The French-led Corot mission has taken off from Kazakhstan on a quest to find planets outside our Solar System.
The space telescope will monitor about 120,000 stars for tiny dips in brightness that result from planets passing across their faces.
The multinational mission will also study the stars directly to uncover more about their interior behaviour.
Corot blasted off from the Baikonur Cosmodrome at 1423 GMT, carried into a polar orbit on a Soyuz-2-1b vehicle.
A European Space Agency (Esa) spokeswoman said the take-off had gone smoothly.
However, officials would not know until later whether the satellite had separated from its launcher correctly, she said.
From its vantage point 827km (514 miles) above the Earth, Corot will survey star fields for approximately 2.5 years.
The French space agency, Cnes, is working with six international partners: Esa, Austria, Spain, Germany, Belgium and Brazil.
Ian Roxburgh, professor of astronomy at Queen Mary, University of London, UK, is the Esa scientist on the mission.
"The exciting part of this mission is to look, or to try to find, planets that are similar to the Earth," he told the BBC.
"That is, they'll be somewhat bigger than the Earth, but they'll be made of rocky material able to sustain an atmosphere, and probably provide the sort of environment in which life could form.
Finding a transit will involve a bit luck
"And of course subsequently, many years downstream, we will have more sophisticated measurements, instruments that will look for signatures of life. But at this stage, we need to understand how often there are planets like the Earth around other stars."
Corot will monitor the brightness of stars, looking for the slight drop in light caused by the transit of a planet.
This is a rare event - it relies on the chance alignment of the star and the planet with Earth. As a consequence, Corot must keep an eye on more than 100,000 stars.
With Corot, astronomers expect to find between 10 and 40 rocky objects slightly larger than Earth, together with tens of new gas giants similar to our Jupiter, in each star field they observe.
Every 150 days, Corot will move to a new field and begin observing again.
Its first target field is towards the centre of our galaxy, the Milky Way. Its next will be in the direction of the constellation Orion.
Corot's instrumentation is also designed to detect the subtle variation in a star's light caused by sound waves rippling across the surface. These waves are the equivalent of seismic waves on the Earth.
By studying these "starquakes", astronomers can gain a detailed insight into the internal conditions of the star.
Corot stands for "Convection Rotation and planetary Transits".
The satellite is the first of a number of spacecraft that will hunt and study distant planets over the next few years.
1. 4CCD camera and electronics: Captures and analyses starlight
2. Baffle: Works to shield the telescope from extraneous light
3. Telescope: A 30cm mirror; it views the star fields
4. Proteus platform: Contains communication equipment, temperature controls and direction controls
5. Solar panel: Uses the Sun's radiation to power the satellite