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Project Progress

Spatially and Spectrally-Resolved Planetary Models: The completed spatially and spectrally-resolved Task 1 planetary models were used for a publication on the Earth model (Tinetti et al., 2006), one publication in press on Earth model experiments on detectability of the vegetation red edge (Tinetti et al, 2006), and one publication on the vegetation red edge for an alternative photosynthesis scheme for a planet around a cooler star (Tinetti et al., 2006). For this latter paper, we explored the detectability of vegetation on the surface of a terrestrial planet orbiting an M-star. The exovegetation was modelled with a pigment-derived surface signature that is red-shifted with respect to the Earth vegetation red-edge (near 1.0µm, rather than being near 0.7um). The red-shift was estimated using a model of leaf optical properties, combined with a three photon photosynthetic scheme calculated for possible exovegetation growing on an M-star planet. To determine the detectability of the exovegetation signature, we used the VPL Task 1 3-D Earth model. This model can generate disk-averaged spectra and broad-band integrated fluxes, useful to future terrestrial planet exploration missions, such as NASA Terrestrial Planet Finder-Coronograph. However, instead of Earth specific data, we input the atmospheric profiles and cloud distributions predicted for a synchronous planet orbiting an M-dwarf, an M-dwarf stellar spectrum, and the distinctive surface reflectance of the exovegetation. While on Earth this pigment-derived surface feature would be almost completely masked by water absorption, even in a cloud-free atmosphere, we found that the strength of the edge feature on our simulated terrestrial planet can exceed that on Earth, given the right conditions. Obviously the detectability of such a biosignature would be highly dependent on the extent of vegetation surface area, cloud cover and viewing angle.

Remote-sensing Observations of Solar System Planets: To continue our exploration of the use of remote-sensing techniques for determining terrestrial planet environmental characteristics, and to provide data input to the Task 1 models, we undertook ground-based telescopic observing runs of Earthshine, Mars, Venus and Titan using the Anglo-Australian Telescope, Gemini North and South, and the Infrared Telescope Facility. We also analyzed Spitzer spacecraft data for Neptune and Titan in search of higher order hydrocarbons and oxygenated compounds that would provide clues to the nature of organics and volatiles in infalling material to these planets. We discovered two new hydrocarbons on Neptune, C₃H₄ and C₄H₂. From our IRTF/CSHELL observations of Martian CO₂ band structures we developed a new ground-based technique to remotely map the distribution of atmospheric pressure (and hence topography) to a sensitivity of ~4 Pa. We also developed an initial version of a new line-by-line planetary atmosphere radiative transfer model (VSTAR).