PASADENA, Calif. (Reuters) - NASA's second Mars rover, Opportunity, scored "an interplanetary hole-in-one" by safely landing inside a shallow impact crater, coming face to face with the first exposed bedrock ever seen on the Red Planet, mission scientists said on Sunday.

The spacecraft's textbook arrival on Saturday came as mission controllers at NASA's Jet Propulsion Laboratory made progress in pinpointing the cause of a malfunction that has idled Opportunity's twin rover, Spirit, on the opposite side of Mars.

As planned, Opportunity touched down in the heart of a wide, flat plain known as the Meridiani Planum, an area believed to contain large deposits of a crystalline, iron-bearing mineral called hematite, which on Earth usually forms in the presence of water.

But the exact landing site could hardly have been more ideal, NASA scientists said.

In a stroke of luck, Opportunity came to rest inside a small, shallow crater -- roughly 65 feet wide and 6 feet deep -- and just a few feet from the intriguing bedrock formation visible on the inside lip of the crater.

"We have scored a 300-million-mile, interplanetary hole in one, and we are actually inside a small impact crater," Steve Squyres, the principal science investigator for the rover mission, told reporters at a Sunday afternoon briefing.

The first pictures beamed back from Opportunity hours after landing showed a terrain unlike any previously seen on the martian surface.

Besides the first bedrock ever found, much of the landing zone appeared darker in color and draped in fine-grain red and gray soils devoid of the rocks and boulders littering other areas on Mars, including Spirit's surroundings in Gusev Crater, a massive basin thought to be the site of an ancient lake bed.

The exposed bedrock was a particularly exciting discovery.

"The beauty of bedrock is you know where it came from," Squyres said, contrasting the terrain with the "churned-up" surface at Gusev Crater. "This is the home neighborhood of these rocks."

HISTORIC FEAT

Squyres said he was further intrigued by a soil texture that looked pebbly, but, where touched by the lander, seemed to have the consistency of talcum powder. He said the fine soil is believed to be the hematite-bearing material that made the Meridiani Planum a target of exploration in the first place.

With the landing of Opportunity at 9:05 p.m. PST Saturday, (12:05 a.m. EST) Sunday, the U.S. space agency has achieved the historic feat of successfully setting down two robotic rovers on Mars, just three weeks apart, to search for signs that the barren planet was once wetter, and more hospitable life, than it is now.

Encased in a protective cluster of air bags upon landing, Opportunity initially came to rest on its side but righted itself as it was designed to do. Still in a compact crouch for its seven-month, 283-million-mile journey from Earth, the rover then unfurled its solar panels to charge its batteries and began sending pictures and data back to Earth.

Barring unforeseen complications, the six-wheeled vehicle will roll off its landing platform in a week and a half or two weeks to begin exploring its surroundings.

While Opportunity emerged from its descent and bouncy landing in perfect health, NASA engineers said they would take their time preparing the rover for its first excursion, taking into account lessons learned from a malfunction this week that paralyzed Spirit.

Scientists believe they have traced the problem to a glitch in Spirit's memory and can work around or cure it within a few weeks. Using the analogy of a hospital patient's condition, Mars exploration rover project manager Pete Theisinger said Spirit's status "is still serious, but ... I think we've got a patient that is well onto its way to recovery."