Shall I compare thee to a distant world? The importance of inter-planet and inter-model comparative studies.

We cannot truly understand the general principles that govern planetary processes by studying only one planet or using only one modelling framework. Fortunately, continuing leaps in solar system exploration and recent exoplanetary discoveries, accelerated by the advent of JWST, allow us to start drawing connections between solar system planets and exoplanets — applying the vast knowledge of Earth and its neighbours to more distant worlds, and vice versa. To this end, solar system objects can offer analogues of some of the more exotic exoplanets, e.g. Jupiter's moon Io as an ultra-hot geologically active rocky planet analogue, or Venus as a habitable-zone Earth-like planet with a decidedly non-Earth climate. Within the solar system itself, a lot of atmospheric and geologic phenomena are present on more than one planet: dust devils are observed on both Earth and Mars, Earth's hydrological cycle has its methane counterpart on Titan, to name but a few. On the other hand, expanding our understanding of exoplanets places our own solar system within the broader context of planetary formation, architectures, atmospheres, and habitability.

 

At the same time, a smorgasbord of numerical models, including 3D general circulation models of the atmosphere, are now routinely being applied to different planets, both to test our theory, predict and interpret observations. Drawing from the success stories in the Earth climate community, it is now recognised that benchmarking and comparing the behaviour of numerical models through intercomparison projects is one of the key ways to advance our knowledge. This has a variety of benefits to the planetary science, from better planning for future observations to identifying bugs in the code to feeding back the model improvements to the Earth climate community. Recently, this effort has been re-invigorated under the CUISINES framework, an international effort to systematically contrast and compare models of various complexity for a range of different planets.

 

In this talk, I will first demonstrate how a state-of-the-art 3D climate model can be used to study different planetary atmospheres, from extrasolar hot Jupiters to temperate rocky planets. Using this model as an example, I will discuss some lessons that can be learnt in building planetary climate models. I will then give some highlights of the recent model intercomparisons for exoplanets and solar system planets. I will conclude with a discussion on how model intercomparison projects benefit both planetary and Earth-focused science.