The journey of 鈥淢oon Sniper,鈥� the robotic explorer that has made Japan only the fifth country to put a spacecraft safely on the lunar surface, hasn鈥檛 gone quite as expected.
Though the mission 鈥� officially known as the Smart Lander for Investigating Moon, or SLIM 鈥� reached its destination last week, an 鈥渁nomaly鈥� 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.
Now, with Moon Sniper鈥檚 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 锘縜 crater called Shioli 鈥� a Japanese female first name pronounced 鈥渟he-oh-lee鈥� 鈥� which sits about 200 miles (322 kilometres) 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 metres) in diameter, it鈥檚 a small crater, but it鈥檚 close to a much bigger one called Theophilus that鈥檚 more than 60 miles (97 kilometres) across. This detail makes it particularly interesting for exploration.
鈥淲hen I was reading up about this a month or so ago, I was super excited to see they had chosen this site,鈥� said Dr. Gordon Osinski, a professor of planetary geology at Western University in Ontario, who鈥檚 also part of the upcoming Artemis III moon mission鈥檚 geology team.
鈥淥ne of the great things about craters is that they excavate rocks from the depth and essentially give us a window into what鈥檚 under the surface of a planetary body,鈥� 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 kilometres), giving researchers a chance to study lunar rock without any drilling.
鈥淚 think they chose this particular crater because the mineral olivine has been found 鈥� and anytime you mention olivine, people鈥檚 eyes light up because we think it probably originates from the mantle of the moon, which we鈥檝e never really sampled on site before,鈥� 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.
鈥淭he moon doesn鈥檛 have an atmosphere like the Earth, so it isn鈥檛 protected and it鈥檚 constantly bombarded with micrometeorites and radiation that damage the surface layers,鈥� said Sara Russell, a professor of planetary sciences and senior research lead at the Planetary Materials Group of London鈥檚 Natural History Museum.
The crater is lighter in colour because radiation and micrometeorites haven鈥檛 had enough time to darken it yet: 鈥淲hen a crater happens, it throws up material that was buried and that might be more pristine, because it hasn鈥檛 experienced this damage, which we call space weathering. It gives us fresh rock to look at that, and potentially learn more about the moon,鈥� she said.
Opportunities to study these rare rock samples make the moon a brilliant geology laboratory, Russell added.
鈥淲hatever the moon has experienced, the Earth has also experienced. Looking at craters can also tell us something about the Earth鈥檚 own history, because rocks form there without any of the complicating factors that we have on Earth, like water and life and the wind,鈥� she said. 鈥淚t鈥檚 a beautiful experiment in the sky.鈥�
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鈥檚 SLIM mission is that its small size was an ideal training ground for the lander鈥檚 pinpoint accuracy, which allowed it to target an area spanning just 328 feet (100 metres) across for touchdown. Living up to its nickname, the Moon Sniper actually landed just 180 feet (55 metres) shy of its target, which JAXA deemed a 鈥渟ignificant achievement.鈥�
鈥淭hey鈥檙e 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,鈥� 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 kilometres wide for touchdown: 鈥淏ut that 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,鈥� he added. 鈥淭hat 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.鈥�
The Moon Sniper鈥檚 landing site is not far from the point where Apollo 16 touched down in 1972. That older mission鈥檚 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鈥檚 a sizable chunk of the 382 kilograms (842 pounds) that NASA brought back from the moon during the entire program.
鈥淚f you think about it, we鈥檙e trying to interpret the geological history of this whole body based on a collection of rocks from quite a geographically small area,鈥� Pernet-Fisher said. 鈥淎nd so it鈥檚 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鈥檚 really important data that we鈥檒l be gathering.鈥�
A sea of lava
The largest lunar feature in the vicinity of Shioli is the Sea of Nectar, a basin 210 miles (339 kilometres) 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鈥檚 surface was created about 3.9 billion years ago.
The Sea of Nectar is much smaller than its neighbour the Sea of Tranquility, which is over 540 miles (875 kilometres) across and is similarly smooth and flat.
鈥淭ranquillity 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,鈥� Western University鈥檚 Osinski said.
鈥淭hat is also applicable for most robotic missions,鈥� he added. 鈥淚鈥檓 the principal investigator for Canada鈥檚 first-ever moon rover and we鈥檙e looking at landing sites now. We鈥檙e being driven towards smooth areas, away from craters or boulders, which actually may sound less scientifically interesting.鈥�
The reason scientists call these basins 鈥渟eas,鈥� or 鈥渕aria鈥� 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.
鈥淎fter the Apollo missions, we brought back samples and learned they were essentially massive lava planes,鈥� Osinski said. 鈥淚t鈥檚 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.鈥�
Water does come into play when looking at another area of the moon that will be targeted by upcoming landings, including NASA鈥檚 first crewed Artemis mission, expected as soon as 2026: 鈥淭he south polar region,鈥� Osinski said, 鈥渁n area that is geologically interesting, and also rich with what we call volatiles 鈥� think water ice but also frozen carbon dioxide or ammonia.鈥�
If humans can find a good, sizable source of water ice in the moon鈥檚 south pole region and it鈥檚 possible to extract it, the result could be a game changer for lunar exploration, according to Osinski.
鈥淲e鈥檇 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鈥檚 so heavy,鈥� he said.
鈥淚f 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.鈥�
