Finding a second Earth through stellar understanding

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People, including me, have wondered for centuries if we are alone in the Universe. Only a mere thirty years ago, the first planet orbiting a star other than the Sun was discovered. These newly discovered worlds were called exoplanets. Over the last three decades we have witnessed an exponential rise in the number of known exoplanets, with more than 5000 discovered so far. This has shown that exoplanets are ubiquitous and come in various sizes and architectures. At the same time, a planet truly resembling Earth or a planetary system resembling the Solar System, has not yet been discovered.My project will for the first time enable to find a planet resembling Earth orbiting a star resembling the Sun. Exoplanets can be detected by observing and modelling the gravitational wobble of their hosting star, seen in their changing radial velocities over time. Furthermore, the technique of using radial velocity changes is currently the only viable way of measuring the mass of small exoplanets. Unfortunately, for small long-period exoplanets such as Earth, these velocity changes are well below the stellar-induced changes in the radial velocity. These stellar signals are due to the surface variability of the stellar magnetic field and thus drown out the smaller signals from far-away exoplanets.I will improve our ability to measure and extract the tiny signals of small exoplanets. This will be done by accounting for the stellar magnetic field variability in the spectroscopic data. I will use our brightest known star, the Sun, as a teststar to develop new techniques to deal with the stellar data. Removing the effect of the known planets in the Solar System, the Sun can act as the only known star where we are certain there are no planetary signals in the data. This creates a unique opportunity to test and improve new techniques before using them on other stars.As a Future Leader Fellow, I will expand our instrumental capacities to study the Sun-as-a-star and characterise the small exoplanets found around other stars. As part of the project, I will build and exploit a new Solar Telescope to measure both stable radial velocities and the simultaneous changes in the Solar magnetic field. This unique instrument would be the first of its kind to have polarimetric capabilities that will open the pathway to discovering smaller and more distant exoplanets.To place Earth and the Solar System into the context of the full exoplanet population, I will study the connection between stellar and planetary composition. I can do this using the same spectroscopic data used already in my project to find and characterise the exoplanets. By accurately characterising exoplanet systems as a whole, we will gain insight into the specific details of planet formation and evolution and the possibilities for existence of life on other planets. This will bring us one step closer to understanding our place in the Universe and how unique Earth could be.