Photo: Near the sun one hundred Earth-like planets revolve around red dwarf stars.
Most recently, astronomers had calculated that there are billions of exoplanets but they did not provide any detail regarding the nature of these planets. The current study clarifies these results now for the class of Earth-like exoplanets in the so-called habitable zone. This is the distance from a star where liquid water can exist and therefore potentially life would be possible. The observations of the team were taken with the HARPS spectrograph on the 3.6-meter telescope at La Silla Observatory ESO in Chile.
Super-Earths are orbiting 40 percent red dwarf stars
"We can show our new observations with HARPS. Probably about 40 percent of all red dwarfs are orbited by a super-Earth, which is located in the habitable zone of the star," says study leader Xavier Bonfils of the Observatoire des Sciences de l'Univers (IPAG) in French Grenoble. Alone in a radius of 30 light years of our solar system there are a hundred super-Earths, which orbit their central star in the habitable zone.
Gas giants like Jupiter and Saturn in our solar system around red dwarfs on the other hand are rare: less than twelve percent of red dwarf stars are orbited by planets with 100 - to 1,000-times the mass of the Earth, so is the estimation of the research team.
102 dwarf stars as a sample
For their study, the team of astronomers monitored tiny changes in the movement of 102 red dwarf stars for six years in the southern sky. They discovered a total of nine planets with masses between one and ten Earth masses. Among these were two super-Earths orbiting their central stars in the habitable zone. Calculated from their observed values the researchers show how often different types of red dwarf stars with exoplanets are.
"We know now that probably there will be many red dwarfs orbiting in the vicinity of the solar system of super-Earths. We have now both HARPS and other future instruments which will help us to prove this." says Xavier Delfosse, co-author and also an astronomer at the IPAG . Then we can also search for traces of life on these planets.
However, we know that red dwarfs are prone to outbursts of brightness, called flares, say the researchers. So some of these planets may face a very intense ultraviolet and x-rays. "The existence of life would be very unlikely under such circumstances," the researchers say.