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When humans return to the surface of the Moon, there could be many circumstances under which gas is released out, from the pressurized components. Some of the cases are as follows:

  • Gas released from the life support system of the Exploration Extravehicular Mobility Unit (xEMU)

  • Accidental depressurization, etc.

What will happen to gas released from the Moon's surface?

Some of the possibilities I could think are as follows:

  • The constituent particles of the gas released will attain a stable orbit around the Moon (@Ags1's comment suggests even lighter molecules can stay in Moon's vicinity. Earlier, I thought lighter molecules would have greater RMS than Moon's Escape Velocity and would escape into somewhere(I don't know) and heavier molecules stay in the moon in sub-orbital trajectory. It would be great if you could clarify this point further.)

  • It may contribute to the gradual buildup of Moon's atmosphere, though very slowly. (After reading the answers linked below (hat-tip to @Uwe's comment), I realised that even though atmosphere buildup happens, there are lot other factors which can nullify this effect. For example, high energetic particles from the sun can peel of the atmosphere to a great extent.)

  • The gas escaped travels towards Earth and combines with its atmosphere.[*]

  • It gets accumulated in Earth-Moon Lagrange Points.[*]

  • It gets lost into deep space.[*]

[*]:The answers to the questions linked below do not explain this point clearly.

It would be great if you could explain which of the above possibilities (or something I forgot to mention) happens and the reason for it.

Even though this seems "meaningless" for some, I feel that there must be an answer for What will happen to the gas released from the Moon's Surface? Where will it eventually go? Is it not possible to estimate their behaviour based on our understanding of science?

Related questions with helpful answers, referenced above:

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    $\begingroup$ Fairly light refrigerants like C2F6 or SF6 are quite stable (so they would persist for significant time in the radiation environment of the Moon) and are massive enough to be trapped by the Moons gravity. I can see these being leaked from Moon bases... $\endgroup$
    – Ags1
    Oct 21, 2019 at 11:41
  • $\begingroup$ The Apollo EMU did not use air, pure oxygen was used in closed loop breathing system. So no air or oxygen was released from the EMU. But when depressurizing the Lunar Modules cabin in preparation of an EVA some oxygen was released. That oxygen release was deliberately but not accidentaly. $\endgroup$
    – Uwe
    Oct 22, 2019 at 11:19
  • $\begingroup$ Thanks for the info @Uwe. I am curious to know what will happen to the air/oxygen released by whatever reason deliberately/accidentally? And the spacesuits being referred here are the Artemis Generation Space Suits, which will vent out waste gases, from its Life-support systems. $\endgroup$
    – Vishnu
    Oct 22, 2019 at 11:26
  • $\begingroup$ Do you have a source that the Artemis Generation Space Suits will vent out waste gases? What are waste gases, carbon dioxide and water vapor? Oxygen may be reused to save a lot of weight. $\endgroup$
    – Uwe
    Oct 22, 2019 at 11:46
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    $\begingroup$ Don’t have time to write a full answer now, sorry, but you can find both the basic physics and some applied answered here: islandone.org/Settlements/DegradeLunarVacuum.html Astra Aeronautica V21 pp183-187 1990 $\endgroup$
    – Bob Jacobsen
    Oct 26, 2019 at 3:50

1 Answer 1

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It was measured during the Apollo 14 mission. The Apollo Lunar Surface Experiments Package (ALSEP) placed on the lunar surface by the astronauts had a gas concentration sensor. enter image description here

During the last depressurization of the LM some oxygen was released. But the oxygen was gone in less than 3 minutes. So the oxygen left the landing spot on the lunar surface very fast. At a temperature of 296 K the mean velocity of the oxygen molecules execeeds the escape velocity of the Moon.

enter image description here

The escape velocity of the Moon is 2.34 km/s but the speed of the molecules is about 5 km/s. Enough to leave the Moon forever. But the speed is too small for an escape of the solar system (617.3 km/s) or the gravitational influence of the Earth (11.186 km/s).

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    $\begingroup$ Thanks. Could you please explain where did the gas go? $\endgroup$
    – Vishnu
    Oct 26, 2019 at 15:55
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    $\begingroup$ "What will happen to gas released from the Moon's Surface?" $\endgroup$
    – uhoh
    Oct 26, 2019 at 16:14
  • $\begingroup$ The temperature on the moon fluctuates between 100K in lunar night and 400K in lunar day (source). From the graph in your answer, I've estimated that some oxygen and nitrogen, with greater amounts of carbon dioxide and xenon, will have velocities less than the moon's escape velocity when the temperature is 100K. Is there any possibility a particle attains a stable orbit around the moon such that it always faces the lunar night (analogous to geostationary orbits) assuming the gas was ejected horizontally with respect to the surface? $\endgroup$
    – Vishnu
    Oct 27, 2019 at 9:48
  • $\begingroup$ I think there must be variation in the amount of gas particles with time and orientation with respect to the sun. Kindly tell whether my hypothesis is correct? $\endgroup$
    – Vishnu
    Oct 28, 2019 at 11:39
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    $\begingroup$ @Uwe how do you get a speed of 5 km/s for a temperature of 296 K? Shouldn't the thermal velocity be roughly the speed of sound, or a few hundred m/s only? I think your answer is wrong. $\endgroup$
    – uhoh
    Nov 1, 2019 at 5:34

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