Martian gullies were initially hypothesized to be carved by liquid water, due to their resemblance to gullies on Earth. Recent observations have highlighted significant sediment transport events occurring in Martian gullies at times and places where CO2 ice should be actively sublimating. Here we explore the role of CO2 sublimation in mobilizing sediment through laboratory simulation. In our previous experimental work, we reported the first observations of sediment slope movement triggered by the sublimation of CO2 frost. We used a Mars regolith simulant near the angle of repose. The current study extends our previous work by including two additional substrates, fine and coarse sand, and by testing slope angles down to 10°. We find that the Mars regolith simulant is active down to 17°, the fine sand is active only near the angle of repose and the coarse sand shows negligible movement. Using an analytical model, we show that under Martian gravity motion should be possible at even lower slope angles. We conclude that these mass-wasting processes could be involved in shaping Martian gullies at the present day and intriguingly the newly reported CO2-creep process could provide an alternative explanation for putative solifluction lobes on Mars.
Supplementary material: Video clips depicting sediment transport types are available at https://doi.org/10.6084/m9.figshare.5208847
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Martian Gullies and their Earth Analogues
CONTAINS OPEN ACCESS
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.