Thermal radiation of magma ocean planets using a 1‐D radiative‐convective model of H 2 O‐CO 2 atmospheres

This paper presents an updated version of the simple 1‐D radiative‐convective H 2 O‐CO 2 atmospheric model from Marcq (2012) and used by Lebrun et al. (2013) in their coupled interior‐atmosphere model. This updated version includes a correction of a major miscalculation of the outgoing longwave radiation (OLR) and extends the validity of the model ( P coordinate system, possible inclusion of N 2 , and improved numerical stability). It confirms the qualitative findings of Marcq (2012), namely, (1) the existence of a blanketing effect in any H 2 O‐dominated atmosphere: the outgoing longwave radiation (OLR) reaches an asymptotic value, also known as Nakajima's limit and first evidenced by Nakajima et al. (1992), around 280 W/m 2 neglecting clouds, significantly higher than our former estimate from Marcq (2012). (2) The blanketing effect breaks down for a given threshold temperature T ϵ , with a fast increase of OLR with increasing surface temperature beyond this threshold, making extrasolar planets in such an early stage of their evolution easily detectable near 4 μm provided they orbit a red dwarf. T ϵ increases strongly with H 2 O surface pressure, but increasing CO 2 pressure leads to a slight decrease of T ϵ . (3) Clouds act both by lowering Nakajima's limit by up to 40% and by extending the blanketing effect, raising the threshold temperature T ϵ by about 10%.