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An ice rainbow seen in cirrus clouds on Earth. (UCSB Dept. Geography)

Five weeks ago a crater from the LCROSS impact formed on the Moon.  The pre-impact build-up had been sensational, but the actual event was largely invisible to observers on Earth. It was a different story on the Moon.  The slowly growing impact ejecta curtain threw water ice particles and vapor far out into space.  When the crater formed, flying ice particles could have refracted the glare of unfiltered sunlight into an “ice rainbow,” similar to those seen through very high altitude clouds on Earth.  For a very brief time, a rainbow might have been visible to an observer standing on the lunar surface.  And like its namesake, this rainbow is a promise – a promise that the Moon is habitable.  It is an invitation to humanity to extend man’s domain to our nearest planetary neighbor.

The LCROSS science team’s initial analysis of ejected impact plume data found evidence for water.  It appears that several other species, particularly some carbon substances also found in the cores of comets, may be present.  The new results suggest that some lunar polar volatiles may have their origins from outside the Moon, deposited there over millions of years by the impact of comets and asteroids.

Over the last 50 years, the idea of water ice at the lunar poles has generated as much angst as excitement within the scientific community.  Ice on the Moon was suggested by Watson, Murray and Brown in 1960.  They recognized that, regardless of the fate of such substances elsewhere on the Moon, the dark, cold floors of polar craters might retain volatile substances.  Rock and soil samples returned by the Apollo missions were not only bone-dry, but crystallized in a very reducing environment, suggesting that any indigenous lunar water, if present, must have been a very minor component.  Apollo scientist Jim Arnold resurrected the Watson et al. hypothesis forty years ago, concluding that their original proposal of water ice at the poles was still feasible and that a polar lunar orbiter was needed to search for such deposits.

We know that over geologic time, the Moon was bombarded by water-bearing objects.  Meteorites contain water, and just as they’ve landed on Earth, they’ve also hit the Moon.  Moreover, we’ve detected water vapor in the tails of comets with Earth-based telescopes.  But it was widely speculated that all this water must be lost from the Moon, which left the issue of polar ice unresolved.

Fifteen years ago, the 1994 Clementine orbiter mission revived our interest in the Moon’s polar regions.  When Clementine’s images of the Moon’s poles revealed large areas of shadowed terrain, it reminded Gene Shoemaker and the science team of the Watson and Arnold papers.  Large shadowed areas suggested that polar cold traps might really exist, so an experiment was improvised using the spacecraft transmitter to beam RF energy into the shadowed areas.  Analysis of the radio echoes suggested the presence of ice in shadowed areas near the south pole.  This result was questioned, largely because our team couldn’t repeat the passes using the improvised experiment.

In 1998, Lunar Prospector found evidence for excess hydrogen in the surface soils of both lunar poles.  These data could not show what form the hydrogen was in and had very low spatial resolution.  The issue, as to whether the observed polar hydrogen represented water ice in the dark cold traps or elemental hydrogen implanted by solar wind protons, was vigorously debated.  The preponderance of evidence in the years since Lunar Prospector, suggests that water ice is present in the polar areas, but its form, distribution and physical state are completely unknown.

The current flotilla of lunar orbiting spacecraft carry several advanced sensors, all designed to better characterize the environment and deposits of the polar regions of the Moon.  We have seen extremely low temperatures in the polar dark regions using the DIVINER instrument on the American Lunar Reconnaissance Orbiter (LRO) spacecraft.  The Japanese Kaguya mission mapped the topography and terrain of the polar areas and showed us the extent of the shadowed areas.  The Indian Chandryaan mission sent a probe into the south pole, mapped the extent of sunlight and carried two NASA instruments – the Moon Mineralogy Mapper (M3) and Mini-SAR radar.  In September, the M3 instrument found significant amounts of water bound into mineral structures at high latitudes.  The Mini-SAR instrument has made maps showing the interior of dark polar craters.  These maps are being analyzed for scattering characteristics to determine whether water ice might be present there; our initial results will be announced soon.

Now, the LCROSS impactor – sent to kick up the dust of the polar dark regions – has shown us that water ice does exist there.  We still don’t know how much water ice in total may be present; from Clementine,  we estimated there are billions of metric tones of water ice present in the south polar area.  Complete analysis of all of the remote sensing information in the next couple of years will ultimately give us a good estimate of the total amount of water available.  Clementine also revealed peaks of near-permanent sunlight in proximity to regions of permanent darkness at the poles (where the sun’s circular rotation keeps temperatures benign).

If you don’t know where you’re going, any path will get you there.

The Moon has the resources needed to bootstrap a sustained, permanent human presence.  It is the place where we can learn how to live and work productively in space.  The Moon has put out a welcome mat.  What are we waiting for?

Collapse breccia near a lava tube entrance (Photo by Dr. Harmon Maher, Univ. Nebraska)

The science team of the Japanese Kaguya mission have just published a paper claiming to have found an opening to a cave on the Moon.  Such a discovery is a potentially important development for future lunar habitation.  Lava tubes are large caves created during the volcanic eruption of a very fluid, highly effusive lava.  They are common on Earth, especially in iron-rich basaltic lavas, such as those that make up most of the Hawaiian islands.

The idea that caves occur on the Moon has been around for a long time.  We have long known that the lunar maria (the dark, smooth, relatively uncratered plains of the Moon) are made up of old basaltic lava flows.  Looking at orbital photographs, we find many narrow, winding channels (or rilles) in the maria.  These channels cannot be the product of water erosion, as flowing liquid water cannot exist in the vacuum of the lunar surface.  So workers looked for another explanation.  They found it in lava channels and tubes.

On Earth, volcanic terrains often show small channels within young lava flows.  Lava tubes form when hot lava erupts, pouring out onto the surface.  The lava immediately begins to cool, with the outermost edges cooling first.  As the lava cools and hardens from the outside edges inward, the flow of still-molten lava becomes constricted to a central, narrow, interior conduit.  When the eruption stops, the still-liquid lava drains out, leaving behind an empty cave-like tube-shaped segment.  In some instances, the roof of the drained tube collapses, exposing the tube interior as a channel or, if less extensive, creating a “skylight” or a hole that allows access to the cave interior.  Lava caves are quite common on volcanoes made up of runny (low viscosity) lava, such as the shield volcanoes of Hawaii.

Caves found on the Moon would be very useful.  Because they form in dense basaltic lava, the space inside a tube is protected from both the hard radiation of the lunar surface and the constant micrometeorite bombardment the Moon experiences.  Moreover, the temperature of the subsurface of the Moon is very stable; below the zone which experiences the extreme temperatures of night and day, lunar temperatures are fairly constant at about -20° C.  On Earth, lava caves can be quite roomy, with diameters tens of meters across and hundreds of meters long.  On the Moon, these dimensions may be much larger – the low gravity of the Moon results in much bigger lunar lava tubes and channels than their terrestrial counterparts, being hundreds of meters across and many kilometers long.  Thus, they offer many potential advantages to future lunar inhabitants.

Before we pack our bags for the Marius Hills, we should take note of some other properties of lava tubes.  Many lava tubes partly or completely collapse immediately after their formation.  If the roofed segments are weakened by flowing lava, earthquakes, or are very thin, they cannot support their own weight and after the lava drains out, the roof falls into the void.  This is seen on both the Earth and Moon.  Hadley Rille, visited by the Apollo 15 astronauts in 1971, is a lava channel, parts of which were roofed over as a tube.  The crew landed near a channel portion, but a roofed segment is only about 12 km from the site.  High resolution images of that segment show no entrance to an underground cave there or elsewhere along the rille (channel).  That doesn’t mean that there is no cave portion of Hadley Rille, but it does suggest there is no entrance to a cave there.

Other candidates on the Moon look more promising.  Numerous lava tube “skylights” have been noted in association with many lava channels on the Moon.  These skylights are typically unconnected to each other or any nearby feature and are found as individual tube segments that appear to start and stop along the trend of a rille.  It is impossible to identify lava cave entrances because most of the images we have for these features are low resolution and have near-vertical viewing geometry.

The new Kaguya pictures show a circular, rimless pit on the floor of the projected segment of a rille.  Collapse pits are not uncommon on the Moon and many of them are not associated with lava channels or tubes.  So while the new Kaguya images are intriguing, they are not definitive evidence for a cave.

There are other issues in regard to the use of lunar lava tubes.  Many (if not most) terrestrial lava tubes are not void; they are either filled with late-stage lava, which plugs up the cave, or by collapse debris, which buries it.  Finding a new void lava tube is celebrated by the caving community simply because void tubes are rare.  But even if a void tube formed on the Moon, it may not remain that way for all time.  Lunar volcanism was active over 3 billion years ago.  Since then the Moon has been constantly bombarded by debris, initiating landslides, infilling craters, and generating seismic waves.  Such a bombardment could well act as a leveler to collapse and fill in void lava caves that might have existed on the Moon.

But the biggest problem with lunar caves is even more fundamental – they aren’t where we want them.  Sustained human presence on the Moon is enabled by the presence of the material and energy resources needed to support human life and operations around the Moon.  After over a decade of study and exploration, we now know that these locations are near the poles of the Moon.  Unfortunately, both poles are in the highlands and finding a lava tube in such non-volcanic terrain is highly unlikely, regardless of the imaginative ramblings of certain science-fiction authors.  If a lunar cave were present there, we would certainly consider using it.  But it makes no more sense to locate a lunar base near the caves, than it does to build a water-park in the Sahara desert.

The formation of lunar lava tubes and caves is an interesting scientific topic, but their utilitarian value is uncertain, at least until we have established a permanent presence on the Moon.  Ultimately, we may be able to use them to live on the Moon, but first, we need to follow the Willie Sutton principle and go where the money is.

The LCROSS impact site seen from LRO

Early last Friday, the public and families of employees at Ames Research Center in California, where the LCROSS mission was conceived, built and operated, camped on the lawn in an all-night vigil.  NASA’s educational outreach and public relations push about the pending lunar impact event was very effective, having reached a wide audience in the weeks leading up to the much hyped event.  Alas, the promised giant plume of impact debris was invisible from Earth, leaving a receptive public feeling cheated and disappointed.

The understanding that a high-velocity impactor can yield important information about planetary composition and state is very old.  The first probes to the Moon (both Soviet and American) were impactors.  We know that when something strikes a planetary surface at high speed, target material is thrown up into space, some of it vaporized by heat generated in the energy of the impact.  By studying this impact ejecta, we learn about the composition of the target object.

I didn’t post on it earlier, but as the LCROSS mission has successfully concluded, I think it is a good time to examine this mission, how it came about, and the lessons that hopefully it has taught NASA about public appeal and its involvement with space.

LCROSS was not originally a part of the robotic precursor program for lunar return. Initially, the Lunar Reconnaissance Orbiter (LRO) spacecraft was to be launched on a Delta II.  By the end of 2005 it had outgrown its booster and was forced onto the much larger Atlas V booster where it had surplus payload margin.  The Associate Administrator for the Exploration Systems Mission Directorate (ESMD) Scott Horowitz, decided to use this margin to fly an additional small spacecraft (called a secondary payload) that would address the raging debate about whether water ice exists at the poles of the Moon.  Horowitz looked to NASA’s field centers for a small payload that would provide data about this contentious and nagging issue.

Although a variety of small missions were proposed, including survivable hard landers and small “hoppers,” the idea of slamming the Centaur upper stage into the Moon and examining the resulting ejecta plume was selected as LCROSS in April 2006.  It was considered a low-risk, low-cost concept, as the used Centaur upper stage had no value and would have been steered into a solar orbit anyway.  A small satellite was built to track the Centaur impact, measure the properties of the ejected plume and with luck, would “settle” the issue of water on the Moon.

A serious defect in this mission concept was that it presupposed that we understood the Moon well enough to identify in advance the most likely site for ice on the Moon.  Lunar investigators knew from previous data that water ice, if present, was not present everywhere – it had a patchy, heterogeneous distribution because the permanent shadow around the poles (where the ice would be stable) is itself patchy.  Moreover, the remote sensing data of the time was ambiguous as to which shadowed locales contained ice, if any.

In March of 2006, because of these uncertainties, those who had worked on the robotic precursor program laid out a sequential, incremental strategy to first map the deposits from orbit and identify the best candidate sites for ice.  Following orbital mapping, we would soft-land with capable rovers and  map and test the surface composition at a minimum of about 20 different sites.  Although this strategy is more costly than a simple impactor mission, it would have provided us an unequivocal answer to the ice issue; we would know without doubt whether there is or is not water ice at the poles of the Moon.  Moreover, rovers would collect information on the possible presence, physical nature and setting of other volatile substances (such as ammonia and methane) that have resource value.  In other words, we would have collected the critical strategic information needed to locate, prospect, harvest and use lunar water.

Instead, the mission chosen and flown and heavily advertised by NASA as a citizen participation viewing event to find water on the Moon, could not answer key questions about polar water.  If LCROSS detects water, we still won’t know where all the ice deposits are located, what other species might be present, what its physical state might be, and how it is distributed laterally and vertically in the surface regolith.  If LCROSS detects nothing, it won’t prove that water doesn’t exist on the Moon, only that the wrong site was selected.  In other words, after this mission, we will still know next to nothing about the material that will enable and advance permanent, sustainable economic presence on the Moon.

An impact plume wasn’t the only thing missing.  Hopefully, NASA will recognize the real discovery of LCROSS – mission hype is a poor substitute for shortcomings in programmatic logic.

The path to Cone crater (LROC image, Ariz. State Univ.)

In 1961, Alan B. Shepard’s successful 15-minute sub-orbital hop gave President Kennedy the high cover needed to announce a reach for the Moon, “by the end of this decade.” America’s spirit was lifted and Alan Shepard became a national hero, getting ticker tape parades and White House receptions. Then, as in a Greek tragedy, he was struck from the flight list after developing Meniere’s syndrome (an imbalance of the inner ear). His flying days were over. Or were they?

Shepard, a smart, tough, no-nonsense aviator, took a job helping Deke Slayton (previously grounded by a heart murmur) run the Astronaut Office. Shepard and Slayton picked all flight crews for the Gemini and Apollo missions. Very early on, it became clear that you did not cross Al Shepard, lest your career come to a screeching halt. Shepard never stopped his Apollo training or flying in the T-38, even though he had to “backseat it” with another astronaut. His personality was memorably captured in Tom Wolfe’s book, The Right Stuff, as “The Icy Commander.”

After taking a chance on experimental surgery to correct his inner ear problem in 1969, he successfully returned to active flight status and looked ahead to an Apollo flight assignment.  Rejected for the Commander’s seat on the next available flight by NASA Headquarters (on the grounds that he needed more training time), he was named to command a subsequent flight, while Jim Lovell was named Commander of Apollo 13.

Geologists who worked on the Apollo training were ecstatic – Lovell was one of their favorite pilot astronauts, a smart, capable guy with a keen eye and an analytic mind. He was being sent to Fra Mauro, the first highland site to be visited on the Moon. This region was considered a key locale to decipher lunar geological history, being located on the ejecta blanket of the Imbrium basin, the largest impact crater on the near side.

Jim Lovell was considered the right man to study this site and collect the key samples scientists needed to help unlock the secrets of the Moon. Unfortunately, with the failure of Apollo 13, Jim Lovell didn’t land on the Moon. Still, the Fra Mauro site was considered so important, it became the designated landing site for Apollo 14, eighteen months later.

Uh-oh. Lunar scientists didn’t have Jim Lovell to explore with—they had drawn the “Icy Commander,” the guy who cheerfully admitted that, compared to aeronautics, he thought geology was a low-grade science. Nevertheless, Shepard assured the Apollo scientists he would try to do the best job he could for them.

While successful in almost every way, the Apollo 14 mission was not without controversy. Cone crater, a large young impact feature, had apparently dug up rocks from deep within the Fra Mauro Formation, including it was hoped, ejecta from the Imbrium basin. During their second moonwalk, Al Shepard and Ed Mitchell trudged up steep slopes leading to Cone, dragging along their Modularized Equipment Transporter (MET), a small pull-cart designed to carry tools and samples with them, getting more winded and disoriented with each step. Getting to the rim of Cone crater was considered critical to the scientific success of the mission.

At 47, Shepard was the oldest man to fly to the Moon and many felt that he was out of shape and not up to the rigors of lunar trekking (which didn’t explain why Ed Mitchell was also having problems.) Moreover, it seemed that Shepard was all too eager to abandon the trek and declare victory after he radioed to the ground that he thought they were already at the rim of Cone crater. (Enough with the hiking trip! We’re running out of time and consumables. Let’s sample this area and call it the rim of Cone crater.)

Scientists in the back room were aghast. Getting Cone crater samples was critical to mission success. And now this old, panting geezer was destroying their chance to unlock a deep secret about the Moon. Although they put on a good face, scientists were resentful; after all their work on geological training, the “Icy Commander” simply declares victory and turns for home. Adding insult to their perceived injury, back at the Lunar Module, Shepard pulled out a 6-iron and conducted a little sand trap practice. (He abandoned the quest for Cone crater – to play golf, no less!)

Now, thirty-eight years later, we’ve just received a magnificent picture of the Apollo 14 landing site from the Lunar Reconnaissance Orbiter Camera (LROC). Its quality is so good we can see the path of the astronauts footprints and MET tracks on the Moon. It is even possible to follow their tracks all the way up to Cone crater—to the point where Al Shepard declared victory.

Oops. Al Shepard was right. He was at the rim of Cone crater. Terrain around the rim is so hilly that he and Ed Mitchell didn’t know they had reached the rim; the deep crater interior is just over a slight rise, a few tens of meters north of where they were. The samples that Shepard and Mitchell collected do represent the deepest ejecta from Cone crater, thereby fulfilling that goal geologists set many moons ago. For almost 40 years, the “Icy Commander” was right. Yet his name lived in infamy in lunar geologic circles.

If there is a moral to this story, it could be that scientists should never state something is absolutely known and settled.  It’s likely they’ll be proven wrong.

A Moon rock on Mt. Everest: Not for keeps

Mr. Ian Sheffield of Edinburgh Scotland is miffed. He claims to have not one, but two dust samples of the Moon—one from the Apollo 11 mission and another from the Apollo 15 mission. He explains that he bought these lunar samples “from a dealer” about 3 years ago. The article does not indicate how much he paid for them, but he does allow that each is valued at “around £2000” (about $3300) each.

A problem arose when he planned to display his samples to the public. He apparently wrote to NASA asking if he could exhibit them. To his astonishment, NASA refused to give him permission and demanded the return of the samples, claiming that the lunar dust in his possession was property of the United States government.

Mr. Sheffield’s story of how the samples came into his possession is interesting. He states the dust came off a camera film pack to which a technician in the Lunar Receiving Laboratory was accidentally exposed. Because no one was sure the lunar samples would not contain some possible primitive (and pathogenic) organisms when the Apollo 11 crew first returned to Earth, they had to spend three weeks in quarantine. Anybody in the LRL exposed to lunar material was compelled to join the astronauts in their quarantine. The technician who was exposed went into isolation and (the story claims) upon his release, “was given the dust as a memento.”

My antennae went up at this point. No lunar samples are “given” to private individuals. Each piece of the Moon returned by the Apollo astronauts is carefully accounted for and resides in the Lunar Curatorial Facility in Houston, where they are kept in two separate hurricane-proof vaults. Many lunar samples are loaned to scientific institutions for study. The only lunar samples given away (of which I am aware) were to about a hundred national leaders during President Nixon’s 1969 world tour. The beautiful “Space Window” in the Washington National Cathedral, honoring man’s landing on the Moon, holds a 7.18-gram basalt from Mare Tranquillitatis, on loan to the Cathedral. Other moon rocks were presented to the Apollo astronauts (and Walter Cronkite) in 2004. However, each plaque came with a catch: the lunar samples can not be personally held by the recipients, and must be displayed at a local school or museum. Recently, Astronaut Scott Parazynski was loaned a sample of the Moon’s regolith that he carried to the summit of Mount Everest.

Some diplomatic gifts of lunar samples have found their way onto the black market. A notorious case is a sample presented to the people of Honduras back in 1969. This sample turned up during a NASA Inspector General “sting” which was designed to catch dealers of fake lunar samples. To the agents’ surprise, they were offered a genuine lunar rock: asking price, $5 million. A meeting was arranged and the rock (and presumably, the seller) was seized. Another lunar sample was stolen from a museum in Malta between 1990 and 1994; it was recovered in another sting operation in 1998.

The federal government forbids private ownership of any Apollo sample. Yet, such samples show up every now and then. The most common form they take is dust stuck to adhesive tape (an easy way to “clean” the surface of some exposed sample container, tool, or space suit used on the lunar surface). Mr. Sheffield’s sample is likely to be one of these pieces. Its status, I was surprised to find out, is legally uncertain. Although NASA has sued in court to recover any such bootleg sample, no prosecution has succeeded, except for those caught (literally) in the act of theft. In an embarrassing incident for NASA, a summer intern and two companions carried a safe full of lunar samples out of a building at Johnson Space Center (as Dave Barry would say, I am not making this up). They were apprehended while trying to sell them at bargain basement prices and subsequently prosecuted.

It was rumored for years that several of the Apollo astronauts held samples from their respective missions. If they did, it was probably inadvertent—the lunar dust is extremely adhesive and it is possible that smudges of lunar dust clung to personal items returned from the Moon in their Personal Preference Kits. Alan Bean, who documents the Apollo experience through his oil paintings, is said to add ground-up patches retrieved from his lunar space suit to his works. His reasoning is that because his suit was dirty with lunar dust, some of that dust must find its way into his paintings, giving them a true “lunar” ambiance.

So Mr. Ian Sheffield of Edinburgh may be home free. I might suggest to him that given their quasi-legal status, he is probably better off not calling attention to his possession of these unique artifacts. In fact, although NASA frowns on owning stolen Apollo lunar samples, there are dozens of lunar samples available for sale on eBay. A number of meteorites recovered on Earth, came from the Moon. Although most of them belong to national governments that sponsor the recovery of meteorites from Antarctica, several are in private hands and can be bought and sold, just as any commodity. Right now, there is a very nice anorthositic breccia from the lunar highlands for sale. Better hurry though – the sale only lasts another day. Oh yes, the asking price: a mere $144,000.

By the way, over the years, I have been asked to look at a few “lunar” samples that were in fact, lunar fakes. Caveat Emptor!