Periodic Reporting for period 4 - WHIPLASH (WHat next? an Integrated PLanetary Atmosphere Simulator: from Habitable worlds to Hot jupiters)
Période du rapport: 2021-03-01 au 2022-02-28
In this project, we will develop a new framework to constrain the physics and composition of exo-atmospheres that will allow us to overcome these difficulties when analyzing and interpreting observations. This will be done by developing and using a new 3D planetary atmosphere simulator that integrates a global climate model and a 3D radiative transfer code to generate observables. Using such an innovative approach, the Whiplash project will thus answer the following fundamental questions:
- What are the limits of current data interpretation tools
- What are the necessary conditions to sustain liquid water on terrestrial exoplanets? How can we infer observationally whether an atmosphere meeting these requirements is actually present?
- Can clouds explain the puzzling features of observed hot, gaseous exoplanets? What can these observations tell us on the dynamical and microphysical properties of clouds inside these atmospheres?
If we want theory to keep pace with the quality of future data, such a project is the necessary counterpart to the huge ongoing observational effort made by the community.
During the second and third reporting period, this tool has allowed us to identify a completely new type of bias in the interpretation of transmission spectra of exoplanets due to the strong day to night side temperature gradient (Pluriel et al. 2020; Pluriel et al. 2022). We are currently testing new data analyzis techniques to overcome these biases when dealing with real data. We have also finalized an open-source, open-access, documented, user-friendly version of the code (Pytmosph3r) that has been publicly released (http://perso.astrophy.u-bordeaux.fr/~jleconte/code.html). This version of the code has been published in Falco et al. (2022; A&A).
Thanks to our planet simulator, we have been able to provide new constraints on the nature of the atmosphere of these planets and make important predictions on their observability. In parallel, we have developed several new tools to study and predict the type of rotation states available for such planets. All this theoretical expertise will be instrumental in proposing future observations and interpreting them when they are available.
In parallel, the PI of the project has developed a new Python library to manage the large volume of radiative data for atmospheric modeling that has been released recently by various projects. The idea is that all these projects use different formats and standards which are generally different from the codes that use them. This library (Exo_k; Leconte, A&A, 2021) proposes a solution to seamlessly and efficiently convert datasets between all these formats, along with other features. It is open-source, open-access, and well documented (http://perso.astrophy.u-bordeaux.fr/~jleconte/code.html)
Overall, this work has contributed to strengthen the case for Ariel (Atmospheric Remote Sensing Infrared Large survey) -- an ESA led space mission whose science advisory team includes the PI of the whiplash project. This mission has finally been selected and adopted during this last reporting period for a launch in 2029.
Simultaneously, the team has participated to the discovery of the first planetary system around a cool, nearby star---the Trappist-1 system. This system is becoming kind of a Rosetta stone for exoplanet science: the central star is among the smallest in the galaxy and is relatively close to us. Only around such stars can we expect to characterize the atmosphere of temperate Earth-like planets with the future space telescope. And it is not one, but seven such planets that we have discovered around it, opening the way to comparative exoplanetology.
On the longer term, we are also using it to prepare the scientific specifications for the ESA/ARIEL mission that has been selected and is being designed. Indeed, it is important to have the most realistic possible idea of what the atmosphere of exoplanets can look like to build the instruments that will observe it. In particular, the new biases that we identify in the interpretation of spectroscopic observations of exoplanets should soon give us ideas about better ways to implement those observations, or how to prioritize some observations over some others.
At the same time, we are currently using this model to shed new light on existing observations. Indeed, being one of the few models able to predict transit spectra in 3D, it has allowed us to identify new biases in current data interpretation techniques. This needs to be properly quantified and expanded in the next phase of the project.
Finally, as new extreme planets are discovered every day, we will keep upgrading the various physical ingredients making the model to keep it versatile and flexible.