5 ms·

One thing not clear to me after reading the article: Are these "atmospheric" particles in orbit around the moon, or is there enough collisions between them (act

by lolc 2y ago

One thing not clear to me after reading the article: Are these "atmospheric" particles in orbit around the moon, or is there enough collisions between them (actual pressure) to keep them afloat? Or both?

cwillu 2y ago
According to https://www.ias.ac.in/article/fulltext/jess/114/06/0637-0644 https://www.ias.ac.in/article/fulltext/jess/114/06/0637-0644, the mean free path of particles in the moon's “atmosphere” is thousands of km. This makes me think it's probably a combination of suborbital and out-gassing during daylight, with the occasional collision boosting a molecule to orbital or escape velocities. Which technically would be pressure I guess, but not on normal timescales.
- zardo 2y ago
  That link talks about gas molecules, but the article is saying ions. Whether or not these are ionized particles would have a big impact on what's happening.
  - JumpCrisscross 2y ago
    > Whether or not these are ionized particles would have a big impact on what's happening The lunar atmosphere is theorised to come from two sources: impact vaporisation and ion sputtering. When immediately produced, the latter will produce ionised particles wihle the former will have no preference. Both will be subject to later photo-ionization once...erm...airborne.
JumpCrisscross 2y ago
> Are these "atmospheric" particles in orbit around the moon No. They "hop on ballistic trajectories until they are either returned permanently to the surface" or are "lost to space" [1]. [1] https://www.science.org/doi/10.1126/sciadv.adm7074 https://www.science.org/doi/10.1126/sciadv.adm7074
- dotancohen 2y ago
  Which is why the term "atmosphere" is a misnomer. There exist molecules is motion above the lunar surface. These molecules are too sparse to be solid or liquid. But also, too sparse to be gas.
  - JumpCrisscross 2y ago
    > too sparse to be gas This isn’t a thing. The interstellar medium, for instance, is gaseous. Vacuum vs gas isn’t clearly, uniformly defined because “true” vacuums really don’t exist.
    - dotancohen 2y ago
      When the mean free path is longer then a typical ballistic trajectory that these molecules and ions are typically on, they do not exhibit any properties associated with gas. Importantly, the property of expanding under pressure to fill a volume is not exhibited.

by lolc 2y ago

cwillu 2y ago

According to https://www.ias.ac.in/article/fulltext/jess/114/06/0637-0644 https://www.ias.ac.in/article/fulltext/jess/114/06/0637-0644, the mean free path of particles in the moon's “atmosphere” is thousands of km. This makes me think it's probably a combination of suborbital and out-gassing during daylight, with the occasional collision boosting a molecule to orbital or escape velocities. Which technically would be pressure I guess, but not on normal timescales.

zardo 2y ago
That link talks about gas molecules, but the article is saying ions. Whether or not these are ionized particles would have a big impact on what's happening.
- JumpCrisscross 2y ago
  > Whether or not these are ionized particles would have a big impact on what's happening The lunar atmosphere is theorised to come from two sources: impact vaporisation and ion sputtering. When immediately produced, the latter will produce ionised particles wihle the former will have no preference. Both will be subject to later photo-ionization once...erm...airborne.

JumpCrisscross 2y ago

> Are these "atmospheric" particles in orbit around the moon No. They "hop on ballistic trajectories until they are either returned permanently to the surface" or are "lost to space" [1]. [1] https://www.science.org/doi/10.1126/sciadv.adm7074 https://www.science.org/doi/10.1126/sciadv.adm7074

dotancohen 2y ago
Which is why the term "atmosphere" is a misnomer. There exist molecules is motion above the lunar surface. These molecules are too sparse to be solid or liquid. But also, too sparse to be gas.
- JumpCrisscross 2y ago
  > too sparse to be gas This isn’t a thing. The interstellar medium, for instance, is gaseous. Vacuum vs gas isn’t clearly, uniformly defined because “true” vacuums really don’t exist.
  - dotancohen 2y ago
    When the mean free path is longer then a typical ballistic trajectory that these molecules and ions are typically on, they do not exhibit any properties associated with gas. Importantly, the property of expanding under pressure to fill a volume is not exhibited.