dune – Cabot Institute for the Environment blog

Dune: what the climate of Arrakis can tell us about the hunt for habitable exoplanets

Posted on March 11, 2024March 11, 2024 by amanda.woodman-hardy

Frank Herbert’s Dune is epic sci-fi storytelling with an environmental message at its heart. The novels and movies are set on the desert planet of Arrakis, which various characters dream of transforming into a greener world – much like some envision for Mars today.

We investigated Arrakis using a climate model, a computer program similar to those used to give weather forecasts. We found the world that Herbert had created, well before climate models even existed, was remarkably accurate – and would be habitable, if not hospitable.

However, Arrakis wasn’t always a desert. In Dune lore, 91% of the planet was once covered by oceans, until some ancient catastrophe led to its desertification. What water remained was further removed by sand trout, an invasive species brought to Arrakis. These proliferated and carried liquid into cavities deep underground, leading to the planet becoming more and more arid.

To see what a large ocean would mean for the planet’s climate and habitability, we have now used the same climate model – putting in an ocean while changing no other factors.

When most of Arrakis is flooded, we calculate that the global average temperature would be reduced by 4°C. This is mostly because oceans add moisture to the atmosphere, which leads to more snow and certain types of cloud, both of which reflect the sun’s energy back into space. But it’s also because oceans on Earth and (we assume) on Arrakis emit “halogens” that cool the planet by depleting ozone, a potent greenhouse gas which Arrakis would have significantly more of than Earth.

Map of Arrakis — The authors gathered information from the books and the Dune Encyclopedia to build their original model. Then they added an ocean with 1,000 metres average depth.
Farnsworth et al, CC BY-SA

Unsurprisingly, the ocean world is a whopping 86 times wetter, as so much water evaporates from the oceans. This means plants can grow as water is no longer a finite resource, as it is on desert Arrakis.

A wetter world would be more stable

Oceans also reduce temperature extremes, as water heats and cools more slowly than land. (This is one reason Britain, surrounded by oceans, has relatively mild winters and summers, while places far inland tend to be hotter in summer and very cold in winter). The climate of an ocean planet is therefore more stable than a desert world.

In desert Arrakis, temperatures would reach 70°C or more, while in its ocean state, we put the highest recorded temperatures at about 45°C. That means the ocean Arrakis would be liveable even in summer. Forests and arable crops could grow outside of the (still cold and snowy) poles.

There is one downside, however. Tropical regions would be buffeted by large cyclones since the huge, warm oceans would contain lots of the energy and moisture required to drive hurricanes.

The search for habitable planets

All this isn’t an entirely abstract exercise, as scientists searching for habitable “exoplanets” in distant galaxies are looking for these sorts of things too. At the moment, we can only detect such planets using huge telescopes in space to search for those that are similar to Earth in size, temperature, available energy, ability to host water, and other factors.

Scatter chart of planets comparing habitability and similarity to Earth. — Both desert and ocean Arrakis are considerably more habitable than any other planet we have discovered.
Farnsworth et al, CC BY-SA

We know that desert worlds are probably more common than Earth-like planets in the universe. Planets with potentially life-sustaining oceans will usually be found in the so-called “Goldilocks zone”: far enough from the Sun to avoid being too hot (so further away than boiling hot Venus), but close enough to avoid everything being frozen (so nearer than Jupiter’s icy moon Ganymede).

Research has found this habitable zone is particularly small for planets with large oceans. Their water is at risk of either completely freezing, therefore making the planet even colder, or of evaporating as part of a runaway greenhouse effect in which a layer of water vapour prevents heat from escaping and the planet gets hotter and hotter.

The habitable zone is therefore much larger for desert planets, since at the outer edge they will have less snow and ice cover and will absorb more of their sun’s heat, while at the inner edge there is less water vapour and so less risk of a runaway greenhouse effect.

It’s also important to note that, though distance from their local star can give a general average temperature for a planet, such an average can be misleading. For instance, both desert and ocean Arrakis have a habitable average temperature, but the day-to-day temperature extremes on the ocean planet are much more hospitable.

Currently, even the most powerful telescopes cannot sense temperatures at this detail. They also cannot see in detail how the continents are arranged on distant planets. This again could mean the averages are misleading. For instance, while the ocean Arrakis we modelled would be very habitable, most of the land is in the polar regions which are under snow year-round – so the actual amount of inhabitable land is much less.

Such considerations could be important in our own far-future, when the Earth is projected to form a supercontinent centred on the equator. That continent would make the planet far too hot for mammals and other life to survive, potentially leading to mass extinction.

If the most likely liveable planets in the universe are deserts, they may well be very extreme environments that require significant technological solutions and resources to enable life – desert worlds will probably not have an oxygen-rich atmosphere, for instance.

But that won’t stop humans from trying. For instance, Elon Musk and SpaceX have grand ambitions to create a colony on our closest desert world, Mars. But the many challenges they will face only emphasises how important our own Earth is as the cradle of civilisation – especially as ocean-rich worlds may not be as plentiful as we’d hope. If humans eventually colonise other worlds, they’re likely to have to deal with many of the same problems as the characters in Dune.

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This blog is written by Cabot Institute for the Environment members Dr Alex Farnsworth, Senior Research Associate in Meteorology, and Sebastian Steinig, Research Associate in Paleoclimate Modelling, University of Bristol; and Michael Farnsworth, Research Lead Future Electrical Machines Manufacturing Hub, University of Sheffield. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dune: how high could giant sand dunes actually grow on Arrakis?

Posted on January 6, 2022March 29, 2023 by janet.crompton

Frank Herbert first published his science-fiction epic Dune back in 1965, though its origins lay in a chance encounter eight years previously when as a journalist he was tasked to report on a dune stabilisation programme in the US state of Oregon. Ultimately, this set the wheels in motion for the recent film adaptation.

The large and inhospitable sand dunes of the desert planet Arrakis are, of course, very prominent in both the books and film, not least because of the terrifying gigantic sandworms that hunt any movement on the surface. But just how high would sand dunes be on a realistic version of this world?

Before the movie was released, we took a scientific climate model and used it to simulate the climate of Arrakis. We now want to use insights from this same model to focus on the dunes themselves.

Sand dunes are the product of thousands or even tens of thousands of years of erosion of the underlying or surrounding geology. On a simple level, they are formed by sand being blown along the path of the prevailing wind until it meets an obstruction, at which point the sand will settle in front of it.

There is certainly no shortage of wind on Arrakis. Our simulation showed that wind would routinely exceed the minimum speed required to blow sand grains into the air, and there are even some regions where speeds regularly reach 162 km/h during the year. That’s well over hurricane force.

Diagram of sand dune formation — How sand dunes are formed. David Tarailo / US National Park Service / Geological Society of America

Sand dunes in the book are said to be on average around 100 metres high. However, this isn’t based on actual science, more likely it’s what Herbert knew from his time in Oregon as well as the world we live in. But we can use our climate model to predict what the general (and maximum) attainable height might suggest.

Where the wind blows

The size and distance between giant dunes are determined not simply by the type of sand or underlying rock, but by the lowest 2km or so of the atmosphere that interacts with the land surface. This level, also known as the planetary boundary layer, is where most of the weather we can see occurs. Above this, a thin “inversion layer” separates the weather below from the more stable higher-altitude part of the atmosphere.

The growth of sand dunes and theoretical height is determined by the depth of this boundary layer where the wind blows. Sand dunes stabilise above the wind at the altitude of the inversion layer. The height of the boundary layer – usually somewhere between 100 metres to 2,000 metres – can vary through the night as well as the year. When it is cooler, it is shallower. When there is a strong wind or lots of rising warm air, it is deeper.

Arrakis would be much hotter than Earth, which means more rising air and a boundary layer two to three times as high over land compared with ours. Our climate model simulation, therefore, predicts dunes on Arrakis would be as high as 250m, particularly in the tropics and mid-latitudes. That’s about three times the height of the Big Ben clock tower in London. Most regions would have a more modest average height of between 25m and 75m. As the boundary layer is generally higher everywhere on Arrakis the average dune height is in general twice that of Earths.

map with shaded areas — Predicted sand dune height (in metres) on Arrakis. Farnsworth et al, Author provided

We were also able to simulate the space between dunes, which can also be determined by the height of the boundary layer. Spacing is highest in the tropics, a little over 2km between the crest of one giant sand dune to the next. However, in general, sand dunes have a spacing of around 0.5 to 1km crest to crest. Still plenty of room for a sandworm to wiggle through. Scientists looking at Saturn’s moon Titan have run this same process in reverse, using the space between dunes – easy to measure with satellite images – to estimate a boundary layer of up to 3km.

As nothing can grow on Arrakis to stabilise these sand dunes they will always be in a state of constant drift across the planet. Some large dunes on Earth can move about 5m a year. Smaller dunes can move even faster – about 20m a year.

A visualisation of the authors’ climate model of Arrakis. Source: climatearchive.org/dune.

Mountain-sized dunes?

Our simulation can only give the general height that most sand dunes would reach, and there would be exceptions to the rule. For instance, the largest known sand dune on Earth today is the Duna Federico Kirbus in Argentina, a staggering 1,234m in height. Its size shows that local factors, such as vegetation, surrounding hills or the type of local sand, can play an important role.

Given Arrakis is hotter than Earth, has a higher boundary layer and has more sand and stronger winds, it’s possible a truly mammoth dune the size of a small mountain may form somewhere – it’s just impossible for a climate model to say exactly where.

Scientists have recently revealed that as the world warms the planetary boundary layer is increasing by around 53 metres a decade. So we may well see even bigger record-breaking sand dunes as the lower atmosphere continues to warm – even if Earth will not end up like Arrakis.

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This blog is written by Caboteers Dr Alex Farnsworth, Senior Research Associate in Meteorology, University of Bristol and Dr Sebastian Steinig, Research Associate in Paleoclimate Modelling, University of Bristol and Dr Michael Farnsworth, Research Lead Future Electrical Machines Manufacturing Hub, University of Sheffield,

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dune: we simulated the desert planet of Arrakis to see if humans could survive there

Posted on November 1, 2021March 30, 2023 by janet.crompton

Dune, the epic series of sci-fi books by Frank Herbert, now turned into a movie of the same name, is set in the far future on the desert planet of Arrakis. Herbert outlined a richly-detailed world that, at first glance, seems so real we could imagine ourselves within it.

However, if such a world did exist, what would it actually be like?

We are scientists with specific expertise in climate modelling, so we simulated the climate of Arrakis to find out. We wanted to know if the physics and environment of such a world would stack up against a real climate model.

Here’s a visualisation of our climate model of Arrakis:

You can zoom in on particular features and highlight things like temperature or wind speed at our website Climate Archive.

When we were done, we were very pleased to discover that Herbert had envisioned an environment that for the most part meets expectations. We might need to occasionally suspend disbelief, but much of Arrakis itself would indeed be habitable, albeit inhospitable.

How do you build a fantasy world like Arrakis?

We started with a climate model commonly used to predict weather and climate here on Earth. To use these sorts of models you have to decide on the physical laws (well-known in the case of planet Earth) and then input data on everything from the shape of mountains to the strength of the sun or the makeup of the atmosphere. The model can then simulate the climate and tell you roughly what the weather might be like.

We decided to keep the same fundamental physical laws that govern weather and climate here on Earth. If our model presented something completely strange and exotic, this could suggest those laws were different on Arrakis, or Frank Herbert’s fantastical vision of Arrakis was just that, fantasy.

Height map (in metres) of Arrakis.
Farnsworth et al, Author provided

We then needed to tell the climate model certain things about Arrakis, based on the detailed information found in the main novels and the accompanying Dune Encyclopedia. These included the planet’s topography and its orbit, which was was essentially circular, akin to the Earth today. The shape of an orbit can really impact the climate: see the long and irregular winters in Game of Thrones.

Finally, we told the model what the atmosphere was made of. For the most part it is quite similar to that of the Earth today, although with less carbon dioxide (350 parts per million as opposed to our 417 ppm). The biggest difference is the ozone concentration. On Earth, there is very little ozone in the lower atmosphere, only around 0.000001%. On Arrakis it is 0.5%. Ozone is important as it is around 65 times more effective at warming the atmosphere than CO₂ over a 20-year period.

Having fed in all the necessary data, we then sat back and waited. Complex models like this take time to run, in this case more than three weeks. We needed a huge supercomputer to be able to crunch the hundreds of thousands of calculations required to simulate Arrakis. However, what we found was worth the wait.

Arrakis’s climate is basically plausible

The books and film describe a planet with unforgiving sun and desolate wastelands of sand and rock. However, as you move closer to the polar regions towards the cities of Arrakeen and Carthag, the climate in the book begins to change into something that might be inferred as more hospitable.

Yet our model tells a different story. In our model of Arrakis, the warmest months in the tropics hit around 45°C, whereas in the coldest months they do not drop below 15°C. Similar to that of Earth. The most extreme temperatures would actually occur in the mid-latitudes and polar regions. Here summer can be as hot as 70°C on the sand (also suggested in the book). Winters are just as extreme, as low as -40°C in the mid-latitudes and down to -75°C in the poles.

This is counter intuitive as the equatorial region receives more energy from the sun. However, in the model the polar regions of Arrakis have significantly more atmospheric moisture and high cloud cover which acts to warm the climate since water vapour is a greenhouse gas.

gif of temperatures — Monthly temperatures on Arrakis, according to the model. Both poles have very cold winters and very hot summers.
Author provided

The book says that there is no rain on Arrakis. However, our model does suggest that very small amounts of rainfall would occur, confined to just the higher latitudes in the summer and autumn, and only on mountains and plateaus. There would be some clouds in the tropics as well as polar latitudes, varying from season to season.

The book also mentions that polar ice caps exist, at least in the northern hemisphere, and have for a long time. But this is where the books perhaps differ the most from our model, which suggests summer temperatures would melt any polar ice, and there would be no snowfall to replenish the ice caps in winter.

Hot but habitable

Could humans survive on such a desert planet? First, we must make an assumption that the human-like people in the book and film share similar thermal tolerances to humans today. If that’s the case then, contrary to the book and film, it seems the tropics would be the most habitable area. As there is so little humidity there, survivable wet-bulb temperatures – a measure of “habitability” that combines temperature and humidity – are never exceeded.

The mid-latitudes, where most people on Arrakis live, are actually the most dangerous in terms of heat. In the lowlands, monthly average temperatures are often above 50-60°C, with maximum daily temperatures even higher. Such temperatures are deadly for humans.

Four people in black rubbery suits in desert — Stillsuit models, autumn 10191 collection.
Chiabella James / Warner Bros

We do know that all humanoid life on Arrakis outside of habitable places must wear “stillsuits”, designed to keep the wearer cool and reclaim body moisture from sweating, urination and breathing to provide drinkable water. This is important as stated in the book that there is no rainfall on Arrakis, no standing bodies of open water and little atmospheric moisture that can be reclaimed.

The planet also gets very cold outside of the tropics, with winter temperatures that would also be uninhabitable without technology. Cities like Arrakeen and Carthag would suffer from both heat and cold stress, like a more extreme version of parts of Siberia on Earth which can have both uncomfortably hot summers and brutally cold winters.

It’s important to remember that Herbert wrote the first Dune novel way back in 1965. This was two years before recent Nobel-winner Syukuro Manabe published his seminal first climate model, and Herbert did not have the advantage of modern supercomputers, or indeed any computer. Given that, the world he created looks remarkably consistent six decades on.

The authors modified a well-used climate model for exoplanet research and applied it to the planet in Dune. The work was carried out in their spare time and is intended as an appropriate outreach piece to demonstrate how climate scientists use mathematical models to better understand our world and exoplanets. It will feed into future academic outputs on desert worlds and exoplanets.

This blog is written by Cabot Institute for the Environment members, Dr Alex Farnsworth, Senior Research Associate in Meteorology and Dr Sebastian Steinig, Research Associate in Paleoclimate Modelling, University of Bristol; and Michael Farnsworth, Research Lead Future Electrical Machines Manufacturing Hub, University of Sheffield.

This article is republished from The Conversation under a Creative Commons license. Read the original article.