I have a question about ice on the moon. How is this 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 by water.
Earth is about 94 million miles from the sun. That's within 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.
The Earth also has an atmosphere over 6,000 miles (9,650 kilometers) thick that is filled with oxygen so we can breathe. This atmosphere, along with a huge magnet at the center of the Earth, helps protect us from the sun's harmful radiation, primarily solar wind and cosmic rays.
But the moon hardly resembles a water world, or even a place with a few puddles. It has a worn-out internal magnet and an atmosphere so weak that it is virtually a vacuum. There are no clouds, rain or snow, just a sky that is simply the darkness of space, with a surface baked by the sun. The moon's temperature reaches 273 degrees Fahrenheit (134 degrees Celsius) during the day and drops to -243 F (-153 C) at night.
But as scientists who study space and develop technologies to detect water, we can say with certainty: yes, there is water on the moon.
The discovery
Astronomers and other scientists had long thought that water on the moon was unlikely. After all, the 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. In 2009, NASA slammed a spacecraft-the Lunar Crater Observation and Sensing Satellite, or LCROSS-into the moon's surface, in Cabeus Crater. When it did, water ice was ejected.
This confirmed to scientists that there was water ice in the crater floors. But determining how much water there is will be difficult. The moon's 10,000 or so craters are essentially large holes, with areas so shadowed that the sun never shines in. These places are really cold, well below -300 F (-184 C). Once these frozen water molecules get trapped in the craters, they stay there virtually forever unless they are dislodged by heat or energy. They are unlikely to evaporate or sublimate into vapor naturally-it's just too cold there.
But that doesn't mean water is only stored in craters. In 2023, scientists using SOFIA, the Stratospheric Observatory for Infrared Astronomy, looked for water on the lunar surface in areas that weren't as cold as craters. And they found it-not on top of the ground, but likely in the soil grains.
No one knows yet how much water there is on the moon or how deep it is. But one thing is certain: there is much more than scientists first thought.
Comets and volcanoes
How does the Moon get its water? No one knows for sure yet, but there are some theories.
Eons ago, comets-which are essentially frozen, dirty snowballs-smashed into Earth, leaving behind their cometary water. That's one way Earth got its oceans; perhaps that's how the moon got some of its water, too.
Other scientists think ancient volcanoes on the moon released water vapor when they erupted billions of years ago. Eventually, that vapor settled to the surface as frost. Over time, layers of that frost accumulated, especially at the poles; much of it may have fallen as ice in lunar craters.
Drinking water for astronauts
Water is heavy. It would be expensive to transport it to the moon on spaceships. So it makes more sense for astronauts to figure out a way to use the water that is already on the moon.
But lunar water is not drinkable as it is; it would have small bits of lunar soil and possibly other molecules mixed in. Astronauts living in lunar colonies would have to purify all the water they collected. This is a difficult process that would require considerable effort and resources.
There is a plan to drill for the water and search for it, much like people searched for underground gold during the 19th century gold rush. The comparison is not a bad one: water on the moon could eventually be more valuable than gold on Earth.
And not just for drinking. Water is of course two parts hydrogen and one part oxygen; it can be split. This is a win-win: astronauts can use the hydrogen for rocket fuel and the oxygen for breathable air. With the sun as an energy source, it is probably possible to split water.
Returning to the moon and establishing a permanent base are enormous commitments that will require 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 in space exploration, pioneers risk destroying or polluting a unique environment that has existed for billions of years-and many scientists feel a deep obligation not to repeat the painful lesson we are now learning here on Earth.
Hello, curious kids! Do you have a question you'd like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Tell us your name, age, and the city you live in. And since curiosity knows no age limit - adults, let us know what you are wondering too. We can't answer all questions, but we'll try our best. This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Thomas Orlando, Georgia Institute of Technology; Frances Rivera-Hernández, Georgia Institute of Technologyand Glenn Lightsey, Georgia Institute of Technology Read more: Thomas Orlando receives funding from NASA and DOE. Frances Rivera-Hernández and Glenn Lightsey are not employees of, consultants to, own stock in, or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointments.