  We have investigated mid-infrared spectra of Earth obtained by the
Atmospheric Infrared Sounder (AIRS) instrument on-board the AQUA spacecraft to
explore the characteristics that may someday be observed in extrasolar
terrestrial planets. We have used the AIRS infrared (R ~ 1200; 3.75-15.4
microns) spectra to construct directly-observed high-resolution spectra of the
only known life bearing planet, Earth. The AIRS spectra are the first such
spectra that span the seasons. We investigate the rotational and seasonal
spectral variations that would arise due to varying cloud amount and viewing
geometry and we explore what signatures may be observable in the mid-infrared
by the next generation of telescopes capable of observing extrasolar
terrestrial planets.
