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| Titel |
Peculiar Phenomena of Sublimating Seasonal Deposits During Northern Spring on Mars |
| VerfasserIn |
Thomas Appéré, Bernard Schmitt, Yves Langevin, Aymeric Spiga, Sylvain Douté, Antoine Pommerol, François Forget, Brigitte Gondet, Jean-Pierre Bibring |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046209
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| Zusammenfassung |
| We report on peculiar phenomena occurring during the martian year (MY) 28 spring retreat
of the northern seasonal deposits. First of all, OMEGA observations show the vanishing of
the CO2 ice spectral signature at Ls ~50- on many regions where a surface temperature of
150K is however indicative of abundant CO2 ice. We thus conclude that CO2 ice is
progressively overlaid by an optically thick cover, either of dust or of water ice. A water frost
layer overlying CO2 ice is consistent with the observations of both high albedo and strong
H2O ice signature on this region. This water frost layer is likely composed of H2O ice grains
included in the CO2 ice layer during its winter condensation and released by its spring
sublimation [1]. Some water vapor coming from the sublimating water ice annulus at
lower latitudes may also be cold trapped on top of the CO2-rich ice and contributes,
from above, to the building of this H2O ice layer. Radiative transfer modeling in
layered media [2] using optical constants of CO2 and H2O ices [3, 4] shows that a
200μm thick layer of H2O ice is sufficient to completely hide the CO2 ice spectral
signature.
The CO2 ice spectral signature suddenly reappears in the spiral troughs and arcuate scarps
of the North permanent cap and in the circumpolar dark dunes field at Ls ranging from 40- to
70-. Winds have been simulated for that range of Ls with the LMD Martian Mesoscale model
[5]. It indicates strong katabatic winds on the permanent cap, particularly in regions
where the CO2 ice signature strongly reappears and H2O ice signature decreases.
Reappearance of the CO2 ice signature on the North permanent cap is thus likely due
to the removing of the overlying water frost layer by wind. A different process
may be involved in the dunes field, where low friction velocities are simulated.
Instead, reappearance of the CO2 ice signature on dunes may be linked with the host
of sublimation-driven features observed by the HiRISE camera [6]. Release of
pressurized CO2 gas could scatter the H2O ice layer while CO2 frost may be formed by
decompression and adiabatic cooling of that gas, contributing to the reappearance of the CO2
ice signature as well. Several different processes could be at the origin of these
peculiar phenomena and the understanding of their origins can shed some light on the
microphysical evolution of ice deposits. These phenomena already witness a very
active surface-atmosphere water cycle and strong wind interaction that may lead
finally to inhomogeneous accumulation rates of H2O ice over the North permanent
cap.
[1] Appéré et al. (2010) JGR, submitted
[2] Douté S. and Schmitt B. (1998) JGR E 103, 31367-31390
[3] Quirico E. and Schmitt B. (1997) Icarus 127, 354-378
[4] Grundy W. and Schmitt B. (1998) JGR E 103, 25809-25822
[5] Spiga A. and Forget F. (2009) JGR 114, E02009
[6] Hansen C. J. et al. (2010) LPI Contribution 1533 |
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