IS THERE LIFE ON MARS?

PASADENA, California (Reuters) - A new chapter in Mars exploration opens on Sunday when a small robotic probe jets down to the planet's arctic circle to learn if ice beneath its surface ever had the right chemistry to support life, mission managers said on Thursday.

NASA approved the mission, known as Phoenix, after the Mars orbiter Odyssey found ice surrounding the polar caps on Mars in 2002.

On Earth, the arctic regions hold the history of the planet's climate changes, which are locked layer by layer into the ice core.

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"This is where the history of life is preserved in its purest form -- organic molecules and cellular bacterial microbes and so forth," Smith said.

"We're wondering if this is true on Mars," he said.

The U.S. space agency faces a formidable obstacle before its new round of Mars studies can begin.

Phoenix has to land in a process that requires it to slow itself from 12,000 mph (19,000 kph) to zero in seven minutes.

"This will be a very nail-biting time for us," said Fuk Li, the Mars Exploration program manager at the Jet Propulsion Laboratory in Pasadena, which oversees Phoenix.

From 170 million miles (274 million km) away, flight controllers will only be able to watch and wait to learn Phoenix's fate. Radio signals from Mars travelling at the speed of light take 15 minutes to reach Earth, so by the time flight controllers learn that the probe has begun its descent it already should have landed.

Finally, Phoenix has to unfurl its solar power panels to begin collecting energy from the Sun. Otherwise its batteries will last just 31 hours.

"All of these events have to occur exactly as planned," said project manager Barry Goldstein. "The team is very confident in that we've done everything we can.