While driving home from a volleyball match with my teen daughter, we noticed the full moon. I reflected on the 50th anniversary of Apollo 11 this week. A mild sense of jealousy also rushed over me (smile) as I thought about fans at the Duran Duran concert in the rocket garden at Kennedy Space Center. While I have seen one of my favorite bands many times, I am sure that it was awesome to hear their space-tinged setlist in that setting and in celebration of the Apollo mission. As I shook myself out of from a fleeting envious moment, I decided to write something about the moon. Since I am a meteorologist and atmospheric sciences professor, it was only natural that I answer the question, "Does our moon have weather?"
To answer that question, we have to answer another one. Does our moon even have an atmosphere? It is tempting to say "no." However, a better answer is "sort of." Before we dig deeper, it is instructive to define "atmosphere" and describe the Earth's atmospheric structure. The American Meteorological Society Glossary of Meteorology is one of my favorite resources. It defines an atmosphere as "A gaseous envelope gravitationally bound to a celestial body (e.g., a planet, its satellite, or a star)." The atmosphere of Earth is divided into several layers. We live in the troposphere. Most of us will never leave the troposphere. It extends up to roughly 6-7 miles (~10 km), but that height can vary according according to altitude (lower in polar regions) and season (lower in winter). About 75-80% of the mass of our atmosphere is within the troposphere and most of the moisture too.
Between 7 and 31 miles above the ground (on average), we find the stratosphere. The tropopause is the transition region between the troposphere and stratosphere. The ozone layer, which protects us from harmful ultraviolet (UV) radiation from the sun, is in the stratosphere. It is also a layer that increases in temperature with altitude because of the UV absorption. We call that an inversion. The mesosphere is 30 to 51 miles above the surface. This layer can have temperatures as cold as -120 degrees F according to NOAA. Between 51 and 400 miles is a strange layer called the thermosphere. Temperatures range from -184 degrees F to several thousands of degrees F. Even at those temperatures it would feel cold to our skin due to the "thinness" of the atmosphere. The very high temperatures are because of the high kinetic energy of the molecules, but it would not feel warm because there are very few molecular collisions. This layer is also the home to the auroras. If you are an astronaut, this is also the layer in which you might start to feel the sensation of weightless. Beyond the thermosphere, the exosphere is found. According to NOAA's satellite division, this is the location of many low earth-orbiting satellites. The graphic below, provided by NOAA, summarizes the layers and some interesting things that happen within them.
Earth has weather because the troposphere is relatively thick, contains water, and hosts a complex display of fluid and thermodynamic interactions. Which brings us to the moon. According to NASA's Lunar Atmosphere and Dust Environment Explorer website:
recent studies confirm that our moon does indeed have an atmosphere consisting of some unusual gases, including sodium and potassium, which are not found in the atmospheres of Earth, Mars or Venus. It's an infinitesimal amount of air when compared to Earth's atmosphere. At sea level on Earth, we breathe in an atmosphere where each cubic centimeter contains 10,000,000,000,000,000,000 molecules; by comparison the lunar atmosphere has less than 1,000,000 molecules in the same volume. That still sounds like a lot, but it is what we consider to be a very good vacuum on Earth. In fact, the density of the atmosphere at the moon's surface is comparable to the density of the outermost fringes of Earth's atmosphere where the International Space Station orbits.
In the troposphere of Earth, there is mostly nitrogen and oxygen, but trace gases like carbon dioxide and water vapor are extremely important in regulating the temperature of our planet. A NASA mission called Lunar Atmospheric Composition Experiment (LACE) discovered that the lunar atmosphere also has traces of methane, carbon dioxide, helium, ammonia, and argon.
Temperatures can swing wildly on the moon. Tim Sharp wrote in a Space.com article:
Temperatures on the moon are extreme, ranging from boiling hot to freezing cold depending on where the sun is shining. There is no significant atmosphere on the moon, so it cannot trap heat or insulate the surface....The moon rotates on its axis in about 27 days. Daytime on one side of the moon lasts about 13 and a half days, followed by 13 and a half nights of darkness. When sunlight hits the moon's surface, the temperature can reach 260 degrees Fahrenheit (127 degrees Celsius). When the sun goes down, temperatures can dip to minus 280 F (minus 173 C).
There are also no seasons on the Moon. We have seasons because the Earth tilts on an axis at roughly 23.5 degrees. Because of the axial tilt as the Earth orbits the Sun, different parts of our planet are heated differently. For this reason, it is currently summer in the Northern Hemisphere and winter in the Southern Hemisphere. The moon is virtually erect (only a 1.54 degree tilt) according to Tim Sharp so there is virtually no seasonal variability.
Our moon obviously does not have weather like we experience on Earth. However, discoveries of water ice on the Moon suggest that there could be some type of "water cycle." Ironically, studies have suggested that the moon once had a more significant atmosphere. A 2017 NASA press release noted:
Research completed by NASA Marshall Space Flight Center planetary volcanologist Debra Needham in Huntsville, Alabama, and planetary scientist David Kring at the Lunar and Planetary Institute in Houston, Texas, suggests that billions of years ago, the Moon actually had an atmosphere. The ancient lunar atmosphere was thicker than the atmosphere of Mars today and was likely capable of weathering rocks and producing windstorms. Perhaps most importantly, it could be a source for some, if not all, of the water detected on the Moon.
This was a long-winded answer to the question, "Does the our moon have weather?" I hope you learned something though.
