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The search for habitable Earth-like planets

Dr. Alejandro Suárez Mascareño
Observatoire Astronomique, Université de Genève

September 5th, 2018


The search of Earth-like extrasolar planets approaches a key moment in its history. With the arrival of ESPRESSO (observing already!), the possibility of detecting Earth-like planets around solar-type stars is at last a reality, and the opportunities to characterize earth-like planets and super-Earths are more numerous than ever. High precision radial velocity (RV) measurements (better than 1 m s−1 for instruments like HARPS and HARPS-N) have given astronomers the possibility of detecting and characterizing small exoplanets for a few years, down to the mass of the Earth, when orbiting M-dwarfs at short orbital periods, or a few Earth-masses at longer periods. The arrival of the new generation of instruments (ESPRESSO) brings a revolution in precision, to the level of 5-10 cm s-1, allowing for the detection or characterization of Earth-mass planets at longer orbital periods, in the habitable zone of Sun-like stars. At these levels of precision, signals induced by stellar activity in the RV curves become the most important limiting factor, even in the case of magnetically quiet stars. Stellar activity can induce apparent Doppler shifts of the stellar spectrum, which cause periodic signals that range from less than one to dozens of meters per second. The correct detection and characterization of the different star-induced signals and their effect in the RVs is one of the most important steps to detect and properly characterize low-mass exoplanets, and its importance will greatly increase with increased precision, as even in the case of the quietest stars, these signals will surface. Unveiling the population of small-mass planets in the range of super-Earths and smaller, especially at long orbital periods (close to the habitable zone of their stars and beyond), is a key step to understand the formation of planetary systems. To really paint the full picture of the systems, and accurately derive their parameters, we need to identify and model together the planetary companions and activity signals present in the data. I will present the current state of the field, the challenges and the techniques to overcome them, focusing on the efforts that I have made during the last years.