The morphology of isolated barchan dunes on Mars and Earth may shed light on the dynamic conditions that form them, their migration direction and the physical properties of the sediments composing them. Thusfar, dune fields have been largely manually analyzed from aerial and satellite imagery, as automatic detection techniques are often not sufficiently accurate in outlining dunes. Here, we employ an instance segmentation neural network to detect and outline isolated barchan dunes on Mars and Earth. We train and test the model on martian targets using Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images, and find it to be robust, with sufficient accuracy ~80% to characterize dune field dynamics. Using our trained model we detect and map the global distribution of barchan dunes relative to previously mapped dune fields, and find that barchan dunes are more abundant in the northern hemisphere than in the southern hemisphere. These contrasting abundances of barchans may reflect latitudinally dependent wind regimes, sediment supply, or sediment availability.

Sand mobilized by wind forms decimeter-scale impact ripples and decameter-scale or larger dunes on Earth and Mars. In addition to those two bedform scales, orbital and in situ images revealed a third distinct class of larger meter-scale ripples on Mars. Since their discovery, two main hypotheses have been proposed to explain the formation of large martian ripples—that they originate from the growth in wavelength and height of decimeter-scale ripples or that they arise from the same hydrodynamic instability as windblown dunes or subaqueous bedforms instead. Here we provide evidence that large martian ripples form from the same hydrodynamic instability as windblown dunes and subaqueous ripples. Using an artificial neural network, we characterize the morphometrics of over a million isolated barchan dunes on Mars and analyze how their size and shape vary across Mars’ surface. We find that the size of Mars’ smallest dunes decreases with increasing atmospheric density with a power-law exponent predicted by hydrodynamic theory, similarly to meter-size ripples, tightly bounding a forbidden range in bedform sizes. Our results provide key evidence for a unifying model for the formation of subaqueous and windblown bedforms on planetary surfaces, offering a new quantitative tool to decipher Mars’ atmospheric evolution.

In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind directions. Here, we characterize near‐surface winds on Mars from the morphology of >700,000 barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with known southern‐summer atmospheric circulation patterns—northerly at mid‐latitudes and cyclonic near the north pole—with the addition of an anti‐cyclonic north‐polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles <100 km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary‐scale aeolian processes on modern‐day Mars, can be used to constrain global circulation models to assist with predictions for future missions.

Evidence in radar, reflectance, and visible imagery indicates surface and subsurface water ice is present inside permanently shadowed regions (PSRs) in the north polar region of Mercury. The origin of this ice and the time at which it was delivered to the planet are both unknown. Finding the smallest, most easily eroded, ice deposits on Mercury can help answer these questions. Here we present evidence for volatiles trapped in cold‐traps of scales ∼1 − 10m. We consider two possible delivery methods for these deposits: a gradual, slow accumulation by micrometeorites or solar wind implantation and an episodic deposition, either primordial or by a recent comet impact. We conclude the mechanism that best explains the presence of volatiles in these micro cold‐traps is a comet impact that most likely occurred in a last ∼100Ma.