= HD 149026 b
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<HD 149026 b> is a transiting, roughly <Saturn>-mass <exoplanet> whose small measured <radius> made it an early test of giant-<planet> composition. The discovery combined <Doppler spectroscopy> at two observatories with ground-based <exoplanet transit photometry>: the first constrains <mass>, the second <radius> and <orbital inclination>. The original <exoplanet interior> models required a substantial inventory of elements heavier than <hydrogen> and <helium> to reproduce the measured compactness.<The N2K Consortium. II. A Transiting Hot Saturn Around HD 149026 With a Large Dense Core by Bun'ei Sato and others>[Abstract: radial-velocity observations, three complete transits, and the mass-radius interpretation]{ref}
The inferred concentration of heavy material is a model result, rather than an image of a planetary core. Its partition between a central core and the surrounding envelope depends on the assumed <equation of state>, age, and <temperature>; this illustrates <exoplanet interior-composition degeneracy>.
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