  The principal goal of the NASA Terrestrial Planet Finder (TPF) and ESA Darwin
mission concepts is to directly detect and characterize extrasolar terrestrial
(Earth-sized) planets. This first generation of instruments is expected to
provide disk-averaged spectra with modest spectral resolution and
signal-to-noise. Here we use a spatially and spectrally resolved model of the
planet Mars to study the detectability of a planet's surface and atmospheric
properties from disk-averaged spectra as a function of spectral resolution and
wavelength range, for both the proposed visible coronograph (TPF-C) and
mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our
model is a spectrum-resolving (line-by-line) atmospheric/surface radiative
transfer model which uses observational data as input to generate a database of
spatially-resolved synthetic spectra for a range of illumination conditions
(phase angles) and viewing geometries. Results presented here include disk
averaged synthetic spectra, light-curves and the spectral variability at
visible + mid-IR wavelengths for Mars as a function of viewing angle,
illumination, season. We also considered the appearance of an increasingly
frozen Mars and simulated its detection versus real Mars with TPF-C and TPF-I
as a function of spectral resolving power, signal-to-noise, integration time.
