I’m old enough to remember a time when some people thought we’d never discover planets beyond the solar system. It’s not that long ago that astronomers first managed to confirm the existence of a few exoplanets. Techniques improved, and the number of known exoplanets started to increase rather rapidly. Then the Kepler mission was launched, and the number of candidate exoplanets simply rocketed (at the time of writing, Kepler has identified 2321 exoplanetary candidates). That’s impressive progress.
Now that astronomers have identified so many exoplanets, it becomes possible to design a mission that can study those bodies in more detail. That’s precisely what the CHEOPS mission will do. (Yes, CHEOPS is yet another acronym. This one stands for CHaracterising ExOPlanets Satellite.) ESA have selected CHEOPS for study as the first “small” or S-class mission.
If all goes well, CHEOPS will launch in 2017 and study stars that we know have planets around them. The satellite will monitor a star’s brightness, looking for the characteristic dip in brightness as a planet transits. This measurement will allow astronomers to determine the radius of the transiting planet; if the planet’s mass is already known from other measurements then astronomers will be able to calculate the planet’s density. This in turn will provide clues about the planet’s internal structure. CHEOPS will tell us a lot about the formation and evolution of planets with a similar mass to Earth. And, just as Kepler has provided targets for CHEOPS to study, CHEOPS in turn will provide targets for follow-up study by the next generation of powerful telescopes such as E-ELT.