyzing their chemistry and mineralogy. And it will deploy an array of cameras to bring back high-definition still photographs and videos to Earth.

Such technology doesn’t come cheap, and NASA officials were asked Saturday if they could justify the $2.5 billion being spent on the Mars Science Lab at a time of great need. Grotzinger said the cost, divided among the entire U.S. population, amounted to no more than the cost of a movie ticket per person. (It works out to about $8.)

“I’ll leave it to you whether that’s a movie you want to see,” he said, adding: “This is the stuff that fuels kids’ imaginations to go into science and engineering…. I think that’s a great investment.”