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ScootysDad t1_iwpd8hp wrote

Interestingly, no human has ever left earth's atmosphere. It actually is larger than the moon's orbit around the earth. Atoms like hydrogen and helium are so light that they travel way up there but they are still gravitationally bound to the earth until they collide with another particle (solar wind, interstellar particles) with enough energy that they are ejected. Large solar flares and gamma ray burst can strip the earth of its atmosphere.

Edit: We are running out of helium (important noble gas for cryogenic work) because 7 billion of balloons are being filled each year. 8 now.

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Chemomechanics t1_iwqk0u9 wrote

> no human has ever left earth's atmosphere.

This seems like an arbitrary definition of "atmosphere." Exactly where do you define the threshold? Can you provide a literature reference?

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ScootysDad t1_iws6mwh wrote

Remember the hydrogen and helium atoms I mentioned above? These wispery clouds extend up to 400,000 miles into space, gravitationally locked to the earth and formed the geocrorona.

So, yes, no human has ever left the confine of earth's atmosphere.

The actual scientific paper was published in 2019 in the Journal Geophysical Research: Space Physics by Baliukin, Quemerais, & Schmidt.

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Chemomechanics t1_iwsa5w7 wrote

Thank you for this reference. The introductory section clarifies: the exophere isn't a cloud or wisp or confine but the region where gas collisions essentially no longer occur—the lower limit of rarefication. Any molecule that happens to have—or ends up having—a speed greater than escape velocity leaves for the void in a ballistic trajectory.

I don't think many would consider this an atmosphere in colloquial terms, but it is undoubtedly associated with our atmosphere (although arguably beyond its meaningful edge), so I appreciate your point: Humans haven't traveled very far from Earth.

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ScootysDad t1_iwsip6m wrote

Scientific definitions have to be precise and we must be ready to give up on our long cherised notions. Except for Pluto. I'm still Team Pluto. Those astronomers...what do they know. :-)

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Ok_Construction5119 t1_iwrf69o wrote

The 100km we chose as the boundary for outer space is the arbitrary thing.

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Chemomechanics t1_iwrhmbc wrote

The purported threshold I'm questioning is the one where molecules are suddenly "gravitationally bound to the earth," as in the parent comment. I'm skeptical about that and would like to read a more complete description.

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ScootysDad t1_iws7hyk wrote

This 100km is an arbitraty value for geopolitical purposes with minimal scientific data.

This was declared space for the purpose of transiting over national territories. Very similar to the 2 mile limit for territorial water and 200 miles national economic water.

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