Colloquium: Polarimetry as a tool for characterising planets and exoplanets
Polarisation is a little known property of light. Maybe because humans cannot really see it with their eyes, polarisation appears to have a hard time getting into our hearts and astronomical instrumentation. Direct light of the sun and sun-like stars is mostly unpolarised, i.e. the electromagnetic waves have no preferential vibrational direction, but when this unpolarised light is scattered by atmospheric particles and/or when it is reflected by a surface, it will usually become polarised. The state of polarisation of this light is very sensitive to the composition and structure of the atmosphere and/or the surface. Polarisation measurements have been shown to provide information that cannot not be retrieved from brightness measurements alone, such as the composition of the clouds of our neighbouring planet Venus. Polarimetry also promises to be a strong tool for the detection and characterisation of exoplanets, because it enhances the star-planet contrast, provides a direct confirmation of the planetary nature of the stellar companion, and could reveal information on the atmosphere and surface of the exoplanet.
Examples of the application of polarimetry for the characterisation of solar system planets and exoplanets will be provided, and SELFIE, a plan for a small spectropolarimeter that is designed to observe the Earth from afar, as if it were an exoplanet, will be introduced.
recording: www.youtube.com/watch