The journey of “Moon Sniper,” the robotic explorer that has made Japan only the fifth country to put a spacecraft safely on the lunar surface, hasn’t gone quite as expected.
Though the mission — officially known as the Smart Lander for Investigating Moon, or SLIM — reached its destination last week, an “anomaly” experienced during descent resulted in the vehicle landing with its solar panels facing the wrong direction, forcing it to operate on limited battery power, according to the Japan Aerospace Exploration Agency.
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Now, with Moon Sniper’s battery turned off to maintain spacecraft functionality, JAXA officials are in wait-and-see mode, hoping the changing angle of the sun will restore power to the vehicle and allow the mission to resume. If the lander turns on again, it could make good on its objectives to collect unprecedented information about a region called the Sea of Nectar.
The spacecraft touched down near a crater called Shioli — a Japanese female first name pronounced “she-oh-lee” — which sits about 200 miles (322 kilometers) south of the Sea of Tranquility, the region near the lunar equator where Apollo 11 first landed humans on the moon.
At around 880 feet (268 meters) in diameter, it’s a small crater, but it’s close to a much bigger one called Theophilus that’s more than 60 miles (97 kilometers) across. This detail makes it particularly interesting for exploration.
“When I was reading up about this a month or so ago, I was super excited to see they had chosen this site,” said Dr. Gordon Osinski, a professor of planetary geology at Western University in Ontario, who’s also part of the upcoming Artemis III moon mission’s geology team.
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“One of the great things about craters is that they excavate rocks from the depth and essentially give us a window into what’s under the surface of a planetary body,” Osinski added. He noted that Shioli stands on ground ejected by the larger nearby crater, which probably comes from a depth of over 1 mile (1.6 kilometers), giving researchers a chance to study lunar rock without any drilling.
“I think they chose this particular crater because the mineral olivine has been found — and anytime you mention olivine, people’s eyes light up because we think it probably originates from the mantle of the moon, which we’ve never really sampled on site before,” Osinski said.
Space weathering
In November, NASA published photographs of Shioli taken by the Lunar Reconnaissance Orbiter, a spacecraft currently orbiting the moon and mapping it to aid future missions. In the black-and-white photo, the crater looks like a splotch of light.
“The moon doesn’t have an atmosphere like the Earth, so it isn’t protected and it’s constantly bombarded with micrometeorites and radiation that damage the surface layers,” said Sara Russell, a professor of planetary sciences and senior research lead at the Planetary Materials Group of London’s Natural History Museum.
The crater is lighter in color because radiation and micrometeorites haven’t had enough time to darken it yet: “When a crater happens, it throws up material that was buried and that might be more pristine, because it hasn’t experienced this damage, which we call space weathering. It gives us fresh rock to look at that, and potentially learn more about the moon,” she said.
Opportunities to study these rare rock samples make the moon a brilliant geology laboratory, Russell added.
“Whatever the moon has experienced, the Earth has also experienced. Looking at craters can also tell us something about the Earth’s own history, because rocks form there without any of the complicating factors that we have on Earth, like water and life and the wind,” she said. “It’s a beautiful experiment in the sky.”
After landing in the crater, the spacecraft captured 257 low-resolution images of its surroundings, and the mission team later gave nicknames to some of the rocks in the pictures. More images will be taken if the lander manages to regain power.
Pinpoint accuracy
Another reason for choosing the vicinity of Shioli as the landing site for Japan’s SLIM mission is that its small size was an ideal training ground for the lander’s pinpoint accuracy, which allowed it to target an area spanning just 328 feet (100 meters) across for touchdown. Living up to its nickname, the Moon Sniper actually landed just 180 feet (55 meters) shy of its target, which JAXA deemed a “significant achievement.”
“They’re really using the technology to show that they can land in very small landing circles, which would be quite a step forward for capabilities to land on different planets,” said Dr. John Pernet-Fisher, a research fellow in geochemistry and cosmochemistry at the University of Manchester in the United Kingdom, in an interview before the landing.
Traditionally, moon missions target areas a few kilometers wide for touchdown: “But that really limits where you can land, because you have to make sure that within the whole landing area every point it is safe to land on,” he added. “That makes things a lot more difficult if you want to land in more challenging or rugged terrain, so this can really open the doors to being able to land in areas that are topographically a bit more varied and therefore might tell us something different about the moon and its formation.”
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The Moon Sniper’s landing site is not far from the point where Apollo 16 touched down in 1972. That older mission’s crew collected 731 individual rock and soil samples for a total mass of 95.7 kilograms (210 pounds), according to the Lunar and Planetary Institute. That’s a sizable chunk of the 382 kilograms (842 pounds) that NASA brought back from the moon during the entire program.
“If you think about it, we’re trying to interpret the geological history of this whole body based on a collection of rocks from quite a geographically small area,” Pernet-Fisher said. “And so it’s really important for us to gather as much data as possible from a huge diversity of different geographic locations. Even though this is still relatively near some of the Apollo missions, it’s really important data that we’ll be gathering.”
A sea of lava
The largest lunar feature in the vicinity of Shioli is the Sea of Nectar, a basin 210 miles (339 kilometers) in diameter that is one of the oldest on the near side of the moon, the hemisphere that always faces Earth. The lunar plain is visible with binoculars or a small telescope, and was formed when the moon’s surface was created about 3.9 billion years ago.
The Sea of Nectar is much smaller than its neighbor the Sea of Tranquility, which is over 540 miles (875 kilometers) across and is similarly smooth and flat.
“Tranquillity was chosen for the Apollo 11 landing not for any scientific reasons, but because it was one of the flattest, smoothest parts for the moon and therefore considered safest to land on,” Western University’s Osinski said.
“That is also applicable for most robotic missions,” he added. “I’m the principal investigator for Canada’s first ever moon rover and we’re looking at landing sites now. We’re being driven towards smooth areas, away from craters or boulders, which actually may sound less scientifically interesting.”
The reason scientists call these basins “seas,” or “maria” in the original Latin, is that ancient astronomers who first looked up at the moon believed they were filled with water, due to the darker hue.
“After the Apollo missions, we brought back samples and learned they were essentially massive lava planes,” Osinski said. “It’s not like there was a massive volcano with lava pouring out, but rather fissure eruptions, so the lava was just literally coming up through fractures. We can think of them as lava seas.”
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Water does come into play when looking at another area of the moon that will be targeted by upcoming landings, including NASA’s first crewed Artemis mission, expected as soon as 2026: “The south polar region,” Osinski said, “an area that is geologically interesting, and also rich with what we call volatiles — think water ice but also frozen carbon dioxide or ammonia.”
If humans can find a good, sizable source of water ice in the moon’s south pole region and it’s possible to extract it, the result could be a game changer for lunar exploration, according to Osinski.
“We’d have water for the astronauts to drink, we can extract the oxygen, and it can be broken down to get the hydrogen for rocket fuel. It also reduces costs, because water is one of the most expensive things to launch from Earth because it’s so heavy,” he said.
“If we want to build lunar bases, which we all hope we do, we are going to have to find a source of water to use on the moon.”