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A diagram showing radius versus mass lower limit for the confirmed exoplanets in a subset of the sample that have measurements of both radius and mass lower limit (sample snapshot for 5 August 2012). Each exoplanet is marked with a cross. The radii and masses are expressed relative to the corresponding values for Earth (i.e., radii are shown in units of Earth radii, and masses are shown in units of Earth masses). Data are from the Extrasolar Planets Encyclopedia. For comparison, the radii and masses 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 solarsystem.nasa.gov). Note that for clarity, the positions of Jupiter and Saturn correspond to the intersections of the dotted lines that are marked by the letters J and S respectively.

Theoretical studies show that many differnt planet compositions can lead to a similar radius versus mass relation. (Advanced readers: see for example, Seager et al. 2007 and Valencia et al. 2007.) The down side of this is of course that it is not generally possible to uniquely determine the chemical composition of a planet from its mass and radius alone.

One also needs to carefully examine the possible selection effects when interpreting the eoxplanets radius versus mass diagram. Read more about exoplanets, and the radius versus mass relation with Exoplanets and Alien Solar Systems, which includes comprehensive references to the scientific literature, and discussion of selection effects.

Note: There are 241 exoplanets shown in the plot, 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). Only the 241 exoplanet shown had both radii and mass measurements or estimates.
File under: How are the radii and masses of exoplanets related to each other. Radius versus mass of exoplanets. Is there a conncetion between exoplanet radius and mass?