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PHYSICS AND CHEMISTRY OF TEMPERATE SUB-NEPTUNES

Séminaire IRAP

4 mars 2021 | 11h00 – 12h00

Benjamin Charnay – Observatoire de Paris

This artist’s impression shows the planet K2-18b, its host star and an accompanying planet in this system. K2-18b is now the only super-Earth exoplanet known to host both water and temperatures that could support life. UCL researchers used archive data from 2016 and 2017 captured by the NASA/ESA Hubble Space Telescope and developed open-source algorithms to analyse the starlight filtered through K2-18b’s atmosphere. The results revealed the molecular signature of water vapour, also indicating the presence of hydrogen and helium in the planet’s atmosphere.

Salle de conférence Roche + Visio

Kepler transit surveys revealed that sub-Neptunes (planets with radii between 1.8 and 3 Earth) are very common, in our galaxy. These planets could be composed of a rocky core surrounded by a thick H2-dominated atmosphere or they could be waterworlds with a steam atmosphere. The atmospheric characterization of sub-Neptunes is a key to understand the nature of these objects and the transition between rocky planets and gaseous planets. Transit observations of the temperate sub-Neptune K2-18b revealed an absorption feature at 1.4 micron which was interpreted as water vapour, placing K2-18b as one of the best sub-Neptunes for atmospheric characterization. During this talk, I will present results from 1D atmospheric modelling of K2-18b which suggests that the observed feature is more likely due to methane. I will also discuss atmospheric dynamics and cloud formation based on 3D modelling. I will finish with perspectives for atmospheric characterization of temperate sub-Neptunes with the next generation of telescopes (JWST, ELT, ARIEL).

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