Many people are convinced the Moon lacks an atmosphere. They believe it is directly exposed to the vacuum of space. But this is incorrect. In fact, there is an atmosphere on the Moon. It is far less dense than Earth’s and wouldn’t be safe to breathe. However, it does exist and has been measured, by instruments carried to the Moon by Apollo astronauts and by reconnaissance satellites put into lunar orbit by NASA in subsequent years.
The atmosphere on the Moon is less than paper thin. On Earth, at sea level, the air we breathe contains about 100 billion billion molecules per cubic centimetre. This sounds incredibly thick, but of course we can’t see the air on Earth, because of the infinitesimal size of even the largest and most complex gaseous molecules.
In comparison, on the Moon there are only about one million molecules in a cubic centimetre of atmosphere. This is vanishingly empty, if we compare it to Earth. Yet the Moon’s atmosphere is very real, and is typical of the thin atmospheres found on other bodies in the solar system.
The gases in the Moon’s atmosphere are mostly found in Earth’s atmosphere as well. They include small quantities of nitrogen, helium, argon, neon, ammonia, methane and carbon dioxide. These gases were detected in samples taken by the Lunar Atmospheric Composition Experiment (LACE), which was included in the last NASA mission to land astronauts on the Moon (Apollo 17).
Sodium and potassium were also found in the Moon’s atmosphere. These chemicals are not a part of the atmosphere on Earth, Mars or Venus. These substances were discovered by Earth-based researchers studying the Moon through special telescopes.