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Project Progress

During the past year my group at the University of Colorado published 10 papers with partial, additional support from the Ames Astrobiology Institute.

We developed a hydrodynamic escape model, which we applied to an extrasolar planet (“Transonic hydrodynamic escape of hydrogen from extrasolar planetary atmospheres”( Tian, F., Toon, O.B., Pavlov, A.A., & DeSterk, H.), Astrophys. J. 621 (2): 1049-1060 Part 1 Mar 10 2005 ) which we then applied to Earth (“A hydrogen-rich early earth atmosphere” (Tian F., Toon O.B., Pavlov A.A., DeSterck H.) Science, 308, 1014 (2005); published online 7 April 2005 (DOI: 10.1126/science.1106983). We showed 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.

We investigated the likely results of the solar system passage through interstellar dust clouds. Such passages must have occurred many times in Earth history. we found that passage through a dense cloud would have caused particles to build up in the stratosphere and block enough sunlight to plunge Earth into a Snowball. We show how this might be shown from the geologic record using various elements and isotopes “Passing through a Giant Molecular Cloud – Snowball Glaciations produced by interstellar dust.” (Alexander A. Pavlov, Owen B. Toon, Anatoli K. Pavlov, John Bally, David Pollard)Geophys. Res. Lett., 32, L03705,doi 10.1029/2004GL021890 (2005).). During a magnetic reversal while passing through a less dense cloud the Earth’s ozone layer may have been destroyed (Catastrophic ozone loss during passage of the Solar system through an interstellar cloud, A. A. Pavlov, A.K.. Pavlov, M.J. Mills, V. M. Ostryakov, G. I Vasilyev, and O. B. Toon, Geophys. Res. Lett., 32, doi 10.10229/2004GL021601, (2005).).

We showed 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 “Mystery of the volcanic mass-independent sulfur isotope fractionation signature in the Antarctic ice-core” (A. A. Pavlov, M. J. Mills, O. B. Toon) Geophys. Res. Lett., in press (2005).)

We showed that the biological record of extinction after the K-T event is consistent with the thermal pulse from the reentering debris. “Survival in the first hours of the Cenezoic” (D. S. Robertson, M. C. McKenna, O. B. Toon, S. Hope and J. A. Lillegraven) Geol. Soc. Am. Bull. 116, 760-768,(2004).)

We showed that Martian gullies likely form under present conditions, and mark an excellent spot to search for life on mars (“Formation of Martian gullies by the flow of liquid water flowing under current Martian environmental conditions” (J. L. Heldmann, O. B. Toon, W. Pollard, M. Mellon, J. Pitlick, C. P. McKay, and D. T. Andersen) J. Geophys. Res. 110, E05004, doi:10.1029/2004JE002261, (2005).)

Finally we investigated the formation of hazes on Titan and the early Earth. Cassini may provide a check on how closely these lab studies resemble a planetary atmosphere. For early Earth we need to understand if these particles are food for the biota, if they alter the climate, and if they are so thick that they make the early Earth look like Titan does now. (“Chemical Composition of Titan’s Haze: Are PAHs present?” Melissa G. Trainer, Alexander A. Pavlov, Jose L. Jimenez, Christopher P. McKay, Douglas R. Worsnop, Owen B. Toon, and Margaret A. Tolbert, Geophys. Res. Lett, 31, L17S08, doi: 10.1029 /2004 GL0 19859 (2004). “Laboratory Studies of Butane Nucleation on organic haze Particles: Application to Titan’s Cloud”, (Curtis, D. B., Glandorf, D. L., Toon, O. B., Tolbert, M. A., McKay, C. P., and Khare, B. N.,) J. Phys. Chem. A 109 (7): 1382-1390 FEB 24 (2005). “Haze Aerosols in the Atmosphere of Early Earth: Manna from Heaven”, Trainer,M.G., Pavlov,A.A., Curtis, D.B., McKay, C.P., Worsnop, D.R., Delia, A.E., Toohey ,D.W., Toon, O.B., & Tolbert, M.A.), Astrobiology, 4,409-419,2004.)