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Exoplanets Radius Distribution

Histogram of the exoplanets radius distribution

A histogram showing the distribution of the radii of the confirmed exoplanets in a subset of the sample that have measured radii (sample snapshot for 5 August, 2012). Plotted is the percentage of the subsample of exoplanets in each radius interval. Radii are shown as ratios of the exoplanet radii to the radius of the Earth (i.e., radii are shown in units of the radius of the Earth). Data are from the Extrasolar Planets Encyclopedia. For comparison, the radii of 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 (numerical values are from

Note that the majority of exoplanets do not yet have radii measurements. On 5 August 2012, only about 32% of confirmed exoplanets had radii measurements. Of the data that are available, it can be seen that the size distribution is broadly peaked in the region of 10 to 18 Earth radii. This can be compared with Jupiter's radius of 10.9733 times that of Earth, indicating that the broad peak in the size distribution reflects the giant planets (notably the hot jupiters) that have been found in abundance. There is another, much smaller peak in the size distribution below 10 Earth radii. However, we are dealing with small-number statistics here so more data is definitely needed. Understanding possible selection effects is also important.

One needs to consider possible selection effects for interpetation of the exoplanets size distribution. Read more about exoplanets, and the radius distribution with Exoplanets and Alien Solar Systems, which includes comprehensive references to the scientific literature, and discussion of selection effects.

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Note: The histogram utilizes data from 252 exoplanets, taken from a snapshot when there were 777 confirmed exoplanets in total (residing in 623 alien solar systems, 105 of which harbored more than one exoplanet).
File under: How big are the discovered exoplanets? What is the size or radius distribution of the exoplanets?

© Tahir Yaqoob 2011.