Periodic Reporting for period 4 - EXOPLANETBIO (Exoplanet atmospheres as indicators of life: From hot gas giants to Earth-like planets)
Reporting period: 2021-03-01 to 2022-11-30
Placing our solar system in the context of other planetary systems is one of the central objectives driving the study of extrasolar planets – planets that orbit other stars than our Sun. One of the most fascinating questions in modern science is whether other life-bearing planets exist. In recent years, we have learned that planet are very common, but also very complex and diverse. Already the planets in our solar system, the gas giants have hydrogen dominated atmospheres with complex systems of clouds and hazes with powerful zonal atmospheric flows and storms. The rocky planets have a variety of secondary atmospheres, such as a super-rotating CO2-based atmosphere supporting opaque sulphuric acid clouds in the case of Venus, an N2-based partially transparent atmosphere with a large abundance of biotic oxygen in the case of Earth, and a teneous CO2 atmosphere in the case of Mars.
This picture is further amplified by the discovery of several new classes of planets around other stars. These include hot Jupiters, gas giants planets in very close-in orbits, a class of super-Earths (or mini-Neptunes) with properties in between rocky and ice-giant planets, and super-Jupiters – very massive planets on very wide orbits. Detailed studies of large numbers of different types of exoplanets are required to properly understand planet atmospheres and their evolutionary histories. Only then will we be in a position to unambiguously identify biomarker gases that point to biological activity. This is the main driver behind the enormous surge in exoplanet atmospheric research, and this ERC project.
EXOPLANETBIO used innovative spectroscopic techniques to study the atmospheres of extrasolar planets, in particular utilizing the spectrographs CARMENES on the Calar Alto Telescope, and CRIRES+ on the Very Large Telescope. Pioneering work was performed to constrain the temperature structures, chemical abundances (first detections of OH and Paschen-Beta absorption), and global circulation patterns. Arguably most important have been the first measurements of a minor isotope in an exoplanet atmosphere, i.e. carbon-13. These provide a new pathway to constrain the formation and evolution of gas-giant planets. The project is an important stepping stone in developing high-dispersion spectroscopic techniques for studying Earth-like planets with the future European Extremely Large Telescope.
This picture is further amplified by the discovery of several new classes of planets around other stars. These include hot Jupiters, gas giants planets in very close-in orbits, a class of super-Earths (or mini-Neptunes) with properties in between rocky and ice-giant planets, and super-Jupiters – very massive planets on very wide orbits. Detailed studies of large numbers of different types of exoplanets are required to properly understand planet atmospheres and their evolutionary histories. Only then will we be in a position to unambiguously identify biomarker gases that point to biological activity. This is the main driver behind the enormous surge in exoplanet atmospheric research, and this ERC project.
EXOPLANETBIO used innovative spectroscopic techniques to study the atmospheres of extrasolar planets, in particular utilizing the spectrographs CARMENES on the Calar Alto Telescope, and CRIRES+ on the Very Large Telescope. Pioneering work was performed to constrain the temperature structures, chemical abundances (first detections of OH and Paschen-Beta absorption), and global circulation patterns. Arguably most important have been the first measurements of a minor isotope in an exoplanet atmosphere, i.e. carbon-13. These provide a new pathway to constrain the formation and evolution of gas-giant planets. The project is an important stepping stone in developing high-dispersion spectroscopic techniques for studying Earth-like planets with the future European Extremely Large Telescope.
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.
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.
Although this ERC project has now come to an end, and many important steps forward have been taken, we are only at the beginning of this exciting endeavor. The results on isotopes is beyond expectations. We have been awarded a large observing program with CRIRES+ on the VLT of 109 hours – to measure carbon isotope ratios for a set of super-Jupiters, free-floating planets and brown dwarfs. Although this is at the end of the ERC project, it is a direct result of all the ground-work we have done with EXOPLANETBIO.
We also have the data in hand to start probing cooler planets above their cloud deck – which could mean another breakthrough in exoplanet characterization, understanding the bulk compositions of sub-Neptune planets. Another great prospect is the measurements of new molecules, such as methane, H3+, ammonia, and/or even oxygen. How far will we be able to push this towards smaller and cooler planets? The project was an important stepping stone in developing high-dispersion spectroscopic techniques for studying Earth-like planets with the future European Extremely Large Telescope.
We also have the data in hand to start probing cooler planets above their cloud deck – which could mean another breakthrough in exoplanet characterization, understanding the bulk compositions of sub-Neptune planets. Another great prospect is the measurements of new molecules, such as methane, H3+, ammonia, and/or even oxygen. How far will we be able to push this towards smaller and cooler planets? The project was an important stepping stone in developing high-dispersion spectroscopic techniques for studying Earth-like planets with the future European Extremely Large Telescope.