This article was originally published on The conversation. (opens in a new tab) The publication contributed the article to Space.com’s Expert Voices: Editorials and Perspectives.
Andrew Gunn (opens in a new tab)Lecturer, Monash University
How does it feel to be on the surface of Mars or Venus? Or even further, like on Pluto or Titan, the moon of Saturn?
This curiosity has advanced space exploration since the launch of Sputnik 1 65 years ago (opens in a new tab) from. But we are only beginning to scratch the surface of what is knowable about the other planetary bodies in the solar system.
Our new study (opens in a new tab)published May 19 in Nature Astronomy, shows how some unlikely candidates — namely sand dunes — can provide insight into the weather and conditions you might encounter if you were standing on a distant planetary body.
Related: Strange ‘blue’ dunes stain the surface of Mars in a NASA photo
What’s in a grain of sand?
The English poet William Blake wondered (opens in a new tab) what it means to “see a world in a grain of sand”.
In our research, we took this at face value. The idea was to use the mere presence of sand dunes to understand what conditions exist on the surface of a world.
For the dunes to even exist, there are a pair of “Goldilocks (opens in a new tab)Criteria that must be met. The first is a supply of erodible but durable grains. There must also be winds fast enough to blast those grains through the ground – but not fast enough to carry them high into the atmosphere.
Until now, direct measurement of winds and sediments was only possible on Earth and Mars. However, we have observed windblown sediment features on several other bodies (and even comets (opens in a new tab)) by satellite. The very presence of such dunes on these bodies implies that the Goldilocks conditions are met.
Our work has focused on Venus, Earth, Mars, Titan, Triton (Neptune’s largest moon) and Pluto. Unresolved debates over these bodies have been going on for decades.
How do you reconcile the seemingly wind-blown features on the surfaces of Triton and Pluto with their thin, tenuous atmospheres? Why do we see such prolific sand and dust activity on Mars, despite measured winds that seem too weak to sustain it?
And does Venus’ thick, sweltering atmosphere move sand the way air or water moves on Earth?
Advancing the debate
Our study offers predictions of the winds needed to move sediment over these bodies and how easily these sediments would break up in these winds.
We built these predictions by pulling together results from a host of 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, relying on telescope and satellite measurements of variables such as gravity, atmospheric composition, surface temperature and sediment resistance.
Studies prior to ours have focused on either the threshold wind speed required to move sand or the strength of various sediment particles. Our work combined them – looking at how easily particles could shatter in sand transport weather conditions on these bodies.
For example, we know that Titan’s equator has sand dunes, but we don’t know what sediments encircle the equator. Is it pure organic mist (opens in a new tab) is it raining from the atmosphere, or is it mixed with denser ice?
It turns out that we discovered that loose aggregates of organic mist would disintegrate in a collision if blown by winds at Titan’s equator.
This implies that the dunes of Titan are probably not made up of purely organic mist. To build a dune, the sediments must be carried by the wind for a long time (some sands in the dunes of the Earth are a million years old (opens in a new tab) Old).
We also discovered that the wind speed must be excessively fast on Pluto to carry either methane or nitrogen ice (which was assumed to be the sediments of Pluto’s dunes). This calls into question whether the “dunes” of the plain of Pluto, Sputnik Planitia (opens in a new tab)are dunes at all.
It may rather be waves of sublimation (opens in a new tab). They are dune-like landforms made from the sublimation of materials, instead of the erosion of sediments (like those seen on the northern polar cap of Mars).
Our results for Mars suggest that more dust is generated by windblown sand transport on Mars than on Earth. This suggests that our models of the Martian atmosphere may not be effectively capturing Mars’ strong “katabatic” winds, which are cold gusts that blow at night.
Space exploration potential
This study comes at an interesting stage in 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 illuminate the goals of these missions and the paths taken by rovers such as Perseverance. (opens in a new tab) and Zhurong (opens in a new tab).
In the far reaches of the solar system, Triton has not been observed in detail since NASA’s Voyager 2 flyby in 1989. There is currently a mission proposal (opens in a new tab) which, if selected, would have a probe launched in 2031 to study Triton, before annihilating itself while flying through Neptune’s atmosphere.
Planned missions to Venus and Titan over the next decade will revolutionize our understanding of both. NASA dragonfly (opens in a new tab) The mission, which is expected to leave Earth in 2027 and arrive on Titan in 2034, will land an unmanned helicopter on the moon’s dunes.
Pluto was observed during a flyby in 2015 (opens in a new tab) by NASA’s ongoing New Horizons mission, but there are no plans to return.
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