High Accuracy Radial Velocity Planet Searcher

Characteristics

The HARPS can attain a precision of 0.97 m/s (3.5 km/h), making it one of only two instruments worldwide with such accuracy. This is due to a design in which the target star and a reference spectrum from a thorium lamp are observed simultaneously using two identical optic fibre feeds, and to careful attention to mechanical stability: the instrument sits in a vacuum vessel which is temperature-controlled to within 0.01 kelvins. The precision and sensitivity of the instrument is such that it incidentally produced the best available measurement of the thorium spectrum. Planet-detection is in some cases limited by the seismic pulsations of the star observed rather than by limitations of the instrument.

The principal investigator on the HARPS is Michel Mayor who, along with Didier Queloz and Stéphane Udry, have used the instrument to characterize the Gliese 581 planetary system, home to one of the smallest known exoplanets orbiting a normal star, and two super-Earths whose orbits lie in the star's habitable zone.

It was initially used for a survey of one-thousand stars.

Since October 2012 the HARPS spectrograph has the precision to detect a new category of planets: habitable super-Earths. This sensitivity was expected from simulations of stellar intrinsic signals, and actual observations of planetary systems. Currently, the HARPS can detect habitable super-Earth only around low-mass stars as these are more affected by gravitational tug from planets and have habitable zones close to the host star.