Dozens of young scientists from all over Europe have gathered this week at Les Houches in Savoie, France, for intensive briefings on ESA's next star- mapping satellite, Gaia. As the successor to the very successful Hipparcos space astrometry project, Gaia was approved last year as an ESA Cornerstone mission to be launched around 2012. Engaging the interest and participation of the next generation of astronomers will be vital for the project's success.

Gaia aims to measure the positions of an extremely large number of stars with unprecedented accuracy. As a result, the distances and motions of the stars in our Galaxy will be determined with extraordinary precision, allowing astronomers to determine our Galaxy's three-dimensional structure, space velocities of its constituent stars and, from these data, further our understanding of our Galaxy's origin and evolution. Photo: ESA

The Hipparcos satellite (1989-93) revolutionized astrometry, the science of star measurement, by fixing the positions, brightnesses, colours and variations of millions of stars in our vicinity far more accurately than ever before. Astrometry was previously a difficult, backwater subject of interest to only a few specialists. Hipparcos changed all that, with results that are still impacting on every branch of astronomy, from comets to cosmology.

Gaia will be 100 times better than Hipparcos. By charting a billion stars, to much greater distances than Hipparcos, it will give an unprecedented picture of the positions and motions of stars across most of the Milky Way Galaxy. Besides transforming the science of stars and galaxies, Gaia will be a top discoverer of asteroids and alien planets.

"Gaia will deliver its first results more than ten years from now," notes Michael Perryman, Gaia's project scientist. "Key individuals have already devoted half their working lives to conceiving and accomplishing Hipparcos, and to inventing Gaia. Who'll pick up the baton when they retire? That's the question."