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Project Progress

This project uses spatially resolved spectral models of planets in our own solar system to determine the instrument sensitivity and spectral resolution required to detect signs of habitability or life in disk-averaged astronomical spectra of extrasolar planets at visible and infrared wavelengths.

This year, we completed the Mars model by using a spectrum resolving (line-by-line) atmospheric/surface radiative transfer model (Spectral Mapping Atmospheric Radiative Transfer (SMART), D. Crisp), and Martian surface albedos (from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES)) and atmospheric data derived from the Ames Mars General Circulation Model (MGCM) simulations to generate a database of spatially resolved synthetic spectra for a range of illumination conditions (phase angles) and viewing geometries. These results were then processed with a model that resamples the spatially resolved spectra to create a synthetic, disk-averaged view of the planet from a specific viewing geometry. These results were validated via comparison with the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). The three-dimensional (3-D) “datacube” of synthetic spectra generated by the model was used to determine the effects of spatial and spectral averaging, and temporal variability on the detectability of surface features, and its potential for habitability. The results include disk-averaged synthetic spectra or images, and lightcurves showing variability at visible and MIR wavelengths as a function of viewing angle. We also explored the ability to detect the CO₂ ice cap in the disk-averaged spectra, using TPF instrument models. We have determined that the ice cap must cover down to 50 degrees latitude before a low-resolution, pole-on disk averaged spectrum would show detectable spectral features of CO₂ ice. Currently we are working on the comparable Earth model, having acquired the relevant satellite data to start the radiative transfer modeling.

Figure 1a, 1b. Disk-averaged spectra at visible (a) and mid-IR wavelengths (b) for increasing extension of the southern polar-cap area to 0 (black curve), 20 (violet curve), 40 (light-blue curve), 50 (gree
n curve), 60 (yellow curve), 70 (red curve), 80 (grey curve), 90 (black curve) degrees from the pole. For larger planet ice coverage, the CO₂ ice feature is seen at wavelengths between 11 and 13.5 microns (G. Tinetti).

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