5 ms·

Sure, it's kinda there... It'll count for free radical oxidation of spacecraft surfaces and cause minute amounts of drag at those altitudes, but it's worth remi

Sure, it's kinda there... It'll count for free radical oxidation of spacecraft surfaces and cause minute amounts of drag at those altitudes, but it's worth reminding people that this is in the range of dozens of atoms per cubic meter. Water boils at body temperature at the Armstrong line, which is only 19.2 km above sea level.

DoctorOetker 8y ago
according to this article: > The denser dayside region of hydrogen is still rather sparse, with just 70 atoms per cubic centimeter at 60 000 kilometers above Earth’s surface, and about 0.2 atoms at the Moon’s distance. At the distance of the moon: 200000 per cubic meter so I think it's a bit higher than you think... of course you don't explicitly mention a height for the spacecraft surfaces...
- FakeComments 8y ago
  There’s around 10^25 atoms per cubic meter of air at sea level, so talking about a 10^5 density, a 10^20 reduction in density, is pushing the definition of “there”. (This also makes it closer to space, at 1 particle per cubic meter, than Earth atmosphere, by a dozen orders of magnitude.) For reference, lead in drinking water is actionable at a 10^8 factor, but beyond that — say 10^12 — we largely talk about it not being there. There’s basically no case we refer to something attenuated by twenty orders of magnitude as qualitatively the same. Edit: For fun, I looked up what it meant as energy differences — twenty orders of magnitude is the difference between you jumping and the total energy from the sun that strikes the face of the Earth each day. https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy) https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy)
  - EForEndeavour 8y ago
    Your comment is consistent with why the parent replied to the grandparent: 2e5 is orders of magnitude greater than "dozens." That's still closer to space than to sea-level atmosphere, but it's not nearly as close as the grandparent comment stated.
    - FakeComments 8y ago
      A density of 10^5 is eight orders of magnitude beyond “ultra high vacuum”, which is about 10^13 particles per cubic meter — or 10^-12 times normal. Poster is more correct to say “dozens” (four orders of magnitude) than that it’s not a vacuum (eight orders before the edge of ultra high). https://en.m.wikipedia.org/wiki/Vacuum https://en.m.wikipedia.org/wiki/Vacuum Poster was completely correct that this accounts for only minuscule interactions such as surface oxidation and teensy drag over prolonged interactions, and nothing like the “atmosphere” behaves.
      - DoctorOetker 8y ago
        at what point exactly did I compare with sea level?
BorRagnarok 8y ago
It's hydrogen atoms as well, which is funny because the solar wind is mainly protons, which is hydrogen minus one electron. Leaves me wondering if it varies in size much, because electron flow is quite easy.
mrfusion 8y ago
You’d still be ok above the Armstrong line if you covered your head though. I think your skin would protect you?

DoctorOetker 8y ago

according to this article: > The denser dayside region of hydrogen is still rather sparse, with just 70 atoms per cubic centimeter at 60 000 kilometers above Earth’s surface, and about 0.2 atoms at the Moon’s distance. At the distance of the moon: 200000 per cubic meter so I think it's a bit higher than you think... of course you don't explicitly mention a height for the spacecraft surfaces...

FakeComments 8y ago
There’s around 10^25 atoms per cubic meter of air at sea level, so talking about a 10^5 density, a 10^20 reduction in density, is pushing the definition of “there”. (This also makes it closer to space, at 1 particle per cubic meter, than Earth atmosphere, by a dozen orders of magnitude.) For reference, lead in drinking water is actionable at a 10^8 factor, but beyond that — say 10^12 — we largely talk about it not being there. There’s basically no case we refer to something attenuated by twenty orders of magnitude as qualitatively the same. Edit: For fun, I looked up what it meant as energy differences — twenty orders of magnitude is the difference between you jumping and the total energy from the sun that strikes the face of the Earth each day. https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy) https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy)
- EForEndeavour 8y ago
  Your comment is consistent with why the parent replied to the grandparent: 2e5 is orders of magnitude greater than "dozens." That's still closer to space than to sea-level atmosphere, but it's not nearly as close as the grandparent comment stated.
  - FakeComments 8y ago
    A density of 10^5 is eight orders of magnitude beyond “ultra high vacuum”, which is about 10^13 particles per cubic meter — or 10^-12 times normal. Poster is more correct to say “dozens” (four orders of magnitude) than that it’s not a vacuum (eight orders before the edge of ultra high). https://en.m.wikipedia.org/wiki/Vacuum https://en.m.wikipedia.org/wiki/Vacuum Poster was completely correct that this accounts for only minuscule interactions such as surface oxidation and teensy drag over prolonged interactions, and nothing like the “atmosphere” behaves.
    - DoctorOetker 8y ago
      at what point exactly did I compare with sea level?

BorRagnarok 8y ago

It's hydrogen atoms as well, which is funny because the solar wind is mainly protons, which is hydrogen minus one electron. Leaves me wondering if it varies in size much, because electron flow is quite easy.

mrfusion 8y ago

You’d still be ok above the Armstrong line if you covered your head though. I think your skin would protect you?