Facts Worth Sharing
- The Moon, our celestial neighbor, is the only world besides Earth ever visited by humans.
- By studying the Moon, scientists can piece together Earth’s origin story, including how life may have started.
- The Moon is an excellent testbed for human and robotic exploration technologies. NASA may fly a Planetary Society-funded sample collection system called PlanetVac to the lunar surface as early as 2022.
Why We Study the Moon
From 1969 to 1972, 12 astronauts walked on the Moon as part of NASA’s Apollo program. Humans have not been back since, and the Moon remains the only world besides Earth we’ve ever visited. The Moon lacks an Earth-like atmosphere, and there is no wind or water to erase the Apollo astronauts’ footprints. The paths they walked can still be seen from orbit—permanent monuments to one of humanity’s greatest achievements.
The Moon’s lack of air and lack of plate tectonics make it a geological time capsule. The surface bears the scars of meteorites, lava flows, and the late heavy bombardment, an event roughly 4 billion years ago where the inner solar system was pummeled by asteroids and comets. We know that life arose on Earth shortly thereafter, so understanding what happened during this period of solar system history is a critical piece of our origin story.
There is water ice hidden in permanently shadowed craters at the Moon’s poles. Studying the ice could help us understand where our own planet’s water came from. The ice is also a potential resource for future human explorers: it could be harvested for breathable air, drinking water, and rocket propellant.
How much water does the Moon have? Based on data from India’s Chandrayaan-1 spacecraft and NASA’s Lunar Reconnaissance Orbiter, scientists estimate the poles may have more than 600 billion kilograms of water ice, enough to fill at least 240,000 Olympic-sized swimming pools. Learn more in our guide to water on the Moon.
The Moon’s proximity to Earth makes it a natural focus of many public and private human spaceflight efforts, including NASA’s Artemis program, which seeks to land humans on the south pole in 2024. Sending astronauts to the lunar surface can help us develop and prove the viability of technologies needed for deep space exploration, including missions to Mars.
Light and Shadow at the Moon's South Pole The Moon's north and south poles have high points that are almost always in sunlight, and low spots that are permanently dark. This NASA visualization starts on the side of the Moon we see from Earth—with the Apollo landing sites labeled—and moves down to the south pole, where a timelapse shows changing illumination conditions for an entire year. The large crater in the center, Shackleton crater, lies in permanent darkness, but its raised rims are nearly constantly illuminated. High-sunlight areas are good locations for human habitats because they stay warm and can draw near-continuous power from solar panels, while nearby permanently dark areas harbor water ice that could be mined for air, water, and rocket propellant.Video: NASA's Scientific Visualization Studio
Surface temperature: -173°C (-280°F) to 127°C (260°F)
Average distance from Earth: 384,400 kilometers (238,855 miles), or about 30 Earth widths
Diameter: 3,475 kilometers (2,159 miles), Earth is 3.7 times wider
Volume: 22 billion km3 (5 billion mi3), the Moon could fit inside Earth 45.5 times
Gravity: 1.6 m/s², or 16% that of Earth’s
Solar day: 29.5 Earth days
How We Study the Moon
Until the advent of spaceflight, we could only study the Moon with telescopes—and starting in the 1940s, radar. The 1960s Space Race between the U.S. and Soviet Union resulted in dozens of robotic spacecraft being launched to fly by, orbit, and land on the Moon. Neil Armstrong and Buzz Aldrin became the first humans to walk on the Moon in 1969 as part of NASA’s Apollo program.
From 1969 to 1972, 6 Apollo missions sent 12 people to the lunar surface. Astronauts returned a total of 382 kilograms (842 pounds) of lunar soil, rocks, and core samples to Earth. The Soviet Union, using 3 robotic sample missions from 1970 to 1976, also returned a small amount of material to Earth.
One of the best ways to piece together the complex history of the Moon is bringing lunar samples back to Earth. The instruments required to precisely determine the age of Moon rocks are still too big and too power-hungry for use on a spacecraft.
The samples returned to Earth by the Apollo and Luna missions taught us a lot about the Moon’s history. But they all came from the Moon’s near side, where spacecraft can communicate directly with Earth, in places near the Moon’s equator and in places where the terrain made for safe landings. To continue piecing together the complex history of the Moon, we need samples from new locations.
In late 2020, China’s Chang’e-5 spacecraft will land in a younger, unexplored region of the Moon, collect up to 4,000 grams (8.8 pounds) of samples, and blast them back to Earth. American scientists list a sample return mission to the South Pole Aitken-Basin as a top planetary exploration priority. We know this basin, which was formed by a huge impact on the lunar farside, is the Moon’s oldest, but we don’t know how old.
Missions to the lunar farside require a communications relay satellite. China launched one in 2018 ahead of the landing the Chang’e-4 mission—which included the Yutu-2 rover—in the South Pole Aiken-Basin in 2019.
Another focus for lunar scientists is the Moon’s water ice on its poles: How did it get there, and how is it related to Earth’s water? India’s Chandrayaan-2 orbiter, launched in 2019, is mapping and measuring the ice. NASA plans to launch a small rover named VIPER to the Moon in 2023 that will venture into the Moon’s permanently shadowed craters and study the ice up close. VIPER is part of NASA’s Commercial Lunar Payload Services program, which seeks to regularly land and orbit missions as soon as 2021.
NASA’s Artemis program aims to place a small space station in lunar orbit and land astronauts near the Moon’s south pole in 2024, as part of a long-term plan to send humans to Mars. Like the Apollo program, Artemis is expected to offer new scientific opportunities, including lunar sample return.
How You Can Support Moon Exploration
Since 2013, The Planetary Society has supported a technology called PlanetVac, a low-cost sample collection system built by Honeybee Robotics in Pasadena, California. Our members funded a lab test of the technology in 2013, and an actual rocket flight in 2018. In 2019 NASA picked PlanetVac to fly to the Moon as early as 2022 for a real-world demonstration mission.
Although the samples collected during the demo won’t get sent back to Earth, the mission will advance sample collection technology, which helps us better understand the Moon and other worlds.
We’re continuing to track NASA’s Artemis program in accordance with our human spaceflight principles. Sign up for the Space Advocate Newsletter and The Downlink to find out when we have specific actions you can take as a space advocate.
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The Moon in Recent Articles, Newsletters, and Podcasts
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Bruce Betts and Sarah Al-Ahmed provided a guide to all total solar eclipses through the end of the 2020s, with dates and locations.
Say hello to a new lunar sample return mission and farewell to a long-lived radio observatory. Plus, celebrate 18 years of Planetary Radio.
Acknowledgements: This page was initially written by Jatan Mehta in 2020.