Lunar regolith

Lunar regolith is the loose material that covers the surface of the Moon and is found floating in the Moon's thin atmosphere. It is often called "moondust" and is made up of tiny grains that are usually one centimeter or smaller in diameter. This material is very different from the soil we find on Earth.

Buzz Aldrin's bootprint on lunar soil was formed during the 1969 Apollo 11 mission.

Lunar regolith was formed mostly through mechanical weathering. Over billions of years, the Moon has been hit repeatedly by meteorites and bombarded by particles from the Sun and stars. These impacts and particles have broken down the Moon's rocky surface into smaller and smaller pieces.

Because it is so fine and easily moved by even small forces, lunar regolith can float around and get into anything exposed on the Moon. The tiny particles are sharp and stick together, making them tricky to handle. Scientists think that lunar regolith might be useful in the future, perhaps as building material or even as soil for growing plants on the Moon.

Formation processes

Further information: Geology of the Moon

Orange dirt found on Apollo 17, the result of volcanic glass beads

Lunar regolith forms mainly through the breaking of rocks by meteorite and micrometeorite impacts, called comminution. These tiny impacts also melt bits of rock together, a process known as agglutination. The Sun’s solar wind and cosmic rays from space further change the soil.

Over time, these processes alter the soil’s look and feel, known as space weathering. Volcanic activity can also play a role, creating small glass beads that fall back to the Moon’s surface. For example, orange dirt was found at Shorty Crater by Apollo 17, and green glass was discovered at Hadley–Apennine by Apollo 15. These beads are also thought to be behind Dark Mantle Deposits in other areas.

Circulation

Further information: Lunar atmosphere

Further information: Lunar horizon glow

Surveyor 7 observes levitating dust

The Moon may have a very thin layer of moving dust particles that jump up from its surface and fall back down. This creates a "dust atmosphere" that looks still but is always moving. Scientists think this happens because of electric charges. On the side of the Moon facing the Sun, strong sunlight knocks tiny particles loose from the surface, and they float up before falling back down. On the side away from the Sun, the dust gets charged differently by particles from the Sun’s wind.

Astronauts have seen strange glowing lights and hazy areas on the Moon from Earth. These might be caused by sunlight reflecting off the floating dust. Experiments left on the Moon have also noticed tiny particles moving around, supporting this idea.

Physical properties

Lunar dust is very fine and difficult to clean off, as with Apollo 17's Harrison Schmitt in a spacesuit working on the Moon being covered in lunar dust

The Moon's surface is covered with a thin layer of dust because of many meteorite impacts. This dust is electrically charged and can stick to anything it touches.

Lunar regolith has a density of about 1.5 g/cm³, and this density gets bigger as you go deeper. The way this dust behaves can be affected by big temperature differentials, the hard vacuum on the Moon, and the lack of a strong lunar magnetic field. This lets charged solar wind particles constantly hit the Moon's surface.

Chemical constituents

The Moon's surface material, called lunar soil, is mostly made up of seven key elements. These are oxygen (about 41-45%), silicon, aluminum, calcium, iron, magnesium, and titanium. The tiny bit left over, just 1-2%, includes manganese, sodium, potassium, and phosphorus.

Mineralogy and composition

The composition of lunar regolith comes from the rocks it covers. Over time, impacts mix the material both up and down, a process called "gardening". While mare and highland regolith have different compositions, they share similar minerals, just in different amounts. The main minerals found in lunar regolith are plagioclase, olivine, augite, orthopyroxene, pigeonite, ilmenite, chromite, quartz, cristobalite, and whitlockite. Glass is common in lunar regolith and forms when impacts melt materials. Ice is important in areas of permanent shadow.

Thin section of Apollo 12 Oceanus Procellarum sample 12005 in cross polarized light showing Lunar minerals

Lunar regolith particles include rock fragments, single-mineral pieces, and different kinds of glass, such as agglutinate particles. Agglutinates form when micrometeorite impacts cause small-scale melting, fusing nearby materials together with tiny bits of iron in each dust particle's glassy shell. Two key differences exist between lunar regolith and Earth dirt. First, the Moon is very dry, so minerals that need water, like clay, mica, and amphiboles, are not found there. Second, lunar regolith is chemically reduced, not oxidized like Earth's crust, partly due to constant bombardment by protons from the solar wind. This means iron on the Moon is found in the elemental (0) and cationic (+2) states, unlike Earth where it is mainly in the +2 and +3 states.

Harmful effects of lunar dust

Lunar dust, the tiny particles found on the Moon, can cause problems for astronauts and equipment. It can make surfaces darker, scratch materials, and damage important parts like lenses and solar panels. It might also affect the health of astronauts if inhaled.

Gene Cernan with lunar dust stuck on his suit from his Apollo 17 moonwalks.

To keep astronauts safe, special steps are needed when they return from the Moon. These can include cleaning their spacesuits and using filters to keep dust out of the air inside spacecraft.

Scientists think lunar dust could be more harmful than dust on Earth because it has sharp edges and reacts more with other materials. If it gets into the lungs, it might cause health problems. During Moon missions, spacesuits can get covered in this dust, which could spread inside when the astronauts come back inside. To reduce these risks, special methods are used, like high air flow in airlocks and magnetic tools to remove dust.

Use

Lunar soil could be useful for building structures, and scientists have been testing this idea for a long time.

Plants have a hard time growing in lunar soil because it is very different from Earth soil. This means that long space trips might need special plans to grow food, like bringing Earth soil or changing lunar soil to make it safer for plants. Tests show that some plants can grow in lunar soil here on Earth.

Availability on Earth

NASA Researchers view a demonstration of the moon dust simulator in the 8- by 6-Foot Supersonic Wind Tunnel facility at the NASA Lewis Research Center (1960).

The Apollo astronauts brought back about 360 kilograms of lunar rocks from six landing sites. Even though this material was stored in special bottles, it can no longer be used for detailed studies because the bottles let in air. Every sample has been changed by Earth's air and humidity. The dust has changed and no longer matches what future astronauts will find on the Moon.

In 2014, the US government allowed some private material collected by astronauts to be sold. Only one item with real Moon dust has been made available for sale—a piece of a spacesuit from the Apollo 12 mission that spent over 32 hours on the Moon. In 2017, lunar regolith collected by Neil Armstrong in 1969 was offered for sale. Many jewelry and watch makers say their products contain "Moon dust," but they actually contain pieces of meteorites thought to come from the Moon. In September 2020, NASA said it would buy lunar regolith from commercial suppliers. In May 2022, scientists grew plants using lunar regolith. Thale cress (Arabidopsis thaliana) was the first plant to grow on Earth using soil from another celestial body.