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Exoplanets surface acceleration ratio distribution

Histogram of the exoplanets surface acceleration ratio distribution


A histogram showing the distribution of a quantity called the “surface acceleration ratio” for a subset of the sample of exoplanets for which the necessary measurements exist (sample from a snapshot on 5 August, 2012) for the quantity to be calculated. Data are from the Extrasolar Planets Encyclopedia. The surface acceleration ratio is a measure of the ratio of the tendency of the surface of the planet to be tugged away by the host star, due to the star-planet gravity becoming comparable to the planet's self-gravity at its surface. Mathematically, the ratio is simply the ratio of the local free-fall acceleration at the surface of the planet due to the planet, to the free-fall acceleration due to the host star. The histogram shows the percentage of exoplanets in the subset that lie in each surface acceleration ratio interval. The calculated surface acceleration ratios are actually lower limits because the exoplanet masses are lower limits. For comparison, the planets in our solar system are marked as Me, V, E, Ma, J, S, U, N, corresponding to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune respectively. The histogram shows that a substantial percentage of the exoplanets in the subset show a very strong clustering of the surface acceleration ratio of around 4. These are close-in hot Jupiters in which the surface layers of the planets are unstable, and they have no counterparts in our solar system. A more detailed discussion can be found in the book Exoplanets and Alien Solar Systems.

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Note: The subsample of 216 exoplanets shown in the histogram is from snapshot at a time when there were 777 confirmed exoplanets in total (residing in 623 alien solar systems, 105 of which harbored more than one exoplanet).
File under: The ratio of free-fall acceleration at the surface of an exoplanet due to the planet, to the free-fall acceleration due to the host star.

© Tahir Yaqoob 2011-2012.