Still hot inside the Moon: Tidal heating in the deepest part of the lunar mantle

This is an artist's conception of internal structure of the Moon based on this science result.
Credit: Image courtesy of National Astronomical Observatory of Japan

An international research team, led by Dr. Yuji Harada from Planetary Science institute, China University of Geosciences, has found that there is an extremely soft layer deep inside the Moon and that heat is effectively generated in the layer by the gravity of Earth.

The results were derived by comparing the deformation of the Moon as precisely measured by Kaguya (SELENE, Selenological and Engineering Explorer) and other probes with theoretically calculated estimates. These findings suggest that the interior of the Moon has not yet cooled and hardened, and also that it is still being warmed by the effect of Earth on the Moon. This research provides a chance to reconsider how both Earth and the Moon have been evolving since their births through mutual influence until now.

When it comes to clarifying how a celestial body like a planet or a natural satellite is born and grows, it is necessary to know as precisely as possible its internal structure and thermal state. How can we know the internal structure of a celestial body far away from us? We can get clues about its internal structure and state by thoroughly investigating how its shape changes due to external forces. The shape of a celestial body being changes by the gravitational force of another body is called tide. For example, the ocean tide on Earth is one tidal phenomenon caused by the gravitational force between the Moon and the Sun, and Earth. Sea water is so deformable that its desplacement can be easily observed. How much a celestial body can be deformed by tidal force, in this way, depends on its internal structure, and especially on the hardness of its interior. Conversely, it means that observing the degree of deformation enables us to learn about the interior, which is normally not directly visible to the naked eye.

The Moon is no exception; we can learn about the interior of our natural satellite from its deformation caused by the tidal force of Earth. The deformation has already been well known through several geodetic observations (*1). However, models of the internal structure of the Moon as derived from past research could not account for the deformation precisely observed by the above lunar exploration programs.

Therefore, the research team performed theoretical calculations to understand what type of internal structure of the Moon leads to the observed change of the lunar shape.
What the research team focused on is the structure deep inside the Moon. During the Apollo program, seismic observations (*2) were carried out on the Moon. One of the analysis results concerning the internal structure of the Moon based upon the seismic data indicates that the satellite is considered to consist mainly of two parts: the "core," the inner portion made up of metal, and the "mantle," the outer portion made up of rock. The research team has found that the observed tidal deformation of the Moon can be well explained if it is assumed that there is an extremely soft layer in the deepest part of the lunar mantle. The previous studies indicated that there is the possibility that a part of the rock at the deepest part inside the lunar mantle may be molten. This research result supports the above possibility since partially molten rock becomes softer. This research has proven for the first time that the deepest part of the lunar mantle is soft, based upon the agreement between observation results and the theoretical calculations.

Furthermore, the research team also clarified that heat is efficiently generated by the tides in the soft part, deepest in the mantle. In general, a part of the energy stored inside a celestial body by tidal deformation is changed to heat. The heat generation depends on the softness of the interior. Interestingly, the heat generated in the layer is expected to be nearly at the maximum when the softness of the layer is comparable to that which the team estimated from the above comparison of the calculations and the observations. This may not be a coincidence. Rather, the layer itself is considered to be maintained as the amount of the heat generated inside the soft layer is exquisitely well balanced with that of the heat escaping from the layer. Whereas previous research also suggests that some part of the energy inside the Moon due to the tidal deformation is changed to heat, the present research indicates that this type of energy conversion does not uniformly occur in the entire Moon, but only intensively in the soft layer. The research team believes that the soft layer is now warming the core of the Moon as the core seems to be wrapped by the layer, which is located in the deepest part of the mantle, and which efficiently generates heat. They also expect that a soft layer like this may efficiently have warmed the core in the past as well.

Concerning the future outlook for this research, Dr. Yuji Harada, the principle investigator of the research team, said, "I believe that our research results have brought about new questions. For example, how can the bottom of the lunar mantle maintain its softer state for a long time? To answer this question, we would like to further investigate the internal structure and heat-generating mechanism inside the Moon in detail. In addition, another question has come up: how has the conversion from the tidal energy to the heat energy in the soft layer affected the motion of the Moon relative to the Earth, and also the cooling of the Moon? We would like to resolve those problems as well so that we can thoroughly understand how the Moon was born and has evolved."

Another investigator, Prof. Junichi Haruyama of Institute of Space and Aeronautical Science, Japan Aerospace Exploration Agency, mentioned the significance of this research, saying, "A smaller celestial body like the Moon cools faster than a larger one like the Earth does. In fact, we had thought that volcanic activities on the Moon had already come to a halt. 

Therefore, the Moon had been believed to be cool and hard, even in its deeper parts. However, this research tells us that the Moon has not yet cooled and hardened, but is still warm. It even implies that we have to reconsider the question as follows: How have the Earth and the Moon influenced each other since their births? That means this research not only shows us the actual state of the deep interior of the Moon, but also gives us a clue for learning about the history of the system including both the Earth and the Moon."

The scientific paper on which this article is based appears in the Nature Geoscience.

Strong tidal heating in an ultralow-viscosity zone at the core-mantle boundary of the Moon.
Note:
*1: Geodetic observation. (This is also called "selenodetic" observation as it is for the Moon.)
Observational results on gravity and rotation of the Moon are used in this research. Precise measurements of the lunar gravity and rotation enable us to know how our natural satellite is deformed by tidal forces.

The gravity of the Moon can be measured by tracking the motion of a satellite orbiting the Moon. This is because the motion of the satellite is influenced by lunar gravity. The motion of the satellite orbiting the Moon can be determined by using radio waves between the Earth and the satellite, and between multiple satellites around the Moon. The gravity of the Moon changes when it deforms due to tidal forces. The change in gravity caused by the lunar deformation due to the tidal force is extremely small, but when the change in location of the orbiter can be determined precisely enough, it is possible to accurately detect the change in lunar gravity caused by the deformation due to the tidal force. During the last several years, the degree of the lunar deformation caused by the tidal forces has been determined by several orbiters, for example, Kaguya from Japan, Chang'e-1 from China, and Lunar Reconnaissance Orbiter (LRO) and Gravity Recovery and Interior Laboratory (GRAIL) from the USA.

The rotation of the Moon can be observed by monitoring the change in position of a kind of mirror placed in several locations on the lunar surface. The same side of the Moon is almost always facing the Earth, but strictly speaking, it changes by a slight amount according to the lunar orbit around the Earth. This means that the locations of the mirrors with respect to the Earth also changes over time. If this change in position is precisely measured, it can also be determined how the direction of the lunar axis changes. This slight change of direction also depends on the deformation caused by the tidal force. It can be seen, therefore, how the Moon deforms due to the tidal force once the change in the axis is measured precisely. Some of the above-mentioned mirrors have been left on the surface of the Moon in the framework of the lunar exploration programs led by the USA or the former USSR several decades ago, such as the Apollo program. The degree of change in the location of each mirror on the Moon can be determined by using laser beams emitted from the Earth. This experiment still continues to be carried out even today.

*2: Seismic observation. (Quakes on the Moon are also called "moonquakes." )

There are seismic activities not only on the Earth, but also on the Moon. As part of the Apollo program in the past, seismometers were placed on the lunar surface for seismological measurements. Waves induced by quakes measured with seismometers suggest what the internal structure of a celestial body is like. The behavior of the seismic waves is very important for understanding how the hardness inside the celestial body will change in accordance with the depth. In particular, the present research considered the following two previous analysis results in order to theoretically calculate the lunar deformation caused by the tidal force.

The first one is the existence of the area deep inside the Moon where the seismic waves become drastically weaker. It is generally known that the energy of the seismic waves tends to reduce more in softer solids, especially when they contain liquids. Therefore, the deepest part of the lunar mantle is softer than the shallower part. Also, a portion of the rocks is thought to be melted.

The second one is the existence of areas deep inside the Moon whose interfaces reflect the 
seismic waves. Three boundaries are considered to exist. Two of them are like the ones in the Earth: one separating the solid inner core and the liquid outer core, and the other one separating the outer core and the mantle. The last boundary is considered to correspond to the one in the mantle separating the solid area and the partially molten area mentioned above.

Source: National Astronomical Observatory of Japan

Solving the mystery of the 'Man in the Moon': Volcanic plume, not an asteroid, likely created the moon's largest basin

The moon as observed in visible light (left), topography (center, where red is high and blue is low), and the GRAIL gravity gradients (right). The Procellarum region is a broad region of low topography covered in dark mare basalt. The gravity gradients reveal a giant rectangular pattern of structures surrounding the region. Credit: NASA/Colorado School of Mines/MIT/JPL/Goddard Space Flight Center

New data obtained by NASA's GRAIL mission reveals that the Procellarum region on the near side of the moon -- a giant basin often referred to as the "man in the moon" -- likely arose not from a massive asteroid strike, but from a large plume of magma deep within the moon's interior.

The Procellarum region is a roughly circular, volcanic terrain some 1,800 miles in diameter -- nearly as wide as the United States. One hypothesis suggested that it was formed by a massive impact, in which case it would have been the largest impact basin on the moon. Subsequent asteroid collisions overprinted the region with smaller -- although still large -- basins.

Now researchers from MIT, the Colorado School of Mines, and other institutions have created a high-resolution map of the Procellarum, and found that its border is not circular, but polygonal, composed of sharp angles that could not have been created by a massive asteroid. Instead, researchers believe that the angular outline was produced by giant tension cracks in the moon's crust as it cooled around an upwelling plume of hot material from the deep interior.

Maria Zuber, the E.A. Griswold Professor of Geophysics and also MIT's vice president for research, says that as cracks occurred, they formed a "plumbing system" in the moon's crust through which magma could meander to the surface. Magma eventually filled the region's smaller basins, creating what we see today as dark spots on the near side of the moon -- features that have inspired the popular notion of a "man in the moon."

"A lot of things in science are really complicated, but I've always loved to answer simple questions," says Zuber, who is principal investigator for the GRAIL (Gravity Recovery and Interior Laboratory) mission. "How many people have looked up at the moon and wondered what produced the pattern we see -- let me tell you, I've wanted to solve that one!"

Zuber and her colleagues publish their results this week in the journal Nature.

Making Less of an Impact

The team mapped the Procellarum region using data obtained by GRAIL -- twin probes that orbited the moon from January to December 2012. Researchers measured the distance between the probes as they chased each other around the moon. As the leading probe passed over a region of lower density, it briefly slowed, caught by that region's gravitational pull. As the probes circled the moon, they moved in accordion fashion, the distance between them stretching and contracting in response to varying gravitational attraction due to the mass variations in the lunar interior.

From the variable distance between the probes, Zuber and her team determined the strength of gravity across the moon's surface, creating a highly detailed map, which they then used to determine where the lunar crust thickens and thins.

From this mapping, the researchers observed that the rim of the Procellarum region is composed of edges that abut at 120-degree angles. As asteroid impacts tend to produce circular or elliptical craters, Zuber says the Procellarum's angular shape could not have been caused by an impact.

Instead, the team explored an alternative scenario: Some time after the moon formed and cooled, a large plume of molten material rose from the lunar interior, around where the Procellarum region is today. The steep difference in temperature between the magma plume and the surrounding crust caused the surface to contract over time, creating a pattern of fractures that provided a conduit for molten material to rise to the surface.

To test the hypothesis, the researchers modeled the region's gravitational signal if it were to contain volcanic intrusions -- magma that seeped up to just beneath the moon's surface and, over time, cooled and crystallized. The resulting simulation matched the gravity signal recorded by GRAIL, supporting the idea that the Procellarum was caused by a magma plume, and not an asteroid.

"How such a plume arose remains a mystery," Zuber says. "It could be due to radioactive decay of heat-producing elements in the deep interior. Or, conceivably, a very early large impact triggered the plume. But in the latter case, all evidence for such an impact has been completely erased. People who thought that all this volcanism was related to a gigantic impact need to go back and think some more about that."

Source: Nasa

Moon mission: Images of LADEE's impact crater captured

LRO has imaged the LADEE impact site on the eastern rim of Sundman V crater. The image was created by ratioing two images, one taken before the impact and another afterwards. The bright area highlights what has changed between the time of the two images, specifically the impact point and the ejecta. Credit: NASA/Goddard/Arizona State University

NASA'S Lunar Reconnaissance Orbiter (LRO) spacecraft has spied a new crater on the lunar surface; one made from the impact of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) mission.

"The Lunar Reconnaissance Orbiter Camera (LROC) team recently developed a new computer tool to search Narrow Angle Camera (NAC) before and after image pairs for new craters, the LADEE impact event provided a fun test, said Mark Robinson, LROC principal investigator from Arizona State University in Tempe. "As it turns there were several small surface changes found in the predicted area of the impact, the biggest and most distinctive was within 968 feet (295 meters) of the spot estimated by the LADEE operations team. What fun!"

The LADEE mission ended on April 18, 2014, with the spacecraft's planned impact into the eastern rim of Sundman V crater on the far side of the moon.

LRO has imaged the LADEE impact site on the eastern rim of Sundman V crater. The image was created by ratioing two images, one taken before the impact and another afterwards. 

The bright area highlights what has changed between the time of the two images, specifically the impact point and the ejecta.

LADEE's engines fired April 11, 2014, to perform a final orbital maintenance maneuver and adjust to guarantee it would impact on the farside of the moon and away from the Apollo landing sites. Over a seven-day period, LADEE's orbit decreased and the spacecraft orbited very low to the surface and close to the walls of lunar craters and mountain ridges to give the team a chance to collect valuable science data. Finally, LADEE impacted the eastern rim of Sundman V crater on April 18. The impact site is about half a mile (780 meters) from the crater rim with an altitude of about 8,497 feet (2,590 meters) and was only about two tenths of a mile (300 meters) north of the location mission controllers predicted based on tracking data.

The impact crater is small, less than ten feet (three meters) in diameter, barely resolvable by the LROC NAC. The crater is small because the spacecraft -- compared to most celestial impacts -- was not traveling very fast, approximately 3,800 miles per hour (1,699 meters per second) and had a low mass and a low density. The size of the impact crater made it hard to identify among the myriad of small fresh craters on the lunar surface. Images acquired of the impact region before the impact, were compared with images obtained after the impact to identify the crater.

Since the NAC images are so large (250 mega-pixels) and the new crater is so small, the LROC team co-registered the before and after images (called a temporal pair) and then divided the before image by the after image. By doing this, changes to the surface become evident.

The ejecta from the impact forms a triangular pattern primarily downrange to the west, extending about 656-984 feet (200-300 meters) from the impact site. There is also a small triangular area of ejecta up range but it extends only about 66-98 feet (20-30 meters). The ejecta pattern is oriented northwest, consistent with the direction the spacecraft was traveling when it impacted the surface.

"I'm happy that the LROC team was able to confirm the LADEE impact point," said Butler Hine, LADEE project manager at Ames Research Center in Moffett Field, California. "It really helps the LADEE team to get closure and know exactly where the product of their hard work wound up."

LADEE launched Sept. 6, 2013 from Pad 0B at the Mid-Atlantic Regional Spaceport, at NASA's Wallops Flight Facility, Wallops Island, Virginia. LADEE gathered detailed information about the structure and composition of the thin lunar atmosphere and determining whether dust is being lofted into the lunar sky.

LRO launched September 18, 2009. LRO continues to bring the world astounding views of the lunar surface and a sizable collection of lunar data for research.

LRO recently received a second two-year extended mission. Under the extended mission, LRO will study the seasonal volatile cycle; determine how many small meteorites are currently hitting the moon and their effects; characterize the structure of the lunar regolith; investigate the moon's interaction with the space environment; and reveal more about the lunar interior using observations of the moon's surface.

"With LRO, NASA will study our nearest celestial neighbor for at least two more years," said John Keller, LRO project scientist from NASA's Goddard Space Flight Center in Greenbelt, Maryland. "LRO continues to increase our understanding of the moon and its environment."

Source: nasa

Turning the Moon into a cosmic ray detector

Artists rendition of the SKA. Credit: SKA Organisation

Scientists from the University of Southampton are to turn the Moon into a giant particle detector to help understand the origin of Ultra-High-Energy (UHE) cosmic rays -- the most energetic particles in the Universe.

The origin of UHE cosmic rays is one of the great mysteries in astrophysics. Nobody knows where these extremely rare cosmic rays come from or how they get their enormous energies. Physicists detect them on Earth at a rate of less than one particle per square kilometre per century.

Dr Justin Bray, a Research Fellow in Cosmic Magnetism at the University of Southampton, is lead author of a proposal to use the Square Kilometre Array (SKA), set to become the largest and most sensitive radio telescope in the world, to detect vastly more UHE cosmic rays by using the Moon as a giant cosmic ray detector.

On Earth, physicists detect these high-energy particles when they hit the upper atmosphere triggering a cascade of secondary particles that generate a short and faint burst of radio waves only a few nanoseconds long.

It is this signal that astronomers hope to pick up from the Moon, but as these signals are so short and faint no radio telescope on Earth is currently capable of picking them up.
With its large collecting area and high sensitivity, the SKA will be able to detect these signals using the visible lunar surface -- millions of square kilometres -- giving the researchers access to more data about UHE cosmic rays than they have ever had before.

The current largest detector on Earth is the Pierre Auger Observatory in Argentina that covers an area of 3,000 square kilometres, about the size Luxembourg. The SKA will be more than 10 times larger (33,0000 square kilometres) and researchers hope to detect around 165 UHE cosmic rays a year from the Moon compared to the 15-a-year currently observed.

Dr Bray announced details of the project at a major SKA conference in Italy.. He says: "Cosmic rays at these energies are so rare that you need an enormous detector to collect a significant number of them -- but the moon dwarfs any particle detector that has been built so far. If we can make this work, it should give us our best chance yet to figure out where they're coming from."

Dr Bray is working with Professor Anna Scaife, also from Physics and Astronomy at the University of Southampton, who leads the development of the SKA's Imaging Pipeline as part of the Science Data Processor (SDP) work package consortium.

Professor Scaife says: "Defining science goals for the telescope is crucial for ensuring that the appropriate technical capabilities are considered during the design phase."

Using a network of radio antennas in the Southern hemisphere, the SKA will advance our understanding of how the Universe evolved and challenge Einstein's theory of relativity. With receivers across Australia and Africa, its dishes and antennas will provide detailed information on the large scale 3D structure of the Universe.

When operational in the early 2020's, the SKA radio telescope will produce more than 10 times the current global traffic of the Internet in its internal telecommunications system. To play back a single day's worth of SKA data on an MP3 player would take about two million years.

Source: University of Southampton

Keeping upright: How much gravity is enough?

The experimental setup. (A) Participants lay on a human centrifuge with their feet out so that centripetal force from the centrifuge produced a centripetal force simulating gravity along the long axis of the body. (B) They viewed a screen mounted above their heads which presented a scene tilted at 112° relative to their bodies. The direction signaled by each cue to upright is indicated by arrow: red, vision; green, simulated gravity and blue, the body. (C) Thus, the three vectors involved in determining the perceptual upright (body, gravity and vision) could be dissociated.
 Credit: Harris et al; doi:10.1371/journal.pone.0106207.g001

Keeping upright in a low-gravity environment is not easy, and NASA documents abound with examples of astronauts falling on the lunar surface. Now, a new study by an international team of researchers led by York University professors Laurence Harris and Michael Jenkin, published today in PLOS ONE, suggests that the reason for all these moon mishaps might be because its gravity isn't sufficient to provide astronauts with unambiguous information on which way is "up."

"The perception of the relative orientation of oneself and the world is important not only to balance, but also for many other aspects of perception including recognizing faces and objects and predicting how objects are going to behave when dropped or thrown," says Harris. "Misinterpreting which way is up can lead to perceptual errors and threaten balance if a person uses an incorrect reference point to stabilize themselves."

Using a short-arm centrifuge provided by the European Space Agency, the international team simulated gravitational fields of different strengths, and used a York-invented perceptual test to measure the effectiveness of gravity in determining the perception of up. 

The team found that the threshold level of gravity needed to just influence a person's orientation judgment was about 15 per cent of the level found on Earth -- very close to that on the moon.

The team also found that Martian gravity, at 38 per cent of that on Earth, should be sufficient for astronauts to orient themselves and maintain balance on any future manned missions to Mars.

"If the brain does not sense enough gravity to determine which way is up, astronauts may get disoriented, which can lead to errors like flipping switches the wrong way or moving the wrong way in an emergency," says Jenkin. "Therefore, it's crucial to understand how the direction of up is established and to establish the relative contribution of gravity to this direction before journeying to environments with gravity levels different to that of Earth."

This work builds upon results obtained in long-duration microgravity by Harris and Jenkin and other members of York's Centre for Vision Research on board the International Space Station during the Bodies in the Space Environment project, funded by the Canadian Space Agency.

Source: York University

Every full moon, Landsat looks to the moon

Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting information on Earth.
Credit: NASA's Goddard Space Flight Center

Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting land-cover information of the sunny side of Earth below.

These monthly lunar scans are key to ensuring the land-imaging instrument aboard Landsat 8 is detecting light consistently. For this, engineers need a consistent source of light to measure. And while there are some spots on Earth -- like the Sahara Desert or other arid sites -- that reflect a relatively stable amount of light, nothing on our planet beats the moon, which lacks an atmosphere and has an unchanging surface, barring the odd meteorite.

We really wanted something we could trust for Landsat 8," said Brian Markham, leader of the calibration team for Landsat 8, which was built and launched by NASA and is now operated by the U.S. Geological Survey. "We do have Earth sites we look at for calibration. But the precision with which you can track things by using the Earth, because of the atmosphere, is not as good as the moon."

Landsat 8's Operational Land Imager, or OLI, collects information on the visible, near infrared and shortwave-infrared light reflecting off Earth's surface. Each wavelength of light provides information about the ground surface below. OLI has 14 detector modules, each of which contains hundreds of individual detectors that record different spectral bands. The calibration team at Goddard and the U.S. Geological Survey's EROS facility in South Dakota is tasked with making sure each of those detectors register light consistently over time.

Aboard the spacecraft, lamps provide light to calibrate OLl's detectors, but the lamps aren't perfect. On the Landsat 7 satellite, the lamps started to fade before the detectors did. Another option, solar diffusers, which use indirect sunlight, can darken as well.

"Everything else we've tried to use to monitor the stability of our instruments has often not been as good as the instruments themselves," Markham said. But the moon is a steady, not-too-bright light in the sky. "As long as we know what its illumination conditions are, we can trend our instrument performance to it because we trust its stability."

So Landsat 8 planners designed this latest satellite to image the moon as a baseline calibration. If, during these lunar tests, the OLI detectors indicate that the moon is getting slightly duller or brighter, then the Goddard scientists will know the instrument -not the moon -- is off. With that data, they can adjust the algorithms that calculate land cover information during Landsat's regular Earth-observation orbits.

It's a fairly complicated operation to scan the moon each month, said Susan Good, a flight dynamics engineer at Goddard who works with Landsat 8.

"There are 14 detector modules," Good said, "each of these has to scan the same path along the moon, so that you collect exactly the same data on each sensor."

The flight dynamics software determines precisely where the spacecraft will need to point during a lunar calibration. The timing is set for just after the moon is completely full. Then, as Landsat 8 passes over Antarctica and heads north in Earth's shadow, the spacecraft maneuvers to the precise location to start the first scan across the lunar surface.

It executes tiny and precise scans to take seven or eight passes across the moon -- each one angled so that a different detector is centered on the moon. This takes about 18 minutes, by which time the spacecraft has almost reached the Arctic. So it maneuvers back to point at 

Earth, and complete its day-lit imaging. Then, Landsat 8 pivots to face the moon again, completing additional passes to test the remaining detectors. After two orbits, the lunar calibration is complete.

In Landsat 8's first year, the lunar calibration tests show that the detectors are stable, Markham said, within a fraction of a percent. If the lunar calibrations and other tests show the detectors are off, the scientists can adjust the calculations that turn the raw Landsat data into information on land cover brightness, maintaining their accuracy.

Since the regular checks on Landsat 8's performance, Good jokes that she will never look at the full moon the same. "I think oh, we're having a lunar calibration," she said. "I always know what Landsat' 8's doing when the moon is full."

Source: Nasa

Solar photons drive water off the moon

Lunar sample in vacuum. A lunar sample in a ultra-high vacuum system is hit with ultraviolet (157 nm) photons to simulate conditions in space. Credit: Image courtesy of Georgia Institute of Technology

Water is thought to be embedded in the moon's rocks or, if cold enough, "stuck" on their surfaces. It's predominantly found at the poles. But scientists probably won't find it intact on the sunlit side.

New research at the Georgia Institute of Technology indicates that ultraviolet photons emitted by the sun likely cause H2O molecules to either quickly desorb or break apart. The fragments of water may remain on the lunar surface, but the presence of useful amounts of water on the sunward side is not likely.

The Georgia Tech team built an ultra-high vacuum system that simulates conditions in space, then performed the first-ever reported measurement of the water photodesorption cross section from an actual lunar sample. The machine zapped a small piece of the moon with ultraviolet (157 nm) photons to create excited states and watched what happened to the water molecules. They either came off with a cross section of ~ 6 x 10−19 cm2 or broke apart with a cross section of ~ 5 x 10−19 cm2.. According to the team's measurements, approximately one in every 1,000 molecules leave the lunar surface simply due to absorption of UV light.

Georgia Tech's cross section values can now be used by scientists attempting to find water throughout the solar system and beyond.

"The cross section is an important number planetary scientists, astrochemists and the astrophysics community need for models regarding the fate of water on comets, moons, asteroids, other airless bodies and interstellar grains," said Thomas Orlando, the Georgia Tech professor who led the study.

The number is relatively large, which establishes that solar UV photons are likely removing water from the moon's surface. This research, which was carried out primarily by former Georgia Tech Ph.D. student Alice DeSimone, indicates the cross sections increase even more with decreasing water coverage. That's why it's not likely that water remains intact as H2O on the sunny side of the moon. Orlando compares it to sitting outside on a summer day.

"If a lot of sunlight is hitting me, the probability of me getting sunburned is pretty high," said Orlando, a professor in the School of Chemistry and Biochemistry and School of Physics. "It's similar on the moon. There's a fixed solar flux of energetic photons that hit the sunlit surface, and there's a pretty good probability they remove water or damage the molecules."

The result, according to Orlando, is the release of molecules such as H2O, H2 and OH as well as the atomic fragments H and O. The research is published in two companion articles in the Journal of Geophysical Research: Planets. The first discusses the water photodesorption. The second paper details the photodissociation of water and the O(3PJ) formation on a lunar impact melt breccia.

Orlando is the associate director of Georgia Tech's Center for Space Technology and Research (C-STAR). C-STAR is an interdisciplinary research center that serves to organize, integrate and facilitate the impact of Georgia Tech's space science and space technology research activities. The center brings together a wide range of Georgia Tech faculty, active in space science and space technology research, and functions as the Institute's focal point for growth of the space industry in the state of Georgia.

Source: Georgia Institute of Technology

New isotopic evidence supporting moon formation via Earth collision with planet-sized body

The moon. A new series of measurements of oxygen isotopes provides increasing evidence that the moon formed from the collision of the Earth with another large, planet-sized astronomical body, around 4.5 billion years ago. Credit: NASA/JPL

A new series of measurements of oxygen isotopes provides increasing evidence that the Moon formed from the collision of Earth with another large, planet-sized astronomical body, around 4.5 billion years ago.

This work will be published in Science on 6th June, and will be presented to the Goldschmidt geochemistry conference in California on 11th June.

Most planetary scientists believe that the Moon formed from an impact between  Earth and a planet-sized body, which has been given the name Theia. Efforts to confirm that the impact had taken place had centred on measuring the ratios between the isotopes of oxygen, titanium, silicon and others. 

These ratios are known to vary throughout the solar system, but their close similarity between Earth and Moon conflicted with theoretical models of the collision that indicated that the Moon would form mostly from Theia, and thus would be expected to be compositionally different from Earth.

Now a group of German researchers, led by Dr. Daniel Herwartz, have used more refined techniques to compare the ratios of 17O/16O in lunar samples, with those from Earth. The team initially used lunar samples which had arrived on Earth via meteorites, but as these samples had exchanged their isotopes with water from Earth, fresher samples were sought. These were provided by NASA from the Apollo 11, 12 and 16 missions; they were found to contain significantly higher levels of 17O/16O than their Earthly counterparts.

Dr Herwartz said "The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia. Theia seems to have been similar to what we call E-type chondrites.If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth. The next goal is to find out how much material of Theia is in the Moon."

Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.

The team used an advanced sample preparation technique before measuring the samples via stable isotope ratio mass spectrometry, which showed a 12 parts per million (± 3 ppm) difference in 17O/16O ratio between Earth and Moon.

Source: European Association of Geochemistry

NASA missions let scientists see moon's dancing tide from orbit

Illustration of Earth as seen from the moon. The gravitational tug-of-war between Earth and the moon raises a small bulge on the moon. The position of this bulge shifts slightly over time.
Credit: NASA's Goddard Space Flight Center

Scientists combined observations from two NASA missions to check out the moon's lopsided shape and how it changes under Earth's sway -- a response not seen from orbit before.

The team drew on studies by NASA's Lunar Reconnaissance Orbiter, which has been investigating the moon since 2009, and by NASA's Gravity Recovery and Interior Laboratory, or GRAIL, mission. Because orbiting spacecraft gathered the data, the scientists were able to take the entire moon into account, not just the side that can be observed from Earth.

"The deformation of the moon due to Earth's pull is very challenging to measure, but learning more about it gives us clues about the interior of the moon," said Erwan Mazarico, a scientist with the Massachusetts Institute of Technology in Cambridge, Mass., who works at NASA's Goddard Space Flight Center in Greenbelt, Md.

The lopsided shape of the moon is one result of its gravitational tug-of-war with Earth. The mutual pulling of the two bodies is powerful enough to stretch them both, so they wind up shaped a little like two eggs with their ends pointing toward one another. On Earth, the tension has an especially strong effect on the oceans, because water moves so freely, and is the driving force behind tides.

Earth's distorting effect on the moon, called the lunar body tide, is more difficult to detect, because the moon is solid except for its small core. Even so, there is enough force to raise a bulge about 20 inches (51 centimeters) high on the near side of the moon and similar one on the far side.

The position of the bulge actually shifts a few inches over time. Although the same side of the moon constantly faces Earth, because of the tilt and shape of the moon's orbit, the side facing Earth appears to wobble. From the moon's viewpoint, Earth doesn't sit motionless but moves around within a small patch of sky. The bulge responds to Earth's movements like a dance partner, following wherever the lead goes.

"If nothing changed on the moon -- if there were no lunar body tide or if its tide were completely static -- then every time scientists measured the surface height at a particular location, they would get the same value," said Mike Barker, a Sigma Space Corporation scientist based at Goddard and co-author of the new study, which is available online in Geophysical Research Letters.

A few studies of these subtle changes were conducted previously from Earth. But not until LRO and GRAIL did satellites provide enough resolution to see the lunar tide from orbit.

To search for the tide's signature, the scientists turned to data taken by LRO's Lunar Orbiter Laser Altimeter, or LOLA, which is mapping the height of features on the moon's surface. 

The team chose spots that the spacecraft has passed over more than once, each time approaching along a different flight path. More than 350,000 locations were selected, covering areas on the near and far sides of the moon.

The researchers precisely matched measurements taken at the same spot and calculated whether the height had risen or fallen from one satellite pass to the next; a change indicated a shift in the location of the bulge.

A crucial step in the process was to pinpoint exactly how far above the surface LRO was located for each measurement. To reconstruct the spacecraft's orbit with sufficient accuracy, the researchers needed the detailed map of the moon's gravity field provided by the GRAIL mission.

"This study provides a more direct measurement of the lunar body tide and much more comprehensive coverage than has been achieved before," said John Keller, LRO project scientist at Goddard.

The good news for lunar scientists is that the new results are consistent with earlier findings.

The estimated size of the tide confirmed the previous measurement of the bulge. The other value of great interest to researchers is the overall stiffness of the moon, known as the Love number h2, and this was also similar to prior results.

Having confirmation of the previous values -- with significantly smaller errors than before -- will make the lunar body tide a more useful piece of information for scientists.

"This research shows the power of bringing together the capabilities of two missions. The extraction of the tide from the LOLA data would have been impossible without the gravity model of the moon provided by the GRAIL mission," said David Smith, the principal investigator for LRO's LOLA instrument and the deputy principal investigator for the GRAIL mission. Smith is affiliated with Goddard and the Massachusetts Institute of Technology.

Source: nasa

Water in moon rocks provides clues and questions about lunar history

This shows secondary electron image of pits left by ion microprobe analyses of a heterogeneous apatite grain in Apollo sample 14321, 1047. Water has now been detected in apatite in many different lunar rock types. Credit: Katharine L. Robinson, University of Hawaii, HIGP

A recent review of hundreds of chemical analyses of Moon rocks indicates that the amount of water in the Moon's interior varies regionally -- revealing clues about how water originated and was redistributed in the Moon. These discoveries provide a new tool to unravel the processes involved in the formation of the Moon, how the lunar crust cooled, and its impact history.

This is not liquid water, but water trapped in volcanic glasses or chemically bound in mineral grains inside lunar rocks. Rocks originating from some areas in the lunar interior contain much more water than rocks from other places. The hydrogen isotopic composition of lunar water also varies from region to region, much more dramatically than in Earth.

The present consensus is that the Moon formed as the result of a giant impact of an approximately Mars-sized planetesimal with the proto-Earth. The water in the Moon is a tracer of the processes that operated in the hot, partly silicate gas, partly magma disk surrounding Earth after that impact.

The source of the Moon's water has important implications for determining the source of Earth's water, which is vital to life. There are two options: either, water was inherited by the Moon from Earth during the Moon-forming impact, or it was added to the Moon later by comets or asteroids. It might also be a combination of these two processes.

"Basically, whatever happened to the Moon also happened to the Earth," said Katharine Robinson, lead author of the study and Graduate Assistant at the University of Hawai'i -- Mānoa (UHM) School of Ocean and Earth Science and Technology.

Robinson and Researcher G. Jeffrey Taylor, both at the UHM Hawai'i Institute of Geophysics and Planetology, compiled water measurements from lunar samples performed by colleagues from around the world, as well as their own. Specifically, they measured hydrogen and its isotope, deuterium (hydrogen with an extra neutron in its nucleus) with ion microprobes, which use a focused beam of ions to sputter ions from a small rock sample into a mass spectrometer. The ratio of hydrogen to deuterium can indicate the source of the water or trace magmatic processes in the lunar interior.

When water was first discovered in lunar samples in 2008, it was very surprising because from the time Apollo astronauts brought lunar samples, scientists thought that the Moon contained virtually no water.

"This was consistent with the idea that blossomed during the Origin of the Moon conference in Kona in 1984 -- that the Moon formed by a giant impact with the still-growing Earth, leading to extensive loss of volatile chemicals. Our work is surprising because it shows that lunar formation and accretion were more complex than previously thought," said Robinson.

The study of water in the Moon is still quite new, and many rocks have not yet been studied for water. The HIGP researchers have a new set of Apollo samples from NASA that they will be studying in the next few months, looking for additional clues about the early life of Earth and the Moon.

Source: University of Hawaii ‑ SOEST

First broadband wireless connection ... to the moon: Record-shattering Earth-to-Moon uplink

The ground terminal, with the sun reflecting off of the solar windows of the uplink telescopes, is shown. Credit: Robert LaFon, NASA/GSFC

If future generations were to live and work on the moon or on a distant asteroid, they would probably want a broadband connection to communicate with home bases back on Earth. They may even want to watch their favorite Earth-based TV show. That may now be possible thanks to a team of researchers from the Massachusetts Institute of Technology's (MIT) Lincoln Laboratory who, working with NASA last fall, demonstrated for the first time that a data communication technology exists that can provide space dwellers with the connectivity we all enjoy here on Earth, enabling large data transfers and even high-definition video streaming.

At CLEO: 2014, being held June 8-13 in San Jose, California, USA, the team will present new details and the first comprehensive overview of the on-orbit performance of their record-shattering laser-based communication uplink between the moon and Earth, which beat the previous record transmission speed last fall by a factor of 4,800. Earlier reports have stated what the team accomplished, but have not provided the details of the implementation.

"This will be the first time that we present both the implementation overview and how well it actually worked," says Mark Stevens of MIT Lincoln Laboratory. "The on-orbit performance was excellent and close to what we'd predicted, giving us confidence that we have a good understanding of the underlying physics," Stevens says.

The team made history last year when their Lunar Laser Communication Demonstration (LLCD) transmitted data over the 384,633 kilometers between the moon and Earth at a download rate of 622 megabits per second, faster than any radio frequency (RF) system. They also transmitted data from Earth to the moon at 19.44 megabits per second, a factor of 4,800 times faster than the best RF uplink ever used.

"Communicating at high data rates from Earth to the moon with laser beams is challenging because of the 400,000-kilometer distance spreading out the light beam," Stevens says. "It's doubly difficult going through the atmosphere, because turbulence can bend light -- causing rapid fading or dropouts of the signal at the receiver."

To outmaneuver problems with fading of the signal over such a distance, the demonstration uses several techniques to achieve error-free performance over a wide range of optically challenging atmospheric conditions in both darkness and bright sunlight. A ground terminal at White Sands, New Mexico, uses four separate telescopes to send the uplink signal to the moon. Each telescope is about 6 inches in diameter and fed by a laser transmitter that sends information coded as pulses of invisible infrared light. The total transmitter power is the sum of the four separate transmitters, which results in 40 watts of power.

The reason for the four telescopes is that each one transmits light through a different column of air that experiences different bending effects from the atmosphere, Stevens says. This increases the chance that at least one of the laser beams will interact with the receiver, which is mounted on a satellite orbiting the moon. This receiver uses a slightly narrower telescope to collect the light, which is then focused into an optical fiber similar to fibers used in terrestrial fiber optic networks.

From there, the signal in the fiber is amplified about 30,000 times. A photodetector converts the pulses of light into electrical pulses that are in turn converted into data bit patterns that carry the transmitted message. Of the 40-watt signals sent by the transmitter, less than a billionth of a watt is received at the satellite -- but that's still about 10 times the signal necessary to achieve error-free communication, Stevens says.

Their CLEO: 2014 presentation will also describe how the large margins in received signal level can allow the system to operate through partly transparent thin clouds in Earth's atmosphere, which the team views as a big bonus.

"We demonstrated tolerance to medium-size cloud attenuations, as well as large atmospheric-turbulence-induced signal power variations, or fading, allowing error-free performance even with very small signal margins," Stevens says.

While the LLCD design is directly relevant for near-Earth missions and those out to Lagrange points -- areas where the forces between rotating celestial bodies are balanced, making them a popular destination for satellites -- the team predicts that it's also extendable to deep-space missions to Mars and the outer planets.

Presentation SM4J.1, titled "Overview and On-orbit Performance of the Lunar Laser Communication Demonstration Uplink," will take place Monday, June 9.

Source: The Optical Society

NASA completes LADEE mission with planned impact on moon's surface

An artist's concept of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft seen orbiting near the surface of the moon. Credit: NASA Ames/Dana Berry

Ground controllers at NASA's Ames Research Center in Moffett Field, Calif., have confirmed that NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the surface of the moon, as planned, between 9:30 and 10:22 p.m. PDT Thursday, April 17.

LADEE lacked fuel to maintain a long-term lunar orbit or continue science operations and was intentionally sent into the lunar surface. The spacecraft's orbit naturally decayed following the mission's final low-altitude science phase.

During impact, engineers believe the LADEE spacecraft, the size of a vending machine, broke apart, with most of the spacecraft's material heating up several hundred degrees -- or even vaporizing -- at the surface. Any material that remained is likely buried in shallow craters.

"At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour -- about three times the speed of a high-powered rifle bullet," said Rick Elphic, LADEE project scientist at Ames. "There's nothing gentle about impact at these speeds -- it's just a question of whether LADEE made a localized craterlet on a hillside or scattered debris across a flat area. It will be interesting to see what kind of feature LADEE has created."

In early April, the spacecraft was commanded to carry out maneuvers that would lower its closest approach to the lunar surface. The new orbit brought LADEE to altitudes below one mile (two kilometers) above the lunar surface. This is lower than most commercial airliners fly above Earth, enabling scientists to gather unprecedented science measurements.

On April 11, LADEE performed a final maneuver to ensure a trajectory that caused the spacecraft to impact the far side of the moon, which is not in view of Earth or near any previous lunar mission landings. LADEE also survived the total lunar eclipse on April 14 to 15. This demonstrated the spacecraft's ability to endure low temperatures and a drain on batteries as it, and the moon, passed through Earth's deep shadow.

In the coming months, mission controllers will determine the exact time and location of LADEE's impact and work with the agency's Lunar Reconnaissance Orbiter (LRO) team to possibly capture an image of the impact site. Launched in June 2009, LRO provides data and detailed images of the lunar surface.

"It's bittersweet knowing we have received the final transmission from the LADEE spacecraft after spending years building it in-house at Ames, and then being in constant contact as it circled the moon for the last several months," said Butler Hine, LADEE project manager at Ames.

Launched in September 2013 from NASA's Wallops Flight Facility in Virginia, LADEE began orbiting the moon Oct. 6 and gathering science data Nov. 10. The spacecraft entered its science orbit around the moon's equator on Nov. 20, and in March 2014, LADEE extended its mission operations following a highly successful 100-day primary science phase.

LADEE also hosted NASA's first dedicated system for two-way communication using laser instead of radio waves. The Lunar Laser Communication Demonstration (LLCD) made history using a pulsed laser beam to transmit data over the 239,000 miles from the moon to the Earth at a record-breaking download rate of 622 megabits-per-second (Mbps). In addition, an error-free data upload rate of 20 Mbps was transmitted from the primary ground station in New Mexico to the Laser Communications Space Terminal aboard LADEE.

LADEE gathered detailed information about the structure and composition of the thin lunar atmosphere. In addition, scientists hope to use the data to address a long-standing question: Was lunar dust, electrically charged by sunlight, responsible for the pre-sunrise glow seen above the lunar horizon during several Apollo missions?

"LADEE was a mission of firsts, achieving yet another first by successfully flying more than 100 orbits at extremely low altitudes," said Joan Salute, LADEE program executive, at NASA Headquarters in Washington. "Although a risky decision, we're already seeing evidence that the risk was worth taking."

A thorough understanding of the characteristics of our nearest celestial neighbor will help researchers understand other bodies in the solar system, such as large asteroids, Mercury and the moons of outer planets.

NASA also included the public in the final chapter of the LADEE story. A "Take the Plunge" contest provided an opportunity for the public to guess the date and time of the spacecraft's impact via the internet. Thousands submitted predictions. NASA will provide winners a digital congratulatory certificate.

NASA's Science Mission Directorate in Washington funds the LADEE mission. Ames was responsible for spacecraft design, development, testing and mission operations, in addition to managing the overall mission. NASA's Goddard Space Flight Center in Greenbelt, Md., managed the science instruments, technology demonstration payload and science operations center, and provided mission support. Goddard also manages the LRO mission. 

Wallops was responsible for launch vehicle integration, launch services and operations. NASA's Marshall Space Flight Center in Huntsville, Ala., managed LADEE within the Lunar Quest Program Office.

Source: NASA