Many people would like to travel in space one day. But in fact, when can we say that we are in space? Why are we not in space when we travel by plane? The answers are simple: you just need to know where the Earth ends and space begins.
A boundary that lies between the layers of the Earth’s atmosphere
When you look up into the sky, it feels like space is endless, and it probably is. On the other hand, it should be known that there is a clear distinction between the sky in our atmosphere and infinite space. So the question is where does the Earth end and where does space begin? To answer this question, one must first understand the structure of the atmosphere. First, the atmosphere is a layered structure that provides our planet with adequate temperature, density, and exposure to sunlight for life on Earth to exist.
The atmosphere is divided into five layers: the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere. Each of these layers plays a role in making Earth a habitable planet. There are boundaries between each of these layers, and they are defined by four key parameters: temperature change, chemical composition, density, and gas movement. And between the mesosphere and the thermosphere is a line that officially serves as the boundary between Earth and space.
This boundary which marks the beginning of space is called Karman’s line. Named after the Hungarian physicist Theodore von Karman, the Karman line is a crucial element in aeronautics and astronomy. Indeed, the Karman line is obligatorily taken into account when determining the height up to which an airplane can fly. Engineers and scientists also consider the Karman line when determining how to keep satellites and spacecraft in orbit around Earth.
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A more or less well-defined boundary between space and Earth
The Karman line is defined as the approximate altitude where orbital dynamic forces are more critical than aerodynamic forces. In other words, it is the altitude from which the air density becomes so low that the atmosphere alone can no longer support spacecraft at suborbital speeds. Theodore von Karman estimated that this famous line is about 80 kilometers above sea level. As science has progressed, scientists have finally agreed that this border is higher, at about 100 kilometers above sea level.
Anyway, the limit used by space and aeronautical agencies is generally 80 kilometers, although this is the source of many disagreements. If there is so much debate on the subject, it is because the atmosphere does not disappear, but thins with altitude. This means that part of the atmosphere is in space. Moreover, it is estimated that the Earth’s atmosphere extends for about 1,000 kilometers, which is well beyond the Karman line. Thus, confusion is permitted, insofar as space is defined as the absence of atmosphere.
This confusion is problematic because international laws and treaties define space as a region free for anyone to explore and use. On the other hand, this is not at all the case with regard to the airspace above the various nations. However, international law does not provide the exact limit for the altitude where this airspace ends. This lack of universal definition of the limit between space and the Earth can thus lead to intrusions into sovereign airspace; an act that can be misconstrued as aggression.
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