Desolate magnificence -The Space Review

LRO images on display at the Smithsonian Air & Space Museum [Dwayne Day/The Space Review].

Dwayne Day

The Space Review

Right now Washington, DC’s museums are filled with the noise of hormonal teenagers on their spring break trips to the nation’s capital. They run around aimlessly, oblivious to their surroundings, or sprawl on the dirty carpet absorbed in their own little worlds. Later, in May, the senior class trips will show up, and those older students are a little less noisy, a little more focused, but they too will probably not be all that interested in the actual museums, even if they take their noses out of their cellphones for more than a second or two. But just maybe, perhaps, one or two of them may accidentally wander into one of the National Air and Space Museum’s new exhibits and they might quiet down for a moment and see something both familiar and alien.

The exhibit is titled “A New Moon Rises” and it is a display of large format photographs from NASA’s Lunar Reconnaissance Orbiter featuring the Moon in all its panchromatic glory. You could look at most of these photos on your computer screen, but seeing them enlarged and displayed on a museum wall like works of art is an entirely different experience.

The Lunar Reconnaissance Orbiter, or LRO, was launched in 2009 and has been chugging away ever since. If nothing breaks, in four or five years the spacecraft will probably run out of fuel and, because the Moon’s gravity field is uneven, it will ultimately fall and silently crash into the surface after more than a decade in orbit.

- Read the full article online, in the latest issue of The Space Review, HERE.

Armstrong's treasure of Apollo 11 artifacts found

Neil Armstrong's "McDivitt Bag," filled with priceless souvenirs of the July 1969 first manned expedition to the lunar surface, has been disclosed to the Smithsonian Institute by his widow. Among them, the 16mm DAC camera that captured the landing from the starboard window.

Jesus Diaz

Sploid/gizmodo

These are the contents of a mysterious white bag found hidden in Neil Armstrong's closet: Weird looking lamps, wrenches, utility brackets, sights, and a film camera that later was identified as the one that captured the famous Apollo 11's descent on the Moon's surface. Nobody knew about it, including his widow.

According to NASA, Carol Armstrong sent photos to Allan Needell, curator of the Apollo collection at the Smithsonian's National Air and Space Museum, who immediately knew what was inside: It was a McDivitt Purse full of parts from the Eagle, Apollo 11's Lunar Module:

After Neil Armstrong's death, his widow, Carol, discovered a white cloth bag in a closet, containing what were obviously either flight or space related artifacts. She contacted Allan Needell, curator of the Apollo collection at the Smithsonian's National Air and Space Museum, and provided photographs of the items. Needell, who immediately realized that the bag—known to the astronauts as the Purse - and its contents could be hardware from the Apollo 11 mission, asked the authors for support in identifying and documenting the flight history and purpose of these artifacts. After some research it became apparent that the purse and its contents were lunar surface equipment carried in the Lunar Module Eagle during the epic journey of Apollo 11.

These artifacts are among the very few Apollo 11 flown items brought back from Tranquility Base and, thus, are of priceless historical value. Of utmost importance is the 16mm movie camera with its 10mm lens.

The on-board 16 mm film camera, with which the landing, first steps, and take off of the lunar module Eagle from Mare Tranquillitatis were filmed, has been unearthed in a bag of similarly priceless small artifacts of the epic mission found in Neil Armstrong's closet in Ohio.

The camera was mounted behind the right forward window of the lunar module and was used to film the final phase of the descent to the lunar surface, the landing, as well as Neil Armstrong's and Buzz Aldrin's activities on the lunar surface including taking the first samples of lunar soil and planting the US flag.

Still from the Apollo 11 16mm DAC film camera shows Armstrong (with visor up) taking his initial, halting steps out onto Mare Tranquillitatis, still tethered to the spacecraft.

Thanks to the Neil Armstrong family, the Apollo 11 purse and its contents are now on loan at the National Air and Space Museum for preservation, research and eventual public display.

Here's a list of everything inside and how it looked inside and outside the Eagle:

Read the full article at sploid.gizmodo, HERE.

The promise of astronomy on the Moon

The Apollo 16 Ultraviolet Telescope. Charlie Duke on the starboard side of by Apollo 16 lunar module ladder, at the end of the first of three EVAs in the nearside southern highlands. AS16-114-18439 and 40, by John Young, April 21, 1972  [NASA/JSC].

Paul D. Spudis
The Once and Future Moon
Smithsonian Air & Space

Imagine that you are an astronomer. You want to gaze at the universe in crystal clarity. Yet you look at the heavens through a murky, partly opaque sky; you must deal with light pollution and the dynamic, wildly unstable platform of the Earth’s surface. It’s frustrating – you dream of the great views you know you could get from space. That’s the ticket! Plus, locating a stable, rock-solid base in space (where you could build extremely sensitive instruments) would be a huge bonus.

For years, the Moon was seen as the ideal place to build and operate sensitive telescopes. Its low gravity permits the building of giant telescopes with enormous seeing power. The stable, seismically quiet base of the lunar surface would allow for the operation of multiple telescopes in unison – arrays, effectively creating one giant telescope with an enormous aperture (a technique called interferometry). The cold, dark sky as seen from space – unimpeded by clouds, air or other meteorological phenomena – affords superb viewing conditions (as twenty years of fantastic Hubble Space Telescope images have documented). So with such considerations, one might conclude that conducting astronomy from the lunar surface would be one of the prime activities desired by the astronomical community. Right?

Well, not quite. Back in 1984, efforts to build a community of supporters for a base on the Moon included many astronomers who supported such efforts on the basis of the considerations listed above. Throughout the early days of the return to the Moon movement, astronomers such as Harlan Smith of the University of Texas and many others campaigned tirelessly for recognition of the value of lunar-based astronomy. These studies culminated in the seemingly outrageous idea for a telescope using a spinning disk of liquid with a reflective surface, lining the interior of one of the millions of bowl-shaped craters on the Moon. Such an instrument would extend for kilometers, making a gigantic “eye” to look at the universe. One might think such an idea is crazy, but liquid mirror telescopes already have been constructed on Earth.

Interestingly enough, the launch and success of the Hubble Space Telescope resulted in the loss of support for lunar astronomy. The biggest advantage of space-based astronomy is views of a dark, clear sky. Such views are available in free space just as easily as they are on the Moon. Moreover, the big advantage of a stable platform on the lunar surface for observations is partly negated by technical developments that permit the assembly of free-flying platforms in space. Such developments might mean that a short wavelength interferometer could be built and operated without the need to go into the (small) gravity well of the Moon. These and other technical innovations led to a general loss of support within the community for astronomical science on the lunar surface.

Image of the southern sky in the far UV, taken by the first astronomical telescope on the Moon, Apollo 16 mission, April, 1972 [NASA].

One might be forgiven for suspecting that a long-standing antipathy against human spaceflight might have had something to do with the attitude of many astronomers. They might possibly have feared that the advent of a new human spaceflight endeavor would divert funds from their lengthy wish list of robotic missions and automated observatories. However, the idea that the Moon is somehow useful to astronomers still holds an attraction.

Recent work has focused on the value of using the Moon’s unique environment to observe some parts of the electromagnetic spectrum that we cannot access from Earth or even near-Earth space. Very long wavelength emissions (meter- and multiple-meter-scales) cannot be seen from the Earth’s surface because the layer of charged particles surrounding the Earth in space (the ionosphere) blocks such radiation. Even in orbit, interference from the ionosphere prohibits observations because of this “noise.” However, the far side of the Moon is permanently shielded from Earth’s radio noise by over 3,600 km of solid rock. From such a truly unique vantage point, we will be able to listen to the whisper of radio noise generated in the aftermath of the origin of the universe.

The Chang’E 3 lander carries a small telescope designed to look at the other end of the spectrum, the far ultraviolet (as the name implies, wavelengths shorter than visible light). The Chang’E telescope is producing data and although of small aperture, it can observe the sky at these wavelengths. Apollo 16 emplaced a UV telescope on the Moon back in 1972 and took ultraviolet photographs of the sky from the lunar surface, including the Earth and images of the southern sky (which includes two satellite galaxies to our own Milky Way galaxy – the Magellanic Clouds). These instruments documented the possible value of such observations from the surface of the Moon.

Other astronomers have looked in detail at how one might begin to utilize the unique environment of the far side to map the earliest stages of the history of the universe. One concept sends a teleoperated rover to the far side with a dual purpose. We could collect samples from the floor of the biggest, oldest basin on the Moon (South Pole-Aitken basin, an impact feature over 2,500 km in diameter) to test ideas about the early cratering history of the Earth-Moon system.  While we’re there, we could also lay out an antenna array designed to map the sky’s low frequency radio emissions.

HDTV still of Tsiolkovskiy crater from Japan's lunar orbiter Kaguya (SELENE-1). The Naval Research Laboratory, MIT and others are refining work on a possible radio telescope array deployed on the floor of the conspicuous farside crater to utilize the radio quiet of the lunar farside to probe the Cosmic Dark Age [JAXA/NHK/SELENE].

The far side L-2 mission concept involves humans stationed 60,000 km above the Moon to operate the rovers and deploy the antennas. These antennas are quite simple. They consist of dipoles (i.e., linear wires) several tens of meters in length, all connected to a receiver capable of listening to those low frequency bands minus the static and noise of the terrestrial RF environment. Over the course of a year, as the Moon orbits the Earth (and both orbit the Sun), nearly the entire sky could be mapped from this robotically emplaced astronomical instrument.

Despite some starts and stops, the promise of conducting astronomy from the Moon continues to draw the attention of imaginative scientists. Using one of the forthcoming commercial lunar landers, a group of private enthusiasts plan to deploy a small telescope on the surface. When we some day stand on the Moon, we will not only look down to study the complex history preserved there, but we will also look outward, into an endless universe, just as many science fiction authors envisioned.

Dr. Paul D. Spudis is a senior staff scientist at the Lunar and Planetary Institute in Houston. This column was originally published by Smithsonian Air & Space, and his website can be found at www.spudislunarresources.com. The opinions he expressed here are his own, and these are better informed than most.

Related:
ILOA to study deep space from Chang'e-3 (September 11, 2012)
Remote-operated lunar deep space telescope concept demonstration (July 26, 2012)
Farside offers radio-quiet to probe cosmic Dark Age (July 2, 2012)
The Moon as a platform for Astrophysics (April 24, 2012)
MIT to lead development of new radio telescope
array on lunar farside (February 19, 2008)
Naval Research Laboratory to design Farside DALI (March 11, 2008)
What better view? (March 26, 2008)
New model of lunar motion from Apollo LLRR (December 27, 2008)
MacDonald LLR defunded by NSF (June 21, 2009)
The continued importance of lunar laser ranging (August 3, 2009)
Laser Ranging and the LRO (August 12, 2009)
A Fundamental Point on the Moon (April 13, 2010)

Clementine - The Legacy, Twenty Years On

Engineering model of the Clementine spacecraft in the Lunar Exploration Vehicles exhibit at the National Air and Space Museum. Interstage and solid rocket motor (bottom half) was discarded before insertion into lunar orbit.

Paul D. Spudis

The Once and Future Moon

Smithsonian Air & Space

The first spacecraft to globally map the Moon left lunar orbit on May 3, 1994.  Clementine, a joint Department of Defense-NASA mission, had systematically mapped the Moon’s surface over 71 days, collecting almost 2 million images.  For the first time, scientists could put results of the Apollo lunar sample studies into a regional, and ultimately, a global context.  Clementine collected special data products, including broadband thermal, high resolution and star tracker images for a variety of special studies.  But in addition to this new knowledge of lunar processes and history, the mission led a wave of renewed interest in the processes and history of the Moon, which in turn, spurred a commitment to return there with both machines and people.  We peeked into the Moon’s cold, dark areas near the poles and stood on the edge of a revolution in lunar science.

Prior to Clementine, good topographic maps only existed for areas under the ground tracks of the orbital Apollo spacecraft.  From Clementine’s laser ranging data, we obtained our first global topographic map of the Moon.  It revealed the vast extent and superb preservation state of the South Pole-Aitken (SPA) basin and confirmed many large-scale features mapped or inferred from only a few clues provided by isolated landforms.  Correlated with gravity information derived from radio tracking, we produced a map of crustal thickness, thereby showing that the crust thins under the floors of the largest impact basins.

Two cameras (with eleven filters) covered the spectral range of 415 to 1900 nm, where absorption bands of the major lunar rock-forming minerals (plagioclase, pyroxene and olivine) are found.  Varying proportions of these minerals make up the suite of lunar rocks.  Global color maps made from these spectral images show the distribution of rock types on the Moon.  The uppermost lunar crust is a mixed zone, where composition varies widely with location.  Below this zone is a layer of nearly pure anorthosite, a rock type made up solely of plagioclase feldspar (formed during the global melting event that created the crust).  Craters and large basins act as natural “drill holes” in the crust, exposing deeper levels of the Moon.  The deepest parts of the interior (and possibly the upper mantle) are exposed at the surface within the floor of the enormous SPA basin on the far side of the Moon.

Topographic map of the Moon made from Clementine laser altimetry in mid-latitudes and stereo images near the poles. Large depression in southern far side is the South Pole-Aitken basin.

Clementine showed us the nature and extent of the poles of the Moon, including peaks of near permanent sun-illumination and crater interiors in permanent darkness.  From his first look at the poles, Gene Shoemaker (Leader of the Clementine Science Team) got an inkling that something interesting was going on there.  Gene was convinced that water ice might be present, an idea about which I had always been skeptical.  At that time, no trace of hydration had ever been found in lunar minerals and the prevailing wisdom was that the Moon is now and always had been bone dry.  With Gene arguing to keep an open mind and Stu Nozette (Deputy Program Manager) devising a bistatic radio frequency (RF) experiment to use the spacecraft transmitter to “peek” into the dark areas of the poles, we moved ahead on planning the observations.

To my astonishment (and delight), a pass over the south pole of the Moon showed evidence for enhanced circular polarization ratio (CPR) – a possible indicator of the presence of ice.  A control orbit over a nearby sunlit area showed no such evidence.  However, CPR is not a unique determinant for ice, as rocky, rough surfaces and ice deposits both show high CPR.  It took a couple of years to reduce and fully understand the data, but collection of the bistatic collection was successful.  In part, our ice interpretation was supported by the discovery of water ice at the poles of Mercury (a planet very similar to the Moon).  We published our results in Science magazine in December 1996, setting off a media frenzy and a decade of scientific argument and counter-argument about the interpretation of radar data for the lunar poles (an argument that continues to this day, despite subsequent confirmation of lunar polar water from several other techniques).

Along with Clementine’s success came a growing interest in lunar resources and a new appreciation for the complexity of the Moon.  This interest led to the selection of Lunar Prospector (LP) as the first PI-led mission of NASA’s new, low-cost Discovery series of planetary probes.  LP flew to the Moon in 1998 and carried instruments complementary to the data produced by Clementine, including a gamma-ray spectrometer to map global elemental composition, magnetic and gravity measurements, and a neutron spectrometer to map the distribution of hydrogen.  LP found enhanced concentrations of hydrogen at both poles, again suggesting that water ice was probably present.  The debate on the abundance and physical nature of the water ice continued, with estimates ranging from a simple enrichment of solar wind implanted hydrogen in polar soils, to substantial quantities of water ice trapped in the dark, cold regions of the poles.

Buttressed by this new information, the Moon became an attractive destination for robotic and human missions.  With direct evidence for significant amounts of hydrogen (regardless of form) on the surface, there now was a known resource that would support long-term human presence.  This hydrogen discovery was complemented by the identification in Clementine images of several areas near the pole that remain sunlit for substantial fractions of the year – not quite the “peaks of eternal light” first proposed by French astronomer Camille Flammarion in 1879 but something very close to it.  The availability of material and energy resources  – the two biggest necessities for permanent human presence on the Moon – was confirmed in one fell swoop.  Combined, the results of Clementine and LP finally gave scientists the Lunar Polar Orbiter mission we had long sought.  These two missions certified the possibility of using lunar resources to provision ourselves in space, permanently establishing the Moon as a valuable, enabling asset for human spaceflight.  Remaining was to verify and extend the radar results from Clementine and map the ice deposits of the poles.

The Clementine bistatic experiment led to the development of an RF transponder called Mini-SGLS (Space Ground Link System), which flew on the Air Force mission MightySat II in 2000.  This experiment miniaturized the RF systems necessary for a low mass, low power imaging radar.  With the 2008 inclusion of our Mini-SAR on India’s Chandryaan-1 lunar orbiter, we finally got the chance to build and fly such a system.  Chandrayaan-1 not only mapped the high CPR material at both poles, it also carried a spectrometer (the Moon Mineralogy Mapper, or M3) that discovered large amounts of adsorbed surface water (H2O) and hydroxyl (OH) at high latitudes.  Coupled with the measurement of exospheric water above the south pole by its Moon Impact Probe, Chandrayaan-1 significantly advanced our understanding of polar water, revealing it to be abundant and present in more varied forms on the Moon than had previously been imagined.

Mosaic of Clementine images of the south pole of the Moon. Dark regions contain water ice and small areas near pole are sunlit for significant fractions of the lunar day.

The ever increasing weight of evidence for the presence of significant amounts of water at the lunar poles led to the LCROSS experiment being “piggybacked” on NASA’s 2008 Lunar Reconnaissance Orbiter (LRO) mission.  LCROSS was a relatively inexpensive add-on, designed to observe the collision of the LRO launch vehicle’s Centaur upper stage with the lunar surface, looking for water in the ejecta plume of that impact.  Water in both vapor and solid form was observed, suggesting the presence of water ice in the floor of the crater Cabaeus (at concentration levels between 5 and 10 weight percent).  LRO orbits the Moon and collects data to this day.  Although much remains unknown about lunar polar water, we now know for certain that it exists; such knowledge has completely revised our thinking about the future use and habitation of the Moon.

The Clementine programmatic template has influenced spaceflight for the last 20 years.  The Europeans flew SMART-1 to the Moon in 2002, largely as a technology demonstration mission with goals very similar to those of Clementine.  NASA directed the Applied Physics Laboratory (APL) to fly Near-Earth Asteroid Rendezvous (NEAR) to the asteroid Eros in 1995 as a Discovery mission, attaining the asteroid exploration opportunity missed when control of the Clementine spacecraft was lost after leaving the Moon.  India’s Chandrayaan-1 was of a size and payload scope similar to Clementine.  The selection of LCROSS as a low-cost, fast-tracked, limited objectives mission further extended use of the Clementine paradigm.

The “Faster-Better-Cheaper” mission model, once panned by some in the spaceflight community, is now recognized as a preferred mode of operations, absent the emotional baggage of that name.  A limited objectives mission that flies is more desirable than a gold-plated one that sits forever on the drawing board.  While some missions do require significant levels of fiscal and technical resources to attain their objectives, an important lesson of Clementine is that for most scientific and exploration goals, “better” is the enemy of  “good enough.”  Space missions require smart, lean management; they should not be charge codes for feeding the beast of organizational overhead.  Clementine was lean and fast; perhaps we would have made fewer mistakes had the pace been a bit slower, but overall the mission gave us a vast, high-quality dataset, still extensively used to this day.  The Naval Research Laboratory transferred the Clementine engineering model to the Smithsonian in 2002.  The spacecraft hangs today in the Air and Space Museum, just above the Apollo Lunar Module.

It is probably not too much of an exaggeration to say that Clementine changed the direction of the American space program.  After the failure of SEI in 1990-1992, NASA was left with no long-term strategic direction.  For the first time in its history, NASA had no follow-on program to Shuttle-Station, despite attempts by Dan Goldin and others to secure approval for a human mission to Mars (then and now, a bridge too far – both technically and financially).  This programmatic stasis continued until 2003, when the tragic loss of Columbia led to a top-down review of U.S. space goals.  Because Clementine had documented its strategic value, the Moon once again became an attractive destination for future robotic and human missions.  The resulting Vision for Space Exploration (VSE) in 2004 made the Moon the centerpiece of a new American effort beyond low Earth orbit.  While Mars was vaguely discussed as an eventual (not ultimate) objective, the activities to be done on the Moon were specified in detail in the VSE, particularly with regard to the use of its material and energy resources to build a sustainable program.  Regrettably, various factors combined to subvert the Vision, thereby ending the strategic direction of America’s civil space program.

Clementine was a watershed, the hinge point that forever changed the nature of space policy debates.  A fundamentally different way forward is now possible in space – one of extensibility, sustainability and permanence.  Once an outlandish idea from science fiction, we have found that lunar resources can be used to create new capabilities in space, a welcome genie that cannot be put back in the bottle.  Americans need to ask why their national space program was diverted from such a sustainable path.  We cannot afford to remain behind while others plan and fly missions to understand and exploit the Moon’s resources.  Our path forward into the universe is clear.  In order to remain a world leader in space utilization and development – and a participant in and beneficiary of a new cislunar economy – the United States must again direct her sights and energies toward the Moon.

Note: Background history for the Clementine mission is described in a companion post at my Spudis Lunar Resources blog, HERE.

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author but are better informed than average.

Some Related Posts

How are places on the Moon named?

Map of the Moon by Grimaldi and Riccioli, 1651. Most of the names on this map are still in use today.

Paul D. Spudis

The Once & Future Moon

Smithsonian Air & Space

The Moon is remarkable for the variety and unusual nature of the names of its surface features.  The dark, smooth maria are named for weather or states of mind (Sea of Rains, Sea of Tranquility) while many of the abundant craters of the Moon are named for famous scientists, philosophers, mathematicians and explorers.  Before the advent of the space age, only the near side of the Moon was visible from Earth, although most scientists believed that the far side probably looked exactly like the facing one. (How wrong they were!)  Naturally, once we had the ability to see uncharted lunar territory, a new era of name assignment commenced.  But even now, many lunar craters and features await something more than mere coordinates.

The drawings of the Moon in 1610 by Galileo show craters and mountain ranges but he did not assign names to them.  As telescopes improved, revealing finer surface details, several maps appeared with names bestowed by their astronomer authors to flatter patrons or express their nationalism.  Most of those early names have been forgotten to history.  In 1651, an influential map by Jesuit astronomers Grimaldi and Riccioli became the foundation for the official naming reference guide that we use today.

With the flight of the Luna 3 probe in 1959, the Soviet Union was the first nation to image the far side of the Moon.  To the surprise of most, large regions of maria (so prominent on the near side) were mostly missing from the far side.  Although the first images were of very low quality, the Soviets couldn’t resist the urge to name newly discovered features for a variety of Russian heroes and place names, such as Tsiolkovsky and the Sea of Moscow.  Some new “features” were misidentified because of the low resolution – the name “Soviet Mountains” (no longer used) was given to a bright linear streak across the far side globe (a feature that turned out to be a long ray from the fresh crater Giordano Bruno and not a mountain range).

Over subsequent years, as both American and Soviet spacecraft filled in the far side coverage with increasingly higher quality images, most major far side craters received names of various scientists and engineers.   From around the world, a mixed bag of names were submitted to the International Astronomical Union (IAU – the body of scientists who authorize the names of planetary surface features) for consideration and approval.  Although some were historically significant, many were people with whom few were familiar.

Though NASA does not have the authority to assign names to features on the Moon, an informal practice of naming landmarks was common during the Apollo missions.  Names were given to the small craters and mountains near each landing site (e.g., Shorty, St. George, Stone Mountain) but official names were used as well (e.g., Hadley Rille).  NASA adopts informal names for the same reason that names are given to geographical features on Earth – as shorthand to refer to landmarks and other mapped features.  The most recent illustration of this practice occurred on December 17, 2012 when NASA named the location where the deliberately de-orbited GRAIL spacecraft crashed onto the Moon near the crater Goldschmidt (73°N, 4°W) the Sally K. Ride Impact Site.  Sally thus joins other women of science and note who have lunar features named for them – Hypatia, Caroline Herschel and Marie Curie, among others.  Most of the informal names assigned during Apollo were later given “official” status by the IAU.

The Apollo basin (a 540 km diameter crater on the southwestern far side) was named to honor the Apollo missions – the only crater on the Moon so designated.  Within a few years of their missions, smaller craters were named for the living crews of Apollo 8 (Borman, Lovell and Anders) and Apollo 11 (Armstrong, Aldrin and Collins).  Also located around the Apollo basin are craters named for deceased astronauts and NASA employees, including the lost crews of Apollo 1 and the lost crews of the final missions of the Challenger and Columbia Space Shuttles.  It is appropriate that some feature honors humanity’s first efforts to reach the Moon, as well as others who gave their lives pioneering space.  In a similar vein, craters near the poles of the Moon tend to be named for famous polar scientists and explorers, such as Nansen, Shackleton, and Amundsen.

Other than these exceptions, the location of specifically named craters has little rhyme or reason.  Neither scientific prominence nor contribution guarantees any crater-endowed immortality.  Copernicus and Archimedes are rightly honored with spectacular craters named for them.  But Galileo and Newton (titans in the history of science) are fobbed off with insignificant or barely detectable features.  One of the most prominent craters on the Moon is named for the astronomer Tycho Brahe, an eccentric who spent most of his career trying to validate a variant of the Earth-centered, Ptolemaic model of the Solar System (Ptolemy also has a prominent crater in the center of the near side named for him).  It’s not clear why Riccioli assigned the names he did to these craters, though he cannot be blamed for giving Newton short shrift, as the future Sir Isaac was only nine years old when the Grimaldi and Riccioli map was published.

It is possible to both suggest a name and to propose a crater for that name, though the IAU is not obliged to accept either.  Often, a suggested name is approved but assigned to a different crater.  Currently, the guidelines for submission and assignment of new names for lunar craters are: 1) a scientist or explorer who has made some significant contribution, preferably to the study of the Moon and planets; 2) deceased for at least three years before a crater name becomes official; 3) it cannot duplicate any existing lunar name.

In 2005, I proposed the name Ryder (to honor my colleague Graham Ryder, a lunar scientist who passed away in 2002) and suggested a small, bright crater on the far side to carry his name.  Both suggestions were adopted.  We have since found that Ryder crater is actually quite a geologically spectacular feature (Graham would be proud of his namesake).  In a truly singular event, the crater Shoemaker (named in 2000 and located near the south pole of the Moon) actually contains some of Gene Shoemaker’s remains – a small portion of his ashes was carried aboard the Lunar Prospector spacecraft in 1998.  At the conclusion of that mission, the vehicle was crashed into the south polar crater that was subsequently named for him.

We don’t know what the IAU will do concerning the designation of the Sally K. Ride Impact Site but as history suggests, granting of official status is not guaranteed.  No matter – we will continue to assign names to features as needed and the IAU will do what they do.  In the early 1970s, the IAU (by fiat) abolished the famous Mädler nomenclature system (wherein a small, nearby crater is given the name of a large neighbor plus a letter, such as Copernicus H).  Most working lunar scientists stubbornly refused to accept this decision and continued using the old crater names.  After 30 years of bureaucratic intractability, the IAU finally surrendered and formally adopted the Mädler system.

Official or not, with the passage of time, named lunar landmarks will become familiar to those visiting and working on our nearest neighbor.  Perhaps interesting monikers will be attached by those locals, as is done here on Earth when we assign nicknames to places – like the Big Apple, the Windy City, the Big Easy and the City by the Bay.

Just published:  The Clementine Atlas of the Moon, Revised Edition, an updated atlas and reference guide to lunar features, by Ben Bussey and yours truly.

Originally published at his Smithsonian Air & Space Magazine blog "The Once and Future Moon," Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Technical Readiness

Future industrial activity on the Moon -- science fiction? (Artwork by Pat Rawlings)

Paul D. Spudis
The Once & Future Moon
Smithsonian Air & Space

Space missions are commonly thought of as the ultimate in “high tech.”  After all, rockets blast off into the wild blue yonder, accelerate their payloads to hypersonic and orbital speeds and then operate in zero gravity in the ice-cold, black sky of space.  It requires our best technology to pull off this modern miracle and even then, things can go wrong.  Why would anyone believe that with high technology, sometimes less can be more – that we’re missing a bet by not utilizing current technology.   Like the intellectual tug of war involving man vs. machine, there also is a tug of war between proven technology and high-tech.  Creating these barriers and distinctions is nonsensical.  We need it all.  And we can have it all.

Point in question – in situ resource utilization (ISRU), which is the general term given to the concept of learning how to use the materials and energy we find in space.  The idea of learning how to “live off the land” in space has been around for a long, long time.  Countless papers have been written discussing the theory and practice of this operational approach.  Yet to date, the only resource we have actually used in space is the conversion of sunlight into electricity via arrays of photovoltaic cells.  Such power generation is clearly “mature” from a technical viewpoint, but it had to be demonstrated in actual spaceflight before it became considered as such (the earliest satellites were powered by batteries).

The reason we have not used ISRU is because we’ve spent the last 30 years in low Earth orbit, without access to the material resources of space.  Many ideas have been proposed to use the material resources of the Moon.  A big advantage of doing so is that much less mass needs to be transported from Earth.  The propellant needed to transport a unit of mass from the Earth to the Moon keeps us hobbled to the tyranny of the rocket equation – a constant roadblock to progress.  If it takes several thousand dollars to launch one pound into Earth orbit, multiply that amount times ten to get the cost to put a pound of mass on the Moon.

In the space business, new technologies tend to be viewed with a jaundiced eye.  Aerospace engineers in particular are typically very conservative when it comes to integrating new technology into spacecraft and mission designs, largely on the basis that if we are not careful, missions can fail in a spectacularly dreadful fashion.  To determine if a technology is ready for prime time, NASA developed the Technology Readiness Level (TRL) scale, a nine-step list of criteria that managers use to evaluate and classify how mature a technical concept is and whether the new technology is mission ready.

Resource utilization has a very low TRL level – usually TRL 4 or lower.  Thus, many engineers don’t think of ISRU as a viable technique to implement on a real mission.  It seems too “far out” (more science fiction than science).  Believing that a technology is too immature for use can become a self-fulfilling prophecy, a “Catch-22” for spaceflight:  a technology is too immature for flight because it’s never flown and it’s never flown because it’s too immature.  This prejudice is widespread among many “old hands” in the space business, who wield TRL quite effectively in order to keep new and innovative ideas stuffed in the closet and off flight manifests.

In truth, the idea that the processing and use of off-planet resources is “high technology” is exactly backwards – most of the ideas proposed for ISRU are some of the simplest and oldest technologies known to man.  One of the first ideas advanced for using resources on the Moon involve building things out of bulk regolith  (rocks and soil of the lunar surface).  

Nothing that we plan to do on the Moon involves magic, alchemy or extremely high technology.

This is certainly not high-tech; the use of building aggregate dates back to ancient times, reaching a high level of sophistication under the Romans, who over 2000 years ago built what is still the largest free-supported concrete dome in the world (the Pantheon).  The Coliseum was made of concrete faced by marble.  The Romans also built a complex network of roads, some which remain in use to this day; paving and grading is one of the oldest and most straightforward technologies known.  Odd as it may seem, sand and gravel building material is the largest source of wealth from a terrestrial resource – the biggest economic material resource on Earth.

Recently, interest has focused on the harvesting and use of water, found as ice deposits, at the poles of the Moon.  Digging up ice-laden soil and heating it to extract water is very old, dating back to at least prehistoric times.  This water could contain other substances, including possibly toxic amounts of some exotic elements, such as silver and mercury.  No problem – we understand fractional distillation, a medieval separation technique based on the differing boiling temperatures of various substances.  Again, this concept is not particularly high-tech as only a heater and a cooling column is needed (basically the configuration of an oil refinery).  Some workers have suggested that lunar regolith could be mined for metals, which can then be used to manufacture both large construction pieces and complex equipment.  Extracting metal from rocks and minerals is likewise very old, developed by the ancients and simply improved in efficiency over time.  Processes like carbothermal reduction have been used for hundreds of years. The reactions and yields are well known, and the machinery needed to create a processing stream is simple and easy to operate.

In short, the means needed to extract and use the material wealth of the Moon and other extraterrestrial bodies is technology that is centuries old.  Even advanced chemical processing was largely completely developed by the 19th Century in both Europe and America.  The “new” aspects of ISRU technology revolve around the use of computers to control and regulate the processing stream.  Such control is already used in many industries on Earth, including the new and potentially revolutionary technique of three-dimensional printing.  A key aspect of the old “Faster-Cheaper-Better” idea (one NASA never really embraced) was to push the envelope by relying more on “off-the-wall” ideas, whereby more innovation on more flights would lead to greater capability over time.

Water, Rare Earths and metals are collected and transferred autonomically, using remotely-operated vehicles in a scenario prepared by MIT and presented a gathering of AIAA Houston last spring [John Frassanito & Associates].

Nothing that we plan to do on the Moon involves magic, alchemy or extremely high technology.  Like most new fields of endeavor, we can start small and build capability over time.  The TRL concept was designed as a guideline.  It was not intended as a weapon eliminating possibly game-changing techniques from consideration or to carve out funding territories.  Attitudes toward TRL must change at all levels, from the lowly subsystem to the complete, end-to-end architectural plan.  A critical first step toward true space utilization and for understanding and controlling our destiny there is to recognize and take advantage of the leverage one gets from lunar (and in time planetary) resource utilization.

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Ocean of Storms, Oceans of Argument

Oceanus Procellarum, the "Ocean of Storms," is easily the largest feature of the Moon's complex topography visible, even to the naked eye, from Earth. But is it a true remnant of a basin-forming impact, merely a low remnant of early lunar morphology or perhaps the largest remnant of a hemisphere-sized impact some have labeled "Gargantua? Thumbnail of a 48-image mosaic captured by Yuri Goryachko, Mikhail Abgarian and Konstantin Morozov (ASTRONOMINSK) of Belarus, August 3, 2010.

Paul D. Spudis
The Once & Future Moon
Smithsonian Air & Space

Once upon a time, back in the Dark ages when I was a young student of lunar science, an idea was advanced that Oceanus Procellarum (the largest dark maria on the near side of the Moon) was the site of an ancient, almost obliterated impact basin.  This “Procellarum basin” (then called the “Gargantuan” basin – superlatives fail us sometimes) has been invoked to explain any and every observed aspect of lunar geology, from the distribution of the dark mare lavas, the near/far side dichotomy, the thickness of the crust, the composition of highland rocks, and the relative amounts of radioactively generated heat flow in the Moon.  Such a useful concept to explain so much!

The acceptance by lunar scientists of a Procellarum basin has waxed and waned over the years.  Originally proposed by Peter Cadogan in 1974, the presence of a large, ancient impact basin covering most of the western near side of this part of the Moon, was advanced to explain the unusually high concentration of the chemical component called KREEP – (K) potassium, (REE) rare earth elements, and (P) phosphorus.  Subsequently, Ewen Whitaker (noted cartographer of the Moon) carefully mapped landforms, such as ridges and massifs (mountains) over this area, which purportedly showed that the patterns were best explained by a three-ring basin – 3200 km across, centered on the western near side.  Whitaker named this feature the “Procellarum basin” after the largest mare region that filled it.  Lunar geologist Don Wilhelms fully embraced this interpretation in his classic book The Geologic History of the Moon, making the Procellarum basin the prime cause for the distribution of geologic units on the Moon.

LRO topographic map of the Moon, showing the approximate outline of the "Procellarum" basin on the near side (left) and the South Pole-Aitken basin on the far side (right). One's real, the other isn't.

Yet doubts persisted.  In 1985, Peter Schultz and I suggested that the quasi-concentric arrangements mapped by Whitaker, were related to the Imbrium basin (not to an earlier, underlying mega-basin) on the basis of the ring pattern of this putative feature.  We also pointed out that the patterns of rock compositions supposedly explained by a Procellarum basin were not consistent everywhere, at least casting doubt on the predictive power of the basin’s presence.  The 1994 Clementine mission gave us our first global topographic map of the Moon.  Interestingly, that map dramatically revealed the presence of a circular mega-basin on the far side of the Moon – the enormous 2600 km-diameter South Pole-Aitken basin.  The Procellarum region was also shown to be a low region, but it is not circular (more horseshoe-shaped) and is not as clearly defined as Whitaker’s ring structure suggested.  The stock in the existence of Procellarum basin declined.

But some ideas in lunar science never really go away.  Since that time, several attempts have been made to resurrect the basin.  The latest effort, just published in Nature Geoscience, comes from mineralogical mapping data obtained from the Japanese Kaguya (SELENE) mission.  The authors of this study claim that orthopyroxene (a magnesium-silicate mineral) is distributed on the Moon in association with its largest basins – South Pole-Aitken and Imbrium.  However, in addition to those occurrences, additional outcrops occur in the highlands adjacent to Oceanus Procellarum.  Therefore, these rocks were made during the slow cooling of an enormous impact melt sheet created by the impact which formed the Procellarum basin.

The logic here seems weak.  It has not been established that orthopyroxene only forms from the slow cooling of an impact melt sheet.  When this mineral occurs with the most abundant mineral of the lunar highlands (plagioclase), it makes up a rock type called norite.  Norite is very abundant on the Moon.  It is the dominant rock type at the Apollo 14, 15 and 17 landing sites and occurs elsewhere on the Moon in quantity.  It is particularly prevalent around the edges of the Imbrium basin and one could argue that norite is a characteristic of that basin and the presence of Procellarum basin to explain its occurrence is unnecessary.  Likewise, the existence here of a large differentiated impact melt sheet is inferred from analogy to a terrestrial example, the Sudbury igneous complex, but even in this case, the impact origin of the terrestrial igneous body is not universally accepted.

Evidence for the existence of Procellarum basin must be sought in its topography.  The clarity and preservation of the far side’s South Pole-Aitken basin in the topographic data is surprising.  This feature is one of the oldest on the Moon, yet it preserves relief of over 12 km (the depth one would expect of a fresh feature).  One might expect such an old feature to be indistinct at best, making the discovery of its large relief one of the surprises of the Clementine mission.  At the same time, Procellarum is a vast irregular depression averaging less than 3-4 km deep; its lack of topographic expression is more in line with what one might expect for the oldest basin on the Moon.  However, unlike all other lunar basins, a topographic bulge 2-3 km high occurs near the center of this feature (near the crater Copernicus).  No other basin on the Moon (or on any other planet) contains interior topography higher than the elevation of its topographic rim; at SPA, all of the terrain within the 2600 km diameter rim crest is lower than its rim.  The unusual relation of a bulge within Procellarum does not support the concept that it is an impact basin.  It seems more likely that it is either a feature of internal origin (possibly related to early melting episodes) or a coalescence of several overlapping impact craters and basins.

The elliptical South Pole-Aitken (SPA) basin, mostly on the Moon's farside though it's mountainous outer ring encompasses the the nearside's polar south and the Moon's lowest elevations. The oldest and largest of the Moon's definitively identified impact basins, recent studies appear to have pushed it's formation back beyond 4.1 billion years ago, within less than 500 million years after the formation of Earth and Moon [NASA/GSFC/LOLA].

As we search for the truth, Procellarum basin may well crop up again.  But for today and contrary to the current space press, the new results do not uniquely point to the existence of a large basin here.  In fact, the observations tend to support previous ideas that it is the smaller, overlying Imbrium basin that is associated with a large regional ejecta blanket of roughly noritic composition.

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Water from the Sun

The Sun exudes a constant stream of hydrogen, called the "solar wind."

Paul D. Spudis

The Once & Future Moon

Smithsonian Air & Space

New data returned from a fleet of orbiting satellites changes our perceptions of the history and processes of the Moon.  Concentrated at both lunar poles, and to date the most striking discovery, is the documentation of the presence of large amounts of water.  Though this water has been confirmed by several differing techniques (from multiple missions), we remain uncertain about its source.  Two principal origins have been proposed: 1) water added by the in-fall of water-bearing meteorites and comets during the impact bombardment of the Moon; and 2) the manufacture of water from hydrogen implanted in the lunar soil by the wind from the Sun.

A recent discovery may shed some new light on the origin of lunar water.  Researchers conducting detailed examination of tiny fragments of glass in soil returned by the Apollo astronauts found the molecule hydroxyl (OH) present in the glass.  Interestingly, the isotopic composition of these OH molecules indicates the bulk of the hydrogen comes from the Sun, not from cometary and asteroidal impacts.

The Moon has no atmosphere and no global magnetic field.  As a result, the solar wind – the stream of atoms and molecules constantly emitted by the Sun – directly impinges upon the lunar surface.  Most of this solar wind consists of hydrogen, either in the form of neutral atoms or positively charged ions (i.e., protons).   After it encounters the Moon, this spray of hydrogen has a complex fate, with at least some of it being implanted into the lunar dust.  In a process called adsorption, many of the hydrogen atoms stick to the surfaces of the dust grains.  The amount of adsorbed hydrogen varies by position and chemical composition around the Moon, but it can be present in quantities ranging from less than 10 to over 100 parts per million (ppm).

Impact glass is a major component of lunar regolith – up to 60% by weight of the soil at some landing sites.  The constant bombardment of the lunar surface by microscopic meteorites crushes and grinds up the surface rock, continually mixing the outer layer of the Moon.  When a micrometeorite strikes a rock, it forms a micro-crater (wholly melting the surface beneath this pit) and creates a clear, chemically homogeneous glass particle.  However, when a micrometeorite strikes lunar soil instead of rock, its energy is converted mostly into heat.  This flash heating creates a mixture of melt and mineral debris called agglutinate glass.

The new work details results of analyses of agglutinates returned from several lunar landing sites.  Their study measured both the amounts of hydroxyl present and its isotopic composition.  A normal atom of hydrogen is a single proton and an electron.  But in a rare form of hydrogen, called deuterium, the nucleus contains both a proton and a neutron.  The ratio of this form of “heavy hydrogen” to “normal” hydrogen is unique for different materials throughout the Solar System.  By tracking the D/H ratio in the sample, one can assign a source origin to the measured hydrogen.

When the lunar agglutinate glasses were studied, it was found that their D/H ratios indicated that most of the hydrogen in the hydroxyl molecules came from the Sun and not from cometary or meteoritic sources.  However, the source of the hydrogen is not completely solar, as the D/H ratios suggest some mixing with a subordinate component of either lunar or cometary origin.  The authors of this study suggest that the hydroxyl found on the Moon was created when a small impact flash heated the soil, releasing the adsorbed hydrogen and chemically reducing the metallic oxides in the soil into native metal (found as extremely tiny grains on the surfaces of the agglutinates) and hydroxyl molecules.  Multiplied by billions, such a process could account for the generation of water on the lunar surface.  Subsequent migration of these molecules toward cooler-than-average areas of the Moon (i.e., the higher latitudes, up to and including the poles) may have created the polar ice deposits found by numerous techniques.  In the view of the authors of this study, lunar water comes mostly (but not entirely) from the Sun.  This constant process, occurring on the sunlit hemisphere of the Moon, could create an enormous reservoir of hydroxyl molecules (in motion due to their thermal instability), slowly but constantly moving toward the poles.

If such a process occurs on the Moon, one might expect the accumulation of water in every location where water is stable (i.e., within every permanently dark and cold region near both poles).  But it appears that ice at the poles is not uniformly distributed, occurring in high concentration in some areas while absent in others.  This pattern suggests that the source of polar water might be controlled by a non-equillibrium process, such as episodic bombardment by asteroids and comets.  In fact, both solar wind-produced and cometary water may be present at the poles, but until the ice there is actually analyzed for its D/H content, we cannot be certain of its origin.  Such a measurement does not require the return of a polar ice sample to the Earth.  It could be made remotely in situ on the Moon with a properly instrumented robotic spacecraft.

It is important to emphasize that although the quantities of water generated by this process are potentially very large, the hydroxyl in agglutinate glass should not be considered an economic resource.  These molecules occur globally but at very low levels of concentration (tens of ppm).  Even if this water is the primary and ultimate source reservoir of lunar water, the migration of the molecules and their subsequent collection by the cold traps near the poles serve as a concentrating mechanism, where ice accumulates in large quantities, confined within small areas — the classic definition of an ore body.

What a change has occured in the mindset the lunar science community in the past few years!  From a bone-dry lump of rock in space to a complex, still mysterious body with a dynamic hydrological cycle.  It’s clear that many more discoveries about our Moon and its resources have yet to be revealed.  The more we learn about the Moon, the greater the range of processes we must account for and the more subtle and complex its history becomes.

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

'Once in a Blue Moon,' Our Satellite's True Color

"True" color (left) and "false" color (right) images of the near side of the Moon from Clementine. "Blue" units in Mare Tranquillitatis (right middle of false color image) are ilmenite-rich lavas.

Paul Spudis
The Once & Future Moon
Smithsonian Air & Space

The color of the Moon has been studied for years.  Lunar color is a subtle, yet fascinating phenomenon.  Just when it seemed that we had an explanation, complications would arise.  We now think we have a reasonable explanation for it.  So, why is the Moon gray?  Or to ask the question “scientifically”— What factors account for the range of spectral reflectance seen on the Moon?

Early Apollo astronauts were very impressed with the Moon’s lack of color.  During Apollo 8 (first mission to orbit the Moon in 1968) Jim Lovell remarked, “The Moon is basically gray – no color.”   The Apollo 10 crew was struck by the numerous brownish hues exhibited by the Moon – from a bright tan to a dark, chocolate brown.  When the first astronauts landed and walked on the Moon (Apollo 11), they had an even closer view.  Buzz Aldrin mentioned that although the surface color was basically gray, he could see interesting colors within some rocks outside the LM window.  During the EVA, Aldrin mentioned to Neil Armstrong that he had seen “some purple rocks.”  Purple? — perhaps so.

The Apollo 15 crew was surprised on their 1971 mission to catch a fleeting glimpse of green on the surface (in film shot earlier by crews on the lunar surface, color was too subtle to be seen). When they raised the sun visors of their helmets to again see that the soil was gray, the disappointment in their voices was palpable.  But then, at the very next station, they again saw a flash of green and this time, it was still green when the visors were raised.  Despite the predictable remarks about “green cheese,” this lunar material – consisting of volcanic glass erupted from deep (> 400 km depth) within the Moon under high pressure – was still green when brought back to Earth.

During their second lunar traverse in 1972, the crew of Apollo 17 found orange soil at Shorty crater.  Also volcanic glass, this soil is made up of tiny (~50 micron) beads of orange glass, again erupted from great depth.  It is orange (as opposed to the Apollo 15 green glass) because of its relatively high titanium content.  It is mixed with black glass beads, of identical composition, but in this case, partly crystallized.  Subsequent study of the Apollo samples have found volcanic glass fragments in almost every color in the spectrum, from red to yellow and brown in addition to the two described above.

True colors of some selected lunar samples. Top left - green glass pyroclastics from the Apollo 15 landing site. Top right - orange and black glass from Apollo 17. Bottom left -- troctolite showing yellow-brown olivine crystals. Bottom right - brownish crystals of orthopyroxene in Apollo 17 norite sample.

At this point, it is tempting to ascribe lunar color seen at a distance to the intimate mixing of a variety of colors present at fine scale.  But this is not quite correct.  Most returned lunar samples are also gray, ranging from a very dark charcoal to a light, almost white-gray shade.  Minor variations can be seen as a result of the presence of certain minerals.  In particular, the mineral olivine (an Mg- and Fe-rich silicate) is abundant in the lunar crust and is often green or a brownish yellow.  Ilmenite (and iron- and titanium oxide) is bluish-black and probably the source of the  “purple” Aldrin saw in some rocks during the Apollo 11 EVA.  Moreover, the astronauts could sometimes see significant color units from space.  After his surface visit, Apollo 17 astronaut Jack Schmitt (in orbit) saw orange material, excavated by small craters on the southwestern rim of the Serenitatis basin.  He suggested that this material might be related to the orange soil collected at the landing site a few days earlier.

Interestingly, one can detect subtle color differences on the Moon with telescopes and from spacecraft.  Although the Moon appears gray at first glance, one notices different hues of gray in certain places.  The dark Mare Tranquillitatis on the eastern near side is a noticeably darker and “bluish-gray” compared to the dark mare plains just to the north in Mare Serenitatis.  Part of the reason the Moon looks whitish-gray in the sky can be attributed to the fact that it is the brightest object in the night sky – dazzling the eye when first looked at (either with your naked eye or through a telescope).  Spacecraft views also reveal color differences.  It is common practice for lunar scientists to work with “false color” composite images, where color variations are “stretched” to extreme degrees to exaggerate differences in order to make them easier to work with.  The typical “false color” version of the near side of the Moon shows brilliantly colored “blue” and “red” maria; these color units do not coincide with mare-highland boundaries.  The received wisdom is that the different color units in the lunar maria represent lava flows of differing composition. That some lavas are enriched in titanium was a major finding from the Apollo sample studies.  Interestingly, these high-titanium lavas come from “blue” regions in the maria.  Initially, this was only an empirical correlation but we now know that it is the presence of ilmenite (the iron-, titanium-rich oxide) in these basalts that makes them “blue.”

It should be noted that color differences on the Moon are extremely subtle, requiring intensive image processing to display them clearly.  Typically, color differences on the Moon are less than about one percent or so.  We are able to see these differences with a careful look, but mapping the detailed boundaries of individual lava flows requires image processing to make the “false color” composites.

Lunar soil from the Apollo 11 landing site. Mostly gray, the fine material shows splashes of colors, including green, red and brown. Image by Randy Korotev, Washington Univ.

The “true” color of the Moon is a brownish (i.e., reddish) gray, but overall, the surface is fairly neutral in tone.  If the Earth had no atmosphere, hydrosphere or biosphere, it too would be largely a brownish-gray, as its crust is made up (more or less) of the same silicate and oxide minerals as the Moon (in slightly different proportions).  It is the weathering effects of air and water and biological activity at the Earth’s surface that makes it so colorful.  The Moon – having none of these processes – displays the “true color” of the rocky planets of the Solar System.  The dominant mineral in the lunar crust is plagioclase, a calcium/aluminum-rich silicate mineral.  Plagioclase is gray.  Thus, the dusty surface of the Moon, derived from plagioclase-rich rocks, is likewise gray.  When we talk about “red” and “blue” in lunar terms (as in “blue mare basalts”), we mean bluer, or less reddish, than comparable mare deposits elsewhere on the Moon.  So in reality, lunar color differences are really just varying degrees of reddish gray, some more so than others.

And what of the blue Moon?  As Conan the Barbarian might say, “But that is another story…..”

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Hit-and-Run Science

From 'A new hit and run Giant Impact scenario,' July 28, 2012;  Figure 1a: Five snapshots from the 30° impact angle and 1.30vesc impact velocity case (cC06) showing cuts through the impact plane. Colour coded is the type and origin of the material. Dark and light blue indicate target and impactor iron; Red and orange show corresponding silicate material. The far right shows the situation at the time of impact. At 0.52h, it can be seen how the impactor ploughs deep through the targets mantle and pushes considerable amount of target material into orbit. A spiral arm of material forms and gravitationally collapses into fragments. The outer portions of the arm mainly consist of impactor silicates and escapes due to having retained a velocity well above escape velocity. The silicate fragments further inward are stronger decelerated and enter eccentric orbits around the target. The impactor's iron core also looses much of its angular momentum to the outer parts of the spiral arm and re-impacts the proto-Earth. -  Figure 1b: The origin of the disk material highlighted, half a collisional timescale ( (Rimp + Rtar) / vimp ) after impact. In the grazing reference case (cA08), the majority of the proto-lunar disk originates from a spill-over of the impactor. In the head-on cases (cC01, fB06, iA10), much more material comes from the target mantle, being pushed out into orbit by the impactor core. Colours are identical to figure 1. Turquoise on the right shows water ice for the icy impactor case iA10. Reufer, et al. (2012) Icarus 221, 296

Paul Spudis

The Once & Future Moon
Smithsonian Air & Space

The origin of the Moon is a long-standing problem in planetary science.  Reconstructing complex events in the distant past is difficult and requires both knowledge and imagination.  The facts to be explained are relatively straightforward.  The Moon’s overall density (about 3.3 grams per cubic centimeter) and bulk chemical composition are about the same as that of the mantle of the Earth, suggesting a possible relationship between the two.  The idea that Earth and Moon are compositionally related is supported by the ratio of isotopes of oxygen in the lunar samples, which indicate that Earth and Moon are made from matter derived from the same region of the solar nebula (material that is compositionally distinct from that making up the various meteorite groups).  Finally, the Earth and Moon collectively have a very high angular momentum, mostly as a consequence of the high spin rate of Earth and the relatively large mass of our Moon compared to its primary planet.

Prior to the Apollo missions, three different models (capture, fission, binary accretion) vied for acceptance among the lunar science community.  The capture model proposed that the Moon formed elsewhere in the Solar System before a close, chance encounter resulted in the Earth capturing the Moon into orbit.  The fission model proposed that a large mass of molten material spun off a rapidly spinning early Earth, was thrown into orbit and over time, coalesced into the Moon.  The binary accretion model suggested that Earth and Moon assembled themselves independently as two distinct and separate bodies from the beginning.  None of these models seemed able to account for all the “constraints” mentioned above, but no one had any better ideas.

About 30 years ago, the problem of lunar origin was widely considered “solved” with the general acceptance of the Giant Impact model.  In this concept, four and a half billion years ago, the proto-Earth shared its orbit around the Sun with an object about the size of the planet Mars (dubbed Theia, in Greek mythology, the titan who gave birth to Selene, goddess of the Moon).  A chance encounter between these two planetoids resulted in their merging as the Earth-Moon system.  It was thought that a grazing (low angle) impact would serve to both spin up the Terra-Luna system, resulting in its relatively high angular momentum, and hurl vaporized mantle material from Theia into orbit around the Earth.  The disk of orbiting debris quickly coalesced into the Moon and this rapid accumulation resulted in the release of large amounts of heat, which proceeded to melt at least the outer few hundred kilometers of the Moon, creating an “ocean” of molten rock, or magma.

The Giant Impact model seemed to nicely account for most of the properties of the Moon.  But like many big ideas in science, the closer and longer we look at it, the more issues seem to arise.  It was long assumed that the Moon was made of material derived mostly from mantle of the impacting planet (Theia); in this view, the Giant Impact was really just a variant of the capture model.  As such, it did not explain either the chemical similarity of the Moon to the mantle of the Earth, nor their identical oxygen isotope compositions.  This objection was usually brushed away with the admonition that complications might be expected from planet-scale impacts.

A new set of computer models has looked at the consequences of a slightly more head-on planetary collision.  In contrast to the traditional oblique (few degrees) off-center Big Whack, researchers modeled the effects of an impact at about 30° incidence and relatively high velocity (about 1.3 times escape velocity, or roughly 14 km/sec).  They find that in this case, most of the material from which the Moon forms comes not from the impactor Theia, but from the mantle of the Earth.  This result might better explain the compositional attributes of the Earth-Moon system.  In fact, several models were run (slightly varying these conditions) and while none perfectly fit the chemical and dynamical constraints, this one matched them most closely.

While this modeling was underway, another group was analyzing the composition of isotopes of titanium in samples from the Earth, the Moon and meteorites.  The work has established that the chemical fingerprints that relate Earth and Moon are not merely close – they are virtually identical (to the best precision of the measurements).  The authors of this study claim that this result creates problems for the Giant Impact model, as that idea had called for most of the Moon to be derived from the mantle of the impacting planet Theia.  However, with the results of the new computer models of giant impacts discussed above demonstrating that the parameters of the collision can be adjusted to match the constraints on lunar origin, perhaps this is not such a problem for the Giant Impact model after all.

These developments should probably give lunar scientists pause.  After all, the Giant Impact model became popular because the earlier, traditional three models (capture, fission, binary accretion) were all inadequate and their boundaries and defining parameters had to be adjusted to permit their (barely acceptable) viability.  In other words, the models were stretched to fit any inconvenient facts or problem observations.  Now it appears that the same thing is happening to the new, “explains-it-all” Giant Impact model.  A scientific idea that can be stretched to fit any observable fact is not very useful as an explanatory principle – it is simply a glorified “Just So” story.  The late Karl Popper argued that often in science, an idea cannot be shown to be true, but it can always be shown to be wrong – that is, “falsified.”  If a hypothesis cannot be falsified, Popper argued, then it was not scientific. We need a mechanism in science to enable us to dismiss useless or irrelevant concepts and falsification is one way to do that.

So where does such philosophy leave the origin of the Moon?  Perhaps more knowledge and imagination is needed before we can pronounce lunar genesis a “solved problem.”

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Related Posts:
A Sawtooth-like timeline for the first billion years of lunar bombardment (August 28, 2012)
A new 'hit and run' Giant Impact scenario (July 28, 2012)
"Our view of the Moon has turned upside down" (April 26, 2012)
Ti paternity test fingers Earth as Moon's parent (March 28, 2012)
NLSI team sheds light on 'late heavy bombardment' (February 28, 2012)
Spudis: Cataclysmic Conundrum (February 14, 2012)
'Significant change' in bombardment timing (January 6, 2012)
LOLA reveals distinct populations in bombardment record,
Diviner finds "no pristine lunar mantle" even within SPA (September 16, 2010)
'The Grand Lunar Cataclysm and how LRO can help test it' (September 7, 2009)