Hot and cold starts of a giant planet
= Hot and cold starts of a giant planet
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Accretion releases gravitational energy. Efficient radiation at an accretion shock leaves a lower-entropy cold start, while greater retained energy gives a higher-entropy hot start; intermediate outcomes are possible. Initial entropy changes a young planet's radius, luminosity and spectrum. Consequently an <exoplanet direct imaging> luminosity and age need not uniquely fix mass without a formation/evolution model.