Pasadena, Calif. ? NASA’s Opportunity rolled off its lander and onto the rusty soil of Mars early Saturday, a week after the six-wheeled rover arrived on the Red Planet — and just hours after confirmation of its first major geologic discovery.

Scientists at NASA’s Jet Propulsion Laboratory erupted in cheers as the first photograph taken by Opportunity after its roll-off appeared on a screen in mission control. More pictures flooded in minutes later to continued cheers and applause.

The images, received shortly after 3 a.m., confirmed Opportunity had joined its twin, Spirit, on the ground.

“Two for two, one dozen wheels on soil,” flight director Chris Lewicki said.

Hours earlier, scientists confirmed that the rover discovered gray hematite, a mineral that typically forms in water — a finding that could indicate the dry and dusty Red Planet was once wetter and more hospitable to life.

Rowdy, jubilant scientists filled the back of the auditorium for an early morning news conference, sipping champagne as they listened.

The initial black-and-white picture taken by Opportunity’s rear hazard camera showed the rover’s empty lander and a parallel set of tracks leading away from it, traced in the pebbly Martian dirt 128 million miles from Earth.

Opportunity took 83 seconds to cover the 10 feet to the dark floor of the 72-foot-wide crater where it landed.

“That was probably the scariest part of the drive we’ll have on Mars,” said mission manager Jim Erickson.

The roll-off went without a hitch, said Kevin Burke, who gave the roll forward command to Opportunity.

Mission plans called for Opportunity to spend several days parked beside its lander after rolling off, allowing it to conduct further chemical and elemental analysis of the Martian soil.

The iron-rich hematite was detected by Opportunity’s minithermal emissions spectrometer, a heat-sensing instrument nicknamed Mini-TES. Another NASA spacecraft previously spied the mineral on Mars from orbit.

“Mini-TES has indeed discovered hematite on the surface of Mars,” instrument scientist Phil Christensen, of Arizona State University, announced during the news conference.

Preliminary evidence suggests the hematite formed in low-temperature chemical reactions in liquid water, Christensen added. NASA designed the $820 million double-barreled mission to seek exactly that sort of geologic evidence.

Spirit has rolled just a short distance across the rockier surface at its landing site. Software problems drew its mission to a temporary halt on Jan. 21. NASA expected Spirit to fully recover by today.