I've noticed that the average low temperature at Gale Crater is -78.5 degrees, curiously the freezing temperature of Mars' atmosphere's main component. Is that more than a coincidence?

Perhaps the freezing of carbon dioxide presents an obstacle which stabilizes, at least for some time, the temperature at that value. As energy is removed from the atmosphere, instead of the temperature dropping the CO2 freezes. Does that sound plausible? And if this is the case, are other areas of the solar system similarly constrained to a temperature that produces a phase-change in some other atmospheric gas?

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    $\begingroup$ The freezing point of carbon dioxide on Mars is closer to -120 degrees due to to the much lower pressure. This is a pure coincidence. $\endgroup$ Apr 24, 2017 at 12:00

1 Answer 1


The mechanism is plausible, especially if you are measuring air temperature. However, that specific case is just a coincidence.

CO2 does freeze at -78.5 on Earth, but the much lower atmospheric presure on Mars moves the freezing point to below -120.

  • $\begingroup$ Thank you. I just checked the phase diagram, you are correct! However, the absolute record low is -127 degrees. Might that be the "temperature obstacle"? In fact it does make sense that the obstacle would be represented by the record low, not the average low. $\endgroup$
    – dotancohen
    Apr 24, 2017 at 12:06
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    $\begingroup$ @dotancohen Now you are looking for data to match a theory instead of theories to match data. Be careful. $\endgroup$ Apr 24, 2017 at 12:09
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    $\begingroup$ @Hohmannfan: Why? Was that not how relativity was proven in 1919, fourteen years after being proposed as a theory? $\endgroup$
    – dotancohen
    Apr 24, 2017 at 12:15
  • $\begingroup$ Excellent answer. Like the man said, "Science Rules!" youtu.be/UtVJdPfm0F8?t=11 $\endgroup$
    – uhoh
    Apr 24, 2017 at 15:06

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