Electrons from Earth may be forming water on the Moon

A team of researchers, led by a University of Hawai'i (UH) at Manoa planetary scientist, discovered that high energy electrons in Earth's plasma sheet are contributing to weathering processes on the Moon's surface and, importantly, the electrons may have aided the formation of water on the lunar surface. The study was published today in Nature Astronomy.

Understanding the concentrations and distributions of water on the Moon is critical to understanding its formation and evolution, and to providing water resources for future human exploration. The new discovery may also help explain the origin of the water ice previously discovered in the lunar permanently shaded regions.

Due to Earth's magnetism, there is a force field surrounding the planet, referred to as the magnetosphere, that protects Earth from space weathering and damaging radiation from the Sun. Solar wind pushes the magnetosphere and reshapes it, making a long tail on the night side. The plasma sheet within this magnetotail is a region consisting of high energy electrons and ions that may be sourced from Earth and the solar wind.

Previously, scientists mostly focused on the role of high energy ions on the space weathering of the Moon and other airless bodies. Solar wind, which is composed of high energy particles such as protons, bombards the lunar surface and is thought to be one of the primary ways in which water has been formed on the Moon.

Building on his previous work that showed oxygen in Earth's magnetotail is rusting iron in the Moon's polar regions, Shuai Li, assistant researcher in the UH Manoa School of Ocean and Earth Science and Technology (SOEST), was interested in investigating the changes in surface weathering as the Moon passes through Earth's magnetotail, an area that almost completely shields the Moon from solar wind but not the Sun's light photons.

"This provides a natural laboratory for studying the formation processes of lunar surface water," said Li. "When the Moon is outside of the magnetotail, the lunar surface is bombarded with solar wind. Inside the magnetotail, there are almost no solar wind protons and water formation was expected to drop to nearly zero."

Li and co-authors analyzed the remote sensing data that were collected by the Moon Mineralogy Mapper instrument onboard India's Chandrayaan 1 mission between 2008 and 2009. Specifically they assessed the changes in water formation as the Moon traversed through Earth's magnetotail, which includes the plasma sheet.

"To my surprise, the remote sensing observations showed that the water formation in Earth's magnetotail is almost identical to the time when the Moon was outside of the Earth's magnetotail," said Li. "This indicates that, in the magnetotail, there may be additional formation processes or new sources of water not directly associated with the implantation of solar wind protons. In particular, radiation by high energy electrons exhibits similar effects as the solar wind protons."

"Altogether, this finding and my previous findings of rusty lunar poles indicate that the mother Earth is strongly tied with its Moon in many unrecognized aspects," said Li.

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Flat, pancake-sized metalens images lunar surface in an engineering first

Astronomers and amateurs alike know the bigger the telescope, the more powerful the imaging capability. To keep the power but streamline one of the bulkier components, a Penn State-led research team created the first ultrathin, compact metalens telescope capable of imaging far-away objects, including the moon.

Metalenses comprise tiny, antenna-like surface patterns that can focus light to magnify distant objects in the same way as traditional curved glass lenses, but they have the advantage of being flat. Though small, millimeters-wide metalenses have been developed in the past, the researchers scaled the size of the lens to eight centimeters in diameter, or about four inches wide, making it possible to use in large optical systems, such as telescopes. They published their approach in Nano Letters.

"Traditional camera or telescope lenses have a curved surface of varying thickness, where you have a bump in the middle and thinner edges, which causes the lens to be bulky and heavy," said corresponding author Xingjie Ni, associate professor of electrical engineering and computer science at Penn State. "Metalenses use nano-structures on the lens instead of curvature to contour light, which allows them to lay flat."

That is one of the reasons, Ni said, modern cellphone camera lenses protrude from the body of the phone: the thickness of the lenses take up space, though they appear flat since they are hidden behind a glass window.

Metalenses are typically made using electron beam lithography, which involves scanning a focused beam of electrons onto a piece of glass, or other transparent substrate, to create antenna-like patterns point by point. However, the scanning process of the electron beam limits the size of the lens that can be created, as scanning each point is time-consuming and has low throughput.

To create a bigger lens, the researchers adapted a fabrication method known as deep ultraviolet (DUV) photolithography, which is commonly used to produce computer chips.

"DUV photolithography is a high-throughput and high-yield process that can produce many computer chips within seconds," Ni said. "We found this to be a good fabrication method for metalenses because it allows for much larger pattern sizes while still maintaining small details, which allows the lens to work effectively."

The researchers modified the method with their own novel procedure, called rotating wafer and stitching. Researchers divided the wafer, on which the metalens was fabricated, into four quadrants, which were further divided into 22 by 22 millimeter regions -- smaller than a standard postage stamp. Using a DUV lithography machine at Cornell University, they projected a pattern onto one quadrant through projection lenses, which they then rotated by 90 degrees and projected again. They repeated the rotation until all four quadrants were patterned.

"The process is cost-effective because the masks containing the pattern data for each quadrant can be reused due to the rotation symmetry of the metalens," Ni said. "This reduces the manufacturing and environmental costs of the method."

As the size of the metalens increased, the digital files required to process the patterns became significantly larger, which would take a long time for the DUV lithography machine to process. To overcome this issue, the researchers compressed the files using data approximations and by referencing non-unique data.

"We utilized every possible method to reduce the file size," Ni said. "We identified identical data points and referenced existing ones, gradually reducing the data until we had a usable file to send to the machine for creating the metalens."

Using the new fabrication method, the researchers developed a single-lens telescope and captured clear images of the lunar surface -- achieving greater resolution of objects and much farther imaging distance than previous metalenses. Before the technology can be applied to modern cameras, however, researchers must address the issue of chromatic aberration, which causes image distortion and blurriness when different colors of light, which bend in different directions, enter a lens.

"We are exploring smaller and more sophisticated designs in the visible range, and will compensate for various optical aberrations, including chromatic aberration," Ni said.

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Astronauts may one day drink water from ancient moon volcanoes

Billions of years ago, a series of volcanic eruptions broke loose on the moon, blanketing hundreds of thousands of square miles of the orb's surface in hot lava. Over the eons, that lava created the dark blotches, or maria, that give the face of the moon its familiar appearance today.

Now, new research from CU Boulder suggests that volcanoes may have left another lasting impact on the lunar surface: sheets of ice that dot the moon's poles and, in some places, could measure dozens or even hundreds of feet thick.

"We envision it as a frost on the moon that built up over time," said Andrew Wilcoski, lead author of the new study and a graduate student in the Department of Astrophysical and Planetary Sciences (APS) and the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder.

He and his colleagues published their findings this month in The Planetary Science Journal.

The researchers drew on computer simulations, or models, to try to recreate conditions on the moon long before complex life arose on Earth. They discovered that ancient moon volcanoes spewed out huge amounts of water vapor, which then settled onto the surface -- forming stores of ice that may still be hiding in lunar craters. If any humans had been alive at the time, they may even have seen a sliver of that frost near the border between day and night on the moon's surface.

It's a potential bounty for future moon explorers who will need water to drink and process into rocket fuel, said study co-author Paul Hayne.

"It's possible that 5 or 10 meters below the surface, you have big sheets of ice," said Hayne, assistant professor in APS and LASP.

Temporary atmospheres

The new study adds to a growing body of evidence that suggests that the moon may be awash in a lot more water than scientists once believed. In a 2020 study, Hayne and his colleagues estimated that nearly 6,000 square miles of the lunar surface could be capable of trapping and hanging onto ice -- mostly near the moon's north and south poles. Where all that water came from in the first place is unclear.

"There are a lot of potential sources at the moment," Hayne said.

Volcanoes could be a big one. The planetary scientist explained that from 2 to 4 billion years ago, the moon was a chaotic place. Tens of thousands of volcanoes erupted across its surface during this period, generating huge rivers and lakes of lava, not unlike the features you might see in Hawaii today -- only much more immense.

"They dwarf almost all of the eruptions on Earth," Hayne said.

Recent research from scientists at the Lunar and Planetary Institute in Houston shows that these volcanoes likely also ejected towering clouds made up of mostly carbon monoxide and water vapor. These clouds then swirled around the moon, potentially creating thin and short-lived atmospheres.

That got Hayne and Wilcoski wondering: Could that same atmosphere have left ice on the lunar surface, a bit like frost forming on the ground after a chilly fall night?

Forever ice

To find out, the duo alongside Margaret Landis, a research associate at LASP, set out to try to put themselves onto the surface of the moon billions of years ago.

The team used estimates that, at its peak, the moon experienced one eruption every 22,000 years, on average. The researchers then tracked how volcanic gases may have swirled around the moon, escaping into space over time. And, they discovered, conditions may have gotten icy. According to the group's estimates, roughly 41% of the water from volcanoes may have condensed onto the moon as ice.

"The atmospheres escaped over about 1,000 years, so there was plenty of time for ice to form," Wilcoski said.

There may have been so much ice on the moon, in fact, that you could, conceivably, have spotted the sheen of frost and thick, polar ice caps from Earth. The group calculated that about 18 quadrillion pounds of volcanic water could have condensed as ice during that period. That's more water than currently sits in Lake Michigan. And the research hints that much of that lunar water may still be present today.

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Lunar radar data uncovers new clues about moon’s ancient past

The dusty surface of the moon -- immortalized in images of Apollo astronauts' lunar footprints -- formed as the result of asteroid impacts and the harsh environment of space breaking down rock over millions of years. An ancient layer of this material, covered by periodic lava flows and now buried under the lunar surface, could provide new insight into the Moon's deep past, according to a team of scientists.

"Using careful data processing, we found interesting new evidence that this buried layer, called paleoregolith, may be much thicker than previously expected," said Tieyuan Zhu, assistant professor of geophysics at Penn State. "These layers have been undisturbed since their formation and could be important records for determining early asteroid impact and volcanic history of the moon."

The team, led by Zhu, conducted new analysis of radar data collected by China's Chang'e 3 mission in 2013, which performed the first direct ground radar measurements on the moon.

The researchers identified a thick layer of paleoregolith, roughly 16 to 30 feet, sandwiched between two layers of lava rock believed to be 2.3 and 3.6 billion years old. The findings suggest the paleoregolith formed much faster than previous estimates of 6.5 feet per billion years, the scientists said.

The moon has experienced volcanic activity throughout its history, depositing lava rock on the surface. Over time, the rock breaks down into dust and soil, called regolith, with repeated asteroid impacts and space weathering, only to be buried by subsequent lava flows, the scientists said.

"Lunar scientists count craters on the moon and use computer models to determine the rate that regolith is produced," Zhu said. "Our findings provide a constraint on what happened between two and three billion years ago. This is the very unique contribution of this work."

Previous studies have examined the dataset, created when the Yutu rover sent electromagnetic pulses into the lunar underground and listened as they echoed back. Zhu said his team developed a four-step data processing flow to enhance the signal and suppress noise in the data.

The scientists observed changes in polarity as the electromagnetic pulses traveled down through the dense lava rock and the paleoregolith, allowing the team to distinguish between the different layers.

"Our paper is really providing the first geophysical evidence to see this electromagnetic permittivity changed from a small value for the paleoregolith to a large value for the lava flows," Zhu said. "We discovered this polarity change in the data and created a detailed geophysical image of the subsurface up to a few hundred meters depth."

The results may indicate higher meteoric activity in the solar system during this period billions of years ago, according to the team, who recently reported their findings in the journal Geophysical Research Letters.

Zhu said the data processing tools may have use for interpreting similar data collected during future missions to the moon, Mars or elsewhere in the solar system. His team is now working with machine learning technology to further improve the findings.

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