  Recent studies have unequivocally proven the existence of clouds in
super-Earth atmospheres (Kreidberg et al. 2014). Here we provide a theoretical
context for the formation of super-Earth clouds by determining which
condensates are likely to form under the assumption of chemical equilibrium. We
study super-Earth atmospheres of diverse bulk composition, which are assumed to
form by outgassing from a solid core of chondritic material, following Schaefer
& Fegley (2010). The super-Earth atmospheres that we study arise from planetary
cores made up of individual types of chondritic meteorites. They range from
highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are
both subsolar and super-solar, thereby spanning a range of atmospheric
composition that is appropriate for low-mass exoplanets. Given the atomic
makeup of these atmospheres, we minimize the global Gibbs free energy of
formation for over 550 gases and condensates to obtain the molecular
composition of the atmospheres over a temperature range of 350-3,000 K. Clouds
should form along the temperature-pressure boundaries where the condensed
species appear in our calculation. We find that the composition of condensate
clouds depends strongly on both the H:O and C:O ratios. For the super-Earth
archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at
solar composition, in agreement with previous work (Morley et al. 2013;
Miller-Ricci Kempton et al. 2012). However, for oxidizing atmospheres, K2SO4
and ZnO condensates are favored instead, and for carbon-rich atmospheres with
super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds
form from a wide variety of rock-forming and metallic species.
