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Sand Dunes, an epic science fiction novel by Frank Frank Herbert, has been adapted for release as a movie of the same name. The story of the novel takes place in the distant future, on the desert planet Arrakis. Herbert painstakingly outlines a world so rich in detail that we can imagine ourselves in the desert at first glance.

However, if such a world does exist, will it be as real as it is in novels and movies?

We are scientists who specialize in climate models, and in order to answer the above questions, we used climate models to simulate the desert planet Erlakos. We want to know whether the physics and environment in the world depicted in the novel run counter to the real climate model.

Note: a visual demonstration of the Erlakos climate model. On the Climate Archive website, this is a 3D ball that can be rotated and dragged freely. On the left menu, you can choose different display layers such as cloud, temperature, precipitation, wind and so on. After completing this model, we are pleased to find that the environment envisioned by Herbert in the book is largely in line with expectations. Although this is science fiction, we viewers and readers occasionally need to press the pause button for our doubts: it will be difficult for humans to survive in most parts of the desert planet. In addition, we also found some very interesting things about Erlakos.

How to build a fantasy world? How to build a climate model of a desert planet? Now that we have some climate models that are often used to predict the weather and climate on the earth, let's start from here. Before using these different types of models, we have to enter all the data from the direction of the mountains to the intensity of solar radiation to the composition of the atmosphere. The model can then start to simulate the climate and give you a rough idea of what the weather might be like on the planet.

First of all, although this is science fiction, let's assume that the basic physical laws of the desert planet Erlakos that affect weather and climate are the same as those on Earth. Of course, if our model shows something bizarre and bizarre, it may also mean that the laws of physics are not the same as the earth on Erlakos, or that Frank Herbert's fantasy about Erlakos is just a fantasy.

Note: height map of Erlakos (in meters) Source: Farnsworth et al., provided by the author, then we need to set specific parameters of the climate model for Erlakos, including the planet's topography and its orbit, based on all the details found in the novel and the accompanying encyclopedia of sand dunes. The orbit of Erlakos is basically round, similar to the earth today. The shape of the planetary orbit does significantly affect the climate on the planet-the winter in Game of Thrones is long and irregular, and the so-called "winter is coming" may be caused by complex planetary orbits.

Finally, we want to tell the model what the atmosphere of Erlakos is made of. Although the amount of carbon dioxide in Uracos is slightly lower than that on Earth (350 parts per million, compared with 417 parts per million on Earth), most of the composition is very similar to the composition of the atmosphere on Earth today. The biggest difference is the concentration of ozone: on Earth, the concentration of ozone in the atmosphere near the surface is very low, only about 0.0001%, but in Erlakos, it is 0.5%.

The proportion of ozone in the atmosphere is very important in climate models. Because the proportion of components in the atmosphere is actually dynamic, if we take 20 years as the evaluation time period, the global warming potential of ozone is about 65 times higher than that of carbon dioxide.

Photo note: most of Erlakos is a desolate desert. Source: after Chiabella James / Warner Bros. has entered all the necessary data into the model, the next thing we have to do is sit down and wait, because it usually takes more than three weeks to run such a complex model. We need a huge supercomputer to process the complicated calculations needed to simulate Erlakos day and night.

In the end, our discovery is worth waiting for.

How can that be reasonable? In the depiction of novels and movies, Erlakos is a planet with ruthless hot sun and desolate sandy wasteland, and a planet in need of "sunrise warning". But as you approach the polar cities of Arrakeen and Carthag on the Erakos, the climate begins to become pleasant.

Is this really the case?

Climate models tell us a different story. In our Uracos climate model, the hottest month in the tropics is about 45 °C, and in the coldest months, the temperature will not be lower than 15 °C. This is not far from the situation on earth. On this desert planet, extreme temperatures are more common in mid-latitudes and polar regions. In the polar regions, the highest summer temperature in the desert can be as high as 70 °C (also mentioned in the book). Winters there are also extreme, with temperatures as low as-40 °C in mid-latitudes and-75 °C in polar regions.

Note: monthly temperature distribution map of Erlakos. The polar regions are very cold in winter and very hot in summer. The author provides that in the book, Erlakos has never rained. However, our model shows that there are actually some precipitation processes in Erlakos, albeit in very small amounts. The distribution of these precipitation is limited to the mountains and plateaus at high latitudes in summer and autumn. In the tropics and polar regions, there may be some clouds that vary more or less with the seasons, but there is no rain.

The author also mentions that there are some historic polar ice caps, at least in the northern hemisphere. This is probably the biggest difference between the novel and the model. In the model, the summer temperature is high enough to melt any polar ice sheet, and in winter, there will be no precipitation to give the ice sheet a chance to grow.

Although hot, but livable human beings can survive on such a desert planet?

First of all, we must assume that the races such as the Fremans in the novel and in the film are similar to the heat tolerance of human beings today. If so, the result of science is contrary to the plot depicted in books and movies, and the tropics seem to be the best place to live in Erlakos.

Because of the low humidity in the tropics, although the temperature here is high, it will never reach the upper limit of the adiabatic saturation temperature (wet bulb temperature, wet-bulb temperature) for human survival-a measure of "livability" that combines temperature and humidity. Generally speaking, the wet bulb temperature is the lowest temperature that can be achieved in the current environment only by evaporating water. When the ambient temperature is high and the humidity is high, the human body cannot discharge heat by evaporating sweat.

In fact, the mid-latitudes where most people live in Erakos is the most dangerous. In the lowlands, the monthly average temperature is usually above 50-60 °C, and the daily maximum temperature is even higher. Obviously, such high temperatures are fatal to human beings.

Photo Note: the protagonist in "Distilling suit" in the desert. Source: in Chiabella James / Warner Bros. movies, everyone who moves outside the residence on Uracos must wear "distilled clothes". This suit cools the body, keeps the wearer cool, recovers body water from sweating, urinating and breathing, and provides drinking water. In the book, there is no precipitation, no rivers, lakes and seas, and there is little water that can be recovered in the atmosphere, so "distillation clothes" are very important.

In winter, the desert planet gets very cold outside the tropics. Although there is a way to survive the hot weather, low temperatures in winter will make the place unlivable without technology, and cities in non-equatorial areas such as Araken and Carthage will be challenged by both heat and cold. it can almost be seen as a more extreme version of the climate in parts of Siberia on earth. There are uncomfortable hot summers and bitterly cold winters.

Although we have mentioned a lot of unreasonable points in the Dune, it is important to remember that Herbert wrote the first novel Dune as early as 1965. It took two years for Nobel laureate Shuro Makoto to publish his groundbreaking first climate model. At that time, Herbert did not have the surging computing power of modern supercomputers, not even the common personal computers today.

In view of this, the desert world he created looks really unique sixty years later.

Original text link:

Https://www.google.com/amp/s/theconversation.com/amp/dune-we-simulated-the-desert-planet-of-arrakis-to-see-if-humans-could-survive-there-170181

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: A. Farnsworth, Michael Farnsworth, Sebastian Steinig, translator: NKXXX, revision: zhenni

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