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Liquid hydrogen in space?

  1. Aug 10, 2014 #1
    Hi,
    I was wondering why there is no liquid hydrogen in space? Space is very cold, more cold then the temperature that is required to convert gas hydrogen to liquid here on earth? Therefore, why is hydrogen in space in gas form and not liquid?
    Thanks
     
  2. jcsd
  3. Aug 10, 2014 #2

    e.bar.goum

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    While it is very cold in space, the pressure is also extremely low. As I'm sure you know, both pressure and temperature dictate the phase of matter.
     
  4. Aug 10, 2014 #3

    davenn

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    hi there
    welcome to PF

    In the vacuum of space, there is no pressure. This is critical for most liquids to remain in a liquid state because with no pressure, the temperature at which they start to boil drops.
    so hence Hydrogen and pretty much any other gas ( at Earth's atmospheric pressure) cannot become a liquid in the vacuum of space

    cheers
    Dave
     
    Last edited: Aug 10, 2014
  5. Aug 10, 2014 #4
    Thanks davenn. Just a sub-question here. What about interstellar cloud, when there is a pressure? Would a mix of helium and dust in a cloud be an obstacle for hydrogen to liquefy? I suppose that even the pressure in the interstellar could would increase, so would temperature, preventing hydrogen to liquefy?
    Thanks
     
  6. Aug 10, 2014 #5

    e.bar.goum

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    The pressures and densities even in interstellar clouds are extremely low. In cold, 'dense' regions, the density is around 10^6 molecules per cubic meter, compared to around 10^19 for air on earth!

    Yes, when you increase the pressure, you increase the temperature, hence the ionized regions. But in the hot regions, the matter is incredibly diffuse - 10^-4 ions/m^3 !!
     
  7. Aug 10, 2014 #6
    Thanks
     
  8. Aug 11, 2014 #7
    Like the others said. You must have pressure and temperature for it to liquify. My question is. Would it be possible for any gas to solidify is space and skip liquefying?, Or would that need more pressure to bring the particles together?
     
  9. Aug 11, 2014 #8

    davenn

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    what do you think ?

    if there isn't enough pressure to liquefy, then .......

    Dave
     
  10. Aug 11, 2014 #9

    sophiecentaur

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    I remember reading a SF story in which people were mining (with robot machines) on a cold planet, with solid, 'metallic hydrogen' near the surface. I don't remember finding that idea too unthinkable at the time. Now, I would give the idea a bit more scrutiny, perhaps. (But it was a very good tale, as I remember.)
     
  11. Aug 11, 2014 #10

    davenn

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    LOL yup ... ya have to watch SciFi for what it is ... fiction
    the moment we try to analyse it with physics ... the story is destroyed :smile:


    Dave
     
  12. Aug 11, 2014 #11

    TheDemx27

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    Just intuitively the story, for instance in the Gravity movie,
    when the main character is flung at the end of a rope attached to the satellite, you would expect the rope to go taught and recoil back the way it came, but NOOO. The main character was stretched out at the end of a taught rope, holding onto another astronaut for several seconds as if holding his hand off a cliff. As soon as the main character let go of the other astronaut, the main character floated safely back to the satellite. Bam. The main turning point in the story absolutely soiled by this blatantly obvious error.

    It was awful. Other than that it was a good movie.
     
  13. Aug 12, 2014 #12

    sophiecentaur

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    Afaic, Sandra Bullock can get as much Science wrong as she likes.
     
  14. Aug 12, 2014 #13

    QuantumPion

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    I never understood this complaint. When I was watching the movie, I just assumed:

    that the rope was elastic, like a bungee cord, but the character's combined weight would have been too much and caused the rope to break if they both held on.

    Although admittedly, a better idea for that scene would have been if they had both just missed the station, and Clooney simply pushed Bullock back, thereby pushing himself away due to conservation of momentum. That would have made more sense visually and be more of an active act of self-sacrifice I think.
     
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