[PCG25-P04] The influence of carbon escape on the evolution of the Martian atmosphere
Keywords:Mars, Atmospheric escape, Atmospheric evolution
We investigated the effect of carbon escape on the accumulation of O2 in the atmosphere using two models. The first is a 1-box model that considers only the supply and loss of atmosphere from the atmospheric boundaries. This model was used to get an overview of the atmospheric evolution. The second is a 1-dimensional photochemical model. This model investigated the evolution of atmospheric composition taking into account atmospheric photochemistry in addition to the supply and loss from the atmospheric boundaries. This model was applied during periods when the atmosphere was expected to regenerate to be an O2-dominated atmosphere after a massive loss of the atmosphere. The results of our 1-box model suggested that an O2-dominated atmosphere was formed during times when oxygen thermal escape was diminished and carbon thermal escape was still strong. Applying the 1-dimensional photochemical model in the same period, i.e., early in Noachian, ~1 mbar of O2-dominated atmosphere was formed in about 104 years. However, the period of the O2-dominated atmosphere formation is inconsistent with the Curiosity measurement.
Therefore, we invoked the uncertainly in the evolution of stellar EUV flux due to the difference in the initial rotational speed of the star. When the star's initial rotation speed is fast, the period when the stellar EUV is strong lasts longer. Hence, the period during which the atmosphere cannot be maintained due to massive escape would be longer. This effect shifts the period when the O2-dominated atmosphere is formed, so that it is in the Hesperian period. Our study suggests that ~1 mbar O2-dominated atmosphere may be formed during the Hesperian period by taking into account carbon escape, if the stellar evolution is the type of the fast rotator. This is consistent with the results of the Curiosity measurement.