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2013 Annual Science Report

Pennsylvania State University Reporting  |  SEP 2012 – AUG 2013

Biosignatures in Ancient Rocks - Kasting Group

Project Summary

The work by Ramirez concerned updating the absorption coefficients in our 1-D climate model. Harman’s work consisted of developing a 1-D code for modeling hydrodynamic escape of hydrogen from rocky planets.

4 Institutions
3 Teams
0 Publications
3 Field Sites
Field Sites

Project Progress

Here, we will just describe the major result of paper (i) below. Because of higher absorption of solar visible/near-IR radiation by H2O, the inner edge of the liquid water habitable zone around the Sun has moved significantly outwards, from ~0.95 astronomical units (AU) to 0.99 AU. A figure showing the new habitable zone boundaries for different types of stars in terms of effective stellar flux is shown in Fig. 1 below.

Figure 1.
Figure 1. Comparison of the multiple S isotope data on natural samples (>2.4 Ga) with those of experimental products of thermochemical sulfate reduction using amino acids, including our and O’duro’s data (2012) (Choney et al., in prep).

Diagram showing different HZ boundaries for stars ranging in spectral type from F0 to M7. The “1st CO2 condensation” limit is no longer considered valid for the outer edge, for reasons discussed in the text. Various planets within our Solar System are shown, along with selected exoplanets. [From Kasting et al., PNAS, submitted (ref. iii) above]

Additional research described in our other papers shows that early Mars could have been warmed above the freezing point of water by the greenhouse effect of a CO2-H2 atmosphere. We also showed that increases in atmospheric CO2 cannot cause a runaway greenhouse on Earth, no matter how much CO2 is added.