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Where does space begin?  National Geographic Arabic Magazine

Where does space begin? National Geographic Arabic Magazine

When adventurers climb Mount Everest, They routinely carry oxygen cylinders, devices that allow them to breathe freely at high altitudes. This is necessary because the closer you are to the edge of Earth’s atmosphere, the less oxygen is available compared to the abundance at sea level. This is just one example of how much the Earth’s atmosphere has changed and shows the elementary composition of its layers, from the troposphere, near sea level, to the exosphere, in its outer regions. The place where each layer ends and begins is determined by four main characteristics, which are the change in temperature, chemical composition, density, and the movement of gases within it.

Here, the question arises, where does the Earth’s atmosphere actually end? Where does space begin? Each layer of the atmosphere plays a role in ensuring our planet can host all types of life, doing everything from blocking cancer-causing cosmic radiation to creating the pressure needed to produce water, according to NASA. “As you move away from Earth, the atmosphere becomes less dense, the composition also changes, and lighter atoms and molecules start to dominate, while heavier molecules stay closer to the surface of the Earth,” says Katrina Bossert, an astrophysicist at Arizona State University. As you move through the atmosphere, the pressure or weight of the atmosphere above you quickly weakens. Although planes have pressurized cabins, rapid changes in altitude can affect the thin eustachian tubes that connect the ear to the nose and throat. This is the reason for the ringing in the ears that you feel during takeoff on a plane, explains Matthew Eagle, assistant professor of atmospheric sciences at the University of California, Davis. Eventually, the air becomes too thin for conventional aircraft to fly at all, with this craft not being able to generate enough lift. This is the region that scientists have determined marks the end of our atmosphere, and the beginning of space.

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This area is known as the “Karmann Line”, after “Theodor von Karmann”, The Hungarian-American physicist who, in 1957, became the first person to attempt to define the boundary between Earth and outer space. This line, as it represents the boundary between Earth and space, not only indicates where the plane’s boundary is, but is also important to scientists and engineers when figuring out how to keep spacecraft and satellites orbiting the Earth. Bossert points out that the Karman line is an approximate area that indicates the height above which satellites will be able to orbit the Earth without burning out or falling out of orbit before orbiting the Earth at least once. “The Karmann Line is usually defined as 100 km above the Earth’s surface,” Eagle comments.

It is possible that something orbits around the Earth at altitudes lower than the Karmann Line, But that would require a very high orbital velocity, which would be difficult to maintain due to friction. Various factors, such as a satellite’s size and shape, play a role in determining how much air resistance it will encounter, and thus its ability to successfully orbit the Earth, according to Bossert. Bossert explains that the atmosphere does not disappear once you enter the region in which the satellites orbit, it is thousands of kilometers before the evidence of the Earth’s atmosphere disappears. And that if someone reached the Karman line, he wouldn’t notice anything? And wouldn’t he be aware that he was, essentially, straddling the boundary between Earth and space? According to Eagle, this line is not physical in itself and therefore one will not notice its crossing, especially since it does not have any thickness.

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What about being able to stay – even for a short time – in the Karman streak? What if you fell in there without a custom spacesuit or a mountaineering-style oxygen tank? If you could reach it, would you be able to breathe at such a high altitude? Can birds reach such heights? Eagle answers: “In principle, flight is still possible up to the Karmann Line, but in practice, animals cannot survive at altitudes above the Armstrong limit, which is about 20 kilometers above the surface, where the pressure is very low.

Source: Live Science