Image caption Corot and other telescopes measure the light change when a planet "transits"

Ten new planets outside our Solar System have been spotted by the French-led Corot satellite, bringing the total number of known exoplanets to 561.

They include one planet orbiting an unusually young star, and two Neptune-sized planets orbiting the same star.

Corot, launched in 2006, spots planets by measuring the tiny dip in stellar light that occurs when planets pass between the stars and the Earth.

It has now added 23 planetary systems to the ever-growing roster.

Corot, operated by France's space agency CNES, was launched in late 2006. It went into orbit shortly before Kepler, a similar mission by the American space agency Nasa.

Originally scheduled to run only until mid-2008, its remit has since been extended to 2013.

It has since established itself not only as a planet-hunter but also a precise instrument for astroseismology - the study of the composition of stars based on the light they emit.

In the latest list of 10 exoplanet finds, seven are so-called "hot Jupiters", gas giant planets similar to our own Jupiter but far closer to their host star - completing their orbits in just days.

Two more orbit the star Corot-24, with diameters equal to and about 1.4 times that of Neptune, completing their orbits in five and 12 days, respectively.

One of the hot Jupiter planets orbits the star Corot-18, which is believed to be just 600 million years old. This is of particular interest to astrophysicists because there is much to be learned from the earliest stages of planet formation.

"If we want to understand the conditions in which planets form, we need to catch them within the first few hundred million years," said Suzanne Aigrain, a University of Oxford astrophysicist who is part of the Corot team.

"In the case of Corot-18, different ways of determining the age give different results, but it's possible that the star might be only a few tens of millions of years old. If this is confirmed, then we could learn a lot about the formation and early evolution of hot gas giant planets by comparing the size of Corot-18b to the predictions of theoretical models."