A new technique to detect the topography of exoplanets

What does an exoplanet look like? At the moment, no instrument has been able to image rocky exoplanets, as they are small and distant. For the first time, a research team from GEOPS (CNRS, Univ. Paris Sud, Univ. Paris Saclay) and the Physics Department at McGill University (Montreal, Canada) has proposed a technique to digitally synthesise realistic topographies of rocky exoplanets. With your web browser, you can approach and land on these synthetic celestial bodies. This progress will make it possible to better prepare analysis of actual data from future direct observation campaigns of exoplanets.

Exoplanets are bodies which revolve around other stars than the sun. They are extremely distant, faint and small. For now, no instrument has managed to detect an image of a rocky exoplanet, as the challenge is considerable. A research team has proposed a technique to digitally synthesise realistic topographies of rocky exoplanets to visualise these distant worlds and to prepare the analysis of future data.

A statistical study of solar system bodies (the Earth, the Moon, Mercury and Mars) demonstrated that the topographies of rocky bodies share similar characteristics. The model, called “multifractal”, makes it possible to present the complexity of these bodies that are sometimes smooth and sometimes rough at all scales. This model is an extension of the well-known fractal model popularised by Benoît Mandelbrot.

In a study published in the journal, “Monthly Notice of Royal Astronomical Society”, the group of researchers were able to generate “multi-fractal” surfaces in spherical geometry for the first time. These include smooth and rough areas at all scales, as in real life. The tool is based on a random seed and is capable of generating as many examples as required. These synthetic topographies will solve several enigmas about the exoplanets, but also about solar system bodies and primitive Earth.

Become a planetary traveller without moving from your living room

By way of illustration, this initial study proposes to examine the statistics of land masses (islands, continent, etc.) and seas (lakes, oceans, etc.) according to the liquid water fill level. The results show that the size of the largest ocean is vary variable: in cases where there is little water, 90% of the surface is covered by continent and 10% by sea, the largest ocean has an average size of 75% of the seas, but can range between 25% and 95%. In a similar case to Earth, 70% of the planet’s surface is covered by ocean and 30% by continent, but the largest continent is on average 75% of the land mass (between 25% and 90%), as opposed to 55% on Earth. This study demonstrates that Earth’s configuration is more likely with larger connected continents. This situation occurred 300 million years ago: the Earth in the form of a unique supercontinent called “Pangaea”.

An online 3D visualisation tool (usable on all platforms, including tablets and smartphones) was set up with several examples of exoplanets in order to better detect these synthetic topographies. So, you can become a planetary traveller without moving from your lounge !

https://data.ipsl.fr/exotopo/

These synthetic topographies have made it possible to study the geometry of potential oceans outside the solar system, an important point for habitability. Indeed, the interfaces between continental surfaces and oceans have been suggested as essential for the emergence of life. On the other hand, this study paves the way for the detailed characterisation of exoplanets, which will soon be observable with a new generation of space and ground-based instruments like the James Webb Space Telescope in 2021 and European Extremely Large Telescope by 2024.

Reference:

Landais., F. Schmidt, F., Lovejoy, S. Topography of (exo)planet, Monthly Notice of Royal Academy of Science, 2019, 484, 787-793, http://dx.doi.org/10.1093/mnras/sty3253

Landais, F.; Schmidt, F. & Lovejoy, S. Multifractal topography of several planetary bodies in the Solar System, Icarus, 2019, 319, 14-20, http://dx.doi.org/10.1016/j.icarus.2018.07.005

Contacts:

François Landais: francois.landais @ u-psud.fr, UMR 8148 GEOPS, Université Paris-Sud, CNRS, Orsay

Frédéric Schmidt: frederic.schmidt @ u-psud.fr, UMR 8148 GEOPS, Université Paris-Sud, CNRS, Orsay

Shaun Lovejoy: lovejoy @ physics.mcgill.ca, Physics Department, McGill University, Montréal