I've been reading about water on the Sun. The water they talk about is supposedly in a gaseous state because the Sun is so hot. But I'm wondering how even that could exist. Wouldn't the extreme temperature of the Sun ($> 5000^\circ{\rm C}$ on the surface) split it into hydrogen and oxygen through thermolysis, which can occur at just $2000^\circ{\rm C}$?

  • $\begingroup$ Sunspots are cooler than the rest of the sun, about 3800K. If there is oxygen in the sun, there is plenty of hydrogen around for it to combine with. Some fraction may be water molecules even if they don't last long. $\endgroup$
    – mmesser314
    Dec 3, 2017 at 1:07
  • $\begingroup$ @mmesser314 So I guess the question that remains is weather or not their is oxygen on the sun. But even if their is, to me Oxygen + Hydrogen + 3800K spells out hydrogen explosion, not rain clouds;) thanks anyways :) $\endgroup$
    – Hashbrowns
    Dec 4, 2017 at 23:00

1 Answer 1


It's true that the temperature on the Sun will split water molecules very rapidly. However, the research you referred to discovered trace amounts of water on sunspots, not an atmosphere of water vapor (or worse: oceans)

The water molecules form then are broken down by the temperature very quickly. It is not that no water vapor can form on the Sun, rather the conditions are unfavorable thus the quantities are very small.

For reference, at 2200C, around 3% of water molecules are dissociated. At 3000C, around half of the molecules are split. From a chemistry POV, this thermal energy is required to overcome the bond energy within water.

The rate constant of the reaction is $k=Ae^\frac{-Ea}{RT}$, where Ea is activation energy and T is Temperature. A is a constant based on the reaction and R is ideal gas constant. You can see the correlation between temperature and rate here, k will never reach infinity as long as the temperature is finite.


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