What is it like being on the surface of Mars or Venus? Or even further away, such as on Pluto, or Saturn’s moon Titan? This curiosity has fueled advances in space exploration since Sputnik 1 was launched 65 years ago.
But we are just beginning to scratch the surface of what is known about other planetary bodies in the sky Solar system.
Our new researchpublished today in Nature Astronomy, shows how some unlikely candidates – sand dunes in particular – can provide insight into the weather and conditions you may encounter. if you are standing on a distant planet.
What’s in a grain of sand? The English poet William Blake famously wondered what it meant to “see a world in a grain of sand”.
In our research, we took this literally. The idea is to use only the presence of dunes to understand what conditions exist on the world’s surface.
For the dunes to even exist, there are certain “Goldilocks” criteria that must be met. The first is a source of edible but durable grains.
There must also be winds fast enough to make those particles fly over the ground – but not fast enough to get them high in the atmosphere.
However, we have observed wind-blown sedimentary features on many other celestial bodies (and even comets) using satellites.
The presence of such dunes on these bodies means that the conditions of Goldilocks have been met.
Our work focuses on Venus, Earth, Mars, Titan, Triton (Neptune’s largest moon) and Pluto. Endless debates about these bodies have been going on for decades.
How do we balance the apparent wind-blown features on the surfaces of Triton and Pluto with their fragile atmospheres? Why do we see such abundant active sand and dust on Mars, despite measuring winds that seem too weak to sustain it? And would Venus’s thick and oppressively hot atmosphere move sand in a similar way to how air or water moves on Earth? Sparking the Debate Our study makes predictions about the winds needed to move sediment over these celestial bodies, and how easily that sediment will break apart in those winds. .
We built these predictions by piecing together results from a range of other research papers and testing them against all the experimental data we could get our hands on.
We then apply theories to each of the six, based on telescope and satellite measurements of variables including gravity, atmospheric composition, surface temperature, and the strength of the sediment.
Our previous studies looked at the wind speed threshold needed to move sand, or the strength of different sediment particles.
Our work has brought these together – look at how easily particles can break apart in weather that transports sand on these objects.
For example, we know Titan’s equator has sand dunes – but we’re not sure what sediment surrounds the equator.
Is that pure organic haze falling from the atmosphere, or is it mixed with denser ice? As it turns out, we’ve found that loose aggregates of organic haze would disintegrate on impact if they were blown by Titan’s equatorial winds.
This implies that Titan’s dunes may not be made up of purely organic haze. To build a dune, the sediment must be blown away in the wind for a long time (some sand dunes on Earth are millions of years old).
We also found that wind speeds would have to be too fast on Pluto to transport methane or nitrogen ice (which is hypothesized for Pluto’s dune deposits).
This raises the question of whether the “sand dune” on Pluto’s plain, Sputnik Planitia, is a dune.
Instead they can be sublimation waves. These are dune-like landforms created from the sublimation of matter, rather than the erosion of sediments (such as those seen on Mars’ north polar cap).
Our results for Mars show that more dust is generated from wind-driven sand transport on Mars than on Earth.
This suggests that our models of the Martian atmosphere may not be able to effectively capture Mars’ strong “katabatic” winds, which are cold winds that blow downhill at night.
This research enters an exciting phase of space exploration.
As for Mars, we have a relatively abundant amount of observations; Five space agencies are on active missions in orbit, or in situ. Studies like ours help inform the goals of these missions and the paths taken by laners like Perseverance and Zhurong.
In the outermost regions of the Solar System, Triton has not been observed in detail since NASA’s Voyager 2 flight in 1989.
There is currently a proposed mission that, if chosen, would launch a probe in 2031 to study Triton, before self-destructing by flying into Neptune’s atmosphere.
The planned missions to Venus and Titan over the next decade will revolutionize our understanding of these two.
From NASA The Dragonfly mission, which is expected to leave Earth in 2027 and arrive on Titan in 2034, will land a rudderless helicopter on the dunes of the moon.
Pluto was observed during a 2015 flyby by NASA’s ongoing New Horizons mission, but has no plans to return.