Japan has identified underground caves on the Moon near the lunar equator, likely associated with large vertical holes caused by past volcanic activity. Additionally, lava tubes formed by meteorite impacts have also been observed near the polar regions. The confirmation of water stored as ice is considered a primary motivation for exploration, particularly near the Moon’s south pole. Potential sources of this water include asteroid impacts and the solar wind. While significant quantities of water have yet to be detected on the lunar surface, these underground caves, shielded by substantial overhangs and in permanent darkness, are considered locations where water stored as ice is expected to accumulate due to its difficulty in escaping. This paper outlines a proposed mission to investigate areas near these polar holes throughout the lunar day, finding a traversable route by land from a prospective landing site to these polar vertical holes and considers methods of investigating the interior of shallow vertical holes. Furthermore, this paper examines possible missions within the lunar landing plan currently being developed for the NASA-led Artemis program. Based on information about the program, we consider the feasibility of Japan independently exploring and utilizing the Moon. Artemis III, which plans to have nine landing sites near the south pole and is expected to use Starship for landing, and JAXA’s ongoing development of a pressurized manned rover, will significantly faci Additionally, lava tubes formed by meteorite impacts have also been observed near the polar regions. The confirmation of water stored as ice is considered a primary motivation for exploration, particularly near the Moon’s south pole. Potential sources of this water include asteroid impacts and the solar wind. While significant quantities of water have yet to be detected on the lunar surface, these underground caves, shielded by substantial overhangs and in permanent darkness, are considered locations where water stored as ice is expected to accumulate due to its difficulty in escaping. Introduction In recent years, numerous nations have actively pursued lunar exploration projects. NASA’s Artemis program, for instance, aims to enable long-term lunar resource exploration, both in orbit and on the surface. Achieving this goal necessitates a comprehensive understanding of lunar water and mineral resources, including their quantit ies, distribution, and potential for future utilization. Consequently, missions like the Volatiles Investigating Polar Exploration Rover (VIPER) were designed to explore lunar ice deposits using autonomous rovers, although its deployment has been temporarily paused. Similarly, LUPEX, a collaborative effort between JAXA and ISRO, seeks to evaluate the abundance and distribution of water in the lunar south polar region. China’s Chang’e program has also significantly advanced lunar exploration through orbital remote sensing, rover and lander deployments, and sample return missions. Collectively, these initiatives reflect a notable shift in lunar exploration priorities, moving from purely scientific research toward resource exploration. Based on prior observations and research, subsurface water stored as ice is strongly suspected to exist within the permanent shadowed regions (PSRs) of polar craters on the Moon. It is hypothesized that cold traps at the lunar poles may harbor ice mixed with dry regolith. The Moon’s resources, particularly water, are considered vital for the sustainability of long -duration lunar missions. Significant water deposits would substantia lly alleviate the logistical burdens for future astronauts by providing essential resources such as drinking water, oxygen, and rocket propellant. Therefore, the state and water distribution on the Moon carr ies profound implications for future space activities. Recent lunar exploration missions have renewed discussions and investigations into the presence of both surface and subsurface water on the Moon. II. Given that sunlight will be a crucial energy source for any future lunar base, understanding regions with high solar illumination will be essential for identifying potential base locations. Conversely, our analysis of the topographic data revealed the presence of permanently shadowed regions at both lunar poles. These perpetually dark areas are prime candidates for harboring water stored as ice, a resource of crucial importance for any future lunar base. Therefore, detailed knowledge regarding the location and extent of these permanently shadowed areas is also essential when considering potential sites for a lunar outpost. While comet impacts and volcanic activity were significant in the Moon’s early history if the extensive PSRs only began to form around 3.4 billion years ag o, much of the water delivered to the Moon during its earlier epochs would likely have been lost through volatilization. Currently, the Moon’s axial tilt relative to the Sun is about 1.5°. However, around 3.3 billion years ago, it was significantly larger, approximately 6°, resulting in a smaller area of permanent shadow than exists today 2, as illustrated in Figure 3. III. Function of Polar Vertical Holes as Water- stored as ice Accumulation Devices A. Presence of water in subterranean cavities in polar regions The presence of water on the Moon holds significant implications for understanding the origin of volatile materials both on the Earth and within the lunar Due to the water’s high volatility and the Moon’s tenuous atmosphere, it is believed to undergo repeated cycles of evaporation and adsorption on the surface, potentially moving several hundred kilometers during a single lunar day (approximately one Earth month). The observed spectra lack the characteristic absorption features of major lunar surface minerals, suggesting that icy frost blankets these shadowed regions or that ice particles are lofted and transported across the lunar surface.

The Moon is the only natural satellite of Earth. It orbits around Earth at an average distance of 384,399 kilometers (238,854 mi), a distance roughly 30 times the width of Earth. It completes an orbit (lunar month) in relation to Earth and the Sun (synodically) every 29.5 days. The Moon and Earth are bound by gravitational attraction, which is stronger on the sides facing each other. The resulting Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind, leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon. Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow. The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive. In years since, signatures of water have been found to exist on the lunar surface. In 1994, the bistatic radar experiment located on the Clementine spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo, suggest these findings may rather be rocks ejected from young impact craters. In 1998, the neutron spectrometer on the Lunar Prospector spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions. Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior. The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice, using the on-board M Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind, leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon. Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow. The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive. In years since, signatures of water have been found to exist on the lunar surface. In 1994, the bistatic radar experiment located on the Clementine spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo, suggest these findings may rather be rocks ejected from young impact craters. In 1998, the neutron spectrometer on the Lunar Prospector spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions. Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior. The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice, using the on-board Moon Mineralogy Mapper. The spectrometer observed absorption lines common to hydroxyl, in reflected sunlight, providing evidence of large quantities of water ice, on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1,000 ppm. Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018. In 2009, LCROSS sent a 2,300 kg (5,100 lb) impactor into a permanently shadowed polar crater, and detected at least 100 kg (220 lb) of water in a plume of ejected material. Another examination of the LCROSS data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb). In May 2011, 615–1410 ppm water in melt inclusions in lunar sample 74220 was reported, the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. Although of considerable selenological interest, this insight does not mean that water is easily available since the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument. Analysis of the findings of the Moon Mineralogy Mapper (M3) revealed in August 2018 for the first time "definitive evidence" for water-ice on the lunar surface. The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances. The ice deposits were found on the North and South poles, although it is more abundant in the South, where water is trapped in permanently shadowed craters and crevices, allowing it to persist as ice on the surface since they are shielded from the sun. In October 2020, astronomers reported detecting molecular water on the sunlit surface of the Moon by several independent spacecraft, including the Stratospheric Observatory for Infrared Astronomy (SOFIA). The tidally locked synchronous rotation of the Moon as it orbits the Earth results in it always keeping nearly the same face turned towards the planet. The side of the Moon that faces Earth is called the near side, and the opposite the far side. The far side is often inaccurately

NASA’s Moon Mineralogy Mapper. The blue shows areas of confirmed water ice on the lunar surface. ISRO/NASA/JPL-Caltech/Brown University/USGS Confirmation of Moon Water – Sunlit Surface (2020) In 2020, NASA announced the discovery of water on the sunlit surface of the Moon. Data from the Stratospheric Observatory for Infrared Astronomy (SOFIA), revealed that in Clavius crater, water exists in concentrations roughly equivalent to a 12-ounce bottle of water within a cubic meter of soil across the lunar surface. The discovery showed that water could be distributed across the lunar surface, even on sunlit portions, and not confined to cold, dark areas. An illustration of H 2 O molecules on the lunar surface. NASA’s SOFIA confirmed the existence of water on the sunlit surface of the Moon in 2020. NASA First Detailed, Wide-Area Map of Water on the Moon (2023) In 2023, a new map of water distribution on the Moon provided hints about how water may be moving across the Moon’s surface. The map, made using SOFIA data, extends to the Moon’s South Pole – the intended region of study for NASA’s Artemis missions, and the water-hunting rover, VIPER. More to Discover Researchers have confirmed that water exists both in the sunlit and shadowed surfaces of the Moon, yet many questions remain. Lunar scientists continue to investigate the origins of water and its behavior. There is evidence that the water on the Moon comes from ancient and current comet impacts, icy micrometeorites colliding on the lunar surface, and lunar dust interactions with the solar wind. However, more research is needed to understand the full history, present, and future of water on the Moon. Writer: Allison Gasparini and Molly Wasser Science Advisors: Casey Honniball, Tim Livengood, NASA's Goddard Space Flight Center Explore in Depth Water Released from Moon In 2019, scientists discovered that water is being released from the Moon during meteor showers. Watch the video. How Ingredients for Water Could be Made on Creative Commons Totally Dry Moon (1892) American astronomer William Pickering made measurements in the late 1800s that led him to conclude the Moon essentially has no atmosphere. With no clouds and no atmosphere, scientists generally agreed that any water on the lunar surface would evaporate immediately. Pickering’s measurements led to a widespread view that the Moon was devoid of water. An open page of astronomer William Pickering’s book “The Moon: A Summary of Our Satellite with a Complete Photographic Atlas.” Pickering’s observations of the Moon lead to the belief that with such little atmospheric pressure, any ice on the lunar surface would near instantly sublimate. Internet Archive/Knopf Doubleday (This image is in the public domain) Ideas of Water (1960s) As scientists made headway in understanding the behavior of substances that are prone to vaporize at relatively low temperatures – called volatiles – theoretical physicist Kenneth Watson published a paper in 1961 describing how a substance like water could exist on the Moon. Watson’s paper first popularized the idea that water ice could stick to the bottom of craters on the Moon that never receive light from the Sun, while sunlit areas on the Moon would be so hot that water would evaporate near-instantly. These lightless areas of the Moon are called “permanently shadowed regions.” The Shackleton Crater at the Moon’s south pole in a permanently shadowed region of the Moon. NASA Apollo Landings (1969 – 1972) The Apollo era brought humans to the lunar surface for the very first time, giving researchers the opportunity to directly look for signs of water on the Moon. When tested, soil samples brought back by Apollo astronauts revealed no sign of water. Scientists concluded that the lunar surface must be completely dry, and the prospect of water wasn’t seriously considered again for decades. Apollo 17 astronaut Eugene Cernan drives the Lunar Roving Vehicle. NASA Apollo 15 astronaut Jim Irwin uses a scoop to collect soil samples on the lunar surface. NASA Possible Frozen Water in Shadowed Craters (1994, 1998) NASA’s Clementine mission launched in 1994 to orbit the Moon for two months and collect information about its minerals. Clementine data suggested there was ice in a permanently shadowed region of the Moon. The Lunar Prospector Mission focused on permanently shadowed craters to look deeper into the discovery and in 1998 found that the largest concentrations of hydrogen exist in the areas of the lunar surface that are never exposed to sunlight. The results indicated water ice at the lunar poles. Later that year, LCROSS intentionally discharged a projectile into a crater believed to contain water ice, and flew through the debris from the projectile’s impact. Four minutes later, LCROSS itself intentionally impacted the Moon while LRO observed. The combined observations showed grains of water ice in the ejected material . The LRO and LCROSS findings added to a growing body of evidence that water exists on the Moon in the form of ice within permanently shadowed regions. LRO continues to orbit the Moon and provide data used to characterize and map lunar resources, including hydrogen. Artist rendering of the LCROSS satellite. The blue shows areas of confirmed water ice on the lunar surface. ISRO/NASA/JPL-Caltech/Brown University/USGS Confirmation of Moon Water – Sunlit Surface (2020) In 2020, NASA announced the discovery of water on the sunlit surface of the Moon. Data from the Stratospheric Observatory for Infrared Astronomy (SOFIA), revealed that in Clavius crater, water exists in concentrations roughly equivalent to a 12-ounce bottle of water within a cubic meter of soil across the lunar surface. The discovery showed that water could be distributed across the lunar surface, even on sunlit portions, and not confined to cold, dark areas. An illustration of H 2 O molecules on the lunar surface.