A new study suggests that the best strategy for discovering signs of life in the atmosphere of exoplanets is to study K-dwarf stars. Link to the study: looking for life try around k dwarfs
One way to identify life on other planets is by detecting atmospheric biosignatures. If Earth-like exoplanets both have the presence of methane and oxygen in the atmosphere it would be a possible proof that there exists life on the planet, but it is very difficult to detect it. Because the methane is destroyed by chemical reactions driven by the host stars light. Smaller and dimmer stars than our G-type Sun is better candidates. A problem with small red dwarf M-type stars is their stellar activity and radiation could be deadly for living organisms. The best candidate stars are K-type stars which are in size between G-type and M-type stars.
We have so far discovered several possible habitable candidates exoplanets around K-type stars. I have picked some of the most interesting planets for this article.
HD 85512 b is an exoplanet that is orbiting the K-type star HD 85512 was discovered in 2011. It was considered along with Gliese 581 d (that probably does not exist) to be one of the best candidates for habitability. It is 3.6 times the mass of Earth on is just outside the inner edge of the Goldilocks zone of its star, where it could be too hot and it possible that the planet is tidally locked. HD 85512 is 36 light-years away from Earth in the constellation Vela.
HD 40307 g is located 42 light-years away in the constellation Pictor. The planet was discovered in 2012 by using the ESO HARPS telescope that is using the radial velocity method to find exoplanets. It is inside the Goldilocks zone of its star. The discoverer Hugh Jones said that the longer orbit of the planet means that it has the correct climate and atmosphere to support life. Later studies suggest that the planet could be a mini Neptunian that has migrating inward.
Image credit: NASA Ames/JPL-Caltech/T. Pyle
The most interesting K-type star with a planet system is Kepler-62. It is located about 1200 light-years away in the constellation Lyra. The system has two potentially habitable candidates Kepler-62f and Kepler-62e. The planets were announced in 2013. Studies have suggested that the planets are water worlds with oceans that cover the entire surface. That suggests that life on Kepler 62e and Kepler 62f would be different than on our planets. Life could exist there but technology advanced civilizations would have problems to evolve with no access to metals or fire for metallurgy. Kepler-62f orbits its host star every 267.29 days and is a Super Earth with 1.41 of Earth radius and it is possible that it could have a moon. Kepler-62 system is much older than our solar system. Intelligent life would have 3 billion years more than us to evolve. A study released in a June 2018 suggests that Kepler-62f may have seasons and a climate similar to Earth. Kepler 62 is being specially targeted being targeted by the SETI program in search of extraterrestrial life.