The Mariner Mars 6 and 7 infrared spectrometer spectra of Mars include a broad absorption near 3 μ that can be ascribed to water of hydration in the surface minerals and/or ice. Laboratory experiments show that an increase in either form of condensed phase water is accompanied by a decreased intensity ratio R1 = I(3.10 μ)/I(2.20 μ). Evidence for the presence of ice is provided by the intensity ratio R2 = I(2.90 μ)/I(3.10 μ) since R2 is below unity for silicate hydrates and exceeds unity for ice. Near the Martian equator both the surface temperature and R1depend inversely upon brightness at 2.2 μ: a doubling of B(2.2 μ) is accompanied by a 19° temperature drop and a 30% drop in R1. BothR1 and R2 depend upon latitude: R1 is low near the equator and at latitudes more southerly than 50°S, whereas R1 is high in between. These data show that condensed phase water is present throughout the observed surface of Mars, the brighter areas near the equator (and north of it) and the regions south of 50°S being the most hydrated. All three variables, B(2.2), R1, and R2, change dramatically and in concert in a 5° latitude range at the polar cap edge. The characteristic spectral signature of ice can be discerned as well, indicating that ice is forming in this region, most likely on the planetary surface.
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