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Project Progress

The results of our coupled climate-chemical modeling of Earth-like planet atmospheres around M stars was published (Segura et al., 2005). We found that planets around quiescent and active M dwarfs with similar biogenic fluxes to Earth’s may have larger amounts of atmospheric methane, nitrous oxide and methyl chloride than modern Earth as a result of longer atmospheric lifetimes. This means that signs of life maybe easier to detect on those planets than on planets around other types of stars.

We are studying the effects of intense recurrent flaring on the photochemistry, climate, and biosignatures of planets with oxygen-rich atmospheres. A new planetary climate-chemistry model was developed to simulate the effect of stellar flares on the atmospheres of habitable planets. To provide the time-dependent stellar radiation input to this model, an algorithm was written for generating a synthetic time series of flux consisting of a very large number of flares whose properties are sampled from probability distributions that have been derived for solar and stellar flares. An example of the incident flux is shown in the figure. The first step of the study is to irradiate an Earth-like atmosphere with a single flare strong enough to disrupt the photochemistry, in order to learn which reactions limit the recovery to the former steady state, and how this recovery time depends on intensity, duration, and spectral distribution. The next step will use a series of flares that are exactly periodic, to find the time between flares below which return to steady state does not occur. This work will be followed by irradiation by a realistic synthetic times series of flares.

In a third sub-project, we performed a set of simulations of uninhabited planets with different amounts of CO₂ interacting with the present solar UV flux, and higher UV flux, from a solar-like young star (EK Draconis). These models are being used to determine the possibility of a false positive detection of life due to the abiotic formation of O₃ and O₂ in planets with high CO₂ atmospheres (Fig.1). Our results indicate that even in the best scenario for the abiotic formation of O₂ and O₃, that is a planet with 2 bars of CO₂ under a high UV environment, the O₂ and O₃ concentrations are not enough to be detectable (Fig. 2). We also found that in the MIR, CO₂ dominated atmospheres may produce sufficiently strong features to allow the determination of the isotopic ratios of O in the atmosphere.