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Project Progress

Co-I O.B. Toon and colleagues at the University of Colorado published several papers with partial support from the Ames Astrobiology Institute, (as described in this and the following 4 paragraphs). A hydrodynamic escape model was applied to an extrasolar planet (Tian,F., et al., Astrophys. J. 621 (2): 1049-1060 Part 1 Mar 10 2005 ) and was also applied to Earth (Tian F., Toon O.B., Pavlov A.A., DeSterck H.) Science, 308, 1014 (2005); published online 7 April 2005 (DOI: 10.1126/science.1106983). It was shown that early Earth had an atmosphere with tens of percent H₂, and an H₂/CO₂ ratio greater than 1. This means the rebiotic atmosphere was a good source of organic molecules and the past 25 years of searching for extraterrestrial delivery of organics, or inspecting hydrothermal systems is not necessary. Life likely originated in the oceans using the atmospherically generated organics.

The probable results of the solar system passage through interstellar dust clouds was shown to likely cause particles to build up in the stratosphere and block enough sunlight to plunge Earth into a snowball state, and how this might be shown from the geologic record using various elements and isotopes (Alexander A. Pavlov, et al., Geophys. Res. Lett., 32, L03705,doi 10.1029/2004GL021890 (2005); A. A. Pavlov et al., Geophys. Res. Lett., 32, doi 10.10229/2004GL021601, (2005)).

It was shown that mass independent fractionation of sulfur isotopes , the key to quantifying oxygen levels prior to 2.3 bya, can be understood in modern ice cores (A. A. Pavlov, M. J. Mills, O. B. Toon) Geophys. Res. Lett., in press (2005)).

It was shown that the biological record of extinction after the K-T event is consistent with the thermal pulse from the reentering debris. (D. S. Robertson, et al., Geol. Soc. Am. Bull. 116, 760-768,(2004)).

Martian gullies are likely to form under present conditions, and mark an excellent spot to search for life on mars (J. L. Heldmann, et al., J.
Geophys. Res. 110, E05004, doi:10.1029/2004JE002261, (2005)).

Co-I Hollenbach working with outside collaborator U. Gorti has been modeling the photoevaporation of protoplanetary disks around young stars. During the past year a numerical code has been constructed which calculates the evaporation of disks around low mass (solar-type) stars caused by the ultraviolet and X-ray radiation field created by the young, low-mass, central stars themselves. Hollenbach & Gorti (2005a, b, book chapters in separate books, see reference worksheet) presented preliminary results of the heating, cooling, thermal structure, and emission spectra of disks derived from their models. Hollenbach & Gorti (2005b) also presented the first estimates of mass loss rates and dispersal timescales for disks being evaporated by the ultraviolet and X-ray emission from their central stars. Richling, Hollenbach, & Yorke (2005, book chapter, see reference worksheet) reviewed mechanisms for dispersal of disks, and described preliminary results on the photoevaporation caused by the central star.

Co-I Greg Laughlin and his student Aaron Wolf have nearly completed the “Systemic” public-domain radial velocity and photometric data analysis package. During Summer 2005, they plan to release an initial version of the package to the www.transitsearch.org amateur astronomy community for beta testing. The focus of the initial test will be an attempt to obtain a better, self-consistent orbital model for the 55 Cancri 4-planet system, and to test stability of the fit family. Indeed, the Systemic package has already proved to be of great utility. Laughlin and Wolf have used it to obtain a joint radial-velocity — photometric solution for the newly discovered Saturn-mass transiting planet HD 149026b. (Laughlin and Wolf are co-authors on the discovery paper, which acknowledges the Ames NAI grant for supporting their portion of the work). The planet orbiting HD 149026b has important astrobiological consequences. Its small transit radius indicates that it has an extremely massive solid core (60-80 Earth Masses) which indicates that the core accretion hypothesis (and by extension, the common formation of terrestrial planets) is almost certain to be correct.

Co-I Davis has investigated the thermodynamic and physical environment in the early solar nebula. A new cumulative-planetary-mass-model (an integrated form of the surface density) is shown to predict a surface density more consistent with planetary data than that obtained from the commonly used Hayashi minimum mass distribution (S.Davis, Ap. J. Letters, 2005). The condensation/sublimation front in the early solar system is investigated to determine the phase state (gas or ice) of important species relating to organic chemical processes. The two-dimensional water condensation/sublimation front is also computed and contrasted with that predicted by one-dimensional theory (S. Davis, Ap. J., 2005). With Collaborator D. Richard, a new dynamical turbulence model was developed to predict evolutionary growth of a protoplanetary nebula. This analytical model is used as the basis for the chemical-physical modeling activities. In parallel work, the physical basis of the dynamic turbulence model was investigated in light of classical finite amplitude hydrodynamic stability theory. Progress in chemical-physical modeling included: a) application of the analytical solution to the radial drift, evaporation, and diffusion of condensable substances in the nebula b) a study of the condensation front associated with condensable substances in the solar nebula and c) simulation of the deuterium fractionization in the protoplanetary nebula.

Co-I Hollingsworth in collaboration with Co-I Young modeled extreme atmospheric environments and habitable planet climates. Preliminary extreme orbital configuration simulations for the Earth’s climate system have been completed using a realistic 3D climate model which is basically a recent version of the National Center for Atmospheric Research (NCAR), Community Atmospheric Model (CAM). A summary of findings for a particular experiment, wherein the planet’s eccentricity was altered from its present value (epsilon = 0.017) to a highly elliptical orbit (epsilon = 0.500) was carried out for one entire Earth year. The results of these simulations were presented at the 2005 Biennial Meeting of the NASA Astrobiology Institute.