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The Diverse Densities of Ten Kepler Exoplanets

5 Jan 2016, 22:00 UTC
The Diverse Densities of Ten Kepler Exoplanets
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Figure 1: Artist’s impression of a pair of exoplanets.Measuring a planet’s size and mass is essential in determining the planet’s density and hence its bulk composition. The masses of most of the small planets detected by NASA’s Kepler space telescope are beyond the sensitivity of radial velocity (RV) measurements. As a result, another technique known as transit timing variations (TTV) is required to determine the masses of these small planets. TTV involves precisely measuring the gravitational perturbation one planet has on another in the same planetary system with two or more planets. The gravitational perturbation shows up as a change in the transit timing of the planet (i.e. the planet transits its host star slightly earlier or slightly later).From the analysis of TTV data, Jontof-Hutter et al. (2015) present mass measurements of 10 exoplanets that range from super-Earth-size to Neptune-size. All 10 planets are below 8 Mᴇ, whereby Mᴇ denotes the mass of Earth. Although their radii range from 1.31 (Kepler-105c) to 3.35 (Kepler-29b) times the radius of Earth, they span over an order of magnitude in density, indicating a huge compositional diversity. The densest of the 10 planets, Kepler-105c, has a density that is consistent with an Earth-like rocky ...

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