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I have a question about ice on the moon. How is that possible? – Olaf, age 9, Hillsborough, North Carolina
We are lucky to live in a water world. More than 70% of the Earth’s surface is covered with water.
Earth is about 94 million miles from the Sun. That’s inside the Goldilocks zone: the place in our solar system where a planet has just the right temperature for water to exist as liquid in oceans and rivers, and as ice at the north and south poles.
Earth also has an atmosphere more than 6,000 miles (9,650 kilometers) thick, filled with oxygen for us to breathe. This atmosphere, along with a giant magnet at the center of the Earth, helps protect us from the Sun’s harmful radiation, mostly the solar wind and cosmic rays.
But the Moon is not much of a water world or a place with a few puddles. It has an eroded inner magnet and an atmosphere so weak it’s almost a vacuum. There are no clouds, no rain, no snow, just a sky that’s the blackness of space and a surface baked by the Sun. The Moon’s temperature reaches 273 degrees Fahrenheit (134 Celsius) during the day and drops to -243 F (-153 C) at night.
But as scientists who study space and work to develop water-seeking technologies, we can say this with certainty: Yes, there is water on the Moon.
Discovery
For a long time, astronomers and other scientists thought it was unlikely that there would be water on the Moon. After all, Apollo astronauts brought back many rock samples from the Moon, and they were all dry, with no detectable water.
But recent spacecraft visits have shown that there is some water there. In 2009, NASA crashed a spacecraft called the Lunar Crater Observation and Sensing Satellite, or LCROSS, into the moon’s surface, inside the Cabeus crater. When this happened, water ice was ejected.
This confirmed to scientists that there is water ice at the bottom of the craters. But it will be hard to determine how much water there is. The approximately 10,000 lunar craters are essentially big holes, with areas so shadowed that the Sun never shines light into them. These places are really cold, well below -300 F (-184 C). Once these frozen water molecules are trapped in craters, they stay there almost forever unless some heat or energy dislodges them. It’s unlikely they would evaporate naturally or sublimate into vapor—it’s just too cold up there.
But that doesn’t mean water is stored only in craters. In 2023, scientists using SOFIA (the Stratospheric Observatory for Infrared Astronomy) looked for water on the Moon’s surface in areas that were not as cold as craters. And they found it — not on top of the soil, but likely inside the soil grains.
No one yet knows how much water the Moon contains or how deep it goes, but one thing is certain: There’s a lot more than scientists first thought.
Comets and volcanoes
How did the moon get its water? No one is sure yet, but there are some theories.
A long time ago, comets—which are basically frozen, dirty snowballs—crashed into the Earth, depositing cometary water. That’s one way Earth developed its oceans, and maybe the Moon got some of its water that way, too.
Other scientists think that ancient volcanoes on the Moon erupted billions of years ago and released water vapor. Eventually, this vapor settled on the surface as frost. Over time, layers of this frost accumulated, especially at the poles; much of it may have settled into lunar craters as ice.
Drinking water for astronauts
Water is heavy. It would be expensive to transport it to the Moon by spacecraft, so it makes sense for astronauts to find a way to use the water already on the Moon.
However, lunar water is not drinkable as is; it contains small particles of lunar soil and possibly other molecules. Astronauts living in lunar colonies must purify the water they collect, a difficult process that requires significant effort and resources.
There’s a plan to drill for water and search for it, just like people hunted for gold underground during the 19th century gold rush. The analogy isn’t bad – water on the moon could eventually be more valuable than gold on Earth.
And not just for drinking. Water, of course, is two parts hydrogen and one part oxygen; it can be split. It’s a win-win: Astronauts can use the hydrogen for rocket fuel and the oxygen for breathable air. Using the sun as a power source, splitting water could probably be done.
Returning to the Moon and establishing a permanent base is a monumental undertaking, requiring decades of work, billions of dollars, the cooperation of many countries, and many new technologies yet to be developed. But as the world enters this dramatic new chapter of space exploration, pioneers risk destroying or contaminating a unique environment that has existed for billions of years—and many scientists feel a deep responsibility not to repeat the painful lesson we are now learning on Earth.
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This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and trusted analysis to help you understand our complex world. By Thomas Orlando Georgian Institute of Technology; Frances Rivera-Hernandez, Georgian Institute of Technologyand Glenn Lightsey, Georgian Institute of Technology
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Thomas Orlando receives funding from NASA and DOE.
Frances Rivera-Hernández and Glenn Lightsey do not work for, consult, own shares in, or receive funding from any company or organization that would benefit from this article, and have disclosed no affiliations beyond their academic appointment.