What kind of planets can the spectrograph HARPS see?
HARPS does not directly “see” planets. It detects them indirectly, measuring the velocity at which a star wobbles because of the gravitational pull of one or more orbiting planets. By measuring and analysing these variations in velocity, astronomers can calculate the mass and the orbits of the planets around a star. The less massive the planet, the tinier the effect it produces on the star, and the more precise the instrument needed to detect it is. HARPS is able to detect movements at velocities of just a metre per second — the speed of a person walking — in a star hundreds of light-years away. This has allowed planets only a few times more massive than the Earth to be discovered. HARPS is currently the most powerful exoplanet hunter in the world.
