Koskinen et al. (2010a) demonstrated that the H Lyman α transit observations (Ben-Jaffel, 2007, 2008) can be explained with absorption by H in the thermosphere if the base of the hot layer of H is near 1 μbar, the mean temperature within the layer is about 8250 K, and the atmosphere is mostly ionized above 3Rp. These parameters are based on fitting the data with a simple empirical model of the upper atmosphere. The density and temperature profiles from our new hydrodynamic model agree qualitatively with these constraints, demonstrating that the basic assumptions of Koskinen et al. (2010a) are reasonable. This confirms once again that a comet-like tail (Vidal-Madjar et al., 2003) or energetic neutral atoms (Holström et al., 2008) are not necessarily required to explain the H Lyman α observations.
hot layer of H
base
near 1 μbar
μbar
hot layer of H
mean temperature
8250 K
K
atmosphere
mostly ionized
above 3Rp
Rp