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Project Progress

This project was composed of three separate research objectives: 1) to improve our modeling of planetary atmospheres to better understand factors governing planetary habitability and for purposes of remote detection of habitable conditions and signs of life, 2) to better understand the likely habitability of recently discovered super-Earths around other stars, and 3) to test the limits for life on Earth in extreme, cold environments, similar to those that might be found at the outer edge of the habitable zone, or in Mars-like environments.

Exploring Planetary Habitability and Remotely-Detectable Signs of Habitability and Life

In this first task, we worked on several different topics. First, we continued our investigations of planets around M stars as possible abodes for life (Scalo et al., 2007), and are currently developing 3-D dynamical models for the habitability of tidally locked planets. We also addressed the question of whether O₂ might be produced abiotically in CO₂-rich atmospheres on planets orbiting young G stars (Segura et al., 2007). Contrary to the conclusion reached by other authors (F. Selsis et al., Astron. & Astrophys., 2002), we found that O₂ is unlikely to build up abiotically in such atmospheres, even if the stellar UV luminosity is very high. Our model balances the atmospheric hydrogen budget, whereas the Selsis et al. model did not. We also worked with Franck Selsis and colleagues (Selsis et al., 2007a) to study the possibility that hot ocean planets might be observed with the ESA space telescope CoRoT and with NASA’s forthcoming Kepler space telescope. The tentative answer is 'yes’, assuming such planets exist. Such planets would have hot, dense steam atmospheres and would almost certainly be uninhabitable, but this would be a first step towards showing that H₂O-rich rocky planets exist around other stars. We have also explored habitability on on Enceladus, a planetary moon in our Solar System that our outside the classical habitable zone (Parkinson et al., 2007, 2008)

In addition to these research papers, review papers were published on “Habitable planets around the Sun and other stars” (Kasting, 2008) and “Planetary environmental signatures for habitability and life” (Meadows, 2008).

Planetary Habitability Modeling for Observed Super-Earths

We again worked with Franck Selsis (Selsis et al., 2007b) to study the habitability of the observed planets around Gliese 581. Gliese 581 is a dim, red M star which has 3 planets orbiting around it, as shown by Doppler velocimetry. The two outermost planets, 'c’ and 'd’, orbit close to the inner and outer edges of the habitable zone, respectively. Gliese 581c was initially reported to be within the habitable zone (S. Udry et al., Astron. & Astrophys., 2007); however, our modeling showed that this was unlikely to be the case, as this planet receives ~30% more starlight than does Venus in our own Solar System.

Field Work Exploration of the Limits of Life in Cold Environments

We have measured several environmental parameters associated with the distribution of microbial life in regolith in Svalbard. This field site has Mars analog regolith and obvious contacts between surface environments with obviously habitable and less habitable zones. Some of the factors that influence the distribution and functional diversity of microbial life are wavelengths and intensity of available light, bioavailability of water, mechanical stability, mineral abundances, optical properties of the minerals for rock-dwelling microbes, temperature, wind speed and direction, radiation environment, etc.