April 8, 2013
Though unremarkable in appearance compared to the roughly 4,000 craters on the Moon in its size range, the 20 km diameter crater Shackleton has been the source of relentless scientific controversy for the past 20 years. Shackleton is located at the south pole of the Moon; indeed, its near side rim is the precise location of the geographic pole itself. Its location makes observation by Earth-based telescopes difficult and it was not well photographed by the Lunar Orbiter series (our principal source of lunar images) of the 1960s. That all changed in 1994 with the flight of the joint DoD-NASA mission to the Moon, Clementine.
Clementine carried cameras that globally imaged the Moon in eleven visible and near-infrared wavelengths. In addition, it mapped the surface and lighting of the poles of the Moon at uniform resolution over the course of almost three lunar days (74 Earth days). When the Science Team first saw the south polar mosaic, the extent of darkness in the map was striking. Because the Moon’s spin axis is close to perpendicular to the ecliptic plane, the Sun is always at the horizon at the lunar poles. Instead of rising and setting, the Sun circles around the poles at or near the horizon. Because of this grazing incidence, an area in a topographic depression may be in permanent shadow. And so it appeared for Shackleton crater in the Clementine data, setting off bells in the heads of the Science Team.
A key controversy of the post-Apollo era was whether the lunar poles might contain water or not. Although the Apollo samples had been studied and found to be “bone-dry,” we had not been to the poles on any Apollo mission. We knew that any shadowed areas had to be extremely cold as well as permanently dark. As water-bearing debris in the form of asteroids and comets constantly strike the Moon, it was thought that some of that water might get into a polar “cold trap” and would be kept there (essentially) forever – billions of years of impacting cosmic “debris” can add up.
Clementine was not configured to measure the presence of water, but a cleverly improvised experiment used the spacecraft’s data transmitter to beam radio waves into the dark regions near the poles and listen to their reflected echoes on the enormous (70 m) dish antenna of NASA’s Deep Space Network. Interestingly, the reflections indicated an enhancement of “same sense” polarization within the (very large) resolution cell that contained Shackleton crater. A collect of data from a nearby sunlit area (taken as an experimental control) did not show this peak. The Clementine team interpreted the RF peak as evidence for the presence of a few percent water ice within the dark, cold interior of Shackleton crater. The media quickly spread the startling news about water on our “bone-dry” Moon.
Such a controversial conclusion did not go unchallenged. Some in the radar community argued that abundant wavelength-sized rocks on the surface were the source of the enhanced same sense reflection. Since the lunar surface is indeed rocky, this interpretation could not be ruled out. Then a few years later, the Lunar Prospector (LP) mission found an enhancement of hydrogen concentration at both poles of the Moon; as hydrogen is a major constituent of water, the idea ice exists in the dark areas gained credence and has lead to a decade-long scientific search (using a variety of techniques) for lunar polar ice. Though many areas near the poles were studied in detail, attention continued to be drawn back to Shackleton and the area near the south pole.
From studying Clementine images, we discovered that part of the rim crest of Shackleton is one of the most sunlit areas on the Moon. Now we had a double-attraction: constant sunlight with water ice nearby. At a press briefing in 1996, I called this area of water and sunlight “the most valuable piece of real estate in the Solar System.” Nothing found subsequently has changed my mind on that judgment.
So what have we learned about Shackleton lately? Many different, new sensors have flown to the Moon in the last few years, including radar, ultraviolet (UV) imaging, laser reflections, and low-light level imaging. And yet again, Shackleton crater continues to confound us with contradictory evidence, both for and against the presence of water ice in its interior.
In 2009, the question regarding the presence of water ice somewhere near the lunar south pole was answered when the LCROSS impactor threw up a cloud of water vapor and ice particles during its collision with the floor of the nearby crater Cabaeus. Spectral mapping instruments on three different spacecraft (Chandrayaan-1, Cassini, and EPOXI) documented the presence of adsorbed water on the lunar surface, increasing in concentration with latitude toward both poles. A small impact probe flown by India (MIP) passed through a water vapor zone in the exosphere just above the lunar south pole. And radar images from Mini-RF, our radar imaging experiment on both Chandrayaan-1 and Lunar Reconnaissance Orbiter (LRO), found evidence of high same sense reflections (just as Clementine had suggested in 1994) within the interior of Shackleton crater. These new lines of supporting evidence were countered by Japanese researchers, whose Kaguya spacecraft imaged the interior of the crater and found morphology similar to other lunar craters in the same size-class. But no one had ever claimed that the interior of Shackleton was a skating rink of pure ice – the lunar polar ice is partly covered by waterless dust and mixed with an unknown amount of dry regolith.
Interpretation of the new data continues to vex us. The LOLA (laser altimeter) team on LRO recently published a paper that documents the high reflectivity (at 1 micron wavelength) of the walls of Shackleton. Although the team’s favored interpretation is that this is caused by a constant exposure of fresh material on a steep slope, they also note that it is consistent with the presence of water ice on the walls of the crater. In addition, a team analyzing neutron spectrometer data from both LP and LRO found evidence in the fast neutron data (never before analyzed) that water in the interior of Shackleton is a possible explanation for its signal. Detailed analysis of the Mini-RF data for Shackleton corrected for its steep wall slopes and found that the presence of 5-10 wt.% water there provides the best model fit to the observed data. Newly obtained UV images from LRO show the existence of water frost in the interiors of the craters Haworth and Shackleton, and the neutron detector on LRO shows enhanced hydrogen within both Shoemaker and Shackleton craters. The Japanese team from Kaguya continue to insist that the no-ice interpretation is the correct one.
So we are left with a mystery. Some evidence is pro-ice and some is contra-ice. I find it interesting that for most of the investigators, new data does not necessarily change any minds, but tends to be interpreted in a way most favorable to their previously published ideas. This should not be terribly surprising; the people who have argued for some specific interpretation presumably did so for good reasons and desire hard and clear-cut evidence to the contrary before abandoning a previously held position, one no doubt reached after much thought and soul-searching.
The way to unravel the water-ice mystery is to go to the surface of the lunar south pole (or both poles) and measure the composition of the surfaces in question. Getting a definitive answer about the nature of lunar water would be game changing. Some say the bigger mystery is: Why hasn’t the United States sent a rover to the south pole of the Moon to take a closer look?
March 13, 2013
The news of the day is abuzz with the new and astounding discoveries from the Curiosity rover that Mars once had an environment conducive to life. Once it was warmer, wetter, more hospitable. Water flowed over its surface. The chemicals necessary for life’s emergence and development are present on Mars, suggesting that life may have arisen there in the distant past. So why do I have this sense of déjà vu? Perhaps because this new “result” gets trumpeted anew every few years.
The fixation on the possibility of martian life has been a constant throughout the history of the space program, starting before the first planetary mission to Mars in 1965 (Mariner 4) and then waxing and waning in likelihood every few years. Mariner 4 showed us a moon-like Mars, with a rough, cratered surface and thin cold atmosphere. The stock for martian life fell accordingly. A few years later, the twin probes Mariners 6 and 7 flew by Mars, again returning pictures of a cratered surface, but with hints of the presence of unusual terrain, possibly the result of subsurface ice. The stock of the life story rose slightly, but the barren cold desert of the martian surface was hardly a Garden of Eden.
A big breakthrough came with the flight of Mariner 9 in 1971. To the astonishment of most planetary scientists, it revealed a world of giant volcanoes, canyons much larger than the Grand Canyon on Earth, and amazingly, channels that looked as though they were carved by running water. The idea of life on Mars – at least in the distant past – gained credence and served as a springboard for the Viking missions of 1976, America’s bicentennial year. These two missions consisted of both a lander and an orbiter and were specifically designed to test the surface of Mars for the possibility of life. Both landers returned results that were immediately interpreted as negative (although there was some dissent); the surface materials of Mars had a very reactive chemistry, but no organic material was found in the soil, even at concentration levels measured in parts-per-billion. Thus, we had the conundrum of abundant landform evidence for an early, warm and wet climate yet chemical evidence for an almost sterilizing environment at present. If Mars had life, it must have been present only in the distant past. The results from Viking were considered so definitive that no mission was sent to Mars for over 20 years.
What precipitated the new flurry of interest in Mars about twenty years ago was the finding that, astonishingly enough, we have samples in our possession from Mars in the form of meteorites, the so-called “SNC meteorites” (the initials of Shergotty, Nakhla, and Chassigny, the first three meteorites recognized to be of martian origin). It had been thought that the preservation of rocks intact during ejection from the planet at escape velocities and greater was not possible, but in this case, observations trumped theory. Even more amazing, it was claimed that in one of these putative martian rocks, small features within it were actually fossils of ancient bacteria. Although highly controversial then (and now), this finding was given widespread publicity (including even a Rose Garden Presidential statement) and the agency used this discovery to sell a program to send a series of probes to Mars at every two-year opportunity for the next decade.
This fleet of orbiters and landers returned an abundance of new, high-quality data on the martian surface, its composition, the locations of water and its environment. Each mission confirmed that water had once been present on Mars. Each mission confirmed that at present, the surface was not conducive to life. Each lander went to a site that was thought to have been more promising for the development of life than the ones that preceded it. As the years rolled on, each “new discovery” of the former presence of water and favorable environmental conditions on Mars became something of a joke among my colleagues in the planetary science business – how many times can you claim the discovery of something already known?
Lest you think that I am simply expressing my lunar parochialism, I note that this same media phenomenon occurs in regard to the existence of water ice at the poles of the Moon. The theoretical possibility of ice on the Moon had been known for many years. We first found direct evidence for it in 1996 with an improvised radio experiment on the Clementine mission. Subsequent studies from Earth and a variety of other space missions caused the stock for lunar polar water to rise and fall, depending on who issued the latest press release for their published work. Finally, the collision of the LCROSS impactor in 2010 removed all doubt – there was and is ice there, at least at the south pole and in quantities greater than could be reasonably expected to have resulted simply from solar wind deposition. Yet each new finding was announced as a new “discovery” in the press. So this media frenzy is not simply related to Mars mania or even to the over-preoccupation with finding life elsewhere.
The basic fact is that most in the news business do not understand (or at least, do not fully appreciate) the incremental, cumulative nature of modern science. It is seldom indeed when a single experiment or observation causes a scientific revolution. Moreover, it is equally seldom that a breakthough comes from one person or even one research team. Science is a complex, interdisciplinary effort. It makes progress, but slowly and in a manner that includes both leaps forward and (sometimes) backward. Only over long periods of time (decades and greater) is it apparent what the key observation or measurement is and how it fits into a pattern of understanding. Each new mission result adds knowledge, sometimes in great leaps and sometimes in increments so tiny that one can question whether anything new is being learned at all. But even a repeated observation has value in science – in fact, if an observation is not repeatable, it is not a valid scientific observation.
The new inferences from Curiosity suggest a more benign and hospitable environment for life, but few working Mars investigators doubted that such existed in the past. Even if it did not, we have found in the past few decades that even extreme environments on the Earth can support certain types of microbial life. So the new results broaden and deepen our understanding of martian surface properties and processes, they do not revolutionize them. That’s just how science normally works. If some scientists tend to oversell their results, well, they’re only human.
February 13, 2013
Samples are currently making news for NASA’s planetary exploration program. Last August, the rover Curiosity, equipped with a package of laboratory instruments, landed on Mars. On February 9th the rover’s robotic arm drilled its first hole in a rock selected by scientists. In their attempt to gain more information about Mars, scientists will use the rover’s science package to remotely analyze these samples on the martian surface. The results will give them some fairly detailed knowledge on the chemical and mineral make up of these rocks. But what else can we possibly learn from samples?
Geologists in general and planetary scientists in particular often emphasize that “such and such” cannot be known for certain “until we obtain samples” of some planetary surface or outcrop. What is this obsession with samples? Why do (some) scientists value them so highly and exactly what do they tell us? Answers to this question (for there is not a single, simple one) are more involved than you might think.
With today’s technology providing us with only the most rudimentary information, sample analyses made remotely on a distant planetary surface is limited. Some of the things we want to know, such as the formation age of rocks, can only be discovered with high precision, careful laboratory work. That’s a tall order for remote systems. For example, one of the most common techniques used to “date” a rock’s age requires the separation of individual minerals that make up the rock. Next, the ratio of minute trace elements and their isotopes in each grain must be determined. Assuming that the rock has not been disturbed by heating or a crater shock event, this information can be used to infer an age of formation. If we can convince ourselves that the rock being studied is representative of some larger unit of regional significance, we can use this information to reconstruct the geological history of the region and eventually, the entire alien world. So sample analysis is an important aspect of geological exploration.
As I have written previously, we used images to geologically map the entire Moon, noting its crater, basin and mare deposits, and their relative sequence of formation. When the first landing missions were sent to the Moon, great emphasis was placed on obtaining representative samples of each landing site. It was thought that such samples could be studied in detail in Earth laboratories and then extrapolated to the larger regional units shown on the geologic maps. With few exceptions, this approach worked pretty well. As we moved from the landing sites on the maria (ancient lava flows) into the complex highlands, the “context” of the samples – their relation to observed regional landforms or events – became more obscure. A lunar highland rock is typically a complex mixture of earlier rocks, sometimes showing evidence for several generations of mixture, re-fragmentation, and re-assembly. Loose samples lying on the surface were collected from the highlands, none of them were sampled “in place” (i.e., from bedrock). Although this is also true of the rocks from the maria, we observed bedrock “in place” at most of the mare sites and may have actually collected at least one sample from lava bedrock at the edge of Hadley Rille near the Apollo 15 site.
None of the highland samples possess the same degree of contextual certainty as the mare samples. This fact, coupled with their individual complexity, sometimes leads to consternation over exactly what the samples are telling us. It doesn’t help that the Moon’s early history was itself very complex, with magmas solidifying, lavas erupting, volcanic ash hurled into space and laid down in bedded deposits. On top of all those processes were cratering events that mixed and reassembled everything into a complex geologic puzzle, a virtual stew of processes and compositions that hold clues to billions of years of the Moon’s (and Earth’s) history. Nonetheless, we can still perceive most of the story of the Moon’s history, enough at this point to tell us that without those lunar samples in hand, we would be well and truly ignorant of even its most important events and basic processes. The fixation with sample return stems from the science community’s belief that with just a few more carefully selected samples from some key units, all that is now dark will be made light.
There may be severe consequences to the science community’s insistence on the primacy of sample return. The most recent “decadal survey,” the ten-year community study that gives NASA our wish lists for missions and exploration, made a sample return from Mars the centerpiece and sine qua non of future robotic missions. The NRC report was so emphatic in its insistence that it might be paraphrased as saying, in effect, “Give us a Mars sample or give us death!” (with apologies to Patrick Henry). Alas, that formulation may be more apt than anyone desired, as proposed out year budgets for the next five years of NASA funding cuts planetary exploration by almost 30% – a landscape of shifting priorities that raises questions and uncertainty for the future.
Robotic sample return missions to large bodies like the Moon or Mars are expensive because they consist of multiple spacecraft – a lander, which softly places the spacecraft on the surface, a device (such as a rover) to collect and store the samples and an ascent vehicle to bring the sample back to Earth. While none of these functions individually are exceedingly difficult to achieve, all of them (done correctly and in proper sequence) add up to a substantially difficult, complex mission profile.
In the space business (as with most endeavors), more difficult and complex means that more money is required. Moonrise, a proposed robotic mission to return about a kilogram of sample from the far side of the Moon, was projected to cost around one billion dollars. A Mars sample return mission consisted of three separate missions: one to land, collect and store the samples, another one to retrieve those samples and place them into orbit around Mars, and a final mission to return the samples to Earth. With each step costing up to several billion dollars, such a technically challenging Mars sample return mission would be unaffordable.
Although samples have many advantages over remote measurements, those benefits must be weighed against the cost and difficulty of obtaining them. Perhaps the complete extent of what can be accomplished remotely has yet to be fully explored. As mentioned above, absolute ages are key information that we get from samples. Several dating techniques could be adapted to a remote instrument; these methods may not be the most precise imaginable, but they might be of adequate precision to answer the most critical questions. On the Moon, we do not know the absolute age of the youngest lava flows in the maria; age estimates range from as old as ~ 3 billion years to as young as less than 1 billion years. In such a case, a measurement with 10-20% precision is adequate to resolve the first-order question: When did lunar volcanism cease? In addition, such a result would enable us to calibrate the cratering curve for this part of lunar history, a function that is widely used to infer absolute ages throughout the Solar System. A solid result obtained from a robotic lander – even such a relatively imprecise one – would have important implications for lunar volcanic processes, thermal history, impact flux, and bulk composition.
Complex robotic operations in space are always dicey, especially when attempting something for the first time. Samples are a key part of a planetary scientist’s toolbox but their acquisition is difficult, time-consuming and expensive. Samples from robotic missions are more likely to have ambiguous context, thus rendering less scientific value. Scientifically useful sample collection may remain problematic until people can physically go to exotic places in space and fully use their complex cognitive skills. This trade-off between cost and capability must be carefully considered when weighing future exploration alternatives and desired outcomes.
Previous relevant posts:
January 25, 2013
Many people are surprised when they learn that well before the first landing of Apollo in 1969, we already understood the geological history of the Moon. The idea that such a thing was even possible drew considerable skepticism during early preparations for landing on the Moon. The principles for the remote mapping of the geology of the Moon came from several closely related but distinct threads. Eugene M. Shoemaker, a geologist with the U. S. Geological Survey (USGS) who founded the Branch of Astrogeology, laid out the methodology in broad outline from and through the systematic study of lunar surface images in the early 1960s.
One of the basic principles of geology is that younger rocks lie on top of (or intrude into) older rocks. Interestingly, this relationship can be discerned from a photograph. In the case of the Moon, images show the dark smooth plains of the maria (lava) and the rough, cratered highlands. Some craters were found on top of the dark mare plains, while others were filled with mare. Clearly, the craters on top of the mare formed after those plains existed and were thus younger than the maria. On the other hand, dark mare that fills a crater must have formed after that crater existed and so in this case, the crater was older.
By following these simple relations over large areas, it is possible to determine the relative ages of mare and craters, both among themselves and to each other. But such information is trivial unless we can relate these individual ages to some unit or event of regional significance. In principle, if such a relationship can be defined we can extend relative age assignments over large areas, ultimately on a global basis.
The first effort to map the geology of the Moon was by the USGS, but not by the then-newly created Astrogeology Branch. Branch of Military Geology scientists Arnold Mason and Robert Hackman produced the “Engineer’s Special Study of the Moon” in 1960. This special one-off product documented the principal terrain types of the Moon (maria and highlands) and ordered features into three categories of relative age: post-mare craters (youngest), maria, and highlands (oldest). Additionally, the map showed the distribution of linear features, presumed to be faults (fractures along which movement has occurred), and mare ridges (presumed to be folds) over the near side. In this sense, the Engineer Special Study was a geological map because it showed the spatial distribution of rock types, their relative ages, and the inferred structure of the lunar surface. This map was accompanied by a detailed text chart, which showed a region-by-region evaluation of the terrain and construction challenges for each area. But a critical element was still missing.
On Earth, the geologist recognizes the rocks in the field, maps their locations and orientation, and documents the structure of the area under study. But a key part of this work is to figure out where a particular area fits in the global column of geologic units. On Earth, by documenting the slow, gradual nature of geological processes the stratigraphic column was developed slowly over the course of about a hundred years. The terrestrial stratigraphic column also provided key evidence needed to show the gradual transition of life forms from simple invertebrate organisms in the earliest rocks, to the complex and varied life forms in succeeding strata. With the development of a global stratigraphic system and accompanying geologic time scale for the Earth, a framework for understanding the history and processes of the Earth was created.
Gene Shoemaker recognized the need for an organized stratigraphy to aid in our understanding of the Moon. He wanted to understand the Moon’s evolution and age, but also to correlate events on the Moon with events in Earth history. He recognized that a major step forward to such an end was to define a formal stratigraphic system for the Moon – a clear succession of rock types with key regional units defining the system boundaries. He began mapping the area around the crater Copernicus, which lies on the central near side of the Moon, recognizing that the rocks exposed there (from what had been discerned from images) represented all the distinct phases of lunar history.
The basic sequence is easy to follow. The oldest rocks (1) are those that form the highland units of the large, circular Imbrium impact basin. These units are the mountains that make up the rim of the basin as well as the regional highlands around Copernicus, which are ejecta from the basin forming event. Partial flooding by the dark, smooth maria followed (2), including both dark, ash-like materials and smooth flood-like plains (interpreted even then as flows of basalt, the most common volcanic rock type on Earth). These eruptions were followed by the formation of impact craters, of which two kinds could be recognized: an older group (3) that had slightly eroded and lost their bright rays (such as Eratosthenes) and a younger group (4) that preserved the bright rays and showed a fresh, unmodified form (such as Copernicus.)
Shoemaker used these rock units to define the lunar time-stratigraphic systems: the Imbrian, Procellarian, Eratosthenian and Copernican Systems were each assigned to represent an archetypical deposition event. Rocks that existed before the formation of the Imbrium basin were assigned to an informal category, the pre-Imbrian. Thus, Shoemaker created a geologic map that not only showed the distribution of rock units and the structure of a given area, but also classified these rock types into a stratigraphic column for the Moon, one that (because of the enormous extent of the Imbrium basin) could be applied to areas across the lunar near side. With slight modification (the “Procellarian” System is no longer used and the pre-Imbrian has been subdivided into the Nectarian System and pre-Nectarian), this classification scheme subsequently has been applied to the entire Moon.
Shoemaker’s work on geologic mapping of the Moon gave us the ability to immediately put the lunar samples returned by Apollo into a regional and global context. We found that most lunar events occurred very early in its history, with intense geological activity in the first 1-2 billion years and little activity since. Thus, the Moon’s geological record perfectly complemented that of the Earth, whose traces of earliest activity have been erased over time by the active processes of erosion and plate tectonics.
The 1960 Copernicus Prototype Chart LPC-58, the first true geological map of the Moon, was not formally published by the USGS, though a modified and updated version was published later in that decade. By then, Gene had picked up a couple of co-authors for his effort, including one Harrison Hagan Schmitt (a young geologist with the USGS in the early 1960s), who in 1972 ultimately got the chance on the Apollo 17 mission to do what Gene Shoemaker originally got into the space business to do – check the interpretations of the remote lunar geologic mapping by doing field work on the Moon.
December 31, 2012
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, although most scientists believed that the far side probably looked exactly like the one facing Earth. (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 by Galileo of the Moon in 1610 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.
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