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Tidally Distorted Rocky Exoplanets

23 Oct 2014, 22:00 UTC
Tidally Distorted Rocky Exoplanets
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Exoplanets in close-in orbits around their host stars can become tidally distorted. Being in a close-in orbit also makes it likely that the planet is tidally-locked with the same planetary hemisphere perpetually facing its host star. For a tidally-locked exoplanet, the effect of tidal distortion tends to stretch the planet into a triaxial ellipsoid where the planet’s longest axis is always oriented towards its host star. If the planet transits its host star, the effect of tidal distortion and the resulting asphericity in the planet’s shape can cause the planet’s size to be underestimated, and subsequently, if the mass of the planet is measured, the planet’s density to be overestimated.Figure 1: Artist’s impression of a planet transiting a star.The effect of tidal distortion on close-in, tidally-locked exoplanets has been explored only for gas giant planets due to the general assumption that tidal distortion is only relevant for such planets. It is commonly assumed that the effect of tidal distortion is too small for rocky exoplanets. A study done by Saxena et al. (2014) show this is not the case. Rocky-exoplanets in close-in orbits around smaller red dwarf stars can become tidally distorted to an observable extend. In particular, the study ...

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