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Prospecting for Water on the Moon

In the fall of 2023, a U.S. rover is slated to land at the south pole of the moon. Its mission: to explore the water ice that scien­tists know lurks within the lunar shadows, and which they believe could help sustain humans who may one day explore the moon or use it as a launching pad for more distant space exploration.

NASA recently selected Kevin Lewis, an associate pro­fessor in the Krieger School’s Department of Earth and Planetary Sciences, as a co-in­vestigator of the mission. Using part of the rover’s navigational system, he plans to explore the moon’s subsurface geology from his office in Olin Hall.

“I have been on other rover missions, but on Mars, so I’m a little bit new to the moon,” Lewis says. “We’re going to see into shadows that have never seen the sun, let alone been seen by humans. So it could be a very different type of surface than we’ve seen in other photos of the surface of the moon.”

artist's rendering of VIPER
Nasa / Daniel Rutter

Above, an artist’s concept of the completed design of NASA’s Volatiles Investigating Polar Exploration Rover, or VIPER.

The Moon’s Environment

Most of the moon is com­pletely without water. That’s because of the way the satellite was formed, in a giant impact between the proto-Earth and a Mars-size object. Temperatures were high enough not only to melt rock, but to vaporize it, causing a cloud of rock vapor to orbit Earth. The vapor eventually coalesced to form the moon.

Those temperatures were also high enough to drive off any water, not even leaving appreciable traces trapped within rocks the way it is on Earth. But over time, meteors and comets containing water ice bombarded the moon, sending ice molecules hopping around the lunar surface.

The sun’s angle at the moon’s poles is steep, creat­ing long shadows. This means that some of the polar craters receive no sunlight at all. When the water molecules happen to hop into one of those unlit areas, whose temperatures are among the coldest in the solar system at just tens of degrees above absolute zero, it drains their thermal energy and they remain stuck to the surface.

“So, over time, you could build up ice deposits in these permanently shadowed regions, which might be basically the only source of water on the entire moon in useful quanti­ties,” Lewis says.

The Science of the Rover

The Volatiles Investigating Polar Exploration Rover, or VIPER, is a golf cart-sized robot designed for the extremes and unknowns of the moon’s south pole. The rover, which will travel several kilometers over several lunar days—or about 100 Earth days—will assess things like what form the water is in, how much of it is there, whether it’s more like frost on the surface or ice at depth, and whether there’s more of it in some areas than others.

Currently being assembled at NASA’s Johnson Space Center in Houston, VIPER has to be customized for the specific con­ditions it will encounter. There’s the cratered soil with various levels of compaction, requiring four independently controlled wheels that can handle slopes of 25 to 30 degrees. And there are the moon’s drastic temper­ature swings, ranging from 225 degrees Fahrenheit in the sun during the day to -400 degrees in those permanent shadows. VIPER’s boxy shape protects the instruments, and calibrations of the high-precision technol­ogy are currently underway to guard against those swings.

Then there’s the darkness itself, necessitating the first headlights ever used on a rover, to illuminate places on the moon that have never seen sunlight.

And there are the conflicting needs of science and logistics— the science calls for VIPER to spend its time in the shadows, but the rover will also need to periodically climb out of the cra­ters to recharge its batteries in the sunlight. Most rovers’ solar arrays are located on their roofs, but the angle of the polar sun­light requires VIPER’s arrays to be mounted on its sides instead.

The Artemis program

After a request for proposals, NASA added eight co-investiga­tors to its existing VIPER science team, in part to bring new ideas and expertise to the team. Lewis’ investigation effectively gives the rover a whole new science instru­ment for probing the moon.

VIPER is part of NASA’s Artemis program, a multiphase process to return humans to the moon. Artemis I will be the first test of the rocket that will eventually carry humans, and is scheduled for launch this year. Artemis II, scheduled for 2023, will orbit the moon with humans aboard. Artemis III is planned to land humans on the surface of the moon in 2024.

As a member of the science team, Lewis isn’t involved in constructing VIPER, and he won’t be directly handling any of the controls during the mission. But since joining the team, he’s been involved in simulated operations, where the team practices using the rover’s technology and making the kind of decisions that will need to be made on the spot.

“It’s really exciting to be prospecting for water that could potentially be used by human explorers someday,” Lewis says.

Planetary and lunar scien­tists Kathleen Mandt and Parvathy Prem from the Johns Hopkins Applied Physics Laboratory were also selected as VIPER team members.

Watch Now

VIPER’s survey in 2023 will help pave the way for a new era of human missions to the lunar surface.

Video: NASA AMES Research Center