Periodic Reporting for period 2 - PEVAP (Planet Evaporation as a Window into Exoplanetary Origins)
Période du rapport: 2021-08-01 au 2023-01-31
We have discovered a large number of planets close to their host stars. In fact, we now know most stars host planets inside the orbit of Mercury in our own Solar System. Yet unlike the solar system terrestrial planets, these exoplanets often contain large atmospheres rich in hydrogen gas. It is currently an unsolved problem how these planets form or how the Earth sits within the zoo of all possible planets. Given many of these planets are extremely highly irradiated by their host stars, they are vulnerable to having their atmospheres heated up and lost to space through a process known as "photoevaporation".
It is thought that this photoevaporation process is responsible for many of the features detected in the exoplanet population today. Thus, rather than using the observed exoplanets to inform about their origins, we need to account for this photoevaporation process. Thus, in this project, we will develop new photoevaporation models and then use them to determine how the planets evolved into those we see today.
Our objectives are:
1. What are the mass-loss rates and photoevaporative flow structures for the full spectrum of observed planets?
2. How can we use observations of photoevaporating planets to learn about their compositions and histories?
3. How does photoevaporation affect and control the evolution of exoplanets and their atmospheres?
It is thought that this photoevaporation process is responsible for many of the features detected in the exoplanet population today. Thus, rather than using the observed exoplanets to inform about their origins, we need to account for this photoevaporation process. Thus, in this project, we will develop new photoevaporation models and then use them to determine how the planets evolved into those we see today.
Our objectives are:
1. What are the mass-loss rates and photoevaporative flow structures for the full spectrum of observed planets?
2. How can we use observations of photoevaporating planets to learn about their compositions and histories?
3. How does photoevaporation affect and control the evolution of exoplanets and their atmospheres?
So far, we have begun developing new photoevaporation models for atmospheres that contain more elements than hydrogen. We have developed a new computer code that can simulate the photoevaporative outflows from these planets and have applied it to hot terrestrial planets where their surfaces are melted. Furthermore, we have used our models for the photoevaporation of hydrogen atmospheres to understand the evolution of these planets. By building a model of how the hydrogen atmospheres of exoplanets evolve in time, we have used it to unwind the billions of years of evolution that exoplanets have undergone. In doing so, we have uncovered how many of the observed exoplanets formed. We found that most observed exoplanets did not form like those in our Solar System, rather they formed through a previously unidentified pathway where they grew quickly acquiring a small amount of primordial gas close to their host stars.
In the project's next phase, we expect to apply the same statistical analysis to the hydrogen-dominated atmospheres to atmospheres more akin to the terrestrial planets in our Solar-System. In doing so, we will be able to put Earth in the context of exoplanets and answer the question of how rare we really are.