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Our view of exoplanets is one derived primarily from Solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around so called low-mass stars or M dwarfs is much more cursory. The discovery of Proxima b was an exciting development though it should not have been a big surprise because (1) red dwarfs are the most numerous stars, (2) previous surveys already indicated an abundance of small planets in compact orbits around red dwarfs, and (3) warm terrestrial planets around red dwarfs are 50 to 100 times easier to detect than around Sun-like stars. Based on combining radial velocities of nearby M dwarfs obtained with HARPS, UVES and HIRES data we find many new M dwarf planets. By computing the estimated detection probability function the occurrence rate of planets less than 10 Earth masses around nearby M dwarfs is found to be around two planet per star. Techniques to overcome the practical issue of obtaining good quality radial velocity data for M dwarfs are considered: (1) the wavelength sensitivity of radial velocity signals, (2) the combination of radial velocity data from different experiments for robust detection of small amplitude signals and (3) optimum selection of targets. |
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