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Project Progress

The likelihood that Earth-like planets exist in orbit around stars similar to the Sun has been investigated using computer simulations of planetary accretion. It is found that terrestrial planets should form in orbit around Sun-like stars provided that a star’s protoplanetary nebula and giant planets are not too dissimilar to those of the Solar System. However, the simulations demonstrate that Earth-like planets do not form if a star has giant planets moving on orbits with periods of less than a few years, or moving on highly eccentric or inclined orbits. These results were presented at the 2002 Astrobiology Science conference, Moffett Field, CA (AMES), April 7-11 (J. Chambers, Terrestrial Planet Formation in Extrasolar Systems) and a paper is nearly ready for submission to the journal Icarus for publication.

The radiative-convective climate model of Kasting has been updated by including a new routine for calculating infrared fluxes. This routine uses 16-term correlated-k coefficient sums to parameterize absorption by CO₂ and H₂O. The k’s are spaced so that they give good resolution of the Doppler cores of absorption lines. This allows us to calculate accurate temperature profiles in the stratosphere?something that the previous climate model was not good at.

During the previous year the group led by Brian Toon and Margaret Tolbert at the University of Colorado made progress in a number of areas. Through a combination of laboratory studies {“The condensation of carbon dioxide on water ice: Implications for the Martian atmosphere” (D. Glandorf, A. Colaprete, M. A. Tolbert, O. B. Toon), Icarus submitted (2002) and numerical modeling (“Carbon dioxide clouds at high altitude in the tropics and in an early dense Martian atmosphere”, (A Colaprete, and O. B. Toon), Icarus submitted, (2002)}, it has been shown that carbon dioxide clouds are unlikely to have provided a significant greenhouse warming in the early history of Mars. Therefore, the greenhouse model to explain the ancient river valleys on Mars is seriously flawed.?

Further work in progress has shown what types of particles may have formed in the early terrestrial atmosphere {Trainer, MG., Daniel B. Curtis, Alice E. Delia, Owen B. Toon, Margaret A. Tolbert, Christopher P. McKay, and Douglas R. Worsnop, 2002, Mass Spectrometric Laboratory Studies of Tholin Particles: Application to Early Earth and Titan, Presented at the 2002 Astrobiology Science Conference, Moffett Field, CA (AMES), April 7-11; and Trainer, MG., Daniel B. Curtis, Alice E. Delia, Darin W. Toohey, Owen B. Toon, Margaret A. Tolbert, Christopher P. McKay, and Douglas R. Worsnop, 2002, Laboratory Studies of Early Earth Tholin Particles, Presented at the 2002 Laboratory Astrophysics Workshop, Moffett Field, CA (AMES), May 1-3}.

Analysis of data returned from the Clouds and Earth’s Radiant Energy System (CERES) instrument onboard the Earth Observing System (EOS) satellites shows the same behavior as found in data from the predecessor Earth Radiation Budget Experiments (ERBE) over the warm pool in the Pacific Ocean. Namely, the outgoing IR radiative energy flux maximizes and then decreases as a function of increasing sea surface temperature (SST), a signature of the runaway greenhouse effect. It has been shown that there is a clear distinction between maximum SST and SST at which the outgoing infrared (IR) flux is a maximum. In addition, it has been shown that there is an excellent inverse correlation between outgoing IR flux and amount of water vapor above 5 km altitude. A paper on this work was presented at the 2002 Astrobiology Science Conference, Moffett Field, CA (AMES), April 7-11 (The Runaway Greenhouse Effect on Earth and Its Implications for Other Planets, M. Rabbette, C. McKay, P. Pilewskie, R. Young, S. Clanton), and a paper has been submitted for publication to the journal Science (2002) (Rabbette, McKay, Pilewskie, Young).