Re: Let me get this straight: The moon has an atmosphere?

I asked this before, and after I searched the archives I found that in a few of those answers the scientists said that the moon has one trillionth of the Earth's atmospheric pressure. Does the moon REALLY have an atmosphere? And if so, what is the moon's atmospheric pressure? (To moderator: please answer without saying to look in the archives, I already looked!)

OK, I won't refer you to the archives; instead, I'll refer you to a Google search for "lunar atmosphere".

Here's the gist:

• The lunar atmosphere is estimated to have a density of about ten million (10⁷) molecules per cubic centimeter, according to the New York Times' science column. This sounds like a lot, but it is indeed one trillionth (10^-12) of a standard "atmosphere," a pressure you need an excellent vacuum system to even approach in an Earthly laboratory.

• Nevertheless, the lunar atmosphere is a million times denser than interplanetary space. In interstellar space, only the densest clouds of matter approach even a thousandth of the density of the lunar atmosphere.

• The source of the lunar atmosphere is thought to be a combination of outgassing (mostly by meteoric impact) and sputtering of the surface by the solar wind. This is similar to the source of the Europan atmosphere, which is probably the result of the impact of meteors and the solar wind on its icy surface. (Water ice is dissociated into hydrogen and oxygen, but the hydrogen escapes because of the low gravity.)

Remember that an "atmosphere" is simply a detectable concentration of gases at the surface of a solid body. The term says nothing about how thick or thin it is, except relative to the surrounding medium. The lunar atmosphere is real because the moon does have a concentration of gaseous matter at its surface that is much denser than the interplanetary medium. Q.E.D.

Dan Berger
Bluffton University