The Infrared Colors of 51 Eridani b: Micrometeoroid Dust or Chemical Disequilibrium?

We reanalyze the near-infrared spectra of the young extrasolar giant planet 51 Eridani b, which was originally presented in Macintosh et al. and Rajan et al. using modern atmospheric models, including a self-consistent treatment of disequilibrium chemistry due to turbulent vertical mixing. In addition, we investigate the possibility that significant opacity from micrometeors or other impactors in the planet's atmosphere may be responsible for shaping the observed spectral energy distribution (SED). We find that disequilibrium chemistry is useful for describing the mid-infrared colors of the planet's spectra, especially in regard to photometric data at the M band around 4.5 μm, which is the result of superequilibrium abundances of carbon monoxide, while the micrometeors are unlikely to play a pivotal role in shaping the SED. The best-fitting, micrometeoroid dust–free, disequilibrium chemistry, patchy cloud model has the following parameters: effective temperature Teff = 681 K with clouds (or without clouds, i.e., the grid temperature Tgrid = 900 K), surface gravity g = 1000 m s−2, sedimentation efficiency fsed = 10, vertical eddy diffusion coefficient Kzz = 103 cm2 s−1, cloud hole fraction fhole = 0.2, and planet radius Rplanet = 1.0 RJup.