One of the most interesting things we can learn from studying the planets and bodies of our Solar System is how much they have in common. Mars has polar ice caps and features that formed in the presence of water. Venus is similar to Earth in size, mass, and composition and may have once been covered in oceans. And countless icy bodies in the Solar System experience volcanism and have active plate tectonics, except with ice and water instead of hot silicate magma. Another thing they have in common, which may surprise you, is sand dunes!
According to a new study by researchers from Monash University and the University of Pennsylvania, multiple planets in our Solar System have sand dunes on their surfaces – just in different forms! These features further indicate that the mechanisms for dune formation are ubiquitous throughout the Solar System. These findings could lead to new methods for assessing the surface conditions of planets and moons and could have significant implications for future robotic and crewed missions to study them up-close.
The research was conducted by Andrew Gunn, a lecturer in physical geography at the School of Earth, Atmosphere and Environment at Monash University in Victoria, Australia; and Douglas J. Jerolmack, a professor with the Department of Earth and Environmental Science and Mechanical Engineering and Applied Mechanics at the University of Pennsylvania. The paper that describes their findings, “Conditions for aeolian transport in the Solar System,” recently appeared in the journal Nature.
Mars’ Barchan Dunes, captured by the MRO’s HiRISE Camera. Credit: NASA/ HiRISE/MRO/LPL (UofA)
As they indicate in their paper, the mere presence of sand dunes can be used to infer what conditions exist on the surface of an astronomical body. Specifically, they considered the two criteria that need to be satisfied for sand-dune formation. These include the presence of loose sediment that is sufficiently strong to survive collisions and winds that are fast enough to transport these grains across the surface. As Gunn explained in an article with The Conversation, this is similar to habitability studies – where surface conditions are inferred on an exoplanet based on how close it orbits to its parent star:
“For dunes to even exist, there are a pair of “Goldilocks” criteria that must be satisfied. First is a supply of erodible but durable grains. There must also be winds fast enough to make those grains hop across the ground – but not fast enough to carry them high into the atmosphere.”
“So far, the direct measurement of winds and sediment has only been possible on Earth and Mars. However, we have observed wind-blown sediment features on multiple other bodies (and even comets) by satellite. The very presence of such dunes on these bodies implies the Goldilocks conditions are met.”
For their study, Gunn and Jerolmack focused on Venus, Earth, Mars, Titan (Saturn’s largest moon), Triton (Neptune’s largest moon), and Pluto. In all cases, scientists have noted the presence of dune-like features and indications that the surfaces of these bodies are dynamic (they move over time). These observations have been the subject of debate for decades because of how remarkably different these planetary environments are. For instance, Triton and Pluto both have extremely tenuous atmospheres that are believed to be incapable of moving grains.
Mars has a denser atmosphere, but scientists still consider it to be too whispy to generate the wind speeds required to create its massive dust storms and an extensive system of dunes. On the other hand, Titan has an abundance of hydrocarbon “grains” on its surface and a dense atmosphere capable of generating stronger winds. During its descent into the atmosphere, the Huygens lander clocked wind speeds of up to 120 m/s (430 km/h; 267 mi) in the upper atmosphere. Wind speeds closer to the surface were relatively gentle (just a few m/s) but still strong enough to transport grains.
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