Abstract
SPICAM-IR, an AOTF spectrometer onboard Mars Express spacecraft with a
resolving power of 2,000 covering the spectral range 1-1.7 μm has been
observing Mars since 2004. In this wavelength range, it is possible to
distinguish between CO2 and H2O ices and measure their band depths. We
obtained about 200,000 high-fidelity spectra of CO2 ice in different
seasons and locations over the Martian polar caps. The spectra have been
associated with slab ice, fine-grained ice, permanent caps, and dark and
dirty ice at the cryptic region of the south polar cap. Also, we
observed more than 200,000 water ice spectra, specifically its broad
feature around 1.5 μm. Water ice is present at the surface or in the
atmosphere resulting in a variety of different band depths, often in
combination with the CO2 ice. We mapped the equivalent width of 1.43 μm
CO2 ice band and the depth of 1.5 μm water ice band, which are the
proxies for grain size, and followed their seasonal evolution. From the
maps, we produced the edge (outer crocus line) of the CO2 south and
north caps for nine Martian Years. The cap edges evolve similarly
through all years and are in good agreement with previous OMEGA/Mars
Express observations. We also discuss the impact of the global dust
storms on the cap edges. Lastly, we interpret some of the water ice
observations as water ice clouds in the aphelion cloud belt and the
polar hoods.