KlimaCampus Kolloquium: Remote Sensing of Exoplanetary Atmospheres

Short of interstellar travel, understanding the nature of exoplanets and potential habitats beyond the Solar System must necessarily proceed via remote sensing. Specifically, the problem reduces to measuring and interpreting spectra of exoplanetary atmospheres, which is currently one of the frontier topics in astronomy and astrophysics. The specific format of the data measured implies that the traditional methods of the Earth and planetary sciences cannot be imported without modification and generalisation. In the current talk, I will focus on the physics of radiative transfer concerning transmission spectroscopy, which quantifies the variations in the amount of starlight occulted by an exoplanet, across wavelength, due to the varying opacity of its atmospheric constituents. In the first part of the talk, I will explain the theory of transmission spectra, including the elucidation of a "normalisation degeneracy" that prevents absolute abundances from being straightforwardly extracted unless sufficient wavelength coverage and spectral resolution are available. In the second part of the talk, I will discuss how we solve the inverse problem of inferring chemistry and atmospheric properties from analysing the transmission spectrum, which is known in exoplanet science as "atmospheric retrieval". I will focus on a Bayesian technique known as nested sampling, which allows Occam's Razor to be formally enforced. In the third part of the talk, I will discuss a novel technique of atmospheric retrieval that uses machine learning. The development of these theoretical techniques prepares us for order-of-magnitude improvements in the quality of exo-atmospheric spectra in the coming decade, as the James Webb Space Telescope and other observatories become operational.

Datum

01.02.2018

Uhrzeit

15:15 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Kevin Heng, University of Bern, Center for Space and Habitability

Chair

Bjorn Stevens

Zur Übersicht