New satellite to study alien planets

Artist impression of Cheops
29 October 2012
From Earth, we can sometimes see Venus and Mercury as black spots passing across the Sun. During such events – called transits - the planet blocks a tiny amount of light, making the Sun appear slightly dimmer. Similar dimming events can be caused by exoplanets – worlds that orbit more distant stars. Now ESA has decided to develop a new science mission to search for these transits.
The mission, known as CHEOPS (short for CHaracterising ExOPlanets Satellite), is expected to be launched in 2017. It will target bright, nearby stars already known to have some planets in orbit around them. The spacecraft will monitor each star’s brightness with high precision, searching for the telltale signs of a transit.
Planet transit in front of a star
Planet transit in front of a star
Detailed analysis of changes in the incoming starlight will allow the diameter of each transiting planet to be measured very accurately. For those planets with a known mass, it will be possible to calculate their density, providing clues to their internal structure.

Knowledge of the exoplanets’ sizes and masses will help scientists to understand the formation of planets from a few times the mass of the Earth – ‘super-Earths’ – up to Neptune-sized worlds. It will also identify planets with sizeable atmospheres, which will be ideal targets for more detailed studies by the next generation of telescopes. These include the ground-based European Extremely Large Telescope and the James Webb Space Telescope.

CHEOPS is being developed by ESA and Switzerland, with some other ESA Member States also taking part. The satellite will fly in a near-polar orbit, some 800 km above the Earth, and operate for 3 ½ years.