= Hot Neptune
{wiki}
A <hot Neptune> is an <exoplanet> in approximately the <Neptune> <mass> or <radius> range receiving strong stellar <irradiance>. The name describes size and heating; it does not imply that its <exoplanet interior> or <exoplanet atmosphere> matches <Neptune>. A <molecular hydrogen>-rich envelope can supply a large fraction of the measured <radius> while containing a much smaller fraction of the <mass>.
Short <orbital periods> make repeated <exoplanet transit photometry> and <Doppler spectroscopy> practical. Comparing the inferred <mass density> with <exoplanet interior> models helps distinguish a retained gas envelope from a denser body. Strong irradiation also makes <atmospheric escape> relevant: losing a light envelope can substantially change <radius> without removing most of the solid material.
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