After a seven-month voyage spanning 300 million miles from Earth to Mars, the Opportunity rover ended up inside a tiny crater to the utter delight of mission scientists.

Imagery from Opportunity is combined to generate this "overhead" view of the rover sitting on its lander at Meridiani Planum. Credit: NASA/JPL Download a larger version of this image here.

The second of NASA's two Mars Exploration Rover safely arrived in an area known as Meridiani Planum at 12:05 a.m. EST (0505 GMT) Sunday. Opportunity was sent there to study a mineral, called gray hematite, which usually forms in the presence of water.

"We knew going in that there are two fundamental geological units here," Steve Squyres, the Mars rover principal investigator, said of the flat plains of Meridiani. "One of them is a thick sequence of layered rocks, fairly light in tone. We do not know what they are. And then draped on top of that is a thin coating of what appears to be some kind of fine-grain material, and that's the stuff we think contains the hematite.

"My fondest hope after looking at pictures from orbit before we landed was that we would land some place that we would be close enough to a crater that we would have a chance of traversing to it and actually getting to the layered material.

"Instead, what has happened is we have scored a 300-million mile interplanetary hole in one and we are actually inside a small impact crater!"

Images taken by Opportunity soon after touchdown revealed the $400 million craft was sitting in a shallow crater about 65 feet in diameter.

"I don't know what the odds would be for us hitting a crater like this, but this is just sensational," said Squyres.

A side wall of the crater is covered with a light-colored layer of fractured rock. This tantalizing rock outcrop along with the surface-covering material means Opportunity has its scientific objectives dead ahead.

"If it got any better, I couldn't stand it," said Dr. Doug Ming, rover science team member.

This "postcard" from Opportunity's panoramic camera shows the strange martian landscape southwest of the rover. Credit: NASA/JPL/Cornell Download a larger version of this image here.

NASA's orbiting Mars Global Surveyor discovered a couple of years ago that Meridiani Planum featured gray hematite, prompting researchers to send a rover to the locale. Opportunity carries a set of sophisticated science tools -- spectrometers, multiple cameras and a rock-grinding device -- to unveil the composition of soil and rock samples.

The rover will probe the hematite to determine if the material is from sediments of an ancient ocean, from volcanic deposits altered by hot water, or from other environmental conditions in the planet's distant past.

"Hematite forms in a number of different ways on Earth but most of them involve the action of liquid water," Squyres said.

The battle cry of NASA's Mars exploration program is "follow the water." Proving that Mars once had liquid water would help to determine if the planet could have supported life long ago.

"Knowing just how the hematite on Mars was formed will help us characterize the past environment and determine whether that environment was favorable for life. One big question, of course, is whether life ever started on Mars. This mission probably won't tell us that, but it may well lead to future mission that can answer that question," said Joy Crisp, rover project scientist.

As Opportunity was descending to the surface, a camera package on the lander snapped three photographs. The imagery shows a much larger crater -- about 500 feet across -- within a half-mile of the landing site.

"It is surely, I think, within our reach," said Squyres.

"The way I envision this mission going: we drive off the lander, we look at the soil, we investigate this hematite mystery, we go to the outcrop, we explore it in some detail because it is right there in front of us, ripe for the pickin', we look at that carefully, we understand that geologic unit, then we climb out of the crater, look around and then head for the big one. And it is going to be a wonderful adventure."

But before Opportunity can depart its lander base, it must first stand up, deploy its wheels and cut a series of umbilicals. Engineers believe it will be the end of next week before the craft rolls onto the surface.

This first image from the lander's descent camera was taken at an altitude of 1,986 meters (6,516 feet). The image spans approximately 1.6 kilometers (1 mile) across the surface of Mars. Credit: NASA/JPL Download a larger version of this image here.

This second image from the lander's descent camera was taken at an altitude of 1,690 meters (5,545 feet). The image spans approximately 1.4 kilometers (7/8 of a mile) across the surface of Mars. Credit: NASA/JPL Download a larger version of this image here.

This second image from the lander's descent camera was taken at an altitude of 1,404 meters (4,606 feet). The image spans approximately 1.2 kilometers (3/4 of a mile) across the surface of Mars. Credit: NASA/JPL Download a larger version of this image here.

Video coverage for subscribers only:
   VIDEO: DESCENT CAMERA IMAGERY WITH EXPERT NARRATION QT
   VIDEO: SCIENTIST DESCRIBES LANDSCAPE AROUND OPPORTUNITY QT
   VIDEO: SUNDAY P.M. SPIRIT & OPPORTUNITY NEWS BRIEFING QT

   VIDEO: CONTROLLERS ANNOUNCE CRUISE STAGE JETTISON QT
   VIDEO: LIVE LANDING COVERAGE FROM ENTRY TO TOUCHDOWN QT
   VIDEO: OPPORTUNITY'S FIRST IMAGES RECEIVED ON EARTH QT
   VIDEO: FIRST COLOR IMAGERY FROM OPPORTUNITY UNVEILED QT
   VIDEO: SCIENCE LEADER NARRATES THE FIRST BATCH OF IMAGES QT
   VIDEO: OVERNIGHT POST-LANDING NEWS CONFERENCE QT
   VIDEO: STATUS BRIEFING ON OPPORTUNITY'S HEALTH QT
   MORE: PREVIOUS MISSION COVERAGE!
   SUBSCRIBE NOW