VOA常速英语:ESA Spacecraft to Land on a Comet

After a long flight through deep space, a European Space Agency probe is finally approaching its target - a comet millions of kilometers away from earth. Scientists say the mission may lead to some startling discoveries about the origins of the water on earth.

Ten years ago, a European Space Agency rocket took off with a spacecraft called Rosetta, on a mission to perform the most detailed study of a comet.

While asteroids are large rocks, almost like small planets, comets are mostly made of ice, says Ralph Cordey, the business manager for Airbus Defense and Space, which built the Rosetta spacecraft.

“We know today that our Earth has a great deal of water on it, we don't know exactly where it came from and it's likely that comets had a lot to do with that process," said Cordey.

It took more than 10 years for Rosetta to make three swings around Earth and one around Mars - gathering enough speed to reach the comet named 67P / Churyumov-Gerasimenko, 400,000 kilometers from Earth.

For the last two-and-half years many of its onboard systems were in the sleep mode to save energy, says Airbus engineer Simon Barraclough.

“So when we're close to the Sun, a lot of things are on. When we're further from the Sun, a lot of things are off," said Barraclough.

A 'wake-up call' in January brought cheers in the mission headquarters in Darmstadt, Germany, as a signal from Rosetta indicated that its computer was wide awake again.

The spacecraft will soon start orbiting the comet at a distance of about 10 kilometers, taking measurements and mapping its surface.

In November, it is scheduled to release a smaller probe called Philae, which will land on the comet.

Cordey says both Rosetta and Philae will measure the comet’s gas and dust and send pictures of its surface.

“It will also have a very nice radar system onboard it which will communicate with the orbiting spacecraft - the mothercraft - and use the radar signals to probe the heart of the comet's nucleus. So it's not just looking at the surface or the environment around it, it's actually going to be probing what's underneath the surface," he said.

The probes will travel with the comet for a full year.

Rosetta will continue measuring how the comet changes as it approaches the sun and starts to warm up, while Philae will analyze samples of the its surface and subsurface.