Lunar Farside Gets Highest Resolution Look Yet from LRO

The lunar farside as never seen before! LROC WAC orthographic projection centered at 180° longitude, 0° latitude. Credit: NASA/GSFC/Arizona State University.

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The first time humans were able to catch a glimpse of the far side of the Moon was back in 1959 when the Soviet Luna 3 spacecraft sent back 29 grainy images taken during its successful loop around the Moon. “What a surprise – the farside was a different world, geologically,” said Mark Robinson, principal investigator for the camera on board the Lunar Reconnaissance Orbiter. “Unlike the widespread maria on the nearside, basaltic volcanism was restricted to a relatively few, smaller regions on the farside, and the battered highlands crust dominated.”

Since then, just a handful of spacecraft have taken images of the far side of the Moon, but now, Robinson has had a hand in creating the most detailed view yet of the farside of the Moon. A mosaic of the far side released today is comprised of over 15,000 Wide Angle Camera images acquired between November 2009 and February 2011.


“This WAC mosaic provides the most complete look at the morphology of the farside to date, and will provide a valuable resource for the scientific community,” Robinson wrote on the LROC website. “And it’s simply a spectacular sight!”

And how!

Every month, as LRO circles the Moon, the WAC gathers images to provide nearly complete coverage of the Moon under unique lighting. This mosaic knits together images all with similar lighting. As an added bonus the orbit-to-orbit image overlap provides stereo coverage, and even more images will be released on March 15.

“As the mission progresses, and our knowledge of the lunar photometric function increases, improved and new mosaics will be released!” Robinson said. “Work your way around the Moon with these six orthographic projections constructed from WAC mosaics.”

Click here for more stunning, high resolution views of the Moon.

Source: LROC

When Will We Return to the Moon and Who Will it Be?

At the end of the movie “Apollo 13,” when the character of Jim Lovell says “I look up at the Moon and wonder, when will we be going back, and who will that be?” he probably didn’t have anything like the Google Lunar X PRIZE in mind. Similarly, when the GLXP was announced back in 2007, the founders had no idea that nearly 30 teams would be vying for the $30 million in incentive prizes to return to the Moon’s surface with a robotic craft.

Will Pomerantz, the former Senior Director of Space Prizes from the X PRIZE Foundation recalled an advisory committee meeting several years ago before the prize was announced. “We went around the room and asked everyone to estimate how many teams are going to compete in this,” Pomerantz said. “The answers ranged from zero on the low end to maybe a dozen or fifteen at the absolute max and that probably came either for myself or from Peter Diamandis, our founder. The fact that we have almost thirty blows us away, and we couldn’t be more thrilled.”

The X PRIZE Foundation recently announced the official roster of 29 teams that will attempt to send a robot to the Moon that travels at least 500 meters and transmit video, images, and data back to the Earth. The organization says this signifies a “new era of exploration’s diverse and participatory nature.”

The teams are headquartered all over the world — seventeen different headquarter nations — and most of the teams are actually multinationals, so team members are working in almost seventy different countries on every continent except for Antarctica.

“This is going to be the first time anything has been on the lunar surface since the final Soviet robotic mission in 1976,” Pomerantz said and those of us in the states really haven’t seen any data directly from the lunar surface since 1972, so we think that there’s at a ton to be learned scientifically, but also there’s a huge inspirational factor there for people to be able to see those images again.”

Of course, the robotic missions being designed are much less complicated and expensive than a human mission to the Moon.

Synergy Moon's spherical rover. Credit: GLXP

The concepts range from snake-like robots that slither along the surface to ball-shaped vehicles that can shift their mass internally move along the lunar surface to small robotic vehicles – “not too much bigger than the cell phone you’ve got your pocket,” Pomeranzt said – to rovers that look very much NASA- or ESA-designed vehicles. Others won’t rove at all, but reignite their engines to take off and fly to another location. This may allow them to explore totally different types of terrain that is totally inaccessible to a rover.

The landing sites that the various teams are shooting for differ as well. “Essentially everyone is going on the near side for obvious communication reasons,” Pomerantz said. “Almost everyone is going in a fairly low latitude and going in the equatorial zones.”

There are bonus prizes of several million additional dollars for teams that can go to particular sites, such the South Pole, where they could possibly confirm the findings at the LCROSS impact site, or if they go back to visit one of the Apollo landing sites or one of the sites of a non-human mission.

“I know that causes some concern for some people,” Pomerantz said. “People very rightly want to make sure that we are being respectful of those treasured historical sites. But I think it is important to recognize that no one values those sites more than the men and women around the world who are dedicating their careers to getting back to the surface of the Moon. They absolutely understand that those are our valuable treasures that need to be respected but they also understand that there’s an enormous amount to be gained from going back and respectfully revisiting the. There is some very interesting science that we can do by going back and seeing how the site and how those materials have changed over the past forty years.”

Why offer a prize to return to the Moon?

“We want to open the space frontier in the way similar to what we did it for the first X PRZE, the Ansari X PRIZE,” Pomerantz said. “We want to make space exploration and lunar exploration in particular radically cheaper. We think when you create a much lower price point, when you bring the price of missions down to a tenth to what it historically has been or even a hundredth of what it historically has been, you’re opening it up to a huge variety of new customers, new science communities, new industries that just can’t exist at the current price points.”

All the teams have to come up with their own funding.

“This is really a cash on delivery kind of model,” Pomerantz said. “But we don’t want to pay people to try. There are enough other people out there that are funding people to try new things. We want to reward people upon success. That means that no matter how crazy an idea might seem today, if it happens to be the best one, then we’ll reward it.”

Right now, the prize money is set to expire by the end of 2015, but the GLXP organizers are quite confident that at least one of the 29 teams will successfully reach the Moon before then. And obviously, NASA is confident, as well, as the space agency is offering a program called the Innovative Lunar Demonstration and Data Program, which is essentially $30 million dollars worth of data purchases from commercial efforts that reach the Moon.

“This is NASA saying for first time ever we are able to buy data about conducting lunar missions and about the Moon itself, rather than having to go out and pay for the acquisition of that data directly on the hopes that it will work,” Pomerantz said. “This is a great buy for NASA and I think they are getting a tremendous value and is a great way for teams to show their investors and supporters that, hey we’ve got a willing customer here. And NASA is not afraid of us; this isn’t an ‘us versus them competition.’ This is an area where our success is their success and vice versa.

Pomerantz is leaving the X PRIZE Foundation to begin work with Virgin Galactic. “I’ve loved every minute of being with the X PRIZE, but this was an opportunity just too good to pass up and I’m extremely excited about it even though I’m sad to be leaving X PRIZE.”

For more information about GLXP, see their website. See the complete roster of competing teams here.

Listen to an interview with Pomerantz on the 365 Days of Astronomy website.

The Moon Just Got Bigger

Lunar Reconnaissance Orbiter Wide Angle Camera mosaic of the lunar nearside. Credit: NASA/GSFC/Arizona State University.

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Take a gander at this brand new image of the Moon from the Lunar Reconnaissance Orbiter, which is one of the largest and highest resolution images ever compiled of the near-side of the Moon. For two weeks in mid-December 2010, LRO’s orbit allowed the spacecraft to remain looking straight down. Gathering over 1,300 images during this time, LRO’s imaging run allowed the team to compile a monstrous 24,000 x 24,000 pixel mosaic from the Wide Angle Camera (WAC), with a resolution of approximately 145 meters per pixel. The detail is nothing short of spectacular.

You can go the LROC website and see a 1400 X 1400 version, another 1400 X 1400 version with labels, and the full version that you can “Zoomify” and see incredible detail like never before.

Source: LROC website.

The Moon Loves You

A heart-shaped crater in the Galilae region on the Moon. Credit: ASA/GSFC/Arizona State University; 3-D by Nathanial Burton-Bradford.

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Happy Valentines Day from everyone here at Universe Today, and the Moon, too. In 3-D, no less.

Thanks to Nathanial Burton-Bradford for sending us this image. He found it while searching through the Lunar Reconnaissance Orbiter Camera’s data set. Check out Nathanial’s Flickr page for larger versions of this one, and more. See the image below in its proper orientation for viewing in 3-D:

A heart-shaped crater in the Galilae region on the Moon. Credit: ASA/GSFC/Arizona State University; 3-D by Nathanial Burton-Bradford.

Interior of Subsurface Cave Imaged on the Moon

The LROC NAC acquired an oblique view of the Marius Hills pit with just the right angle to reveal an overhang, with a pit below, which is about 65 meters in diameter. Credit: NASA/GSFC/Arizona State University.

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Follow-up observations of a potential ‘skylight’ in a lava tube on the Moon has revealed a cavernous lunar pit in the Marius Hills region, with a view of the interior and bottom of the pit. The sun angle, camera angle and lighting conditions were just right for the Lunar Reconnaissance Orbiter camera to look all the way down to the floor of the pit. And this is no small hole in the ground — the LRO team says this pit is about 65 meters in diameter! This latest image confirms this object is actually a subsurface cave; a lava tube close to the surface where part of it has collapsed. These lava tubes could be great locations for lunar bases that could protect human explorers from dangers such as cosmic rays, meteorite impacts, and the extreme temperature differences between the lunar day and night.


This is the fourth time that this particular lunar pit has been imaged. Since LRO is constantly orbiting the Moon and it completes a full cycle of lunar imaging each month, the team can do follow up observations of previous discoveries and re-image targets under different lighting conditions.

An image taken about a year ago showing the dark entrance to the Marius Hills pit. Credit: NASA/GSFC/Arizona State University

Previous images had revealed the dark, cave-like entrance, and another showed part of the pit wall.
For this fourth imaging run, the spacecraft slewed 43° to the east and the solar incidence angle was 34° from vertical. This was just the right angle so that if there actually was an open lava tube extending horizontally its floor would be illuminated.

The LROC team hit paydirt (or pay-regolith, if you will).

With LRO’s Narrow Angle Camera, the team was able to image a few meters under the overhang to show the interior of this sublunarean void. With this oblique angle, they were also able to capture the layered nature of the mare bedrock in the pit walls. These exposed layers give scientists important clues as to how the vast mare were deposited.

The collection of images now verifies this is actually a cavernous subsurface cave. These pits had been predicted to exist, based on the understanding of the geomorphology of mare deposits and lava flow behavior on Earth, but never directly imaged before.

A graphic of the imaging geometry in cross section, which allows a view of the lava tube floor. Arizona State University.

The LROC team will be presenting their findings about this pit and others that have been imaged at the Lunar and Planetary Science Conference. You can read their abstract here. (pdf file).

See more about this new image at the LROC website.

Challenger Astronauts Memorialized on the Moon

Craters in the center of Apollo basin named after Space Shuttle Challenger astronauts. Credit: NASA/GSFC/Arizona State University.

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Shortly after the loss of the Space Shuttle Challenger in 1986, seven craters on the eastern rim of the Apollo basin were named after the crew: Gregory Jarvis, Christa McAuliffe, Ronald McNair, Ellison Onizuka, Judith Resnik, Dick Scobee, Michael Smith. The Lunar Reconnaissance Orbiter Wide Angle Camera recently took this image of the region. Below is a video from the Kaguya spacecraft flying over the area.

According to OnOrbit, the crater “Onizuka” is incorrectly identified in this video. Rather, “Onizuka” is the crater next and to the right of the one labeled in the video as “The Onizuka”.

The Apollo Basin is not where I would have guessed — the area around the Moon’s equator on the near side where all the Apollo landings took place — but instead is a 524 km-diameter impact basin located within the center of the the giant South Pole-Aitken basin, (36°S, 209°E).

See more about the image and explore the entire region with LROC’s “zoomify” feature at the LRO website.

Was the Apollo Program an Anomaly?

Dust flies from the tires of a moon buggy, driven by Apollo 17 astronaut Gene Cernan. These "rooster-tails" of dust caused problems. Credit: NASA

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How often have you heard (or thought) the sentiment that all NASA really needs is a President who will issue a bold challenge for the space agency, like Kennedy did in 1961, initiating the Apollo program to the Moon? Can we ever expect to witness such a call to action again?

“It is very unlikely,” said space historian and author Andrew Chaikin, who believes Apollo was an historical anomaly. “I think for many decades people saw Apollo as a model for how to do a space program; that you get a President to get up and make a challenge and the country follows along and does great things. But that was only true that one time in the context of the Cold War.”

We went to the Moon when we did not because we were a nation devoted to exploration, Chaikin believes, but because it seemed a politically important course of action in the context of our Cold War with the Soviet Union. “Once that was accomplished, then that political imperative evaporated,” he said.

On May 25, 1961, Kennedy announced his support for the Apollo program as part of a special address to a joint session of Congress:

Likely, we won’t hear any bold space-related challenge in tonight’s State of the Union Address by President Obama. Given the state of the economy, NASA might be facing a cut or freeze on their budget, a fact which might emphasize how unique an event the Apollo program ended up to be.

“What is required now is the development of technologies that will allow us to explore space in a sustainable way,” said Chaikin, author of “A Man on the Moon: The Voyages of the Apollo Astronauts,” who I interviewed for the NASA Lunar Science Institute podcast, “a way that won’t break the bank and will allow us to do more and more with reliable transportation systems that get us up into low Earth orbit. Then perhaps we can build the machines that can actually be stored in space to allow us to venture beyond low Earth orbit to the Moon and even further, to Mars and other destinations in the solar system.”

Chaikin said he’s actually very excited about the work being done in the private sector, such as by SpaceX, one of several commercial space companies trying to develop new transportation systems to provide sustainable hardware and sustainable architecture. “That can allow us to really get back in the game of exploring, not only with robots as we have been doing all along, but with humans again,” Chaikin said.

But Apollo’s uniqueness doesn’t mean it wasn’t important, or hasn’t left a lasting legacy for human spaceflight, and the human race in general.

Buzz Aldrin on the Moon
Buzz Aldrin on the Moon for Apollo 11. Credit: NASA

“Simply put Apollo was the opening act in a story that has no end,” Chaikin said. “It’s a story of human beings leaving their home planet and venturing out into the universe, and as far as we go into space in some distant epoch, when we are living in other star systems and venturing throughout the galaxy, Apollo will have been the first step, so it is absolutely monumental when you look at it in that scale. I think Apollo is a lasting inspiration about what humans can accomplish when they work together.”

Apollo also showed people that anything was possible. “There was a phrase that went into our language after Apollo, and that was ‘If we can put a man on the Moon, why can’t we…’ fill in the blank,” said Chaikin. “The spirit that humans can overcome monumental challenges by working together, I think, is a valid legacy of Apollo culturally.”

Chaikin said Apollo was also important because of the technology development it spurred.

“A lot of the challenges that Apollo presented forced the industries to accelerate their development,” he said, “particularly in microelectronics. It is not that NASA invented all of the microelectronics that we use today but rather that the requirements of building a moon-ship and cramming it with all of the electronics that it needed to do its job required the electronics industry to miniaturize at a faster pace, it required the development of computers that could fit on a spacecraft, it required all kinds of analytical techniques and real-time tracking of the spacecraft as it went to and from the Moon. The legacy today is all the communications technologies and information processing technology that we are surrounded by. That really got an amazing jump start as part of the Apollo program.”

Earthrise from Apollo 8
Earthrise from Apollo 8

And Apollo also affected our culture, in unique ways we observe even today. How often have you seen the “Earthrise” image taken by Apollo 8 or the picture of Buzz Aldrin standing on the Moon or other Apollo-related imagery in non-space-related venues?

“We got to a place where humans had never been before,” Chaikin said, “and the other lasting legacy is the view that we got from that ‘mountaintop,’ of our Earth as a very precious oasis of life in space, and a world that really is to be cherished and protected.”

We knew even as it was happening, Chaikin said, that seeing our world floating alone in space was perhaps the most profound impact of the voyage.

“In fact, if you look at the front page of the New York Times the very day after Frank Borman and his crew became the first humans to orbit the Moon,” Chaikin said, “you will see an essay by a poet named Archibald MacLeish talking about the impact of that view and the perspective of us as ‘brothers in the eternal cold riding on spaceship Earth.’ So this is one of the things sets Apollo apart from other earlier explorations is that we were experiencing it as it happened through live television and we were actually absorbing and processing the impact in real time.”

Launch of Apollo 8 lunar orbit mission
Launch of Apollo 8 lunar orbit mission

But then, humans being as attention-challenged as we are, it didn’t take very long for all of it to become old hat and to kind of recede into history. “And that is where we are today,” Chaikin said.

That being said, Chaikin does not see the Moon as a “been there, done that” world.

“As you know, we’ve been finding frozen water at the poles of the Moon and this is a completely different view of the Moon than we had 40 years ago,” Chaikin said. “And there are more and more intricacies that we are finding all the time. The Moon itself is a Rosetta Stone for deciphering the history of the solar system, and is profoundly valuable world for us on so many levels. And it is a spectacular place. The Apollo astronauts – I’ve spent hours talking to all of them about the Moon, about the experience of being on the Moon and they just say it is a spectacular place.”

“It is too bad that the political impetus for going to the Moon was so short-lived because it was part of the Cold war,” Chaikin continued, “and looking back we can see why that was the case. It is too bad we lost interest in the Moon and it has taken us so long to turn our attention back to the Moon and all it has to offer.”


Listen to the entire interview with Chaikin on the NLSI podcast, which can also be heard on the 365 Days of Astronomy podcast.

For more information about Andrew Chaikin, see his website, andrewchaikin.com

Sideways Glance for LRO Provides Spectacular View of Aitken Crater

LROC NAC oblique view of Aitken crater, including the central peak, and northern walls. The scene is about 30 km wide. Credit: NASA/GSFC/Arizona State University

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When people look out of the corner of their eyes, they often don’t see things very clearly. But that’s not the case for the Lunar Reconnaissance Orbiter’s cameras. Occasionally LRO’s cameras are commanded to look off to the side at extreme angles, and the results, thought not frequent, are incredible. This stunning image of the central uplifts inside of Aitken Crater was taken on January 11, 2011. Here, LROC was looking over the southwest ridge of its central peak, and in the distance the lower portion of the northeastern walls of Aitken crater itself is just visible. To quote the Fred Haise character in the movie Apollo 13, this image makes me tempted to take a spacecraft down and “do some prospecting.” …


Mostly, LRO looks straight down for its images, but has collected a limited number of these oblique views of the lunar surface. They are very useful for engineering purposes, but also provide a unique view for visualizing key geologic features on the lunar surface — like Aitken. And usually, they are beautiful shots.

Aitken Crater(~135 km in diameter) is of interest because it is is one of the most geologically diverse settings on the farside. The floor of the crater is covered in mare basalt, which are quite rare on the lunar farside, and lunar scientists are still trying to figure out why. Aitken is also on the northern rim of the great South Pole-Aitken basin, the oldest and largest impact basin on the Moon and one of the oldest and largest impact basins in the whole Solar System! Further exploration of the South Pole-Aitken basin is one of the highest priorities for planetary science in the next decade.

Check out more images from this view of Aitken Crater at the LROC website, where you can “Zoomify” and take a closer look.

Moon’s Water Came From Comets, Study Says

Distance Between the Earth and Moon
The Earth rising over the Moon's surface, as seen by the Apollo 8 mission. Credit: NASA

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A new study reveals that the water within the Apollo Moon rocks – and within the Moon itself — likely came from comets bombarding the nascent lunar surface, shortly after it formed following an impact event with a young Earth and Mars-sized protoplanet. The recent findings of abundant water at the lunar poles by the LCROSS impactor and across the Moon’s surface by various spacecraft have turned the long-standing notion of a dry Moon on its head, and the past year and a half, researchers have been trying to determine where this unexpected water came from.

“The water we are looking at is internal,” said Larry Taylor from the University of Tennessee, Knoxville, a member of an international team. “It was put into the moon during its initial formation, where it existed like a melting pot in space, where cometary materials were added in at small yet significant amounts.”

Using secondary ion mass spectrometry, the researchers measured the water signatures within rocks returned from the Apollo 11, 12, 14, and 17 missions that landed on the moon between 1969 and 1972. They found the chemical properties of the lunar water were very similar to signatures seen in three different comets: Hyakutake, Hale-Bopp and Halley.

The team found significant water in the lunar mineral apatite from both mare and highlands rocks, which indicates “a role for water during all phases of the Moon’s magmatic history,” the team wrote in their paper. “Variations of hydrogen isotope ratios in apatite suggest sources for water in lunar rocks could come from the lunar mantle, solar wind protons and comets. We conclude that a significant delivery of cometary water to the Earth–Moon system occurred shortly after the Moon-forming impact.”

Even though comet impacts may also have created the Earth’s oceans, Taylor said the water signatures from the mass spectrometer show that the water on the Earth and Moon are different, as apatite has a ratio of the deuterium and hydrogen that are distinctive from those in normal Earth water.

“The values of deuterium/hydrogen (D/H) that we measure in apatite in the Apollo rock samples is clearly distinguishable from water from the Earth, mitigating against this being some sort of contamination on Earth,” said James Greenwood of Wesleyan University, who led the research team.

Initially after the Apollo program, the Moon was believed to extremely dry. Many of the rocks returned by the astronauts and also the Soviet Luna program contained trace water or minor hydrous minerals, but those signatures were attributed to terrestrial contamination since most of the boxes of the Apollo program used to bring the Moon rocks to Earth leaked. This led the scientists to assume that the trace amounts of water they found came from Earth air that had entered the containers. The assumption remained that, outside of possible ice at the moon’s poles, there was no water on the moon.

Forty years later, a trio of spacecraft found evidence of water across the surface of the Moon: The Chandrayaan-1 spacecraft’s Moon Mineralogy Mapper (M Cubed) found that infrared light was being absorbed near the lunar poles at wavelengths consistent with hydroxyl- and water-bearing materials. A spectrometer on the re-purposed Deep Impact probe showed strong evidence that water is ubiquitous over the surface of the moon, and archival data from a Cassini Moon flyby also agreed with the finding that water appears to be widespread across the lunar surface.

“This discovery forces us to go back to square one on the whole formation of the Earth and moon,” said Taylor. “Before our research, we thought the Earth and moon had the same volatiles after the Giant Impact, just at greatly different quantities. Our work brings to light another component in the formation that we had not anticipated — comets.”

Taylor added that the existence of hydrogen and oxygen – water – on the moon can literally serve as a launch pad for further space exploration.

“This water could allow the moon to be a gas station in the sky,” said Taylor. “Spaceships use up to 85 percent of their fuel getting away from Earth’s gravity. This means the moon can act as a stepping stone to other planets. Missions can fuel up at the moon, with liquid hydrogen and liquid oxygen from the water, as they head into deeper space, to other places such as Mars.”

Their paper, “Extraterrestrial Hydrogen Isotope Composition of Water in Lunar Rocks” was published in the journal, Nature Geoscience.

Sources: Nature Geoscience, EurekAlert

Apollo Data Retooled to Provide Precise Readings on Moon’s Core

A new look at old data has given scientists more insight into the Moon's core. Credit: Science

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A new look at data from seismic experiments left on the Moon by Apollo astronauts has given researchers a better understanding of the lunar interior. The Moon’s core appears to be very similar to the Earth’s — with a solid inner core and molten liquid outer core — and its size is right in the middle of previous estimates.

“While the presence of a liquid core had previously been inferred from other geophysical measurements, we have made the first direct seismic observation of a liquid outer core,” said Dr. Renee Weber, a planetary scientist at NASA’s Marshall Space Flight Center, who led the team of researchers.

Apollo Passive Seismic Experiment from Apollo 15. Credit: NASA

The Apollo Passive Seismic Experiment measured seismic waves on the Moon and consisted of four seismometers deployed on the lunar near side during the Apollo missions between 1969 and 1972. The instruments continuously recorded ground motion until late-1977. But the data was thought to be rather weak because of the small number of stations, the lack of observation of far-side events, and interference from “moon quakes.” As this was the only direct measurements from the Moon available, various researchers differed on key characteristics such as the core’s radius, composition, and state (i.e., whether it was solid or molten.)

“The moon’s deepest interior, especially whether or not it has a core, has been a blind spot for seismologists,” said Ed Garnero, a professor at Arizona State University and a member of the research team. “The seismic data from the old Apollo missions were too noisy to image the moon with any confidence.”

Weber and her colleagues re-analyzed the Apollo data using a method usually used for processing seismic data on Earth. Called array processing, seismic recordings are added together or “stacked” in a special way and studied together. The multiple recordings processed together allow researchers to extract very faint signals. The depth of layers that reflect seismic energy can be identified, ultimately signifying the composition and state of matter at varying depths.

This method can enhance faint, hard-to-detect seismic signals by adding seismograms together.

“If seismic wave energy goes down and bounces off of some deep interface at a particular depth, like the Moon’s core-mantle boundary, then that signal “echo” should be present in all the recordings, even if below the background noise level,” said Patty Lin, a postdoctoral candidate at ASU and another member of the team. “But when we add the signals together, that core reflection amplitude becomes visible, which lets us map the deep Moon.”

Weber told Universe Today that the shear waves do not penetrate fluid regions. “So while we have observed compression reflections off the solid inner core, we have not (as expected) observed shear reflections off the inner core, since that energy is reflected at the outer core layer.”

Recent studies suggested the Moon had a relatively small iron-rich core, sized between about 250 and 430 km, or roughly 15 to 25% of its 1,737.1 km mean radius. The new measurements put the core slightly larger.
“We have placed the core-mantle boundary at a radius of 330 km, roughly 19% of the Moon’s mean radius,” Weber said in an email.

The iron-rich core has a solid inner ball nearly 240 km (150 miles) in radius, and an 90 km (55-mile) thick outer fluid shell.

The new research also points to volatile-depleted interior, with the lunar core containing a small percentage of light elements such as sulfur, similar to light elements in Earth’s core – sulfur, oxygen and others.

The retooled 30-year-old data also appears to confirm the the leading theory of how the Moon formed.

“The presence of a melt layer and a molten outer core supports the widely-accepted large-impact model of lunar formation, which predicts that the Moon could have formed in a completely molten state,” Weber said.