The HARPS team led by Michel Mayor from University of Geneva, Switzerland, announced the discovery of more than 50 new exoplanets orbiting nearby stars, including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star.
This is the largest number of such planets ever announced at one time. By studying the properties of all the planets found so far, the team using ESO’s world-leading exoplanet hunter HARPS has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.
Artists’s impression of the rocky super-Earth HD 85512 b (ESO/M. Kornmesser)
“The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” says Mayor.
In the eight years since it started surveying stars like the Sun using the radial velocity technique HARPS has been used to discover more than 150 new planets. About two thirds of all the known exoplanets with masses less than that of Neptune were discovered by HARPS. These exceptional results are the fruit of several hundred nights of HARPS observations.
Working with HARPS observations of 376 Sun-like stars, astronomers have now also much improved the estimate of how likely it is that a star like the Sun is host to low-mass planets. The majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.
“These planets will be among the best targets for future space telescopes to look for signs of life in the planet’s atmosphere by looking for chemical signatures such as evidence of oxygen,” explains Francesco Pepe from Geneva Observatory, Switzerland.
One of the recently announced newly discovered planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth and is located at the edge of the habitable zone — a narrow zone around a star in which water may be present in liquid form if conditions are right.
“This is the lowest-mass confirmed planet discovered by the radial velocity method that potentially lies in the habitable zone of its star, and the second low-mass planet discovered by HARPS inside the habitable zone,” adds Lisa Kaltenegger from Max Planck Institute for Astronomy, Heidelberg, Germany and Harvard Smithsonian Center for Astrophysics, Cambridge, USA, who is an expert on the habitability of exoplanets.
The increasing precision of the new HARPS survey now allows the detection of planets under two Earth masses. HARPS is now so sensitive that it can detect radial velocity amplitudes of significantly less than 4 km/hour — less than walking speed.
“The detection of HD 85512 b is far from the limit of HARPS and demonstrates the possibility of discovering other super-Earths in the habitable zones around stars similar to the Sun,” adds Mayor.
These results make astronomers confident that they are close to discovering other small rocky habitable planets around stars similar to our Sun.
