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Project Progress

Habitable Planets (dm)

Our first geochemical modeling study of the aqueous alteration of the parent bodies of carbonaceous (CM) meteorites was completed. Some of these results were presented at the April 2000 Astrobiology Science Conference at Ames, and a manuscript reporting on the study was just completed. The results support a scenario in which low-temperature aqueous alteration of an anhydrous CM parent body and melt water from H2O and CO2 ices produces the altered assemblage observed in CM meteorites.

A model has been developed in which atmospheric carbon dioxide (and therefore climate) is controlled by continental and seafloor weathering. This model predicts that Earth would have been cold in the Archean if there were no other greenhouse gases. A paper reporting this work has been submitted to Journal of Geophysical Research.. A sample from a 3.85 billion year old Banded Iron Formation has been analyzed in a search for meteoritic material. Little was found, which can be explained in part by rapid sedimentation and in part by sampling biases inherent in power law distributions. A paper describing this work was submitted to Journal of Geophysical Research .

Laboratory and theoretical studies were accomplished concerning how carbon dioxide ice clouds affect the greenhouse effect, and hence the outer boundary of the habitable zone. In work done at Pennsylvania State Univerisity, CO2 clouds were shown to be strongly warming, but the clouds can cool the surface if they are low and/or optically thick. A paper summarizing this work was submitted to the journal Icarus . Laboratory work investigating cloud condensation is being conducted at the University of Colorado. This work provides critical information on cloud condensation microphysics needed to model carbon dioxide clouds in early atmospheres of Mars and possibly Earth, as well as in the current atmosphere of Mars. A paper on this work has been submitted to Geophys. Res. Lett. A study of the radiative fluxes in the Earth’s atmosphere over the Pacific Ocean has been initiated at Ames because satellite observations indicate the signature of the runaway greenhouse effect in localized regions, together with an unidentified mechanism, perhaps clouds, that limit sea surface temperature. Initial radiative transfer calculations show that with sufficient and reasonable amounts of water vapor distributed appropriately, a maximum is reached in the emitted upward thermal infrared flux at the top of the atmosphere, consistent with the satellite observervations.