What is it like to be on the surface of Mars or Venus? Or even further away, like on Pluto, or Saturn’s moon Titan?
This curiosity has led to advances in space exploration since Sputnik 1 was launched 65 years past. But we are just beginning to surface what is known about other planetary bodies in the solar system.
Us new studyPublished today in Nature Astronomy, shows how some unlikely candidates — namely sand dunes — could provide insight into the weather and conditions you might experience standing on a distant planetary body.
What’s in a grain of sand?
English poet William Blake famous wondered what it means “to see a world in a grain of sand”.
In our research, we took this quite literally. The idea was to use the mere presence of sand dunes to understand what conditions exist on the world’s surface.
To make dunes even exist, there are a few”goldilocks” criteria that must be met. First, there is a supply of erodible but sustainable grains. There must also be winds that are fast enough to jump those grains across the ground, but not fast enough to carry them high into the atmosphere.
Until now, direct measurement of wind and sediment was only possible on Earth and Mars. However, we have observed windblown sediment features on multiple other bodies (and even Come eat) by satellite. The mere presence of such dunes on these bodies implies that Goldilocks’ conditions are met.
Our work focused on Venus, Earth, Mars, Titan, Triton (Neptune’s largest moon), and Pluto. Unresolved debates about these bodies have been going on for decades.
How do we relate the apparent windblown features on the surfaces of Triton and Pluto to their thin, tenuous atmospheres? Why do we see such abundant sand and dust activity on Mars, despite measuring winds that seem too weak to support it?
And does Venus’s thick and suffocatingly hot atmosphere move sand in the same way as air or water on Earth?
Foster the debate
Our study provides predictions for the winds needed to move sediment on these bodies, and how easily that sediment would break apart in those winds.
We constructed these predictions by pooling the results of many other research papers and testing them against all the experimental data we could get our hands on.
We then applied the theories to each of the six bodies, using telescope and satellite measurements of variables such as gravity, atmospheric composition, surface temperature and sediment strength.
Previous studies have looked at the wind speed threshold required to move sand, or the strength of various sediment particles. Our work combined these together – looking at how easily particles could break apart in sand-transporting weather on these bodies.
For example, we know that Titan’s equator has sand dunes, but we’re not sure what sediment surrounds the equator. Is it pure? organic haze is it raining from the atmosphere, or is it mixed with denser ice?
As it turned out, we found that loose aggregates of organic haze would disintegrate on impact if blown by the wind at Titan’s equator.
This means that Titan’s dunes are probably not made of purely organic haze. To build a dune, sediment has to be blown around in the wind for a long time (some dune sands on Earth are a million years old).
We also found that wind speeds on Pluto would have to be extremely fast to transport methane or nitrogen ice (which was the hypothesis of Pluto’s dune sediments). This raises the question of whether “dunes” on Pluto’s plain, Sputnik Planitiaare no dunes at all.
They can be instead sublimation waves† These are dune-like landforms made from the sublimation of material, rather than sediment erosion (such as those seen on Mars’ northern polar cap).
Our results for Mars suggest that more dust is generated by wind-driven sand transport on Mars than on Earth. This suggests that our models of the Martian atmosphere may not effectively capture the strong “katabaticwind, these are cold gusts of wind that blow downhill at night.
Potential for space exploration
This study enters an interesting stage of space exploration.
For Mars we have a relative abundance of observations; five space agencies conduct active missions in orbit or in situ. Studies like ours help inform the objectives of these missions, and the paths taken by robbers like Perseverance and Zhurong†
In the outer reaches of the solar system, Triton has not been observed in detail since the NASA Voyager 2 flight in 1989. There is currently a mission proposal which, if selected, would launch a probe in 2031 to study Triton, before destroying itself by flying into Neptune’s atmosphere.
The planned missions to Venus and Titan over the next decade will revolutionize our understanding of the two. NASAs Dragonfly The mission, scheduled to leave Earth in 2027 and arrive on Titan in 2034, will land an unmanned helicopter on the dunes of the moon.
Pluto was observed during a 2015 fly past by NASA’s ongoing New Horizons mission, but there are no plans to return.
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