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Beyond Earthly Skies

Refraction of Starlight by Exoplanet Atmospheres

14 Jul 2014, 22:00 UTC
Refraction of Starlight by Exoplanet Atmospheres
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When a planet transits its host star, some of the star’s light passes through the planet’s atmosphere and generates a transmission spectrum which carries information about the planet’s atmosphere. This technique of transmission spectroscopy has been used to characterise the atmospheres of exoplanets ranging from hot-Jupiters to super-Earths. The upcoming James Webb Space Telescope (JWST) and the development of larger ground-based telescopes might make it possible for transmission spectroscopy to characterise the atmospheres of smaller, Earth-size exoplanets.Light refracts or bends when it passes through a planets’ atmosphere due to the atmosphere’s index of refraction gradient. This is because the index of refraction is altitude-dependent. In the rarefied upper atmosphere of a planet, the index of refraction is lower compared to the dense lower atmosphere. During the events associated with the transit of a planet in front of its host star, the main effect of refraction is that some of the star’s light passing through the planet’s atmosphere can be refracted towards a distant observer prior to a transit and refracted away from a distant observer during a transit.Taking into account the effect of refraction, Amit Misra et al. (2014) modelled the transmission spectrum of an Earth-analogue (i.e. a planet that ...

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