of Planet b {#sec:planetmass}
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Because the wide-separation HR 8799 planets are relatively accessible to optical and near-infrared observations, they have become key benchmark objects for models of planetary atmospheres and evolution. Evolutionary models are highly degenerate in planet mass, luminosity and age, however, in part because the imprint of initial conditions can persist for 100’s of Myr [@marley07]. Depending on initial thermal content, giant planets can exhibit a wide range of luminosities. In principle, independent constraints on planet mass from dynamics offer the potential to break these model degeneracies. Such constraints have the potential to help distinguish between planet formation models, in particular hot-start models where most entropy is retained, e.g. by gas that collapses directly to form planets, from cold-start models where most entropy is lost, e.g. by gas cooling in core accretion. Notably, the core accretion mechanism is challenged to form $5-10$ M$_{\rm Jup}$ planets [*in situ*]{} at the large orbital radii of the HR 8799 planets [@kratter10]. The observed luminosities of the HR 8799 planets cannot be reproduced by the most extreme cold-start models proposed by @marley07. However, they are compatible with the intermediate “warm-start” models discussed by @spiegel12 and @marleau14, since luminosity increases with both 