Martian water vapor: Mars Express PFS/LW observations

Abstract

We present the seasonal and geographical variations of the Martian water vapor monitored from the Planetary Fourier Spectrometer Long Wavelength Channel aboard the Mars Express spacecraft. Our dataset covers one Martian year (end of Mars Year 26, Mars Year 27), but the seasonal coverage is far from complete. The seasonal and latitudinal behavior of the water vapor is globally consistent with previous datasets, Viking Orbiter Mars Atmospheric Water Detectors (MAWD) and Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES), and with simultaneous results obtained from other Mars Express instruments, OMEGA and SPICAM. However, our absolute water columns are lower and higher by a factor of 1.5 than the values obtained by TES and SPICAM respectively. In particular, we retrieve a northern midsummer maximum of 60 pr-μm, lower than the 100-pr-μm observed by TES. The geographical distribution of water exhibits two local maxima at low latitudes, located over Tharsis and Arabia. Global Climate Model (GCM) simulations suggest that these local enhacements are controlled by atmospheric dynamics. During Northern spring, we observe a bulge of water vapor over the seasonal polar cap edge, consistent with the northward transport of water from the retreating seasonal cap to the permanent polar cap. In terms of vertical distribution, we find that the water volume mixing ratio over the large volcanos remains constant with the surface altitude within a factor of two. However, on the whole dataset we find that the water column, normalized to a fixed pressure, is anti-correlated with the surface pressure, indicating a vertical distribution intermediate between control by atmospheric saturation and confinement to a surface layer. This anti-correlation is not reproduced by GCM simulations of the water cycle, which do not include exchange between atmospheric and subsurface water. This situation suggests a possible role for regolith-atmosphere exchange in the Martian water cycle.

The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity

“…Seasonal water reservoirs include water ice on or within the seasonal or residual polar caps, surface or subsurface ice in high-latitude regions, physically adsorbed and chemically-bound water within the near-surface regolith, and possibly surface and subsurface liquid water in the form of liquid saline solutions (brine) (Jakosky 1985). Satellite and telescopic observations of variations in the integrated H 2 O column abundance (Conrath et al 1973;Jakosky and Farmer 1982;Sprague et al 1996;Smith 2004;Fedorova et al 2006;Fouchet et al 2007;Melchiorri et al 2006), in combination with numerical modeling, have been used to determine the relative importance of the various processes controlling the seasonal H 2 O cycle (Flasar and Goody 1976;Jakosky and Farmer 1982;Haberle and Jakosky 1990;Richardson and Wilson 2002;Böttger et al 2005). The seasonal H 2 O cycle is important for the Martian climate because it leads to the formation and affects the stability of water ice deposits on the surface and of water ice clouds in the atmosphere (Jakosky and Haberle 1992;Richardson and Wilson 2002;Smith et al 1997;Haberle et al 1999;Montmessin et al 2004;Madeleine et al 2012).…”

Water vapor map of Mars near summer solstice using ground-based infrared spectroscopy

“…However this assumption may be incorrect, due to possible fractionation effects associated to water condensation and sublimation (Fouchet & Lellouch 2007) or photodissociation. Montmessin et al (2005) have calculated the expected D/H ratio on Mars as a function of latitude and season.…”

A study of the Martian water vapor over Hellas using OMEGA and PFS aboard Mars Express

“…Mars Express instruments disagree whether the watervapor mixing ratio stays constant from the bottom to the top of the volcano. Using PFS/LW data, Fouchet et al (2007) found the H 2 O mixing ratio to be constant within a factor 2 over Olympus Mons, while Maltagliati et al (2006Maltagliati et al ( , 2008 used OMEGA data to find some spatial and temporal variabilities with, in most of the cases, a local enhancement of the water mixing ratio by a factor of 4 around the summits. Assuming a conservative maximum possible enhancement by a factor of 4 in the mixing ratio over Olympus Mons, the resulting water-vapor column density would be 6.4 pr-µm instead of 1.6 pr-µm.…”

“…The PFS long-wavelength data were used in the thermal regime (Fouchet et al 2007), while both the OMEGA and SPICAM analyses were based on the reflected part of the spectrum. The OMEGA analysis used the H 2 O 2.6-µm band (Encrenaz et al 2005;Melchiorri et al 2007a;Maltagliati et al 2007), and the SPICAM results were obtained from the 1.38-µm water band (Fedorova et al 2007).…”

“…In addition, because of the high surface pressure of this area, the water-vapor band depths are usually stronger and can be measured with better accuracy than elsewhere on the Martian disk, and reliable information can be retrieved for each individual orbit by integrating the spectra over the region of lowest altitude. The PFS work is based on the analysis of the H 2 O rotational lines in the thermal regime (Fouchet et al 2007). Observations and data analysis are presented in Sect.…”