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  ⚡ Where does space begin?

Image: a Franco-Russian team calculated that the atmosphere extended up to 630,000 km beyond the Earth (almost twice as far as the Moon).

NB: The space station orbit 400 km.
A plane flies at an altitude of 10 km.

...and where does the atmosphere end?

We have the impression that space begins beyond the terrestrial atmosphere but that is not a good definition because the more the altitude increases and the less the atmosphere is dense, without really disappearing, it gradually becomes scarce.
The atmosphere begins at the Earth's surface (troposphere 0 km to 20 km altitude) and continues at extremely high altitudes (exosphere 1000 km to 50,000 km altitude).
From data collected by the Soho mission, a Franco-Russian team calculated that the atmosphere extended up to 630,000 km beyond the Earth (1.5 times farther than the Moon).
The atmosphere is diluted in space until it forms a scattered cloud extremely held in hydrogen atoms (10 to 70 atoms per cm3) called « geocrown ».
At the level of the Moon, there are only 200 atoms per cubic decimetre, in other words almost empty.

Composition of the atmosphere
Gaz
Volume or ppmv (part-per-million)
Dinitrogen (N2)
78.084 %
Dioxygen (O2)
20.946 %
Argon (Ar)
0.934 %
Carbon dioxide (CO2)
0.0415 %
Neon (Ne)
18.18 ppmv
Helium (He)
5.24 ppmv
Methane (CH4)
1.745 ppmv
Krypton (Kr)
1.14 ppmv
Dihydrogen (H2)
0.55 ppmv

Kármán Line

Image: The altitude of 120 km marks the border where the atmospheric effects become noticeable for an object when it re-enters the atmosphere.

We have the impression that space begins beyond the terrestrial atmosphere but that is not a good definition because the more the altitude increases and the less the atmosphere is dense, without really disappearing, it gradually becomes scarce.
The atmosphere begins at the Earth's surface (troposphere 0 km to 20 km altitude) and continues at extremely high altitudes (exosphere 1000 km to 50,000 km altitude).
From data collected by the Soho mission, a Franco-Russian team calculated that the atmosphere extended up to 630,000 km beyond the Earth (1.5 times farther than the Moon).
The atmosphere is diluted in space until it forms a scattered cloud extremely held in hydrogen atoms (10 to 70 atoms per cm3) called « geocrown ».
At the level of the Moon, there are only 200 atoms per cubic decimetre, in other words almost empty.