Morphological characterization of landforms produced by springtime seasonal activity on Russell Crater megadune, Mars
Published:January 01, 2019
Gwenaël Jouannic, Susan J. Conway, Julien Gargani, François Costard, Marion Massé, Olivier Bourgeois, John Carter, Frédéric Schmidt, Chiara Marmo, Gian G. Ori, Marion Nachon, Kelly Pasquon, 2019. "Morphological characterization of landforms produced by springtime seasonal activity on Russell Crater megadune, Mars", Martian Gullies and their Earth Analogues, S. J. Conway, J. L. Carrivick, P. A. Carling, T. de Haas, T.N. Harrison
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We describe in detail an annual seasonal process that occurs on the surface of the Russell Crater megadune on Mars. We give these features the name ‘perennial rills’, because their surface topographical expression persists from year-to-year and they form a distinctive, downstream-branching network of small channels, or rills. We used time-series images, elevation data from stereophotogrammetry and spectral data to characterize the evolution of these features over 6 Mars years. Growth and modification of these networks occurs abruptly in spring (at a solar longitude of c. 200°) after most of the seasonal CO2 ice has sublimated. We find that the peculiar morphology of perennial rills seems to be the only aspect that sets them apart from active linear dune gullies. By comparison to terrestrial analogues, we identified two conditions favouring the production of such a network: (a) the presence of an impermeable layer; and (b) the repeated formation of obstacles in front of propagating channels. We find that the most plausible formation mechanisms that can explain the formation of both the perennial rills and the active linear dune gullies are levitating CO2 blocks or liquid debris flows of water/brine, but neither can completely satisfy all the observational evidence.
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Martian Gullies and their Earth Analogues
Gullies on Mars resemble terrestrial gullies involved in the transport of abundant material down steep slopes by liquid water. However, liquid water should not be stable at the Martian surface. The articles in this volume present the two main opposing theories for Martian gully formation: climate-driven melting of surficial water-ice deposits and seasonal dry-ice sublimation. The evidence presented ranges from remote-sensing observations, to experimental simulations, to comparison with Earth analogues. The opposing hypotheses imply either that Mars has been unusually wet in the last few million years or that it has remained a cold dry desert – both with profound implications for understanding the water budget of Mars and its habitability. The debate questions the limits of remote-sensing data and how we interpret active processes on extra-terrestrial planetary surfaces, even beyond those on Mars, as summarized by the review paper at the beginning of the book.