Browsing Science by Publisher "American Geophysical Union (AGU)"
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Aram Dorsum: An Extensive Mid‐Noachian Age Fluvial Depositional System in Arabia Terra, MarsA major debate in Mars science is the nature of the early Mars climate, and the availability ofprecipitation and runoff. Observations of relict erosional valley networks have been proposed as evidencefor extensive surface runoff around the Noachian‐Hesperian boundary. However, these valley networks onlyprovide a time‐integrated record of landscape evolution, and thus, the timing, relative timescales andintensity of aqueous activity required to erode the valleys remain unknown. Here, we investigate an ancientﬂuvial sedimentary system in western Arabia Terra, now preserved in positive relief. This ridge, “AramDorsum,” is ﬂat‐topped, branching, ~85 km long, and particularly well preserved. We show that AramDorsum was an aggradational alluvial system and that the existing ridge was once a large river channel beltset in extensive ﬂood plains, many of which are still preserved. Smaller, palaeochannel belts feed themain system; their setting and network pattern suggest a distributed source of water. The alluvial successionis up to 60 m thick, suggesting a formation time of 105to 107years by analogy to Earth. Our observationsare consistent with Aram Dorsum having formed by long‐lived ﬂows of water, sourced both locally, andregionally as part of a wider alluvial system in Arabia Terra. This suggests frequent or seasonal precipitationas the source of water. Correlating our observations with previous regional‐scale mapping shows thatAram Dorsum formed in the mid‐Noachian. Aram Dorsum is one of the oldest ﬂuvial systems described onMars and indicates climatic conditions that sustained surface river ﬂows on early Mars.
Morphology, Development, and Sediment Dynamics of Elongating Linear Dunes on MarsLinear dunes occur on planetary surfaces, including Earth, Mars, and Titan, yet their dynamics are poorly understood. Recent studies of terrestrial linear dunes suggest they migrate by elongation only in supply‐limited environments. Here, we investigate elongating linear dunes in the Hellespontus Montes region of Mars which are morphologically similar to terrestrial systems. Multitemporal, high‐resolution orbital images show these linear dunes migrate by elongation only and that the fixed sediment source of the dunes probably restricts any lateral migration. Some linear dunes maintain their along‐length volume and elongate at rates comparable to adjacent barchans, whereas those which decrease in volume show no elongation, suggesting they are near steady state, matching morphometric predictions. Limited sediment supply may restrict Martian linear dunes to several kilometers, significantly shorter than many terrestrial linear dunes. Our results demonstrate the close similarities in dune dynamics across the two planetary surfaces.
Quantified Aeolian Dune Changes on Mars Derived From Repeat Context Camera ImagesAeolian systems are active across much of the surface of Mars and quantifying the activity of bedforms is important for understanding the modern and recent Martian environment. Recently, the migration rates and sand fluxes of dunes and ripples have been precisely measured using repeat High Resolution Imaging Science Experiment (HiRISE) images. However, the limited areal extent of HiRISE coverage means that only a small area can be targeted for repeat coverage. Context Camera (CTX) images, although lower in spatial resolution, have wider spatial coverage, meaning that dune migration can potentially be monitored over larger areas. We used time series, coregistered CTX images and digital elevation models to measure dune migration rates and sand fluxes at six sites: Nili Patera, Meroe Patera, two sites at Herschel crater, McLaughlin crater, and Hellespontus Montes. We observed dune displacement in the CTX images over long‐term baselines (7.5–11 Earth years; 4–6 Mars years). Bedform activity has previously been measured at all these sites using HiRISE, which we used to validate our results. Our dune migration rates (0.2–1.1 m/EY) and sand fluxes (2.4–11.6 m3 m−1 EY−1) compare well to measurements made with HiRISE. The use of CTX in monitoring dune migration has advantages (wider spatial coverage, faster processing time) and disadvantages (ripples not resolved, digital elevation model dune heights may be underestimates); the future combined use of HiRISE and CTX is likely to be beneficial.