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Thursday, 5 August 2021

Rate of nuclear reaction in exploding stars



New research by Surrey's Nuclear Physics Group has shown that it's possible to mimic excited quantum states with exotic nuclei, opening up a host of opportunities for next generation radioactive beam facilities, such as the Facility for Rare Isotope Beams (FRIB).

The results of the project—which was a collaboration between the University of Surrey and Michigan State University, U.S.—were published in Physical Review Letters in January 2021. The lead author was Surrey Ph.D. student Samuel Hallam, who also studied for his undergraduate physics degree at Surrey.

One of the biggest challenges in nuclear physics is measuring reactions that occur on excited quantum states, such as are found in exploding stars due to extreme temperature and density. Until now, physicists have had to determine the rates at which nuclear reactions occur in these conditions through theoretical estimates.

This pioneering study has shown, for the first time, that it is possible to mimic an excited quantum state by using a completely separate nucleus.

Dr. Gavin Lotay explains: "Our results now indicate that proton capture on the first, excited state of Aluminium-26 (found in stars) is likely to be ten times slower than was previously expected from theoretical estimates. This provides crucial insight into the analysis of meteoritic material and impacts on future theoretical studies of nucleosynthesis in exploding stars."

Reference:

S. Hallam et al, Exploiting Isospin Symmetry to Study the Role of Isomers in Stellar Environments, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.126.042701


Researchers discover new strategy for developing human-integrated electronics


Polymer semiconductors—materials that have been made soft and stretchy but still able to conduct electricity—hold promise for future electronics that can be integrated within the body, including disease detectors and health monitors.

Yet until now, scientists and engineers have been unable to give these polymers certain advanced features, like the ability to sense biochemicals, without disrupting their functionality altogether.

Researchers at the Pritzker School of Molecular Engineering (PME) have developed a new strategy to overcome that limitation. Called "click-to-polymer" or CLIP, this approach uses a chemical reaction to attach new functional units onto polymer semiconductors.

Using the new technique, researchers developed a polymer glucose monitoring device, demonstrating the possible applications of CLIP in human-integrated electronics. The results were published August 4 in the journal Matter.

"Semiconducting polymers are one of the most promising materials systems for wearable and implantable electronics," said Asst. Prof. Sihong Wang, who led the research. "But we still need to add more functionality to be able to collect signals and administer therapies. Our method can work broadly to incorporate different types of functional groups, which we hope will lead to far-reaching leaps in the field."

Functionalizing polymers without decreasing their efficacy

To achieve new functionalities of these semiconducting polymers—also referred to as conjugated polymers—many researchers have previously tried to build them from scratch by incorporating advanced features into the molecular designs directly. But conventional procedures for doing this have failed, either because the molecules have been unable to withstand the conditions needed to attach them to the polymer chains, or because the synthesis process decreased their efficacy.

To overcome this, Wang, with graduate student Nan Li, developed the CLIP method, which uses a copper-catalyzed azide-alkyne cycloaddition to add functional units to a polymer. Because this "click reaction" happens after the polymer is created, it does not affect its initial properties much.

Not only that, the reaction could be used in bulk functionalization of the polymer and in surface functionalization—both essential for creating functional electronics.

A potentially game-changing system

To demonstrate the effectiveness of CLIP, the researchers attached units that could photo-pattern the polymer, important for designing circuits within the material. They also added functionality to directly sense biomolecules. Their biomolecule sensor used a glucose oxidase enzyme to detect glucose, which then causes changes to the polymer's electrical conductance and amplifies the signal.

Now the group is building upon their success by adding other bio-active and biocompatible functionalities to these polymers, which Li says "has the potential of becoming a game-changing technology."

"We hope researchers across the field will use our method to endow even more functionality into this material system and use them to develop the next generation of human-integrated electronics as a key tool in healthcare," Wang said.

Reference: 

A universal and facile approach for building multifunctional conjugated polymers for human-integrated electronics, Matter (2021). DOI: 10.1016/j.matt.2021.07.013

Space scientists reveal secret behind Jupiter's 'energy crisis'



New research published in Nature has revealed the solution to Jupiter's 'energy crisis', which has puzzled astronomers for decades.

Space scientists at the University of Leicester worked with colleagues from the Japanese Space Agency (JAXA), Boston University, NASA's Goddard Space Flight Center and the National Institute of Information and Communications Technology (NICT) to reveal the mechanism behind Jupiter's atmospheric heating.

Now, using data from the Keck Observatory in Hawai'i, astronomers have created the most-detailed yet global map of the gas giant's upper atmosphere, confirming for the first time that Jupiter's powerful aurorae are responsible for delivering planet-wide heating.

Dr. James O'Donoghue is a researcher at JAXA and completed his Ph.D. at Leicester, and is lead author for the research paper. He said:

"We first began trying to create a global heat map of Jupiter's uppermost atmosphere at the University of Leicester. The signal was not bright enough to reveal anything outside of Jupiter's polar regions at the time, but with the lessons learned from that work we managed to secure time on one of the largest, most competitive telescopes on Earth some years later.

"Using the Keck telescope we produced temperature maps of extraordinary detail. We found that temperatures start very high within the aurora, as expected from previous work, but now we could observe that Jupiter's aurora, despite taking up less than 10% of the area of the planet, appear to be heating the whole thing.

"This research started in Leicester and carried on at Boston University and NASA before ending at JAXA in Japan. Collaborators from each continent working together made this study successful, combined with data from NASA's Juno spacecraft in orbit around Jupiter and JAXA's Hisaki spacecraft, an observatory in space."

Dr. Tom Stallard and Dr. Henrik Melin are both part of the School of Physics and Astronomy at the University of Leicester. Dr. Stallard added:

"There has been a very long-standing puzzle in the thin atmosphere at the top of every Giant Planet within our solar system. With every Jupiter space mission, along with ground-based observations, over the past 50 years, we have consistently measured the equatorial temperatures as being much too hot.

"This 'energy crisis' has been a long standing issue—do the models fail to properly model how heat flows from the aurora, or is there some other unknown heat source near the equator?

"This paper describes how we have mapped this region in unprecedented detail and have shown that, at Jupiter, the equatorial heating is directly associated with auroral heating."

Aurorae occur when charged particles are caught in a planet's magnetic field. These spiral along the field lines towards the planet's magnetic poles, striking atoms and molecules in the atmosphere to release light and energy.

On Earth, this leads to the characteristic light show that forms the Aurora Borealis and Australis. At Jupiter, the material spewing from its volcanic moon, Io, leads to the most powerful aurora in the Solar System and enormous heating in the polar regions of the planet.

Although the Jovian aurorae have long been a prime candidate for heating the planet's atmosphere, observations have previously been unable to confirm or deny this until now.

Previous maps of the upper atmospheric temperature were formed using images consisting of only several pixels. This is not enough resolution to see how the temperature might be changed across the planet, providing few clues as to the origin of the extra heat.

Researchers created five maps of the atmospheric temperature at different spatial resolutions, with the highest resolution map showing an average temperature measurement for squares two degrees longitude 'high' by two degrees latitude 'wide'.

The team scoured more than 10,000 individual data points, only mapping points with an uncertainty of less than five per cent.

Models of the atmospheres of gas giants suggest that they work like a giant refrigerator, with heat energy drawn from the equator towards the pole, and deposited in the lower atmosphere in these pole regions.

These new findings suggest that fast-changing aurorae may drive waves of energy against this poleward flow, allowing heat to reach the equator.

Observations also showed a region of localized heating in the sub-auroral region that could be interpreted as a limited wave of heat propagating equatorward, which could be interpreted as evidence of the process driving heat transfer.

Planetary research at the University of Leicester spans the breadth of Jovian system, from the planet's magnetosphere and atmosphere, out to its diverse collection of satellites.

Reference: 

O'Donoghue, J. et al, Global upper-atmospheric heating on Jupiter by the polar aurorae, Nature (2021). DOI: 10.1038/s41586-021-03706-w

Wednesday, 4 August 2021

NASA Identifies Most Likely Locations of the Early Molten Moon’s Deep Secrets


Shortly after it formed, the Moon was covered in a global ocean of molten rock (magma). As the magma ocean cooled and solidified, dense minerals sank to form the mantle layer, while less-dense minerals floated to form the surface crust. Later intense bombardment by massive asteroids and comets punched through the crust, blasting out pieces of mantle and scattering them across the lunar surface.

Recently, a pair of NASA studies identified the most likely locations to find pieces of mantle on the surface, providing a map for future lunar sample return missions such as those under NASA’s Artemis program. If collected and analyzed, these fragments from deep within the Moon can provide a better understanding of how the Moon, the Earth, and many other solar system worlds evolved.

“This is the most up-to-date evaluation of the evolution of the lunar interior, synthesizing numerous recent developments to paint a new picture of the history of the mantle and how and where it may have been exposed on the lunar surface,” said Daniel Moriarty of NASA’s Goddard Space Flight Center, Greenbelt, Maryland and the University of Maryland, College Park.

Magma oceans evolve as they cool down and dense materials sink while light materials rise. The formation of magma oceans and their evolution are thought to be common processes among rocky planets and moons throughout our solar system and beyond. Earth’s Moon is the most accessible and well-preserved body to study these fundamental processes.

“Understanding these processes in more detail will have implications for important follow-up questions: How does this early heating affect the distribution of water and atmospheric gases of a planet? Does water stick around, or is it all boiled away? What are the implications for early habitability and the genesis of life?” adds Moriarty, lead author of the papers, published August 3 in Nature Communications and January 2021 in the Journal of Geophysical Research.

Large rocky objects such as planets, moons, and large asteroids can form magma oceans with the heat generated as they grow. Our solar system formed from a cloud of gas and dust that collapsed under its own gravity. As this happened, dust grains smacked into each other and stuck together, and over time this process snowballed into larger and larger conglomerations, eventually forming asteroid and planet-sized bodies. These collisions generated a tremendous amount of heat. Also, the building blocks of our solar system contained a variety of radioactive elements, which released heat as they decayed. In larger objects, both processes can release enough heat to form magma oceans.

However, the details of how magma oceans evolve as they cool and how the various minerals in them crystalize are uncertain, which affects what scientists think mantle rocks may look like and where they could be found on the surface.

“The bottom line is that the evolution of the lunar mantle is more complicated than originally thought,” said Moriarty. “Some minerals that crystallize and sink early are less dense than minerals that crystallize and sink later. This leads to an unstable situation with light material near the bottom of the mantle trying to rise while heavier material closer to the top descends. This process, called ‘gravitational overturn’, does not proceed in a neat and orderly fashion, but becomes messy, with lots of mixing and unexpected stragglers left behind.”

The team reviewed the most recent laboratory experiments, lunar sample analysis, and geophysical and geochemical models to develop their new understanding of how the lunar mantle evolved as it cooled and solidified. They used this new understanding as a lens to interpret recent observations of the lunar surface from NASA’s Lunar Prospector and Lunar Reconnaissance Orbiter spacecraft, and NASA’s Moon Mineralogy Mapper instrument on board India’s Chandrayaan-I spacecraft. The team generated a map of likely mantle locations using Moon Mineralogy Mapper data to assess mineral composition and abundance, integrated with Lunar Prospector observations of elemental abundances, including markers of the last remaining liquid at the end of lunar magma ocean crystallization, and imagery and topography data from Lunar Reconnaissance Orbiter.

At around 1,600 miles (about 2,600 kilometers) across, the South Pole – Aitken basin is the largest confirmed impact structure on the Moon, and therefore is associated with the deepest depth of excavation of all lunar basins, so it’s the most likely place to find pieces of mantle, according to the team.

For years, scientists have been puzzled by a radioactive anomaly in the northwest quadrant of the South Pole – Aitken Basin on the lunar farside. The team’s analysis demonstrates that the composition of this anomaly is consistent with the “sludge” that forms in the uppermost mantle at the very end of magma ocean crystallization. Because this sludge is very dense, scientists have previously assumed that it should completely sink into the lower mantle early in lunar history.

“However, our more nuanced understanding from recent models and experiments indicates that some of this sludge gets trapped in the upper mantle, and later excavated by this vast impact basin,” said Moriarty. “Therefore, this northwest region of the South Pole – Aitken Basin is the best location to access excavated mantle materials currently on the lunar surface. Interestingly, some of these materials may also be present around the proposed Artemis and VIPER landing sites around the lunar South Pole.”

References:

“The search for lunar mantle rocks exposed on the surface of the Moon” by Daniel P. Moriarty III, Nick Dygert, Sarah N. Valencia, Ryan N. Watkins and Noah E. Petro, 3 August 2021, Nature Communications. DOI: 10.1038/s41467-021-24626-3

“Evidence for a Stratified Upper Mantle Preserved Within the South Pole-Aitken Basin” by D. P. Moriarty III, R. N. Watkins, S. N. Valencia, J. D. Kendall, A. J. Evans, N. Dygert and N. E. Petro, January 2021, Journal of Geophysical Research. DOI: 10.1029/2020JE006589

Running quantum software on a classical computer


Two physicists, from EPFL and Columbia University, have introduced an approach for simulating the quantum approximate optimization algorithm using a traditional computer. Instead of running the algorithm on advanced quantum processors, the new approach uses a classical machine-learning algorithm that closely mimics the behavior of near-term quantum computers.

In a paper published in Nature Quantum Information, EPFL professor Giuseppe Carleo and Matija Medvidović, a graduate student at Columbia University and at the Flatiron Institute in New York, have found a way to execute a complex quantum computing algorithm on traditional computers instead of quantum ones.

The specific “quantum software” they are considering is known as Quantum Approximate Optimization Algorithm (QAOA) and is used to solve classical optimization problems in mathematics; it’s essentially a way of picking the best solution to a problem out of a set of possible solutions. “There is a lot of interest in understanding what problems can be solved efficiently by a quantum computer, and QAOA is one of the more prominent candidates,” says Carleo.

Ultimately, QAOA is meant to help us on the way to the famed “quantum speedup”, the predicted boost in processing speed that we can achieve with quantum computers instead of conventional ones. Understandably, QAOA has a number of proponents, including Google, who have their sights set on quantum technologies and computing in the near future: in 2019 they created Sycamore, a 53-qubit quantum processor, and used it to run a task it estimated it would take a state-of-the-art classical supercomputer around 10,000 years to complete. Sycamore ran the same task in 200 seconds.

“But the barrier of “quantum speedup” is all but rigid and it is being continuously reshaped by new research, also thanks to the progress in the development of more efficient classical algorithms,” says Carleo.

In their study, Carleo and Medvidović address a key open question in the field: can algorithms running on current and near-term quantum computers offer a significant advantage over classical algorithms for tasks of practical interest? “If we are to answer that question, we first need to understand the limits of classical computing in simulating quantum systems,” says Carleo. This is especially important since the current generation of quantum processors operate in a regime where they make errors when running quantum “software”, and can therefore only run algorithms of limited complexity.

Using conventional computers, the two researchers developed a method that can approximately simulate the behavior of a special class of algorithms known as variational quantum algorithms, which are ways of working out the lowest energy state, or “ground state” of a quantum system. QAOA is one important example of such family of quantum algorithms, that researchers believe are among the most promising candidates for “quantum advantage” in near-term quantum computers.

The approach is based on the idea that modern machine-learning tools, e.g. the ones used in learning complex games like Go, can also be used to learn and emulate the inner workings of a quantum computer. The key tool for these simulations are Neural Network Quantum States, an artificial neural network that Carleo developed in 2016 with Matthias Troyer, and that was now used for the first time to simulate QAOA. The results are considered the province of quantum computing, and set a new benchmark for the future development of quantum hardware.

“Our work shows that the QAOA you can run on current and near-term quantum computers can be simulated, with good accuracy, on a classical computer too,” says Carleo. “However, this does not mean that alluseful quantum algorithms that can be run on near-term quantum processors can be emulated classically. In fact, we hope that our approach will serve as a guide to devise new quantum algorithms that are both useful and hard to simulate for classical computers.”

Reference:

Medvidović M, Carleo G. Classical variational simulation of the Quantum Approximate Optimization Algorithm. npj Quantum Inf. 2021;7(1):1-7. doi:10.1038/s41534-021-00440-z

NASA begins launch preparations for first mission to the Trojan asteroids


NASA's first spacecraft to explore the Trojan asteroids arrived Friday, July 30, at the agency's Kennedy Space Center (KSC) in Florida. It is now in a cleanroom at nearby Astrotech, ready to begin final preparations for its October launch.

The mission has a 23-day launch period beginning on October 16. Lucy will undergo final testing and fueling prior to being moved to its launch pad at Cape Canaveral Space Force Station.

"The coronavirus pandemic required us to re-engineer the way we conducted assembly, integration, and testing," said Donya Douglas-Bradshaw, Lucy project manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "When I think about where the project was a year ago and the challenges we faced, I couldn't be prouder of the entire team. The fact that the spacecraft is safely at KSC is a testament to the sacrifice and dedication shown by every member of the team and their families."

The Lucy mission is the first space mission to explore a diverse population of small bodies known as the Jupiter Trojan asteroids. These small bodies are remnants of our early solar system, now trapped in stable orbits associated with the giant planet Jupiter, forming two "swarms" that lead in front of and trail behind Jupiter in its path around the Sun. These orbits are clustered around stable points of gravitational equilibrium known as Lagrange Points.

Over its twelve-year primary mission, Lucy will explore a record-breaking number of asteroids, flying by one main belt asteroid and seven Trojan asteroids. Lucy also incorporates three Earth-gravity assists to reach the Trojan swarms and accomplish these targeted encounters.

The spacecraft was transported from Buckley Space Force Base in Aurora, Colorado, aboard a U.S. Air Force C-17 cargo plane. Lockheed Martin Space designed and built the spacecraft in its Littleton, Colorado, facility.

"It takes a lot of coordination and careful planning to get this spacecraft to its launch site, and I'm very proud of the team who worked so tirelessly through a global pandemic to get us to this moment," said Rich Lipe, Lockheed Martin Lucy program manager.

Over the weekend, the team transferred the spacecraft from its shipping container into the Astrotech cleanroom and performed post-ship inspections, confirming that Lucy arrived in good condition. The spacecraft is now ready to begin its final round of testing and pre-launch checks, which include software tests, instrument and powered functional tests, propulsion propellent load tests, telecommunication tests, and spacecraft self-tests.

"It is hard to believe that we are finally here after over seven years of hard work," says Hal Levison, Lucy's principal investigator from Southwest Research Institute in Boulder, Colorado. "We would not have made it without an extremely talented and dedicated team. It's now time to get Lucy into the sky so that it can deliver its revolutionary science about the origin of our planetary system."

Source: Link

Scientists Declare Climate Emergency: Earth’s Vital Signs Worsen Amid Business-As-Usual on Climate Change


Scientists reaffirm 2019 climate emergency declaration and again call for transformative change based on updated trends.

In 2019, a coalition of more than 11,000 scientists from across the globe declared a climate emergency and established a set of vital signs for the Earth in order to measure effective climate action. Now, twenty months later, a new study published on July 28, 2021, in BioScience finds that those vital signs reflect the consequences of unrelenting “business-as-usual” on climate change.

Specifically, authors of the study note an unprecedented surge in climate-related disasters since 2019, including devastating floods, record-shattering heat waves and extraordinary storms and wildfires. 2020 was the second hottest year in history, with the five hottest years on record all occurring since 2015. The study also notes that three key greenhouse gases — carbon dioxide, methane, and nitrous oxide — set records for atmospheric concentrations in 2020 and again in 2021. In April 2021, carbon dioxide concentration reached 416 parts per million, the highest monthly global average concentration ever recorded.

In response to these unprecedented findings and the ongoing climate crisis, the study calls for a phase-out of fossil fuels; strategic climate reserves for the storage of carbon and the protection of biodiversity; and a global price for carbon high enough to induce “decarbonization” across the industrial and consumption spectrum.

“The extreme climate events and patterns that we’ve witnessed over the last several years — not to mention the last several weeks — highlight the heightened urgency with which we must address the climate crisis,” said Dr. Philip Duffy, co-author of the study and Executive Director of the Woodwell Climate Research Center. “Without a plan for rapid decarbonization and large-scale investments in natural climate solutions, these climate change indicators will continue to worsen, pushing our essential ecosystems past the point of recovery.”

Other key vital signs the authors highlight:

  • The total burned area in the United States increased in 2020, reaching 4.1 million hectares — the second most ever recorded.

  • Brazilian Amazon annual forest loss rates increased in both 2019 and 2020, reaching a 12-year high of 1.11 million hectares deforested in 2020.

  • Ice sheets in Greenland and Antarctica have continued their precipitous loss of mass, while Arctic sea ice extent continues to decline to near all-time lows each summer.

  • Ocean acidification is near an all-time record. Together with thermal stress, it threatens the coral reefs that more than half a billion people depend on for food, tourism dollars and storm surge protection.

“There is growing evidence we are getting close to or have already gone beyond tipping points associated with important parts of the Earth system, including warm-water coral reefs, the Amazon rainforest and the West Antarctic and Greenland ice sheets,” said Dr. William Ripple, a lead author of the study and distinguished professor of ecology at Oregon State University (OSU). “We need to quickly change how we’re doing things, and new climate policies should be part of COVID-19 recovery plans wherever possible. It’s time for us to join together as a global community with a shared sense of cooperation, urgency and equity.”

Reference: 

World Scientists’ Warning of a Climate Emergency 2021 by William J Ripple, Christopher Wolf, Thomas M Newsome, Jillian W Gregg, Timothy M Lenton, Ignacio Palomo, Jasper A J Eikelboom, Beverly E Law, Saleemul Huq, Philip B Duffy and Johan Rockström, 28 July 2021, BioScience. DOI: 10.1093/biosci/biab079

NASA Says Cold Shadows on the Lunar Surface Can Explain Moon Water Mystery


The shadows cast by the roughness of the Moon’s surface create small cold spots for water ice to accumulate even during the harsh lunar daytime.

Scientists are confident that water ice can be found at the Moon’s poles inside permanently shadowed craters – in other words, craters that never receive sunlight. But observations show water ice is also present across much of the lunar surface, even during daytime. This is a puzzle: Previous computer models suggested any water ice that forms during the lunar night should quickly burn off as the Sun climbs overhead.

“Over a decade ago, spacecraft detected the possible presence of water on the dayside surface of the Moon, and this was confirmed by NASA’s Stratospheric Observatory for Infrared Astronomy [SOFIA] in 2020,” said Björn Davidsson, a scientist at NASA’s Jet Propulsion Laboratory in Southern California. “These observations were, at first, counterintuitive: Water shouldn’t survive in that harsh environment. This challenges our understanding of the lunar surface and raises intriguing questions about how volatiles, like water ice, can survive on airless bodies.”

In a new study, Davidsson and co-author Sona Hosseini, a research and instrument scientist at JPL, suggest that shadows created by the “roughness” of the lunar surface provide refuge for water ice, enabling it to form as surface frost far from the Moon’s poles. They also explain how the Moon’s exosphere (the tenuous gases that act like a thin atmosphere) may have a significant role to play in this puzzle.

Water Traps and Frost Pockets
Many computer models simplify the lunar surface, rendering it flat and featureless. As a result, it’s often assumed that the surface far from the poles heats up uniformly during lunar daytime, which would make it impossible for water ice to remain on the sunlit surface for long.

So how is it that water is being detected on the Moon beyond permanently shadowed regions? One explanation for the detection is that water molecules may be trapped inside rock or the impact glass created by the incredible heat and pressure of meteorite strikes. Fused within these materials, as this hypothesis suggests, the water can remain on the surface even when heated by the Sun while creating the signal that was detected by SOFIA.

But one problem with this idea is that observations of the lunar surface show that the amount of water decreases before noon (when sunlight is at its peak) and increases in the afternoon. This indicates that the water may be moving from one location to another through the lunar day, which would be impossible if they are trapped inside lunar rock or impact glass.

Davidsson and Hosseini revised the computer model to factor in the surface roughness apparent in images from the Apollo missions from 1969 to 1972, which show a lunar surface strewn with boulders and pockmarked with craters, creating lots of shady areas even near noon. By factoring this surface roughness into their computer models, Davidsson and Hosseini explain how it’s possible for frost to form in the small shadows and why the distribution of water changes throughout the day.

Because there is no thick atmosphere to distribute heat around the surface, extremely cold, shaded areas, where temperatures may plummet to about minus 350 degrees Fahrenheit (minus 210 degrees Celsius), can neighbor hot areas exposed to the Sun, where temperatures may reach as high as 240 Fahrenheit (120 Celsius).

As the Sun tracks through the lunar day, the surface frost that may accumulate in these cold, shaded areas is slowly exposed to sunlight and cycled into the Moon’s exosphere. The water molecules then refreeze onto the surface, reaccumulating as frost in other cold, shaded locations.

“Frost is far more mobile than trapped water,” said Davidsson. “Therefore, this model provides a new mechanism that explains how water moves between the lunar surface and the thin lunar atmosphere.”

A Closer Look
While this isn’t the first study to consider surface roughness when calculating lunar surface temperatures, previous work did not take into account how shadows would affect the capability of water molecules to remain on the surface during daytime as frost. This new study is important because it helps us to better understand how lunar water is released into, and removed from, the Moon’s exosphere.

“Understanding water as a resource is essential for NASA and commercial endeavors for future human lunar exploration,” Hosseini said. “If water is available in the form of frost in sunlit regions of the Moon, future explorers may use it as a resource for fuel and drinking water. But first, we need to figure out how the exosphere and surface interact and what role that plays in the cycle.”

To test this theory, Hosseini is leading a team to develop ultra-miniature sensors to measure the faint signals from water ice. The Heterodyne OH Lunar Miniaturized Spectrometer (HOLMS) is being developed to be used on small stationary landers or autonomous rovers – like JPL’s Autonomous Pop-Up Flat Folding Explorer Robot (A-PUFFER), for example – that may be sent to the Moon in the future to make direct measurements of hydroxyl (a molecule that contains one hydrogen atom and an oxygen atom).

Hydroxyl, which is a molecular cousin of water (a molecule with two hydrogen atoms and one oxygen atom), can serve as an indicator of how much water may be present in the exosphere. Both water and hydroxyl could be created by meteorite impacts and through solar wind particles hitting the lunar surface, so measuring the presence of these molecules in the Moon’s exosphere can reveal how much water is being created while also showing how it moves from place to place. But time is of the essence to make those measurements.

“The current lunar exploration by several nations and private companies indicates significant artificial changes to the lunar environment in the near future,” said Hosseini. “If this trend continues, we will lose the opportunity to understand the natural lunar environment, particularly the water that is cycling through the Moon’s pristine exosphere. Consequently, the advanced development of ultra-compact, high-sensitivity instruments is of critical importance and urgency.”

The researchers point out that this new study could help us better understand the role shadows play in the accumulation of water ice and gas molecules beyond the Moon, such as on Mars or even on the particles in Saturn rings.

The study was published in the Monthly Notices of the Royal Astronomical Society on August 2, 2021.

Reference: 

Implications of surface roughness in models of water desorption on the Moon by Björn J R Davidsson and Sona Hosseini, 2 August 2021, Monthly Notices of the Royal Astronomical Society.