Europe's first Mars (search) probe streaked toward a risky Christmas landing early Thursday, while ground controllers readied its trailing mother ship to enter Martian orbit in a maneuver critical to the success of the mission.

Beagle 2 (search), which separated on Friday from the larger Mars Express orbiter (search), was expected to enter the Martian atmosphere at about 3:45 a.m. Christmas morning (9:45 p.m. Wednesday EST) — Mission Control time. It's supposed to land minutes later using parachutes and gas bags to cushion the impact.

At about the same time, Mars Express will fire its main engine for 34 minutes to slow it into orbit, a maneuver critical to the mission's success.

But controllers will have to wait several hours or even days to pick up the first signals from Beagle 2, if it survives the fiery 7-minute plunge through the Martian atmosphere.

The 143-pound lander, shaped like an oversized wok, won't communicate until it can open its solar panels and charge its batteries using the sun's energy.

Confirmation that the Mars Express successfully entered orbit also won't come for several hours, until it emerges from the far side of the planet.

With less than two hours to go to the maneuvers, flight director Michael McKay (search) said the mission was going "absolutely brilliantly."

"The focus level is extremely high. You could cut the excitement with a knife — not stress, excitement," McKay said.

Mission controllers sent the last commands to Mars Express Wednesday morning, telling it to heat its fuel tanks and switch off nonessential equipment so it won't interfere with the maneuver.

"We have loaded the sequence and then we have switched off as many systems as possible — everything that is not absolutely needed," said mission control spokeswoman Jocelyne Landeau-Constantin. "Everything is going fine."

The first chance to hear from Beagle 2 — named for the ship that carried naturalist Charles Darwin on his voyage of discovery in the 1830s — comes Christmas morning in Europe when the U.S. Mars Odyssey spacecraft, already orbiting the planet, has a chance to pick up and relay a signal.

If that doesn't work, the Jodrell Bank Observatory (search) in Britain will try to pick up Beagle's signal later Christmas Day.

Mars Express' entry to orbit is critical for the mission, since the mother craft will relay Beagle's scientific data back to earth.

It won't be in position to make contact with Beagle until Jan. 3 because its initial orbit is too high and will have to be corrected.

Beagle is designed to use a robotic arm to sample surface rock and soil for signs of past or present life.

Meanwhile, Mars Express will orbit overheard for at least a Martian year, or 687 Earth days, probing as deep as 2.5 miles below the surface with a powerful radar to look for underground water. It will also map the surface with a high-resolution stereo camera.

Scientists believe that billions of year ago Mars may have had enough liquid surface water to support life, and that life might have survived in cavities underground. The planet's surface has features that some think could be dry riverbeds and ancient coastlines.

But getting there is risky. Of 34 unmanned American, Soviet and Russian missions to Mars since 1960, two-thirds have ended in failure.

The United States successfully landed two Viking craft in 1976 and Mars Pathfinder in 1997, but two years later lost the Mars Polar Lander during descent. Japan this month abandoned a Mars mission after failing to position the Nozomi probe on planetary orbit.

NASA's Spirit, one of two identical robot explorers, is expected to land Jan. 3. Its sibling, Opportunity, is scheduled to settle on the opposite side of the planet Jan. 24.

European controllers won't give up if no signal from Beagle 2 is detected Thursday. For one thing, NASA's Odyssey craft should have more than one chance in the following days to make contact.

"It doesn't have to mean anything," mission control spokesman Bernhard von Weyhe said. "It can mean it needs more time to be unfolded, or it's at a funny angle."

If all goes well, Beagle is expected to transmit its first pictures from Mars as early as Dec. 29-Dec. 31. The first radar pictures from Mars Express are expected in the spring.