OMEGA/Mars Express: South Pole Region, water vapor daily variability

Abstract

Polar regions on Mars are the most suitable places to observe water vapor daily variability because in any observation crossing the Pole we can observe very different local time and because the poles are considered to be the main permanent and seasonal water reservoir of the planet.We report on a daily variability of water vapor in the south pole region (SPR), observed by OMEGA/Mars Express during the south spring-summer period (Ls∼250 • -270 • ) outside the CO 2 ice cap, that has never been observed before by other instruments. We have been able to estimate an increase of few precipitable microns during the day.A possible scenario includes the presence of regolith, or another component that could gather water from the atmosphere, adsorbing the water into the surface during the night time and desorbing it as soon as the sun reaches sufficient height to heat the ground. This hypothesis is even more plausible considering the presence of observed local enhancements in the morning sections associated with the illumination of the Sun and the We report on a daily variability of water vapor in the south pole region (SPR), observed by OMEGA/Mars Express during the south spring-summer period (Ls∼250 • -270 • ) outside the CO 2 ice cap, that has never been observed before by other instruments. We have been able to estimate an increase of few precipitable microns during the day.A possible scenario includes the presence of regolith, or another component that could gather water from the atmosphere, adsorbing the water into the surface during the night time and desorbing it as soon as the sun reaches sufficient height to heat the ground. This hypothesis is even more plausible considering the presence of observed local enhancements in the morning sections associated with the illumination of the Sun and the total absence in the data of water ice.

MGS TES observations of the water vapor above the seasonal and perennial ice caps during northern spring and summer

“…Formisano et al (2001) studied the water vapor diurnal cycle in southern mid-latitudes at L s = 290-340°with the Mariner 9 data and observed diurnal changes in column abundances of up to 10 pr-lm, which they attributed to exchange with the regolith. Melchiorri et al (2009) observed diurnal variability of several precipitable micrometers near the South Pole during summer and also attributed it to the exchange with regolith. These examples demonstrate the magnitude of the possible diurnal effect.…”

Mars’ water vapor mapping by the SPICAM IR spectrometer: Five martian years of observations

“…Using the OMEGA data Melchiorri et al (2009) have observed a increase in water vapor from 5:00 (2 pr. lm) to 16:00 (10 pr.…”

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

“…The thermal infrared range was used by the IRIS instrument aboard Mariner 9 (Conrath et al 1973), then by TES aboard Mars Global Surveyor (Smith 2002(Smith , 2004) and more recently by PFS aboard Mars Express ). In the reflected spectrum, both the MAWD experiment aboard Viking and SPICAM aboard Mars Express used the 1.38 μm H 2 O band (Farmer et al 1977;Jakosky & Haberle 1992;Fedorova et al 2004Fedorova et al , 2007 while OMEGA aboard Mars Express (Encrenaz et al 2005Melchiorri et al 2007Melchiorri et al , 2009Maltagliati et al 2007Maltagliati et al , 2008 and CRISM aboard Mars Reconnaissance Orbiter ) used the 2.6 μm H 2 O band, still in the reflected solar spectrum. All these analyses however have a common limitation, which is the lack of simultaneous mapping of the planet.…”

“…There is actually an exception, when the orbital sequence crosses the polar region. In this case, morning and evening data can be acquired in a single orbit; however, this method is limited to the study of high latitude regions (Melchiorri et al 2009). …”

“…The interest for such a study was driven by the fact that, using OMEGA/Mars Express data obtained over the south pole just before the southern solstice (L s = 250-270 • ) Melchiorri et al (2009) reported some daily variability for southern latitudes higher than 60 S, with an increase of a few precipitable microns between 4 am and 4 pm. As a possible explanation of this daily variation, it was suggested that the Martian regolith at high latitude might adsorb water during the night and desorb it during the day.…”