Category: The moon

The moon is shrinking, and scientists are narrowing in on exactly how much our natural satellite has dwindled over the years.

The moon is thought to have formed from a violent collision between a massive object and our young Earth roughly 4.5 billion years ago, and its interior is still gradually cooling off from this ancient collision. As it cools, the moon contracts, leading to a long, slow shrinking process. Now, in a new study, scientists think that they have figured out how much smaller the moon is actually getting.

In this new study, scientists analyzing images snapped by the Lunar Reconnaissance Orbiter Camera (LROC) have spotted over 10,000 young faults, or cracks across the moon's surface. This helped them to figure out how much the moon has contracted over time, and they now estimate that the moon's radius has decreased by about 148 feet (45 meters) over the past 400 to 800 million years.

"The number of these young faults revealed in LROC images is much greater than I ever imagined," study lead Thomas Watters, a geologist and scientist emeritus at the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum, said in a statement. "As the interior of the moon continues to cool and contract, it is expected that the growth of existing faults and formation of new faults continues today."

With these LROC observations, researchers in this study saw a variety of different types of cracks and landforms across the lunar surface. This included lobate scarps, or long, curved structures that form when the moon's surface contracts, cracks and is pushed upwards; and small mare ridges, or narrow "wrinkles" in the lunar surface, across the dark plains on the moon.

Tectonic activity on the moon looks a lot different than it does on Earth. On our own planet, there are about 15 major tectonic plates. On the moon, there are no tectonic plates at all. Instead, the moon has a single-plate body meaning its outer shell is a single piece only broken by faults or other such cracks created by the moon contracting. This means that instead of faults or cracks appearing at tectonic plate boundaries, they are instead scattered all over the moon.

By mapping these thousands of different features, all created from the moon cooling and contracting over time, the researchers are piecing together lunar history. In addition to finding the extent to which the moon has shrunk over time, they also found that some areas of the moon are covered in many more faults than other areas, and the areas with fewer cracks and faults have thicker moon crust.

This led them to conclude that not only are these areas with thicker crust more stable, but they suggest that a great deal of the widespread cracks in the lunar surface were created later in the moon's history as, in its earlier years, its thick crust would have insulated the moon's warm interior and prevented cooling, contracting and cracking.

This work was described in a study published Oct. 14 in The Planetary Science Journal.

For as long as humans have watched the night sky, we have wondered about the moon, pondering everything from its alien appearance to its influence over phenomena on Earth such as ocean tides, climate stability, and even the natural rhythms of many organisms.

Among the many questions we have about Earth's lone natural satellite, one remains preeminent: what are the moon's origins, and how long has it orbited Earth?

Today, the leading theory among astronomers is that deep in our planet's past — perhaps within roughly the first 100 million years of solar system history — Earth collided with a planet-sized object, creating the moon within a period that may have been as short as just a few hours. Known as the giant-impact hypothesis, this proposed event involves a hypothetical Mars-sized protoplanet astronomers call Theia. The material ejected into orbit by the powerful impact in question would have accumulated afterward, forming the moon that we observe today.

What do we know?

Birth of a lunar origin hypothesis

The evolution of this striking solution to one of the moon's most enduring mysteries goes back to 1946, when geologist Reginald Aldworth Daly was among the first to suggest that an impact event might explain the formation of the moon.

Before Daly, scientists had been leaning toward theories that involved Earth's rapid spin billions of years ago, when each day may have at one time lasted as little as 2 or 3 hours. Decades later in the 1970s, researchers William Hartmann and Donald Davis developed their own models involving collisions of large bodies left over from planetary formation, which could collide with younger planets.

Building on such ideas, other researchers went on to propose similar scenarios between the early Earth and a Mars-sized object. Early in the following decade, the concept eventually claimed its place as the leading lunar-formation process during a landmark conference held in Kona, Hawaii, in 1984.

Evidence of a planetary-scale collision

The popularity of the giant-impact hypothesis can be attributed to the multiple lines of evidence supporting the impact scenario. For instance, researchers have long recognized the similar stable-isotope ratios between both moon rocks and those from Earth, strongly suggesting a link between their origins.

Additionally, the unusually high angular momentum (or spin) of the Earth-moon system, when compared to observations of other rocky planets, also could be explained as one of the effects of a massive collision.

Further clues can be found in the moon's composition, which reveals a relatively small iron core and lower density. This is significant to astronomers, since a hypothetical giant impact would have seen the suspected Theia protoplanet's metallic core merging with the young Earth's interior — meanwhile, lighter mantle and crust material from both worlds would have become dislodged and blasted into orbit, eventually helping form the moon.

Another important piece of evidence involves the relative depletion of volatile substances (a chemical that easily turns into gas or vapor at room temperatures) in lunar material, which again suggests that it might have been lost during an extremely energetic event, an idea further supported by evidence that the early moon once possessed a substantial magma ocean.

What remains unknown?

New research expands on the Theia hypothesis

Still, several significant questions remain, including what precise conditions led to the impact, and how the resulting planetary material evolved into the moon as it appears today.

Recently, a new study by Adeene Denton of Southwest Research Institute and colleagues at the University of Arizona's Lunar and Planetary Laboratory put a new spin on the Theia hypothesis, suggesting that the suspected ancient impact may have been significantly influenced by the heat and physical strength of the two colliding bodies.

The team's findings challenge some long-held views about the giant-impact hypothesis, while lending new support to others. For instance, the team's simulations revealed that while some impacts lead to the creation of a disk of debris that later coalesces into a moon, under other conditions, simulations support the idea that the moon could have been formed in a remarkably short period of time — perhaps within around five hours.

However, one of the primary issues with determining the exact conditions of the giant-impact hypothesis involves the ongoing debate over the moon's age.

"There is a large controversy regarding the age of the moon," said Dr. Erik Asphaug, a planetary science professor at the University of Arizona's Lunar and Planetary Laboratory and one of the new study's co-authors.

In an email to Space, Asphaug explained some of the issues arising from this, since current estimates place the timing of the moon's formation anywhere from around 40 to 120 million years after the formation of the solar system. Therein lies part of the issue, according to Asphaug, who says this timing could have significant implications for models of the Theia impact.

If it had been an earlier collision, Asphaug says this would have involved a hotter Theia due to the greater degree of radiogenic heating; by contrast, a later impact would have meant a cooler and stronger Theia.

"I don't think we know enough yet to say the moon (and by corollary, the Earth) formed this way or that way," Asphaug told Space. "But knowing how temperature affects the result opens up a new dimension for viewing the problem, and that is always helpful because it shifts our frame of reference, like getting out of the car to have a walk around."

A lunar enigma in time and space

For researchers like Asphaug, understanding the moon's formation requires looking at it as more than just an event in space, but also as one in time. Doing so allows comparisons between three different metrics: isotopic decay, temperature-dependent material strength, and the geological record of debris striking other planets — a process through which he believes tighter constraints could be placed on precisely when the moon-forming impact might have occurred.

Adeene Denton, the study's lead author, also emphasized the introduction of the time component her team's research brings to the table, telling Space in an email that the outcome of the moon-forming impact could have depended significantly on the timing of the collision.

"Before, scientists have generally assumed that the outcome of the collision will be the same regardless of when it takes place," Denton wrote. "But now we know that temperature's effect on material properties, which is dictated by how old and/or cold the proto-Earth and Theia might be, alters things substantially."

By connecting impact simulations to data related to the moon's geochemical record, as well as models of early solar system formation, Denton thinks her team's work could help scientists better constrain precisely how and when the moon formed.

The mystery continues

For now, in terms of which possible scenario — an earlier or later collision event — emerges as being the most likely, Denton says it's still difficult to say.

"It depends on which scenarios for solar system formation you favor," Denton told Space.

"I am generally in favor of an earlier formation of the moon, consistent with a rapid planet-building phase in our solar system," Denton said, "but we can't neglect the possibility that the moon formed late."

While much work remains to be done, Denton and Asphaug believe their findings help significantly advance present efforts to resolve some of the questions about the giant-impact hypothesis — a few of which have lingered now for many years.

For Asphaug, however, such lingering questions may simply be part of the scientific process.

"Science has a way of wandering around for a long time until finally it all comes to focus," Asphaug said.

"I believe that will happen, in part thanks to this work, in the coming decade."

NASA is asking for ideas to stop static electricity from zapping astronauts or critical hardware during moon missions.

The agency opened a "Lunar Grounding Challenge" to avoid situations where an astronaut on the moon could become "a walking, high voltage capacitor." Submissions for the $150,000 competition are due Jan. 15 and you can see the requirements here.

NASA is hoping to put astronaut boots at the lunar south pole in 2028 during the Artemis 4 or 5 missions, on the first landing mission since NASA's Apollo 17 in 1972. But simulations suggest that both "tribocharging" (electric-charge transfer between two objects) and plasma charging (from ambient gas in the region) could build up electric charge on spacesuits. "This problem is severely compounded when entering lunar shadows and permanently shadowed regions," the agency wrote, referring to deeply cratered areas where the sun does not touch the lunar surface.

The concern is that astronauts' spacesuits could become electrically charged, as there would be an excess of electrons (negatively charged particles) compared with ions (positively charged) in these areas.

"The risk occurs when an astronaut returns to the spacecraft," the agency added. The lander would have a slight positive charge, producing an issue once the "highly negatively-charged astronaut approaches the vehicle."

NASA has asked industry partners for ideas that can help an astronaut avoid "becoming a walking, high voltage capacitor", including issues such as an electrical arc that could damage spacesuits, spark fires in the oxygen atmosphere of a spacecraft, or create electrical shocks. (A Mars simulation in 2018 was reportedly derailed due to a crew experiencing electrical issues, so this problem is not unprecedented.)

The challenge aims to create designs that would safely discharge the astronaut and their spacesuit before an astronaut touches the lander. Among the technical requirements, NASA is looking for something small (in terms of mass, volume and power) that would be able to operate even in the extreme temperature swings of the lunar surface. The technology must also be able to help as many as four extra-vehicular activities (moonwalks) that take place over as long as 10 days.

"In addition, the suspended lunar dust and heavy dust buildup on a suit in these environments significantly increases arcing lengths, allowing sparks to jump across larger gaps than they would in a clean vacuum. Therefore, the solution must aim to avoid a sudden arc that may come into contact with the outer pressure garment — suit — or the lander," NASA wrote in the challenge description.

The challenge will include multiple phases, including a concept design, concept refinement after chatting with reviewers, and then a final selection. NASA did not release a target date in its press release for when the tech would be available for astronauts, but the agency is planning on a long-term moon base for astronaut missions that would be largely ready to go in the 2030s if schedules hold.

Are there secret underground caves on the moon? NASA has a new program that aims to find out.

Though we see it in the sky most nights, the moon still holds an incredible amount of mystery. One such mystery is a large underground cave, or a cavernous tube carved out by ancient lava, that scientists think extends past a particular pit on the moon's surface. And to get to the bottom of it, NASA has selected a project known as GIMLI (the Geophysical Instruments for Marius Lunar pit Investigation, not the character from Lord of the Rings). GIMLI was selected along with two other programs that are all intended to expand our understanding of the moon to better support a future moon base, which NASA aims to build near the south pole.

"NASA Science is building the ultimate interplanetary survival guide to ensure that science goes first to the lunar surface to provide our future astronaut crews with the vital information, resources, and safety precautions needed ahead of time to survive the night on the moon," Nicky Fox, NASA's associate administrator for the Science Mission Directorate, said in a statement.

Lunar mysteries

The site of this investigation will be the Marius Hill Pit, which was discovered in 2009 by Japan's Kaguya moon orbiter. You can see the pit clearly in the probe's images. But researchers think that there's more there than just a large hole in the lunar surface.

They think it's possible that the pit is connected to a vast, underground cave likely created by lava flowing in the ancient past. If true, this could shed light on the history of volcanic activity on the moon.

"Confirming a substantial lava tube would give us an insight into how volcanism operated on the moon," GIMLI deputy principal investigator Gareth Morgan said in a different statement. "Lava tubes are a common feature of basaltic volcanism on Earth, so identifying them on the moon means we could use knowledge of such terrestrial caves to better understand lunar history."

Even more, if researchers confirm the presence of this lava tube, astronauts could potentially use it as a natural shelter on the lunar surface. These lava-made caves would provide general shelter as well as protection from the extreme temperatures and radiation exposure experienced on the moon's surface. Lava tubes could also be a safe "bunker" of sorts where future astronauts could be shielded from micrometeorites. While a future moon base will probably have human-made shelters included, natural caves could be an incredible, existing resource that astronauts could tap into.

How to find a moon cave

GIMLI will work directly on the lunar surface, scanning beneath to look for signs of the lava tube. This investigation comes from a proposal led by the nonprofit Planetary Science Institute (PSI) and will be funded through NASA's Payloads and Research Investigations on the Surface of the Moon (PRISM) program.

The investigation is partnering with Honeybee Robotics to help build the equipment and instrumentation that will be necessary for the study. This gear will get to the moon aboard a lander and rover via NASA's Commercial Lunar Payloads Services program, and the data collected will be studied by a team led by PSI associate director and senior scientist Than Putzig. The work done by PSI will be in partnership with the Norwegian Space Agency.

From the lunar surface, GIMLI will gather data using ground-penetrating radar, seismic sensors and a gravimeter to better understand what's really happening underneath the surface. These measurements will allow GIMLI to determine if there is a subsurface lava tube and, if so, how big it is. Could it fit an entire astronaut crew? We will have to wait and see.

The moon is a historical landmark — a celestial body continually peppered with robotic landers shot from our home planet, as well as human footprints planted there by a dozen visiting moonwalkers from 1969 to 1972.

A recent gathering in Italy of the International Scientific Committee on Aerospace Heritage (ISCAH) looked at protecting lunar heritage with an eye toward developing guidelines for spacecraft deorbiting onto the moon's surface.

Particular attention was paid to the risks posed by the impacts of deorbited satellites and rocket stages, recently highlighted by the crash of a SpaceX Falcon 9 upper stage into the moon last August.

As pointed out in the meeting, as lunar traffic increases, controlled crash landings of moon orbiters and rocket stages are becoming an attractive end-of-mission disposal strategy.

And that's a problem.

Limited knowledge

There is limited knowledge regarding ejecta modeling and the effects produced by these impacts, said Luca Forassiepi. He spoke at the Sept. 14 meeting in Piza, which was called "Protecting Lunar Heritage: Developing Guidelines and Recommendations for Controlled Lunar Deorbiting."

"These effects have only been observed, and only partially, in a handful of historical cases. As a result, much of our current understanding relies on simulations, which necessarily involve a number of simplifications compared with reality," Forassiepi told Space.com.

Strong incentive

"Because the moon is an airless world, any movement on the surface is going to stir up sticky, abrasive dust that erodes human materials," pointed out associate professor Alice Gorman, an Australian archaeologist and heritage consultant at Flinders University.

"This is a problem for cultural heritage sites," Gorman said. "Imagine the iconic Apollo 11 landing module, the Eagle, being worn away until it crumbles into dust itself."

"It's also going to be a problem for habitation and mining installations," she added. "So there is a strong incentive for [the] space industry to minimize the impacts of rocket and satellite crashes, protecting both heritage places and new surface missions."

End-of-life planning

Gorman pointed to 51 hard spacecraft impacts on the moon to date, a number that includes nine rocket bodies and 19 lunar orbiters.

"We've reached an inflection point where spacecraft craters aren't just new archaeological sites, they're an environmental hazard that may cause irreversible damage," Gorman told Space.com.

Under the 1967 Outer Space Treaty, Gorman observed, nations are liable for any damage their space hardware causes to the property of other nations. "We could be looking at a situation where a state could demand compensation for a rocket body crash harming its cultural heritage. End-of-life planning is going to become critical."

Cultural landscape

Also taking part in the meeting was Beth O'Leary, a cultural anthropology and archaeology specialist and college professor emerita at New Mexico State University in Las Cruces.

"The moon is part of the cultural landscape of Earth," she said. As such, its environment and heritage deserve international attention.

It's now been more than 60 years since the first successful soft landing on the moon, that of the Soviet Union's Luna 9 spacecraft in February 1966. And lunar traffic is poised to increase greatly in the coming years, as both the United States and China aim to build bases near the moon's south pole.

Given this landscape, "we seek to address the challenges of lunar traffic from crashes, deorbiting spacecraft, and intentional landings and to understand those risks to our aerospace heritage. Our committee attempts to estimate the real consequences of the impacts," O'Leary said.

With global experts in planetary geoarchaeology, site formation processes and heritage management, ISCAH is analyzing and increasing the knowledge base that could prevent the irreversible destruction of the significant historic cultural resources on the lunar surface.

Far-reaching consequences

"Our recommendations should inform consensus-based decisions and support international best practices and policies," said O'Leary.

The ongoing work of the group provides the best opportunities for lunar preservation and protection by and for humanity, she added.

"In our short three years," O'Leary said, "we will have had three conferences, created a mission statement, received World Monuments Fund listing, and will continue as a delegation to the United Nations Committee on the Peaceful Uses of Outer Space."

O'Leary told Space.com that all these issues are complex scientifically and legally, "but it is so important to rely on excellent research and proven heritage management principles in order to make good decisions about preservation which have far-reaching consequences."

Planetary geoarchaeology

One goal the group is addressing is a "post-mission gap," particularly regarding lunar projects.

That is, what happens to lunar heritage following the completion of a successful mission and in the decades that follow?

Also, what are the appropriate end-of-mission practices, and how can we ensure the long-term protection of spacecraft, robotics and other material remains associated with these missions?

Those questions are being deliberated by Justin Holcomb, an assistant research professor with the Kansas Geological Survey, a research unit of the University of Kansas in Lawrence.

Planetary geoarchaeology provides one way to address this issue, by identifying the natural (geological) and anthropogenic (human) processes operating within these environments "that may threaten lunar heritage, while also identifying environmental settings that are more conducive to its long-term preservation," Holcomb told Space.com.

Lunar practices

Forassiepi said that future points of action are on the agenda.

"There is certainly ongoing and continuous work by the ICOMOS International Scientific Committee on Aerospace Heritage on this aspect," said Forassiepi.

ICOMOS is the International Council on Monuments and Sites, a non-governmental organization working to conserve and protect cultural heritage sites on our planet — and off it as well.

"In active collaboration with the World Monuments Fund, we will further refine our research into the potential risks associated with deorbiting and crash landings," Forassiepi noted.

Over the coming months, Forassiepi said, the group will move into a second phase focused on listening and dialogue with all relevant stakeholders in the sector, from space agencies and the scientific community to private actors, heritage experts and communities with social and religious values associated with the moon that could be affected or disrupted by certain lunar practices.

Ultimate goal

"The aim is to initiate an open dialogue and exchange among all these different actors, with a view to collectively developing guidelines based on broad consensus," Forassiepi said.

These will then be presented in the context of the United Nations Committee on the Peaceful Uses of Outer Space in 2027, with the hope that, over time, they may evolve into "internationally recognized standards of behavior" and be adopted and followed by all space actors, Forassiepi added.

"The ultimate goal is to build a lunar future that is sustainable not only from an operational perspective, but also in terms of scientific research and the protection of the earliest traces of human presence in the history of space," he stressed. "These are two irreplaceable forms of heritage, and their damage would represent an enormous loss for future generations."

The discovery of water at the poles of the moon has inspired speculation about whether we can build there – cities, industrial neighborhoods, places where people work and live. But is there enough water, and can we use it efficiently enough? In their new article in Frontiers in Space Technologies, Dr. Martin Elvis and Dr. Jonathan McDowell do the math. Even at the most generous estimates of the available water and recycling efficiency, a city of one million people would only last 100 years before all the water runs out. In this guest editorial, which Frontiers in Space Technologies provided, Elvis breaks down what we can and can't do with the technology available.

The discovery of water in dark craters at the moon's poles has sparked a "moon rush" to establish bases there, and then villages, cities and heavy industry. How sustainable is this rush?

Soon after the moon was formed, asteroids bombarded it, creating its pockmarked topography. Near the moon's poles, there are dozens of crater floors that have not seen direct sunlight in about four billion years. Many of these cryogenically cold "pits of eternal darkness" are below a temperature of 110 Kelvin (minus 262 degrees Fahrenheit), forming "cold traps" in which water ice won't sublimate away by more than a millimeter in a billion years, even in the vacuum at the moon's surface. And there is water to freeze: some of those asteroids brought it along with them. Since 2013 we have known that that water is still there, possibly as much as a billion tons of it, thanks to a succession of moon-orbiting missions that have mapped out likely locations in increasing detail.

The presence of water at the lunar poles changes everything about human visits to the moon. Suddenly it is practical to envisage a "moon village" where people could survive without importing every last bit from Earth. They could grow their own food and have showers and functional toilets, unlike the astronauts on the International Space Station (ISS). This possibility has sparked ambitions from the likes of Jeff Bezos to move heavy industry to the moon and Elon Musk's aims to have "self-growing cities" there. These are enticing visions, but are they attainable?

The good news

We realized that we could make a first feasibility estimate simply by looking at how much power and water a large population would use on the moon, and how long a city of 100,000 or one million people could survive there. How sustainable is a city on the moon?

The good news is that power, even without nuclear reactors, is not a problem. That's because the rims of the craters containing the pits of eternal darkness are in almost permanent sunlight. (That's why they are sometimes, slightly incorrectly, referred to as the "peaks of eternal light.") Up on those highly illuminated rims it would be possible to generate three gigawatts of electricity using kilometer-tall towers covered with photovoltaic arrays. It should be possible to manufacture solar panels on the moon. There's certainly plenty of silicon. This could even make AI data centers on the moon possible, by placing them near these sunny peaks. That would be the start of a true lunar economy.

The bad news

The bad news is that, even assuming a generous one billion tons of water to start with, without recycling the answer to our question of sustainability is that the city would last only a few years. Even in the best-case scenario, with 98% efficient recycling of water — the same as achieved on the ISS — a one-million-person city will run out of water in just over a century. That is a problem for sustainable moon settlement. And today's best estimates of the amount of water on the moon are about 30 times less than a billion tons, shortening the time to water exhaustion by the same factor. This means that even a small city would run dry after just a decade or so. A moon village with a thousand people, or even a town with 10,000 people, would instead be sustainable for several centuries or more.

There are potential solutions. We could improve the efficiency of water recycling by a factor of five or more; lower water usage from new techniques such as vertical farming; import water, probably from accessible asteroids; or, simply, find more water. Of these it may be this last hope that is most promising. Current water surveying techniques do not reach below the surface more than a few meters, while the rubble-like rocks of the surface regolith typically extend tens of meters down and may contain water in the cold traps. If the ambitious plans of the space billionaires are to be realized, then finding more water will be the first step.

We've been studying the moon for a long time. NASA has gathered mountains of data over decades of lunar missions and studies. The data collected by the Lunar Reconnaissance Orbiter (LRO) alone, for example, exceeds that of all NASA's other planetary missions combined.

Analyzing all this information takes lots of time and effort from researchers. So, NASA and IBM have developed an AI model to help sift through the moon data — an advance the agency announced on Thursday (Sept. 10). The open-source model, called the NASA-IBM Lunar Foundation Model, is currently available for free at Hugging Face.

"NASA has spent decades building an extraordinary scientific record of the moon, but collecting data is only part of the job," NASA's Kevin Murphy, chief science data officer and acting chief data and AI officer, said in the announcement.

The new AI model can help researchers with tasks like mapping craters, finding young volcanic features, and modeling possible locations of water ice near the lunar poles, according to NASA.

In the announcement, Murphy said that NASA needs to make scientific data easier to explore and use. To this end, NASA has been developing and releasing science-focused AI models with IBM. Previous models include one focused on Earth observation and another for heliophysics.

This is part of a larger trend of AI use in planetary science. Space agencies and private space companies around the world have been looking into how AI models can help with analysis to increase scientific productivity, reduce costs and streamline workflows.

"The NASA-IBM Lunar Foundation Model shows what's possible when we bring AI to NASA's petabytes of scientific data," Murphy said in the announcement. "That's a real opportunity we see with AI: turning large-scale data into new discoveries."

The AI model was mostly trained on data from the LRO mission. Over 17 years, NASA's lunar orbiter has compiled a nearly complete mosaic of images that detail the moon's surface in high definition.

The moon could have formed in a matter of hours following the giant impact between Earth and a Mars-size protoplanet early in the history of the solar system. The theory comes from new simulations that take into account how the internal temperature of young protoplanets affected their geologic properties and therefore the collisions they experienced.

This giant impact scenario has become the leading theory of how the moon formed, thanks in particular to work done by planetary scientist Robin Canup. Since 2001, she has conducted and refined numerous computer simulations that describe how a Mars-size body called Theia collided at an angle just right to throw debris into orbit around the proto-Earth.

Now other researchers are getting in on the act. Adeene Denton of the South-west Research Institute led a team who performed some of the most detailed simulations of the collision yet, taking into account more of the geologic properties of the colliding worlds.

"Models have evolved to include material strength, something that's really important when you're studying collisions between smaller bodies like asteroids or for my previous paper about the formation of the Pluto–Charon system," said Denton in a statement. "We weren't sure it would matter for the moon or not. When we did the simulations, we found it actually matters quite a bit."

It turns out that warmer bodies are weaker than colder ones. After the planets formed, they were still hot inside from their formation, which would have affected their material strength. Given that the moon-forming impact occurred not long after the solar system's formation, this would have affected the collision with Theia — but to what degree depends on exactly when the collision occurred and how much Theia had cooled.

As Theia smashed into Earth, it was utterly destroyed. While much of what was left of Theia's shattered iron core sank into the Earth, a large ring of debris wrapped around Earth to form the moon.

The main effect of the temperature being warmer in the outer few hundred miles of Theia was that it would have affected its ability to deform upon impact and absorb the momentum of the collision. This, in turn, would have affected how debris was strewn around Earth to form the moon. Therefore, by including varying temperatures and material strengths in the simulations, Denton's team was able to get a better look at how the collision and the resulting formation of our moon played out.

Previous simulations have shown two possible scenarios. One is that the ring of debris hung around for a substantial amount of time, allowing the moon to accrete from it gradually. The other scenario, first depicted in NASA-led simulations in 2022, implies that the moon came together from this debris in a matter of hours.

Now, Denton's models potentially bolster this startling possibility.

If Theia was colder, meaning that the impact occurred a little later in the history of the solar system, perhaps 100 to 150 million years after the birth of the planets, then the ring of debris would have formed in such a way as to allow the moon to accrete gradually. And because it was stronger, more of Theia would have survived intact to merge with Earth.

On the other hand, a warmer Theia that impacted Earth less than 60 million years after the planets' formation, would create a scenario where the moon could form very quickly while Theia itself would be obliterated.

"Depending on how hot the Earth and Theia are prior to the collision, the impact can destroy Theia and produce this massive disk of debris that eventually forms the moon," said Denton. "But when I used the same parameters as original impact modeling – down to the equal temperature structures inside both bodies — within around five hours, an intact moon emerged."

That would have been quite a day in the history of our planet, acquiring a new moon and an almighty headache all at once.

"These surprising and exciting new results imply a potential connection between the physical properties of the moon today, including perhaps its volatile content, and the thermal state of the Earth and Theia at the time of the giant impact," said the Southwest Research Institute's Robin Canup, who was not involved in this study. "This in turn might help scientists better constrain when the moon-forming event occurred."

In both scenarios, the moon appears to be made mostly from Theia's mantle material, with just a little bit of Earth's mantle mixed in. This latter finding is surprising, given the similarities between the moon's composition and Earth's mantle. However, research has shown that there's clearly more to the story because despite the similarities there are also some puzzling differences in the levels of isotopes that cannot be easily explained by current simulations, including Denton's.

The simulations could have repercussions in the search for exomoons. If the moon did form in a matter of hours, then searching for exomoon-forming disks around terrestrial exoplanets might be a fruitless endeavor because such disks would be so short-lived. Moon-forming disks around gas giant exoplanets would be a different matter, however, because those disks do not form from impacts, but rather from material leftover from assembling those planets.

The results were published on Sept. 1 in The Astrophysical Journal Letters.

It's now possible to disentangle the sprinkling of supernova dust on the moon from the lunar dirt it is mixed up in, thanks to a new computer model that opens up the moon's surface as a time capsule holding details about the history of supernova explosions near the Earth as our solar system has travelled through space while orbiting the galaxy.

When stars explode as a supernova, they shower space with debris, some of which is in the form of radioactive isotopes traveling at high velocity. Some of these radioisotopes enter the solar system to fall on all the planets and moons, including Earth and its moon. Studies of radioisotopes in deep-sea sediments on Earth, coupled with those found in samples of lunar dirt – what scientists term 'regolith' – brought back by the Apollo missions, point to two recent peaks in supernova activity, 2.3 and 7.3 million years ago.

"I think it's beautiful that the remains of past stars can be used to navigate the vast history of our Earth–moon neighborhood, if we have knowledge of how to read the stardust," said planetary scientist Emily Costello, of the University of Hawaii at Mānoa, in a statement.

However, because of the process of erosion and subduction through plate tectonics, most Earth-bound records of supernova activity in our cosmic neighborhood have been lost and reliable records on Earth only go back about 10 million years. Earth's moon, however, is a different story. Because the moon has no atmosphere, there's no wind or rain erosion, nor are there any plate tectonics. The moon, therefore, should host a record of supernova activity going back 80–100 million years, or even longer.

However, while the moon lacks Earth's style of erosion, it does experience what planetary scientists refer to as 'impact gardening'. This is when impacts of objects ranging in size from microscopic micrometeorites to large asteroids, turns over the regolith, mixing it all up including the radioactive supernova debris.

In order to disentangle all this and work out at what depths various radioisotopes have been mixed down to, Costello's team developed a mathematical model that can decode what treasures lie in the lunar regolith.

"To model impact gardening, we have to balance a complex web of physical mechanisms, including impact compaction, excavation, radioactive decay and space weathering, all operating simultaneously within a single, elegant continuum model," said Costello.

"Our mathematical model treats lunar impact gardening as a competition between forces burying the soil and impacts digging it back up. It also accounts for radioactive decay of the star remnants while mapping exactly when and where new stardust was delivered by episodic supernovae."

Costello's team validated their model by comparing its predictions for the depth-concentration of supernova radioisotopes to what is found in Earth's deep-sea sediments and the Apollo samples.

"When I first shared my model results, my colleagues were surprised by how well-matched the model and the measurements were," said Costello, "This level of fidelity between empirical observations and a physics model is exciting and remarkable."

Their model accurately predicted the depth-concentration profile of iron-60 found in Apollo regolith samples, as well as heavy elements such as plutonium-244, iodine-129, hafnium-182 and curium-247 that have all been buried over time.

However, the real science will begin when future Artemis astronauts bring back new lunar samples from deeper beneath the surface over the coming years.

"These future samples taken from the moon, when considered in conjunction with our gardening model, could reveal new insights into an untold chapter of supernova history," said Costello. "Understanding the physics of regolith mixing ensures that when future astronauts return deeper cores, we can properly read the scrambled layers to reconstruct the history of our solar system's journey through the galaxy."

The findings were published on Aug. 14 in Physical Review Letters.

Update for Aug. 23: Bad weather has pushed the Chang'e 7 launch back considerably, possibly until 2027. Read our delay story.

China's moon exploration program is readying an ambitious robotic mission, one composed of an orbiter, a lander, a rover, a hopper, and a wide range of international experiments including a U.S.-supported payload.

In April of this year, Chang'e-7 hardware was transported to the Wenchang launch site, targeting an Aug. 24 launch atop a Long March 5 Y14 rocket. The lander's destination is the edge of Shackleton Crater in the lunar south pole region.

After launch, the Chang'e-7 orbiter will spend several months orbiting the moon before releasing its lander for an attempted touchdown near the end of the year. While Chang'e-7 will carry out ambitious, groundbreaking lunar science, it will also serve to lay the groundwork for the first Chinese human landing on the lunar surface by 2030.

James Head is a leading moon scientist at the department of geological sciences at Brown University in Providence, Rhode Island. He says China's upcoming moon launch will set a new benchmark for lunar science voyages.

"Chang'e-7 is the most ambitious, comprehensive, and complex robotic lunar mission ever attempted by any nation or entity," Head told Space.

Likewise, Zhang Jingbo, a spokesman for the China Manned Space Agency (CMSA) agency, said earlier this year that the mission will "fully leverage the technological expertise and practical experience accumulated over decades" to "spare no effort to strive for the goal of achieving the first Chinese landing on the moon by 2030."

Pockets of water ice

Once unleashed from the Chang'e-7 lander, the hopper is slated to "jump" from sunlit areas to shadowed craters in a quest to find pockets of water ice. The hopper utilizes active shock-absorption technology to safely land on slopes. The lander will also deploy China's inaugural deep-space "landmark image navigation" system.

While scientists around the globe believe there's water ice on the moon, said Ye Peijian, an academician with the Chinese Academy of Sciences, no one has definitively found and fully evaluated that resource as yet.

"Now China is going to look for it, [...] And we're using many methods, from searching the surface to exploring inside craters," Ye told China Central Television (CCTV).

Back-to-back duties

The Chang'e-7 mission will adopt an integrated exploration approach, added CCTV, combining orbiting, landing, roving, and hopping, to survey the environment and resources of the lunar south pole, while also carrying out international cooperation.

Moreover, a Chang'e-8 mission is set for around 2028, designed to test technologies for building habitats using lunar soil.

Taken together, the two robotic projects  — Chang'e-7 and Chang'e-8  — are assigned duties to assist in orchestrating China's planned, multi-phased, International Lunar Research Station (ILRS).

Variety of instruments

Chang'e-7 mission hardware is outfitted with a variety of instruments from other nations and organizations, such as:

• On the lander, a Russian Academy of Sciences' PmL-Ch7 suite to detect lunar dust and a Langmuir probe to gauge the temperature and density of nearby plasma.
• An Italian laser retroreflector array on the lander is provided by the Laboratori Nazionali di Frascati.
• A small, state-of-the-art, wide-field optical telescope mounted on the lander developed by the International Lunar Observatory Association (ILOA Hawaii) and the Laboratory for Space Research at the University of Hong Kong (HKU-LSR).
• LunaHcam, a camera attached to the Chang'e-7 orbiter and jointly developed by the Bahrain Space Agency and the Egyptian Space Agency to churn out high-resolution hyperspectral images of the moon's surface.
• Moon Aiming Thai-Chinese Hodoscope (MATCH) onboard the orbiter and developed by the National Astronomical Research Institute of Thailand. It will assess high-energy particles related to space weather and cosmic radiation tossed out by the sun.
• Moon-based Dual-channel Earth Radiation Spectrometer on the orbiter has been provided by Switzerland's Physical Meteorological Observatory.

Compact lunar camera

The ILO-C instrument from ILOA Hawaii and the Laboratory for Space Research at the University of Hong Kong will be housed directly on the Chang'e-7 lunar lander, bound for the illuminated rim of Shackleton Crater.

"The HKU Lab for Space Research is proud to partner with ILOA for this historic lunar mission and we look forward to working with them to maximize the scientific return this exceptional wide field optical lunar camera will deliver," said Quentin Parker, professor emeritus of the University of Hong Kong.

Through visible color imaging, the ILO-C camera project aims to spark public interest in lunar exploration, astronomy, and space science, Parker said, thereby laying a social foundation for future lunar science missions.

Moon-based vantage point

Operating in the extreme lunar environment, the compact camera will conduct first-ever astronomical color imagery from the moon, said Elisa Perednia, President and Chair of ILOA. The camera is designed to capture unprecedented wide-field, full color imagery of the Milky Way's Galactic plane from a stable, moon-based vantage point, she said.

One sad note: The camera onboard China's moon lander was pioneered by ILOA's founding director Steve Durst who passed earlier this year. He was a visionary leader that worked with Chinese aerospace representatives since the 1980s.

The Beijing Institute of Space Mechanics & Electricity (BISME) built the camera to ILO-C team member specifications.

"We are proud to have joined the mission and to help realize Steve's wonderful vision," Parker at HKU-LSR told Space.com.