<p>Hydrogen and oxygen only react when there is sufficient energy. For instance, the autoignition temperature of hydrogen at 1 atmosphere is <a href="https://en.wikipedia.org/wiki/Autoignition_temperature#Autoignition_point_of_selected_substances" rel="noreferrer">536 °C</a>. This is why you can do that experiment with mixed hydrogen and oxygen in a balloon, that only explodes when you touch the balloon with a lit taper.</p>

<p>Space is cold. Molecular clouds have temperatures in the <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/molecular_clouds.html" rel="noreferrer">tens of degrees Kelvin</a>. In the rare (if not impossible) case that a molecular cloud of pure oxygen did exist, and it encountered a molecular cloud of hydrogen, there wouldn't be enough energy for an explosion.</p>

CC BY-SA 3.0
2017-06-22T03:19:50.337Z
Is there really such a thing as a molecular cloud of oxygen? I thought they were almost 100% H2.
Mike H
CC BY-SA 3.0
2017-06-22T04:25:34.907Z
That was why I said it would be rare if not impossible, because they probably don't exist. I didn't get that across very clearly though, sorry.
hartacus
CC BY-SA 3.0
2017-06-22T04:27:31.357Z
Edited for clarity
hartacus
CC BY-SA 3.0
2017-06-22T07:40:12.573Z
Temperature is not the issue. While molecular clouds have temperatures of tens of Kelvin, HI and HII clouds have hundreds, and tens of thousands of Kelvin. You just don't have a cloud of oxygen.
pela
CC BY-SA 3.0
2017-06-22T08:39:35.460Z
@pela do you know why clouds of oxygen aren't a thing? too heavy an element?
hartacus
CC BY-SA 3.0
2017-06-22T11:35:28.067Z
Heavy elements, or "metals", occur in a mix of gas, usually in a mass ratio of roughly 1:100 wrt. hydrogen. Of this 1% only a fraction is oxygen. In cold clouds, oxygen may form oxygen molecules, just as other molecules will form, but it will still be mixed with a much larger fraction of hydrogen and helium. So, when you see an image of some interstellar cloud showing, e.g., oxygen, it's not because it's a "cloud of oxygen", but because the cloud contains oxygen that happens to emit light due to some physical process that makes oxygen emit light, e.g. collisions or ionization/recombination.
pela
CC BY-SA 3.0
2017-06-23T12:18:54.107Z
There are huge amounts of hydrogen and oxygen clouds in space! Most pictures you see from hubble actually use the ionisation wavelength of O-III and H-I to create false color images of nebulas (since Hydrogen and oxygen are the most abundent elements in interstellar nebulas)
RononDex
CC BY-SA 3.0
2017-06-23T13:31:34.773Z
This article suggests that there is very little molecular oxygen: http://www.sciencemag.org/news/2015/05/why-there-so-little-breathable-oxygen-space . I assume that when we're talking about a cloud of oxygen gas we're talking about molecular oxygen? Oxygen ions in other molecules or compounds could contribute to e.g. photos but not factor into this question.
hartacus
CC BY-SA 4.0
2021-01-28T14:18:24.570Z
"Hydrogen and oxygen only react when there is sufficient energy. For instance, the autoignition temperature of hydrogen at 1 atmosphere is 536 °C" You mean molecular H and O, I guess. Atoms are much more willing to react.
Leos Ondra
CC BY-SA 3.0
2017-06-22T01:59:39.177Z
2017-06-22T04:26:46.253Z
2017-06-22T04:26:46.253Z
hartacus
<p>While an oxygen ball of gas isn't possible, an Oxygen rich atmosphere on a planet, through photosynthesis is possible.  Earth for example.   A hydrogen rich planet (Jupiter or Saturn) are also possible, as is a methane rich atmosphere (Titan).  </p>

<p>If two bodies like that were to collide, you probably would see an enormous flame by the oxygen and fuel combustion process.  That said, the gravitational impact would generate far more energy than any chemical combustion.  If you were to collide two planets with atmospheres that together could combust, I'm not sure it would make much difference than two planets combining with atmospheres that wouldn't combust.  The impact is what would stand out. </p>

CC BY-SA 3.0
2017-06-22T05:29:06.950Z
2017-06-22T05:29:06.950Z
userLTK
<p>chemistry tells us that when mixing hydrogen and oxygen the result is an explosion and water.</p>

<p>my question is: does this happen on astronomical scale? for example, did they ever observe planet-size hydrogen cloud collide with planet-size oxygen cloud to produce a huge explosion and planet made primary of water?</p>

CC BY-SA 3.0
2017-06-21T22:29:25.043Z
I'm going to take a wild guess and say that's never been observed.
userLTK
CC BY-SA 3.0
2017-06-21T22:39:39.480Z
Oxygen rare in space. I doubt there has ever been a cloud of oxygen discovered.
Natsfan
<planetary-formation><hydrogen>
Hydrogen and oxygen in space
yigal
# Hydrogen and oxygen in space

(Asked by: username_0 on 2017-06-21)

chemistry tells us that when mixing hydrogen and oxygen the result is an explosion and water.

my question is: does this happen on astronomical scale? for example, did they ever observe planet-size hydrogen cloud collide with planet-size oxygen cloud to produce a huge explosion and planet made primary of water?

**Tags:** planetary-formation, hydrogen
> **Comments:**
> **username_1**: I'm going to take a wild guess and say that's never been observed.  
> **username_2**: Oxygen rare in space. I doubt there has ever been a cloud of oxygen discovered.  

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## 2 answers

### Answer by username_3 on 2017-06-22. Score: 5

Hydrogen and oxygen only react when there is sufficient energy. For instance, the autoignition temperature of hydrogen at 1 atmosphere is [536 °C](https://en.wikipedia.org/wiki/Autoignition_temperature#Autoignition_point_of_selected_substances). This is why you can do that experiment with mixed hydrogen and oxygen in a balloon, that only explodes when you touch the balloon with a lit taper.

Space is cold. Molecular clouds have temperatures in the [tens of degrees Kelvin](http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/molecular_clouds.html). In the rare (if not impossible) case that a molecular cloud of pure oxygen did exist, and it encountered a molecular cloud of hydrogen, there wouldn't be enough energy for an explosion.

> **Comments:**
> **username_4**: Is there really such a thing as a molecular cloud of oxygen? I thought they were almost 100% H2.  
> **username_3**: That was why I said it would be rare if not impossible, because they probably don't exist. I didn't get that across very clearly though, sorry.  
> **username_3**: Edited for clarity  
> **username_5**: Temperature is not the issue. While molecular clouds have temperatures of tens of Kelvin, HI and HII clouds have hundreds, and tens of thousands of Kelvin. You just don't have a cloud of oxygen.  
> **username_3**: @pela do you know why clouds of oxygen aren't a thing? too heavy an element?  
> **username_5**: Heavy elements, or "metals", occur in a mix of gas, usually in a mass ratio of roughly 1:100 wrt. hydrogen. Of this 1% only a fraction is oxygen. In cold clouds, oxygen may form oxygen molecules, just as other molecules will form, but it will still be mixed with a much larger fraction of hydrogen and helium. So, when you see an image of some interstellar cloud showing, e.g., oxygen, it's not because it's a "cloud of oxygen", but because the cloud contains oxygen that happens to emit light due to some physical process that makes oxygen emit light, e.g. collisions or ionization/recombination.  
> **username_6**: There are huge amounts of hydrogen and oxygen clouds in space! Most pictures you see from hubble actually use the ionisation wavelength of O-III and H-I to create false color images of nebulas (since Hydrogen and oxygen are the most abundent elements in interstellar nebulas)  
> **username_3**: This article suggests that there is very little molecular oxygen: http://www.sciencemag.org/news/2015/05/why-there-so-little-breathable-oxygen-space . I assume that when we're talking about a cloud of oxygen gas we're talking about molecular oxygen? Oxygen ions in other molecules or compounds could contribute to e.g. photos but not factor into this question.  
> **username_7**: "Hydrogen and oxygen only react when there is sufficient energy. For instance, the autoignition temperature of hydrogen at 1 atmosphere is 536 °C" You mean molecular H and O, I guess. Atoms are much more willing to react.  

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### Answer by username_1 on 2017-06-22. Score: 2

While an oxygen ball of gas isn't possible, an Oxygen rich atmosphere on a planet, through photosynthesis is possible. Earth for example. A hydrogen rich planet (Jupiter or Saturn) are also possible, as is a methane rich atmosphere (Titan).

If two bodies like that were to collide, you probably would see an enormous flame by the oxygen and fuel combustion process. That said, the gravitational impact would generate far more energy than any chemical combustion. If you were to collide two planets with atmospheres that together could combust, I'm not sure it would make much difference than two planets combining with atmospheres that wouldn't combust. The impact is what would stand out.


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