Planets larger than Earth and smaller than Neptune are some of the most
numerous in the galaxy, but observational efforts to understand this population
have proved challenging because optically thick clouds or hazes at high
altitudes obscure molecular features (Kreidberg et al. 2014b). We present
models of super Earths that include thick clouds and hazes and predict their
transmission, thermal emission, and reflected light spectra. Very thick, lofted
clouds of salts or sulfides in high metallicity (1000x solar) atmospheres
create featureless transmission spectra in the near-infrared. Photochemical
hazes with a range of particle sizes also create featureless transmission
spectra at lower metallicities. Cloudy thermal emission spectra have muted
features more like blackbodies, and hazy thermal emission spectra have emission
features caused by an inversion layer at altitudes where the haze forms. Close
analysis of reflected light from warm (~400-800 K) planets can distinguish
cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models,
which are very dark (0.0-0.03). Reflected light spectra of cold planets (~200
K) accessible to a space-based visible light coronagraph will have high albedos
and large molecular features that will allow them to be more easily
characterized than the warmer transiting planets. We suggest a number of
complementary observations to characterize this population of planets,
including transmission spectra of hot (>1000 K) targets, thermal emission
spectra of warm targets using the James Webb Space Telescope (JWST), high
spectral resolution (R~10^5) observations of cloudy targets, and reflected
light spectral observations of directly-imaged cold targets. Despite the dearth
of features observed in super Earth transmission spectra to date, different
observations will provide rich diagnostics of their atmospheres.Comment: 23 pages, 23 figures. Revised for publication in The Astrophysical
Journa