We have made some major scientific advancements, and developed and refined techniques utilizing high-dispersion spectroscopy for characterizing extrasolar planets. These include several firsts:
For the first time, we have detected helium in the exosphere of an extrasolar planet from the ground. It gives a unique insight into the evaporation of atmospheres for planets very close to their host stars. We have repeated this now for several other planets. Atmospheric evaporation plays an important role in the evolution of planetary atmospheres, also for the early Earth and for other planets in our Solar System. Planets that orbit very distant stars are the only way to see these atmospheric escape processes in action.
We measured for the first time water vapor from the ground in planet HD189733b. Also, we devised a new method using medium-resolution spectrographs, called molecule mapping, that can specifically target different types of molecules in exoplanet atmospheres. This has resulted in very interesting results for two planets. Using these new techniques, we show that this can also be used for the James Webb Space Telescope. We show that we can target the possible Earth-like planet Proxima-b and determine whether it has an atmosphere. It would be a major step towards the characterization of this enigmatic world.
In another first, we measured the mass of a young gas-giant exoplanet for the first time, combining data from two astrometric space satellites, HIPPARCOS, that retired already more than two decades ago, and Gaia – an ESA flagship space telescopes that is currently operational. This important, pioneering measurement confirms the mass expected from theoretical considerations, explained by the way we think planets form. It is a forebode of the many great things to come from Gaia in the coming years, in particular in the field of exoplanets.
Results at the heart of EXOPLANETBIO are measuring isotopologue ratios in exoplanet atmospheres. Isotopologues are molecules with the same chemical properties, with a slightly different mass. These can give great and unique insights in the formation and evolutionary history of the planets they are detected in. For example, the fraction of deuterium (heavy water) is significantly higher in the Earth oceans than elsewhere in the solar neighborhood, which currently points to an origin from bodies in the asteroid belt. First we calculated how well one can measure isotopologues, including deuterium in exoplanet atmospheres, using the Very Large Telescope, but also the future European Extremely Large Telescope (ELT). It shows that deuterium, if Proxima b is water rich, will be within reach of the ELT – a very exciting prospect. We subsequently measured the minor isotope carbon-13 for the first time in an exoplanet atmosphere, showing the planet to be significantly enriched in 13CO. This was followed up with the first such measurement in a brown dwarf (Zhang et al. 2021b), and exploratory work on other isotopes. It provides a new pathway to constrain the formation and evolution of gas-giant planets.
Pioneering work was also performed to constrain the temperature structures, chemical abundances (first detections of OH and Paschen-Beta absorption, and global circulation patterns). These have become possible by the introduction of Bayesian retrieval analyses for high-resolution spectroscopy.
Many results of EXOPLANETBIO have been disseminated to the general public via national and international press releases.
