The French-led Corot mission has spied its first planet - a very hot world bigger than Jupiter - passing in front of a far-off star.
The spacecraft was launched on 27 December last year and is the first to hunt for Earth-like planets from space.
Corot scientists said to find a planet so early on "significantly exceeded pre-launch expectations".
The new body is called Corot-exo-1b and can be found 1,500 light-years away in the constellation of Monoceros.
Corot hunts for planets by monitoring stars for tiny dips in brightness that result from objects transiting their faces.
The instrumentation onboard the 650kg (1,400lb) satellite is so sensitive that it is capable of detecting rocky exoplanets (the term used to describe planets outside our Solar System) just a few times bigger than Earth.
For the next two and a half years, Corot will observe more than 100,000 stars in the hope of discovering other habitable worlds.
Dr Suzanne Aigrain, a co-investigator on the mission and an exoplanet expert from the University of Exeter, UK, was pleased to have found a planet so soon after the launch.
She told BBC News: "It's a giant planet of similar basic structure to Jupiter, but bigger; it is about 1.3 times more massive than Jupiter and has approximately 1.5 to 1.8 times the radius.
"It's a lot closer to its star, which is quite similar to our Sun, and it orbits it every 1.5 days."
The discovery of this large planet indicated that the onboard systems were working well and that discovering smaller, Earth-like planets was well within its grasp, she said.
The spacecraft has also been able to carry out its first asteroseismological observations of a star.
This technique is similar to seismology, which uses earthquake waves to study the Earth's interior. But instead, Corot monitors the subtle changes in light created as "starquakes" - waves generated deep inside a star - ripple across the star's surface.
Analysis of this data, which is still being undertaken, will be used to determine the star's mass, age and chemical composition.
Dr Aigrain said: "Although it will take us some time to analyse the data more systematically as it continues to stream in, the impressive data quality, and the rapid co-ordinated response of the science team on the ground, bode extremely well for the future of the mission."
Corot is a co-operative project between the French space agency Cnes and international partners Esa (European Space Agency), Austria, Belgium, Brazil, Germany and Spain.