Shulou(Shulou.com)11/24 Report--

As far as we know, Uranus has 27 moons. Five of these satellites have enough mass to keep them spherical. Of the five large moons, the smallest and closest to Uranus is Rhea, discovered by American astronomer Gerald Kuiper in 1948.

In the West, Rhea is also known as Miranda, which comes from a character in the Tempest written by Shakespeare, a great British writer.

Rhea has been inconspicuous for a long time. It was not until 1986, when the Voyager 2 probe flew past Rhea while exploring Uranus, that this strange moon attracted people's attention. The picture below is an image of Enceladus taken by Voyager 2. Its density is very small, only 20% higher than water. Further research shows that about 60% of Enceladus is ice. In other words, Rhea is a world ruled by ice.

If you want to use a word to describe the topographical features of Enceladus, it must be "fragmented".

The surface of Rhea is dilapidated, and the plains, mountains and valleys are all intricate. In other words, unlike the earth, Enceladus has no strict concept of topography, because all kinds of landforms are stewed into a hodgepodge. If one day, human beings can emigrate the entire solar system and list the topography of Enceladus as the scope of the geography college entrance examination, it will be very exciting.

Why is the topography of Rhea so fragmented?

The answer is still the tidal forces that we have mentioned repeatedly before. The tidal forces of Uranus and its major moons heat the interior of Enceladus due to friction. These energies frequently break through the surface ice in the form of earthquakes or volcanic eruptions, and then turn Rhea into what it is now. But in this chaotic frozen world, Voyager 2 found something unusual. That is the highest cliff in the solar system.

For comparison, let's take a look at the highest cliff on earth. It is located to the south of the ninth peak of the earth (Nanga Parbart) and is called the Rupal cliff. Its vertical height is about 4600 meters, which is 5.5 times that of the tallest building in the world (Burj Khalifa in Dubai).

Rupal rock, but if you look at the entire solar system, the Rupal wall is negligible. Voyager 2 took the following picture while flying over Rhea in 1986.

There is a cliff in the lower middle of the picture, later known as the Verona cliff. It is named after a city in northern Italy, the hometown of Shakespeare's Romeo and Juliet. At first, people thought that the height of the cliff should be between 5000 meters and 10000 meters. But a 2016 study showed that the actual height of the Verona cliff reached an astonishing 20000 meters, making it the highest cliff in the entire solar system.

As for how the Verona cliff was formed, there is no final conclusion. Some people think it originated from a violent asteroid impact, while others think it originated from Enceladus's own orogeny. Since only Voyager 2 has visited Enceladus, the available observations are simply not enough to judge which theory is correct.

So far, the space departments of countries around the world have not made any plans to return to Rhea, so this will be an unsolved mystery for a long time to come.

Now let's think about what it would be like if someone were bungee jumping on the cliffs of Verona.

To this end, we need to add a little knowledge of physics in junior high school first. I believe many people have heard of freefall. It describes the motion of an object with zero initial velocity under gravity only. Galileo first discovered that the motion of a free fall can be described by a very simple formula, h=1/2gt ². Here h is the height at which the object falls, g is the gravitational acceleration it is subjected to, and t is the time at which it falls.

Galileo, by the way, Galileo's formula is not very applicable to the earth. This is because the mass of the earth is so large that it can retain the atmosphere, so that objects will be resisted by the air in the process of falling instead of freefall.

But on Rhea, the situation is very different. This is because the mass of Rhea is too small to retain the atmosphere, so that the object will not be subjected to air resistance during its fall, thus maintaining its free-fall motion all the time. As mentioned earlier, the height of the Verona cliff is 20000 meters. The observation data of Voyager 2 show that Enceladus's gravitational acceleration is very small. Using Galileo's formula, it is easy to calculate that it takes a total of 707 seconds for a person to fall from the top of the Verona cliff to the bottom. In other words, he has nearly 12 minutes to enjoy the scenery on Enceladus. In addition, his landing speed is about 200 kilometers per hour. It took nearly 12 minutes to accelerate evenly to 200 kilometers per hour.

In this way, jumping off the cliffs of Verona does not seem to be a particularly terrible thing. Now let's think about landing. On earth, parachutes and paragliders are often used when people jump from high altitude. But on Rhea, these two devices are completely useless. This is because Enceladus has no atmosphere at all and cannot produce any air buoyancy.

In addition, the rubber rope commonly used for bungee jumping on the earth does not seem to be reliable. After all, the length of the rubber rope required to jump from the Macao Tower is only more than 200m, but if you jump from the cliff of Verona, the length of the rubber rope needs to reach 20000 m. Therefore, the ideal choice is the kind of anti-thrust rocket used by Iron Man. With the current level of technology, it is certainly impossible for people to fly freely in the sky like Iron Man. But it should not be particularly difficult to land with it alone.

You might as well imagine. One day, human beings will be able to establish settlements on Enceladus. At that time, dressing up like Iron Man and jumping off the highest cliff in the solar system may become a very popular extreme sport.

Let's make a summary.

In 1986, Voyager 2 found the Verona cliff on Enceladus. Later studies showed that its actual height reached 20000 meters, making it the highest cliff in the entire solar system. Based on Voyager 2 observations, it would take nearly 12 minutes to reach the bottom if a person jumped from the top of the Verona cliff. In addition, his landing speed is not fast, about equivalent to 200 kilometers per hour. In this way, as long as equipped with the kind of anti-thrust rocket used by Iron Man, it is possible to land safely.

In this sense, if humans can one day settle on Rhea, dress up as Iron Man and bungee jump on the highest cliff in the solar system, it may become a very popular extreme sport.

Source: cosmic Odyssey: walking the Solar system author: Wang Shuang part of the picture comes from the network copyright belongs to the original author Editor: Zhang Runxin this article comes from Wechat official account: Origin Reading (ID:tupydread), author: Wang Shuang, Editor: Zhang Runxin

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