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Beyond Earthly Skies

Identifying Alien Planets with Clear Skies

5 Oct 2014, 10:00 UTC
Identifying Alien Planets with Clear Skies
(200 words excerpt, click title or image to see full post)

When a planet transits in front of its host star, a tiny fraction of the starlight passes through the planet’s atmosphere and carries with it signatures of the planet’s atmospheric constituents. This can allow the planet’s atmosphere to be characterised using an observational technique known as transmission spectroscopy. However, the atmospheres of planets can be cloudy, hazy or clear-sky (i.e. free of clouds and hazes). The presence of clouds or hazes can obscure the lower layers of the atmosphere and make the planet less desirable for characterisation. As a result, it is worth identifying whether a planet has clear skies before a large amount of telescope time is dedicated to characterising its atmosphere.Misra & Meadows (2014) propose a method to readily distinguish cloudy, hazy and clear-sky planets. This involves measuring the amount of starlight being refracted through the atmospheres of transiting planets using upcoming large collecting area space and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). The refraction of starlight by a planet’s atmosphere can lead to an increase of flux both prior to ingress (i.e. before the start of a transit) and subsequent to egress (i.e. after the end ...

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