GRAIL Data Points To Possible Lava Tubes On The Moon

For years, scientists have been hunting for the stable lava tubes that are believed to exist on the Moon. A remnant from the Moon’s past, when it was still volcanically active, these underground channels could very well be an ideal location for lunar colonies someday. Not only would their thick roofs provide naturally shielding from solar radiation, meteoric impacts, and extremes in temperature. They could also be pressurized to create a breathable environment.

But until now, evidence of their existence has been inferred from surface features such as sinuous rilles – channel-like depressions that run along the surface that indicate the presence of subterranean lava flows – and holes in the surface (aka. “skylights”). However, recent evidence presented at the 47th Lunar and Planetary Science Conference (LPSC) in Texas indicates that one such stable lava tube could exist in the once-active region known as Marius Hills.

Continue reading “GRAIL Data Points To Possible Lava Tubes On The Moon”

There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

Every year since 1970, astronomers, geologists, geophysicists, and a host of other specialists have come together to participate in the Lunar and Planetary Science Conference (LPCS). Jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA’s Johnson Space Center (JSC), this annual event is a chance for scientists from all around the world to share and present the latest planetary research concerning Earth’s only moon.

This year, one of the biggest attention-grabbers was the findings presented on Tuesday, March 17th by a team of students from Purdue University. Led by a graduate student from the university’s Department of Earth, Atmospheric and Planetary Sciences, the study they shared indicates that there may be stable lava tubes on the moon, ones large enough to house entire cities.

In addition to being a target for future geological and geophysical studies, the existence of these tubes could also be a boon for future human space exploration. Basically, they argued, such large, stable underground tunnels could provide a home for human settlements, shielding them from harmful cosmic radiation and extremes in temperature.

The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed (NASA/JAXA)
The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA

Lava tubes are natural conduits formed by flowing lava that is moving beneath the surface as a result of a volcanic eruption. As the lava moves, the outer edges of it cools, forming a hardened, channel-like crust which is left behind once the lava flow stops. For some time, Lunar scientists have been speculating as to whether or not lava flows happen on the Moon, as evidenced by the presence of sinuous rilles on the surface.

Sinuous rilles are narrow depressions in the lunar surface that resemble channels, and have a curved paths that meanders across the landscape like a river valley. It is currently believed that these rilles are the remains of collapsed lava tubes or extinct lava flows, which is backed up by the fact they usually begin at the site of an extinct volcano.

Those that have been observed on the Moon in the past range in size of up to 10 kilometers in width and hundreds of kilometers in length. At that size, the existence of a stable tube – i.e. one which had not collapsed to form a sinuous rille – would be large enough to accommodate a major city.

For the sake of their study, the Purdue team explored whether lava tubes of the same scale could exist underground. What they found was that the stability of a lava tube depended on a number of variables- including width, roof thickness and the stress state of the cooled lava. he researchers also modeled lava tubes with walls created by lava placed in one thick layer and with lava placed in many thin layers.

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. (Purdue University/courtesy of David Blair)
The inside of a theoretical lunar lava tube, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair

David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.

Our work is somewhat unique in that we’ve combined the talents of people from various Departments at Purdue,” Blair told Universe Today via email. “With guidance from Prof. Bobet (a civil engineering professor) we’ve been able to incorporate a modern understanding of rock mechanics into our computer models of lava tubes to see how they might actually fail and break under lunar gravity.”

For the sake of their research, the team constructed a number of models of lava tubes of different sizes and with different roof thicknesses to test for stability. This consisted of them checking each model to see if it predicted failure anywhere in the lava tube’s roof.

“What we found was surprising,” Blair continued, “in that much larger lava tubes are theoretically possible than what was previously thought. Even with a roof only a few meters thick, lava tubes a kilometer wide may be able to stay standing. The reason why, though, is a little less surprising. The last work we could find on the subject is from the Apollo era, and used a much simpler approximation of lava tube shape – a flat beam for a roof.

 Mons Rümker rise on the Oceanus Procellarum was taken from the Apollo 15 while in lunar orbit.
Mons Rümker, an extinct volcanic formation on the Moon’s surface, as imaged by the Apollo 15 spacecraft while in orbit. Credit: NASA

The study he refers to, “On the origin of lunar sinuous rilles“, was published in 1969 in the journal Modern Geology. In it, professors Greeley, Oberbeck and Quaide advanced the argument that sinuous rilles formation was tied to the collapse of lava flow tubes, and that stable ones might still exist. Calculating for a flat-beam roof, their work found a maximum lava tube size of just under 400 m.

“Our models use a geometry more similar to what’s seen in lava tubes on Earth,” Blair said, “a sort of half-elliptical shape with an arched roof. The fact that an arched roof lets a larger lava tube stay standing makes sense: humans have known since antiquity that arched roofs allow tunnels or bridges to stay standing with wider spans.”

The Purdue study also builds on previous studies conducted by JAXA and NASA where images of “skylights” on the Moon – i.e. holes in the lunar surface – confirmed the presence of caverns at least a few tens of meters across. The data from NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) – which showed big variations in the thickness of the Moon’s crust  is still being interpreted, but could also be an indication of large subsurface recesses.

As a result, Blair is confident that their work opens up new and feasible explanations for many different types of observations that have been made before. Previously, it was unfathomable that large, stable caverns could exist on the Moon. But thanks to his team’s theoretical study, it is now known that under the proper conditions, it is least possible.

The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic
NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) mission calculated the thickness of the moon’s crust. Credit: NASA/JPL-Caltech/S. Miljkovic

Another exciting aspect that this work is the implications it offers for future exploration and even colonization on the Moon. Already, the issue of protection against radiation is a big one. Given that the Moon has no atmosphere, colonists and agricultural operations will have no natural shielding from cosmic rays.

“Geologically stable lava tubes would absolutely be a boon to human space exploration,” Blair commented. “A cavern like that could be a really ideal place for building a lunar base, and generally for supporting a sustained human presence on the Moon. By going below the surface even a few meters, you suddenly mitigate a lot of the problems with trying to inhabit the lunar surface.”

Basically, in addition to protecting against radiation, a subsurface base would sidestep the problems of micrometeorites and the extreme changes in temperature that are common on the lunar surface. What’s more, stable, subsurface lava tubes could also make the task of pressurizing a base for human habitation easier.

“People have studied and talked about all of these things before,” Blair added, “but our work shows that those kinds of opportunities could potentially exist – now we just have to find them. Humans have been living in caves since the beginning, and it might make sense on the Moon, too!”

In addition to Melosh, Blair and Bobet, team members include Loic Chappaz and Rohan Sood, graduate students in the School of Aeronautics and Astronautics; Kathleen Howell, Purdue’s Hsu Lo Professor of Aeronautical and Astronautical Engineering; Andy M. Freed, an associate professor of earth, atmospheric and planetary sciences; and Colleen Milbury, a postdoctoral research associate in the Department of Earth, Atmospheric and Planetary Sciences.

Further Reading: Purdue News

You Can Vote to Name America’s New Rocket from ULA

Help ULA name America’s next rocket to space. Credit: ULA
Voting Details below
Watch ULA’s March 25 Delta Launch Live – details below
Update 3/26: 2 new names have been added to the voting list – Zeus and Vulcan !
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United Launch Alliance (ULA) is asking the public for your help in naming their new American made rocket, now under development that “represents the future of space”- and will replace the firms current historic lines of Atlas and Delta rocket families that began launching back near the dawn of the space age.

Eagle, Freedom or GalaxyOne – those are the names to choose from for the next two weeks, from now until April 6.

UPDATE 3/26: 2 new names have been added to the voting list – Zeus and Vulcan !

ULA says the names were selected from a list of over 400 names submitted earlier this year by ULA’s 3400 employees and many space enthusiasts.

ULA has set up a simple voting system whereby you can vote for your favorite name via text or an online webpage.

Currently dubbed the “Next Generation Launch System,” or NGLS, ULA’s new president and CEO Tory Bruno is set to unveil the next generation rockets design and name at the National Space Symposium on April 13 in Colorado Springs, Colorado.

“ULA’s new rocket represents the future of space – innovative, affordable and reliable,” said Bruno, in a statement.

“More possibilities in space means more possibilities here on earth. This is such a critical time for space travel and exploration and we’re excited to bring all of America with us on this journey into the future.”

The NGLS is ULA’s response to what’s shaping up as a no holds barred competition with SpaceX for future launch contracts where only the innovative and those who dramatically cut the cost of access to space will survive.

The first flight of the NGLS is slated for 2019.

Here’s how you can cast your vote for America’s next rocket to April 6, 2015:

Visit the website: http://bit.ly/rocketvote

OR

Voters can text 22333 to submit a vote for their favorite name. The following key can be used to text a vote:

• ULA1 for “Eagle”
• ULA2 for “Freedom”
• ULA3 for “GalaxyOne”

3/26 Update: Zeus and Vulcan have been added to the voting list

One small step for ULA, one giant leap for space exploration. Vote to name America’s next ride to space: Eagle, Freedom, or GalaxyOne? #rocketvote http://bit.ly/rocketvote
One small step for ULA, one giant leap for space exploration. Vote to name America’s next ride to space: Eagle, Freedom, or GalaxyOne? #rocketvote http://bit.ly/rocketvote

“Name America’s next ride to space. Vote early, vote often … ” says Bruno.

I have already voted – early and often.

Over 11,000 votes were tallied in just the first day.

Currently ULA is the nation’s premier launch provider, launching at a rate of about once per month. 13 launches are planned for 2015- as outlined in my earlier article here.

But ULA faces stiff and relentless pricing and innovative competition from NewSpace upstart SpaceX, founded by billionaire Elon Musk.

NGLS is ULA’s answer to SpaceX – they must compete in order to survive.

To date ULA has accomplished a 100 percent mission success for 94 launches since the firms founding in 2006 as a joint venture between Boeing and Lockheed Martin. They have successfully launched numerous NASA, national security and commercial payloads into orbit and beyond.

Planetary missions launched for NASA include the Mars rovers and landers Phoenix and Curiosity, Pluto/New Horizons, Juno, GRAIL, LRO and LCROSS.

A United Launch Alliance Atlas V rocket with NASA’s Magnetospheric Multiscale (MMS) spacecraft onboard launches from the Cape Canaveral Air Force Station Space Launch Complex 41, Thursday, March 12, 2015, Florida.  Credit: Ken Kremer- kenkremer.com
ULA’s new rocket will launch from this pad in 2019
A United Launch Alliance Atlas V rocket with NASA’s Magnetospheric Multiscale (MMS) spacecraft onboard launches from the Cape Canaveral Air Force Station Space Launch Complex 41, Thursday, March 12, 2015, Florida. Credit: Ken Kremer- kenkremer.com

ULA’s most recent launch for NASA involved the $1.1 Billion Magnetospheric Multiscale (MMS) mission comprised of four formation flying satellites which blasted to Earth orbit atop an Atlas V rocket from Cape Canaveral Air Force Station, Florida, during a spectacular nighttime blastoff on March 12, 2015. Read my onsite reports – here and here.

“Space launch affects everyone, every day, and our goal in letting America name its next rocket is to help all Americans imagine the future of endless possibilities created by affordable space launch,” Bruno added.

NGLS will include some heritage design from the Atlas V and Delta IV rockets, but will feature many new systems and potentially some reusable systems – to be outlined by Bruno on April 13.

ULA plans to phase out the Delta IV around 2019 when the current contracts are concluded. The Atlas V will continue for a transitional period.

The Atlas V is also the launcher for Boeing’s CST-100 manned space taxi due to first launch in 2017.

NGLS will launch from Space Launch Complex-41 at Cape Canaveral Air Force Station, Florida, the same pad as for the Atlas V, as well as from Vandenberg AFB, Calif.

ULA’s next Delta IV launch with GPS IIF-9 is scheduled shortly for Wednesday, March 25, with liftoff at 2:36 p.m. EDT from Cape Canaveral.

Live webcast begins at 2:06 p.m. Live link here – http://www.ulalaunch.com/webcast.aspx

Vote now!

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Tory Bruno, ULA President and CEO, speaks about the ULA launch of NASA’s Orion EFT-1 mission on Delta IV Heavy rocket in the background at the Delta IV launch complex 37 on Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer- kenkremer.com
Tory Bruno, ULA President and CEO, speaks about the ULA launch of NASA’s Orion EFT-1 mission on Delta IV Heavy rocket in the background at the Delta IV launch complex 37 on Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer- kenkremer.com

Astronomy Cast Ep. 361: Modern Women: Maria Zuber

Maria Zuber is one of the hardest working scientists in planetary science, being a part of six different space missions to explore the Solar System. Currently, she’s the lead investigator for NASA’s GRAIL mission.

Visit the Astronomy Cast Page to subscribe to the audio podcast!

We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.

Moon’s Blotchy Near Side Has Bigger Craters Than Expected

The familiar blotches that make up “the man in the moon”, from the vantage point of Earth, happened because the moon’s crust is thinner on the near side than the far side to our planet, new research reveals.

The twin GRAIL spacecraft provided the most accurate sizes yet of lunar impact craters on the moon, providing more insight into what happened when Earth’s closest large neighbor was hammered with meteorites over billions of years.

“Since time immemorial, humanity has looked up and wondered what made the man in the moon,” stated Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology in Cambridge.

Artist's conception of the twin GRAIL spacecraft, called Ebb and Flow. Credit: NASA/JPL-Caltech
Artist’s conception of the twin GRAIL spacecraft, called Ebb and Flow. Credit: NASA/JPL-Caltech

“We know the dark splotches are large, lava-filled, impact basins that were created by asteroid impacts about four billion years ago. GRAIL data indicate that both the near side and the far side of the moon were bombarded by similarly large impactors, but they reacted to them much differently.”

The moon’s near side is easily visible in a telescope, but it’s hard to measure the size of the impacts because lava is obscuring their dimensions. The GRAIL spacecraft, however, peered at the internal structure of the moon and also produced information showing how thick the crust is. This showed that there are more, bigger craters on the closer side of the moon to us than the further side.

Closeup of the Moon showing Endymion, Atlas and the distant Mare Humboldtianum. Credit and copyright: Danny Robb.
Closeup of the Moon showing Endymion, Atlas and the distant Mare Humboldtianum. Credit and copyright: Danny Robb.

“Impact simulations indicate that impacts into a hot, thin crust representative of the early moon’s near-side hemisphere would have produced basins with as much as twice the diameter as similar impacts into cooler crust, which is indicative of early conditions on the moon’s far-side hemisphere,” stated lead author Katarina Miljkovic of the Paris Institute of Earth Physics (Institut de Physique du Globe de Paris).

As is common with research projects, learning more about the moon is revealing a new mystery that needs to be examined. It’s commonly cited that the moon was walloped during something called the late heavy bombardment, a period four billion years ago when it was believed that more meteorites impacted the moon.

“The late heavy bombardment is based largely on the ages of large near-side impact basins that are either within, or adjacent to the dark, lava-filled basins, or lunar maria, named Oceanus Procellarum and Mare Imbrium,” NASA stated.

“However, the special composition of the material on and below the surface of the near side implies that the temperatures beneath this region were not representative of the moon as a whole at the time of the late heavy bombardment. The difference in the temperature profiles would have caused scientists to overestimate the magnitude of the basin-forming impact bombardment.”

A research paper on the topic recently appeared in Science. GRAIL successfully concluded its mission last year after nine months of operations, flying into the side of a mountain as planned.

Source: NASA

 

Moon’s Variable Gravity Came From Ancient Impacts

The moon’s gravity has been a headache ever since the Apollo era. Areas of “mass concentration” or mascons, discovered in 1968, affected spacecraft orbits and made landing on Earth’s neighbor a tricky challenge.

The phenomenon has puzzled scientists, but new data shows that mascons might have come to be after asteroids or comets hit the moon a long time ago.

For nine months last year, until their mission ended with a deliberate crash on a moon mountain, twin washing-machine sized spacecraft Ebb and Flow circled the planet. Their work was known as the GRAIL mission (also known as Gravity Recovery and Interior Laboratory.) As they orbited together, gravity changes in the moon below them slightly changed their distances to each other — sometimes closer, sometimes further.

This allowed scientists to map out the mascons to high precision once they combined that information with computer models of big asteroid impacts as well as how craters on the moon evolved.

Craters on the Moon. Image credit: NASA
Craters on the Moon. Image credit: NASA

Mascons, which are invisible on the surface but appear in gravity maps as a sort of bulls-eye, arise “as a natural consequence of crater excavation, collapse and cooling following an impact,” NASA stated.

The center of the bulls-eye has stronger gravity, with a ring of weaker gravity surrounding the bulls-eye, and then another ring of strong gravity surrounding the bulls-eye and inner ring.

“GRAIL data confirm that lunar mascons were generated when large asteroids or comets impacted the ancient moon, when its interior was much hotter than it is now,” stated Jay Melosh, lead researcher and a GRAIL co-investigator at Purdue University.

“We believe the data from GRAIL show how the moon’s light crust and dense mantle combined with the shock of a large impact to create the distinctive pattern of density anomalies that we recognize as mascons.”

What’s more, researchers expect they’ll be able to apply that understanding to Mercury and Mars, as mascons were also discovered on those terrestrial planets.

The findings appeared in the May 30 edition of Science. You can read the entire article here.

Source: NASA

NASA: Reaches for New Heights – Greatest Hits Video

Video Caption: At NASA, we’ve been a little busy: landing on Mars, developing new human spacecraft, going to the space station, working with commercial partners, observing the Earth and the Sun, exploring our solar system and understanding our universe. And that’s not even everything.Credit: NASA

Check out this cool action packed video titled “NASA: Reaching for New Heights” – to see NASA’s ‘Greatest Hits’ from the past year

The 4 minute film is a compilation of NASA’s gamut of Robotic Science and Human Spaceflight achievements to explore and understand Planet Earth here at home and the heavens above- ranging from our Solar System and beyond to the Galaxy and the vast expanse of the Universe.

Image caption: Planets and Moons in perspective. Credit: NASA

The missions and programs featured include inspiringly beautiful imagery from : Curiosity, Landsat, Aquarius, GRACE, NuSTAR, GRAIL, Dawn at Asteroid Vesta, SDO, X-48C Amelia, Orion, SLS, Apollo, SpaceX, Sierra Nevada Dream Chaser, Boeing CST-100, Commercial Crew, Hurricane Sandy from the ISS, Robonaut and more !

And even more space exploration thrills are coming in 2013 !

Ken Kremer

IMG_3760a_SpaceX launch 22 May 2012

Image caption: SpaceX Falcon 9 rocket blasts off on May 22, 2012 with Dragon cargo capsule from Space Launch Complex-40 at Cape Canaveral Air Force Station, Fla., on the first commercial mission to the International Space Station. The next launch is set for March 1, 2013. Credit: Ken Kremer

New Video Shows the GRAIL MoonKAM’s Final Looks at the Moon

As a fond farewell, here are some of the final images taken by the GRAIL MoonKAM educational cameras on board Ebb and Flow, the twin spacecraft for the mission. This footage was shot just three days prior to when the mission ended with the planned impacts on a rim of a crater near the lunar north pole. At that point in the mission, the spacecraft had lowered their orbit to only about 11 km above the lunar surface. While these images aren’t of the highest of resolution, they provide a great sense of what it would be like to orbit close to the Moon. Additionally, they are an inspiration to school children. With MoonKAM (Moon Knowledge Acquired by Middle School Students) the cameras took more than 115,000 total images of the lunar surface, and imaging targets were proposed by middle school students from across the country and the resulting images returned for them to study.

The two probes were purposely crashed into the Moon because they no longer had enough altitude or fuel to continue science operations.

End of Mission: GRAIL Spacecraft Impact a Mountain on the Moon

The planned path of the GRAIL spacecrafts’ final orbit. Credit: NASA

“So long, Ebb and Flow, and we thank you,” said GRAIL project manager David Lehman of NASA’s Jet Propulsion Laboratory after the twin GRAIL spacecraft completed a planned formation-flying double impact into the southern face of 2.5-kilometer- (1.5-mile-) tall mountain on a crater rim near the Moon’s north pole. Mission team members estimate the two spacecraft were traveling at a speed of 1.7 kilometers per second (3,760 mph), and likely broke apart on impact. NASA said that most of what remains of the washing machine-sized spacecraft are probably buried in shallow craters, and the size of those craters will hopefully be determined when NASA’s Lunar Reconnaissance Orbiter is able to image the impact site in about two weeks.

NASA has honored the GRAIL team’s request to name Ebb and Flow’s impact sites after astronaut Sally Ride, who passed away earlier this year. She was America’s first woman in space and a member of the GRAIL mission team.

A simulation of the GRAIL impacts:

Impact occurred at 10:28:51 UTC (5:28:51 p.m. EST) and 10:29:21 UTC (5:29:21 p.m. EST). Right now it is night at the impact site, so sunlight should return within two weeks, enabling imaging of the site. LRO also took “before” images of the site during previous daylight orbits.

The impact marked a successful end to the GRAIL(Gravity Recovery and Interior Laboratory)mission, which in just a 90-day prime mission generated the highest-resolution gravity field map of any celestial body — including Earth — and determined the inner crust of the Moon is nearly pulverized.

“Ebb and Flow have removed a veil from the Moon,” said GRAIL principal investigator Maria Zuber during a televised commentary of the impacts today, adding that the mission will enable discoveries for years to come.

Data from GRAIL’s extended mission and main science instruments are still being analyzed, and the findings will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

GRAIL was NASA’s first planetary mission to carry cameras fully dedicated to education and public outreach. Ride, who died in July after a 17-month battle with pancreatic cancer, led GRAIL’s MoonKAM (Moon Knowledge Acquired by Middle School Students) Program through her company, Sally Ride Science. The camera took more than 115,000 total images of the lunar surface, and imaging targets were proposed by middle school students from across the country and the resulting images returned for them to study.

“Sally was all about getting the job done, whether it be in exploring space, inspiring the next generation, or helping make the GRAIL mission the resounding success it is today,” said Zuber. “As we complete our lunar mission, we are proud we can honor Sally Ride’s contributions by naming this corner of the Moon after her.”

Last Friday, Ebb and Flow, the two spacecraft comprising NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, were commanded to descend into a lower orbit that would result in an impact Monday on a mountain near the Moon’s north pole.

Fifty minutes prior to impact, the spacecraft fired their engines until the propellant was depleted. The maneuver was designed to determine precisely the amount of fuel remaining in the tanks. This will help NASA engineers validate computer models to improve predictions of fuel needs for future missions.

Screenshot of engineering data showing trajectory of the two GRAIL spacecraft about 2 minutes before Ebb’s impact. Via NASA TV.

“Ebb fired its engines for 4 minutes 3 seconds, and Flow fired its for 5 minutes 7 seconds,” Lehman. “It was one final important set of data from a mission that was filled with great science and engineering data.”

Launched in September 2011, Ebb and Flow had been orbiting the moon since Jan. 1, 2012. The probes were intentionally crashed into the lunar surface because they did not have sufficient altitude or fuel to continue science operations.

Endgame: GRAIL Spacecraft to Slam into Lunar Crater Rim on December 17

The GRAIL mission will come to a dramatic end on Monday as the two spacecraft will be commanded to crash into the rim of an unnamed crater near the Moon’s north pole. This is all according to plan, as the two spacecraft are running out of fuel after being in lunar orbit since New Year’s Day 2012.

“We successfully completed our primary science mission,” said Principal Investigator Maria Zuber, “ and, frankly, in my wildest dreams I don’t think this mission could have gone any better than it has. But when you orbit a planetary body that has lumpy gravity field, you use a lot of fuel.”

On Dec. 17 at about 5:28 EST, the spacecraft dubbed Ebb will undergo a controlled impact into a 2 km high “mountain, a rim of a crater that has been buried in ejecta near north pole of the Moon (coordinates are 75.62°N, 26.63°W). About 30 seconds later Flow will impact, about 40 km apart.

Both spacecraft will hit the surface at 3,760 mph (1.7 kilometers per second). No imagery of the impact is expected because the region will be in shadow at the time.

These maps of Earth’s moon highlight the region where the twin spacecraft of NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission will impact on Dec. Image credit: NASA/GSFC

Additionally, Gruber said that while they hope the Lunar Reconnaissance Orbiter will be able to observe the impact region (at the very least image the region both before and after impact), they don’t expect to there to be a “flash” visible from Earth, and do not believe there will be a significant chance of doing science by kicking up volatiles like LCROSS did, mostly because of the GRAIL spacecraft small size (each about the size of a washing machine) and because of the low angle of impact. The spacecraft have been at a low orbit averaging about 11 km above the surface this week, to be able to map at a high resolution before the fuel ran out.

They chose a mountain-side “since we’re coming in at angle of 1.5 degrees, it would only have left “skid marks” on level surface,” Zuber said. “There was interest in the team in impacting a structure, or a wall, so we could learn about mechanical properties of a crater rim. We’ll be looking at the rim of the crater and understanding how much is intact rock and how much is broken up. It will be very low probability but high scientific payoff if it works, if any volatiles they would be liberated from the impacts.”

The twist on this observation, Zuber said, is this crater is in sunlight most of the time, so if any volatiles come out, it would be surprising.

GRAIL project manager David Lehman said that Friday morning (December 14) the spacecraft will each be executing a maneuver will targeting the impact site, that will also position them to avoid what are called “historic heritage sites,” where the US and Russians have put soft landers on the Moon.

Then they’ll turn off the science instruments, followed by a series of engineering demonstrations to help with future missions over the weekend. About 54 minutes before impact, they’ll burn the remaining fuel to complete the last maneuver.

Lehman said there is a bit of challenge in hitting the crater rim. “We need to clear a ridge and then keep from going through a gap in the rim, because otherwise it would keep going and hit the far side of the Moon.”

Lehman added he was sad to see the mission end. “I’m kind of hoping tonight that a gas station will pull up to our spacecraft and refuel it.”

During their prime mission, from March through May, Ebb and Flow collected data while orbiting at an average altitude of 34 miles (55 kilometers). Their altitude was lowered to 14 miles (23 kilometers) for their extended mission, which began Aug. 30 and sometimes placed them within a few miles of the moon’s tallest surface features.

The duo’s successful prime and extended science missions generated the highest-resolution gravity field map of any celestial body. The map will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

“It is going to be difficult to say goodbye,” said Zuber. “Our little robotic twins have been exemplary members of the GRAIL family, and planetary science has advanced in a major way because of their contributions.”