The European Southern Observatory (ESO) has announced a new estimate for the number of planets similar to Earth in the Milky Way Galaxy: tens of billions.
“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” said Xavier Bonfils, leader of the HARPS team at the observatory. “Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”
The HARPS team precicely measures the radial velocity or stars. Using this data, the scientists can measure the doppler effect that planets have on their stars, revealing the presence of those planets.
In this particular survey, the team looked at 102 red dwarf stars. A total of nine 'super-Earths', planets between one and ten times the mass of Earth and located in the habitable zone around a star. Since red dwarf stars make up around 80% of the stars in our galaxy, the team was able to estimate the likelihood that a red dwarf star will have a habitable planet orbiting it.
Since there are many red dwarf stars close to our solar system, the ESO stated this new estimate means there are probably around 100 of these planets at distances of less than 30 light-years.
“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life,” said Xavier Delfosse, a member of the HARPS team.
Life may not be as easy to come by around red dwarf stars, though.
"The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun," says Stéphane Udry, another member of the HARPS team. "But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."