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At what point does the atmosphere become space?

  1. Mar 10, 2017 #1
    A few years ago, a Australian guy jumped from a platform that was attached to a weather balloon, from roughly 24 miles or so in the atmosphere. News articles claimed he jumped "From the edge of space".


    But did he?, I mean clearly 24 miles is an incredible feat, but, I have had conversations with people who tell me that the edge of space is more like 50 miles up.

    I'm not trying to be funny, I really have been wondering.

    I understand that the atmosphere just keeps getting thinner, until at some point the earth's gravity can't keep the gasses from being blown off by the solar winds. Is there a clearly defined point where that happens, or is it more like a shades of grey thing, where we just all agree to say that a certain point is the distance we will discuss, for the sake of making discussions about the topic easier? Or is it a clear demarcation, like the difference between the surface of an ocean, and the shore? (I assume the atmosphere is subject to tides, just like the rest of the planet?)

  2. jcsd
  3. Mar 10, 2017 #2


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    Can you post other links to what you've been reading about the generally accepted dividing lines? It probably depends on the application or viewpoint, no? Are you planning a trip to space? :smile:
  4. Mar 10, 2017 #3


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  5. Mar 10, 2017 #4
    The news articles claiming "edge of space" were so long ago, that the best I could offer would be a random google search. But I do seem to remember the same statement being made in the Red Bull Documentary about the event, which they sponsored.

    I haven't been reading other opinions about where the "edge of space" would/should be.
    They were discussions I had with other live, in-the-flesh human beings. (As I stated...)
    Can you show me how to link to that? :doh:


    It was these discussions that made me decide to ask the question here.

    As far as planning a trip.... Why yes, as a matter of fact I am (thanks for asking BTW!,) and I want to make darn good and sure I know when to close the windows! :oldlaugh: If you're interested in joining me, I might still have a couple bench seats available in the back of the magic bus....

    OK, so re-reading the meteor/meteoroid/meteorite article, I found this gem by mfb:

    "The area density of the atmosphere above 50 km is about 10 kg/m2,
    The area density of the atmosphere above 80 km is about 0.15 kg/m2"
    Clearly, it starts to thin out very quickly at some point...

    Someone else mentioned that meteors can be seen as far up as 120km, because of ionization of the atmosphere... Which is over 74 miles, and more than 3 times the altitude that Felix jumped from.... So there goes the "edge of space" argument, methinks....

    But I'm still looking for the magic number. Seriously, I just wondered how far you have to go, to get to the point where the earth's gravity no longer holds any of the atmosphere in thrall, and instead, the solar winds blow the remaining wisps out into space?

    The search continues....
  6. Mar 10, 2017 #5
    When in doubt, google?

    These are the layers of the atmosphere, starting from the ground:

    • Troposphere - Starts at the ground. Ends somewhere between 7 to 14 kilometres (4.3 to 8.7 miles). The higher, the colder. Weather in this layer affects our daily life.
    • Stratosphere - Starts at 7 to 14 kilometres (4.3 to 8.7 miles). Ends at 50 kilometres (31 miles). The higher, the hotter. There is little water vapor and other substances in this layer. Airplanes fly in this layer because it is usually stable and air resistance is small.
    • Mesosphere - Starts at 50 kilometres (31 miles). Ends at 80 or 85 kilometres (50 or 53 miles). The higher, the colder. Winds in this layer are strong, so the temperature is not stable.
    • Thermosphere - Starts at 80 or 85 kilometres (50 or 53 miles). Ends at 640 kilometres (400 miles) or higher. The higher, the hotter. This layer is very important in radio communication because it helps to reflect some radio waves.
    • Exosphere - Above the thermosphere. This is the top layer, and merges into interplanetary space.
    I get the impression that the exosphere is the layer where gases are swept away by solar winds. Since this layer starts at around 400 miles altitude, I think I may accept 400 miles as the "practical" answer to my question.

    Berkeman - Bring your fishing pole - I plan to stop along the way...
  7. Mar 12, 2017 #6


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    The atmosphere and space are a continuum, so the boundary or edge of space or atmosphere is arbitrary. However, it has been generally accepted that 'edge of space' is 100 km or 62 miles above sea level.

    "The path of an object launched from Earth that reaches 100 km (62 mi) above sea level, and then falls back to Earth, is considered a sub-orbital spaceflight."

    The X-15 is considered the first manned craft to reach space during Flights 90 and 91.

    The article on spaceflight mentions, "The most commonly used definition of outer space is everything beyond the Kármán line, which is 100 kilometers (62 mi) above the Earth's surface. The United States sometimes defines outer space as everything beyond 50 miles (80 km) in altitude."

  8. Mar 12, 2017 #7


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    Just a quick clarification: those flights occurred after Project Mercury (and Vostok), so they weren't the first manned spaceflights. But they would have been the first in a space plane, not launched from the ground, and the pilot also happened to be a civilians, another first.
  9. Mar 12, 2017 #8


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    Thanks for the correction. The X-15 was the first plane (vehicle capable of controlled flying/gliding in the atmosphere) in space, but not orbital.

  10. Mar 12, 2017 #9
    Thank you both.

    It may seem like a trivial subject, but with no background in the subject, it wasn't even easy to google the topic, and find meaningful (on topic) information. It's always nice to have a little help from those who have already been down the path towards this particular subject of enlightenment.

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  11. Mar 13, 2017 #10


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    I remember this being discussed in my workplace at the time. I argued that if a balloon works (the gas inside is less dense than the atmosphere outside), it's not space. Someone else argued that if you need to wear a spacesuit, it's space. Hard to argue with that, especially if it's you in the balloon! Someone else said the boundary is where you see the sign "Space Welcomes Careful Astronauts"!

    BTW, Baumgartner was Austrian, not Australian.
  12. Mar 13, 2017 #11
    No way. Humans would need protection long before space, if a 474's cabin wasn't pressurized, you'd pass out at normal cruising altitude.
  13. Mar 20, 2017 #12
    Another "definition" for the boundary is the altitude at which a descending spacecraft begins to experience air resistance that will begin to destroy the craft - such as stripping off antennae. I see this discussed fairly often when I follow up on current links about impending reentry of old satellites and the live commentary during the reentry often says reentry has occurred when the altitude is around 150 km.
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