PASADENA - NASA scientists hailed the Mars rover Curiosity's flawless descent and landing as a "miracle of engineering" on Monday as they scanned early images of an ancient crater that may hold clues about whether life took hold on Earth's planetary cousin.

The one-ton, six-wheeled laboratory nailed an intricate and risky touchdown late on Sunday, much to the relief and joy of scientists and engineers eager to conduct NASA's first astrobiology mission since the 1970s Viking probes.

"We trained ourselves for eight years to think the worst all the time," Curiosity lead engineer Miguel San Martin said. "You can never turn that off."

Mission control engineers at the Jet Propulsion Laboratory near Los Angeles erupted in cheers when confirmation was received that Curiosity, touted as the first full-fledged mobile science lab sent to a distant world, had landed on the Martian surface.

NASA engineers said the feat stands as the most challenging and elaborate achievement in the history of robotic spaceflight, and opens the door to a new era in planetary exploration.

President Barack Obama hailed the accomplishment as an historic "point of national pride."

The landing also marked a much-welcome success and a major milestone for a U.S. space agency beset by budget cuts and the recent cancellation of its space shuttle program, NASA's centerpiece for 30 years.