Suggested Searches

The Moon’s Atmosphere

Does the Moon have an atmosphere? Yes, but just barely, and it’s very different from the atmosphere we know on Earth. When people talk about the Moon’s atmosphere, they are often referring to its main layer: the lunar exosphere. 

Earth
Moon
Earth surrounded by layers of atmosphere - in order from the surface: troposphere, stratosphere, mesosphere, thermosphere, exosphere. In the distance is the Sun.
NASA/Vi Nguyen
Diagram of the lunar surface and the Moon's atmosphere, which has just one major layer, the exosphere. In the distance is the Sun.
NASA/Vi Nguyen

comparing Atmospheres

Atmospheric Layers

(Images not to scale)

Earth’s atmosphere has five major layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The Moon’s atmosphere contains only one major layer: its exosphere. These images are not to scale; Earth is much larger than the Moon, and neither world’s atmosphere has a fixed outer limit. Credit: NASA/Vi Nguyen

Getting to Know the Lunar Exosphere

The lunar atmosphere is mostly an exosphere, which itself is mostly empty space. If you were to visit the Moon and walk around on its surface, you might think it had no atmosphere at all. Molecules around the Moon are so few and far between that they travel long distances without running into anything, even each other. Earth’s atmosphere, on the other hand, is dense and collisional: air molecules are bumping into each other (and interfering with each other’s movements) all the time. 

Since the Moon’s atmosphere is not collisional, we can study each chemical component independently. For example, some scientists work to understand how water forms and changes on the Moon by investigating the behavior of hydrogen atoms in the exosphere. Chemical components of the lunar exosphere have their own ‘cycles’ of movement between the ground and the space nearby, and distinct migration patterns from place to place on the Moon’s surface.  

Side by side photos: Left photo is of the barren Moon surface with the blue Earth in the distance. Right photo shows a blue sky above Earth's clouds, with the Moon in the distance.blue Earth against a black sky above the barren lunar surface.
The Moon’s atmosphere contains about one million billion (1015) times fewer molecules per cubic centimeter than Earth’s does. This is primarily because Earth is more massive (so it has a stronger gravitational pull holding its atmosphere in place) and Earth has more active sources of atmospheric gases (like erupting volcanoes). Our planet’s magnetic field also helps to protect and preserve our atmosphere. Left: Earth as seen by Apollo 8 astronauts circling the Moon (1968). Right: the Moon as seen by astronauts orbiting Earth on the International Space Station (2024).
NASA/Vi Nguyen

What is the Moon’s Atmosphere Made Of?

The lunar exosphere is almost entirely made up of helium, neon, and argon, with trace amounts of other elements. Hydrogen molecules make up a tiny fraction of the lunar exosphere, but are a topic of serious scientific interest, partly because hydrogen is one of the chemical ingredients in water

Sodium is another scarce but heavily-studied element in the lunar exosphere. Sodium’s chemical signature is relatively easy to detect from far away, making it an appealing target for observers who use Earth-based telescopes or analyze data from spacecraft in lunar orbit.

An instrument with wiring coming out of it sitting on the surface of the Earth's Moon. Also seen nearby are foot prints from the astronauts from the Apollo mission.
The Cold Cathode Gage Experiment (CCGE, also referred to as the Cold Cathode Ion Gage, or CCIG) was deployed as part of the Apollo Lunar Surface Experiments package (ALSEP) on Apollos 12, 14, and 15. It was designed to measure the density of neutral particles to determine the amount of gas present at the lunar surface. The CCGE is the small canister-shaped instrument in this image; the large box-shaped instrument on the right is the Suprathermal Ion Detector Experiment (SIDE), which measured exospheric ions.
NASA

Most lunar exosphere science relies on data collected at a distance, but humans have also set up experiments on the ground. When the crews of Apollo 12, 14, and 15 lifted off from the Moon, they left behind devices designed to measure the amount of gas near the lunar surface. These initial experiments confirmed the presence of an extremely sparse atmosphere. Then Apollo 17 astronauts deployed a spectrometer called LACE (the Lunar Atmospheric Composition Experiment) to identify the atmosphere’s chemical makeup. 

Decades later, new spacecraft brought updated technology into lunar orbit for follow-up observations. THEMIS-ARTEMIS began as a five-satellite Earth-focused mission. When its original assignment ended in 2008, two of its five probes were redirected to locations near the Moon, where they now measure charged particles swept away from the lunar exosphere by solar wind. NASA’s Lunar Reconnaissance Orbiter (LRO), an SUV-sized spacecraft with seven science instruments on board, has been sending data home from lunar orbit since 2009. In 2013-2014, the Lunar Environment and Dust Explorer (LADEE for short) joined LRO for a six-month orbital mission, gathering detailed information about the lunar exosphere’s composition and structure – and giving new insight into how these change over time. 

The Moon’s Changing Environment

In contrast to Earth’s thick layers of air, the Moon’s exosphere is a bit like the haze you get when you whack a dirty rug with a broom: it includes a sampling of particles knocked free by impact. But instead of a rug, these particles come from the lunar surface. Instead of flying through the air, they’re ejected into near-emptiness. And instead of a broom, the Moon is pummeled by space debris. Micrometeorites and other impactors temporarily kick up dust particles and even individual atoms from the Moon’s surface. All the while, the solar wind delivers protons and other materials from the Sun. As some particles settle to the ground or escape into space, new impacts send others aloft. 

Streams of meteoroids striking the Moon's surface.
Some pieces of space debris are too small to make craters, but they still disturb the lunar surface. Impacts of all sizes mix up the Moon’s outermost layers and expose fresh material that was once hidden underground. This shuffling of dust and rock is called impact gardening.
NASA

Human and robotic activity change the lunar exosphere, too. Exhaust from a single lunar lander can briefly dominate the space nearby. Since spacecraft exhaust includes water and other chemical ingredients that also occur naturally on the Moon, studies of the lunar environment must account for exploration-related changes. Scientists are already running simulations to anticipate the atmospheric effects of future Moon landings.

Writer: Caela Barry, NASA’s Goddard Space Flight Center
Science Advisors: Dana Hurley and Parvathy Prem, Johns Hopkins University Applied Physics Laboratory; Bill Farrell, NASA’s Goddard Space Flight Center