What could the Artemis IV astronauts discover on the Moon?

Once they land on the Moon, the crew of NASA’s Artemis IV mission will have no more than 32 hours total to step out and explore its surface. During those moments when the astronauts are walking on another world, they will have a chance to retrace our cosmic origins and discover, firsthand, what the Moon could offer humanity.

That is why Brett Denevi, a planetary scientist at Johns Hopkins Applied Physics Laboratory, is ensuring NASA makes every minute count. As principal investigator of the Artemis IV Geology Team, Denevi is in charge of the planetary science investigation that will be a major part of how the mission’s astronauts explore the Moon.

“It's our job to maximize the science that comes out of this,” Denevi said. “We're working on a lot of things that the science community has wanted to do on the Moon for decades.”

That includes getting to the bottom of how the Moon was born, how sometimes-cataclysmic asteroid impacts shaped it over time, and how hospitable it might be for further exploration. Now, Denevi’s team is helping plan out what the crew will need to do on the lunar surface to achieve these goals. Though much about Artemis IV remains to be decided, Denevi is confident it will solve some of the deepest mysteries about our neighboring world.

A walk in the park

Artemis IV is slated to land two astronauts on the Moon in 2028, at the earliest. While another pair of crewmembers remain in lunar orbit, the two astronauts will descend to the Moon’s surface near the south pole and stay for several days, exiting their spacecraft to explore an area about twice as large as New York City’s Central Park. If all goes well, they will go on at most four separate excursions of up to eight hours each, which means the astronauts are likely to spend no more than 32 hours actually walking on the Moon. 

That’s where Denevi and her team come in. Ahead of each expedition, they will have mapped out the most interesting places to explore, made a wish-list of tasks for the crew, and worked with other mission staff to finalize a plan for the moonwalk. 

Many of the specifics of these plans will have to wait until NASA selects a landing site or until after the crew has touched down. On the other hand, Denevi says, most of the science that they want the astronauts to do has been the same for years. For each of the mission’s most important questions, her team is already charting out how the astronauts could answer them.

Digging for history

One of their top priorities will be uncovering the Moon’s past — starting with how it got made in the first place. 

4.5 billion years ago, a giant collision between Earth and a protoplanet may have spun off debris that went on to form the Moon. While researchers generally agree that this is the most likely story, though, there are still pieces that don’t fit together. For instance, rocks brought back from the Apollo missions have particular chemical signatures that are surprisingly similar to those of Earth’s outer layers. That fact may be hard to explain if much of the material that became the Moon originally came from the would-be planet, called Theia. But it depends on exactly what Theia was like, and how it smashed into Earth. 

The Apollo samples have not settled the issue so far. In part, this is because of the technology the missions had available at the time, and because the areas of the Moon they came from are partly dominated by the debris of a particular impact known to have formed a basin called Imbrium (the sites also have other peculiarities). That makes reading their history more difficult, says Denevi.

By contrast, scientists expect the Moon’s south pole to offer a deeper record of its past. Artemis IV will explore the South Pole-Aitken basin, which is, to current knowledge, the largest and most ancient region on the Moon carved by a collision. Though every big hit to the Moon tends to wrench up material from underground and scatter it across the surface, this impact is thought to have excavated the deepest and oldest rock.

Finding one of these “original” pieces of the Moon’s crust — what would look like a big, pristine chunk of crystal — would be one of the most exciting things the Artemis IV crew could do, says Denevi, and the south pole should offer the best odds for it. 

Rocks like this could provide direct windows into some of the Moon’s earliest history, and the deeper samples might preserve Theia’s chemical fingerprint in a way the Apollo samples don’t. By probing further into just how similar the Moon and Earth are, they could help scientists pinpoint the details of how a collision could have created the Moon. 

Big impacts

According to Denevi, Artemis has good odds of settling a more controversial part of the Moon’s history, too. 

The idea is that around half a billion years after Earth formed, a surge of thousands of asteroids and comets hit both our world and the Moon. This barrage, called the Late Heavy Bombardment or Lunar Cataclysm, would have included asteroids far larger than the one that wiped out the dinosaurs. Such extreme conditions could have dramatically shaped how life first evolved on Earth.

Fittingly, scientists originally developed this concept because of evidence from Apollo. When researchers measured the ages of impact-related rocks near those missions’ landing sites, they found that a surprising number seemed to have been made around the same time. Scientists proposed the Late Heavy Bombardment to explain that pattern. Yet other measurements from both lunar missions and Earth rocks have since pointed at a different spread of impacts over time throughout the Solar System’s history, leading some scientists to argue that there was no Late Heavy Bombardment at all. 

Artemis IV should offer a more definitive test. Since it will be far away from the Imbrium basin event that affected the Apollo landing sites, the mission won’t share the same biases. Artemis IV, Denevi says, has a good chance of clearing up this major chapter of Earth’s history.

“That’s almost the easiest big hypothesis to either topple or prove,” she added.

Ice, ice baby

At the same time that Artemis IV is looking billions of years into the past, it will also be investigating what the Moon has in store for future missions. The Artemis program is ultimately designed to build toward a sustainable lunar base, perhaps by the mid-2030s. By scouting the possibility of building, farming, and mining on the Moon, Artemis IV will test out how the south pole might support such long-term habitation.

The mining would not be for minerals — at least not at first — but for ice. Scientists have known for years that water ice exists on or near the Moon’s surface, mostly in craters near the poles whose interiors never see the Sun. But it’s not clear how much water is buried in these permanently shadowed regions (PSRs), how deep, or exactly how it got there. If water is plentiful near the south pole, there’s a chance that future missions could convert it into propellant and other useful materials, as well as use it to drink and grow food.

Ideally, Artemis IV’s crew will walk into at least one of these PSRs, take vacuum-sealed samples of the lunar soil there, and safely transport any ice back to Earth for testing. But it’s possible that the lander may not come close enough to any PSRs for an in-person visit. 

In that case, the mission could rely on an electric sensor experiment, led by the University of Tokyo and JAXA, to measure the properties of the ground below the landing site. That would allow scientists to glean what sort of water ice might be present there, among other things. 

This experiment is one of three instruments that the crew will deploy on either Artemis IV or Artemis V. Another experiment will study how the lunar environment affects plants, while the third, called the Lunar Environment Monitoring Station (LEMS), will measure moonquakes and other tremors. That will provide information on the structure of the Moon below the surface as well as the sort of hazards a future base might need to take into account.

“If you are about to go build a house somewhere, you probably want to see if it's a flooding area, if it's a seismic area,” said Mehdi Benna, principal investigator for LEMS and a space research scientist at the University of Maryland, Baltimore County’s Center for Space Sciences and Technology. “We're doing pretty much the same thing.”

Cracking the seal

Whatever the crew finds, its full scientific impact will not be obvious while they are up there, Denevi cautions. The samples will have to be brought back to Earth and analyzed by the scientific community. Any strong conclusions would only get published at least several months later, and some may take years. Decades after Apollo, scientists are still making discoveries with the Moon rocks collected by its crews. 

But Denevi will get a sneak peek. In order to provide general descriptions of the samples to the scientific community (who will then be able to propose specific Moon rock experiments to NASA), she and her team will be among the first people on Earth to take a look at what the crew finds.

“Seeing those samples opened — oof,” Denevi said. “It's going to be exciting.”

As she looks through those pieces of another world, Denevi will have her mind on the next crewed trip to the Moon, Artemis V. She is the geology team lead for that mission, too, which means it will be her job to take what Artemis IV finds and use it to help plan out Artemis V’s science. That way, when humanity returns to the Moon, the hours they spend on the surface will lead once again to decades of discoveries.