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Rozhdestvensky K, near the north pole of the Moon

The Mini-SAR imaging radar aboard the Indian Chandryaan-1 spacecraft currently orbiting the Moon has been sending back some amazing images for the last couple of months. We are nearing the end of our first radar mapping season (which occurs when the sun illumination conditions on the Moon are unfavorable for normal surface or mineral mapping) and I think it’s an appropriate time to look at and evaluate the data in hand.

To refresh your memory, Mini-SAR works by sending radio pulses to the Moon from the orbiting spacecraft and then very precisely recording the radio echoes bounced off the surface along with their timing and frequency. From this information, we construct images of the Moon that not only show the terrain in areas we could not otherwise see, such as permanently shadowed areas near the pole, but also contains information on the physical nature of the surface covered, specifically, the presence of terrain with unusual scattering properties. Such properties can be caused by many different things, such as composition, particle size, and physical configuration. Most famously, radar reflections can indicate the presence of water ice, based upon the distinct signature of planetary polar caps and the icy moons of Jupiter.

Typically, radar instruments are very massive and use copious amounts of power, but Mini-SAR is less than 10 kg (22 lbs.) and uses less power than the reading light in your living room. It does, however, generate large amounts of data and only a certain amount can fit in the data recorder aboard the Chandrayaan spacecraft. As imaging cameras and spectral instruments also produce large data volumes, we operate Mini-SAR during times when it does not compete against these instruments. Fortunately, because radar imaging provides its own illumination, we do not need the Sun and all of Mini-SAR’s operations occur during lunar night, when the cameras cannot operate anyway.

Our mapping season began in mid-February, 2009. Over the past six weeks, we’ve mapped about 85% of the polar areas. A curious result of SAR imaging is that we never image the areas directly beneath the spacecraft (the nadir groundtrack), so the poles themselves end up as an excluded zone. There are ways to mitigate this effect and get images of the poles, but orbital mechanics dictate that it will take many months to fill in this gap in coverage. In the mean time, we have lots of data of the near polar regions to analyze, including areas in permanent darkness that may contain water ice.

The initial images look very clean, with a few collection artifacts and some missed orbits. Some of the mosaics have mismatched, offset features, not because of any fault in the instrument but because we still do not have a precise global cartographic control net for the Moon, a missing data set that will be filled by the mapping currently taking place by Chandrayaan, the Japanese Kaguya, the Chinese Chang’E and soon, the American Lunar Reconnaissance Orbiter missions. Much of the shadowed terrain covered by Mini-SAR shows a surface much like the surface of the Moon not in shadow, with small craters of a variety of shapes and sizes present. Some images show spectacular surface features, including wall slumping, central peaks and flat, smooth floors.

A particularly interesting and unusual feature was imaged by Mini-SAR almost by accident. Because of a timing error, we started a few mapping passes of the south pole early, before the scheduled start at 80° south latitude. Good thing we did! We covered the fresh, spectacular Schrödinger impact basin, on the lunar far side. Schrödinger shows an unusual, keyhole-shaped crater along a long fissure on the basin floor. This crater is surrounded by optically dark material, which has been interpreted as volcanic ash deposits. The new Mini-SAR image shows that this material is also dark in radar reflectivity, exactly what would be expected from a fine-grained, block-free deposit. Thus, our radar images confirm the geological interpretation first derived in 1994 from Clementine images.

The new radar images are not only visually arresting, but they will be extremely useful in unraveling the complex geological history of the Moon as a whole. We are hard at work finishing the calibration of our instrument, which is required in order to make definite statements about the nature of the radar backscatter signature, the tell-tale sign of the presence or absence of water ice. This determination is extremely important and one of our major experimental goals, so you’ll appreciate that we want to get it right and be as certain as we possibly can be before we pronounce on it. I’ll keep you posted on this blog of our progress.

Note: The images described in the this post are now up at the Mini-RF web site.

The Smithsonian National Air and Space Museum. Photo by Eric Long/NASM, National Air and Space Museum, Smithsonian Institution

The Daily Planet, my new companion blog here at Air & Space magazine, highlights a speech recently given by my good friend Dr. Neil Tyson at the Space Foundation breakfast. Noted is Neil’s oft-mentioned concept that historically, three drivers are responsible for societies or nations undertaking great collective endeavors, such as pyramid- or cathedral-building, New World exploration, or Apollo Moon programs. These drivers are waging war, seeking wealth, and the praise or worship of a deity. Neil believes that the first two are still operative in today’s world, but the last one is a quaint relic of some bygone era.

I feel the need to reconsider this elimination of the third driver. On many very fundamental levels, humanity never really changes. However, our terminology changes over time and I think that all three rationales are as valid today as ever. For the last category, we still construct monuments, have an elite priesthood to preside over it, and constantly revise and extend the current dogma. But we call it “science.”

I can already hear howls of protest from my scientific colleagues, but let’s step back a minute and examine the role and nature of science in today’s society. Science is commonly portrayed as the objective search for truth, as opposed to the superstitious or faith-based (depending upon which side of the fence you are) approach of religion. But science is not really as objective and pure as it is often portrayed and probably never was.

Modern science is a collective, social experience and as such, is subject to human failures and imperfections as is any societal institution. Moreover, science is most often funded by government, adding a layer of political accountability to what should be the objective search for truth. Most problems that we study in modern science are driven by social pressures and direction. Important problems are defined as those that the scientific community thinks are important. Often, these problems are deemed politically important and Congress will vote significant sums of money for their study.

Science deals with verifiable facts and observations. Scientists invent hypotheses to explain phenomena; the media often confuse the concept of hypothesis with that of theory, but in science, we have lots of hypotheses (which are a dime a dozen) but very few theories (which are well established edifices of knowledge, verified and confirmed by observation and experiment over a long period of time.) Scientific concepts and ideas should be subjected to vigorous question and debate.

But in fact, no modern scientist can investigate all phenomena to verify the results of others; we rely on peer review and the opinions of experts to evaluate the validity or lack thereof of new claims and discoveries. Thus, faith is an element of modern science too. The scientific establishment deals with heretics and mavericks, sometimes with amusing condescension and at other times with ostracization. Sometimes, particularly for scientific issues that have serious political or economic effects, the current paradigm becomes a catechism and woe to the scientist who dares to dissent from the “consensus” (which in science, sometimes merely reflects the absence of definitive evidence.) As in religion, we scientists also have our fundamentalists, ecumenicalists, and schismatics.

Science is indeed self-correcting in the long run, but the time constant of this corrective mechanism is sometimes longer than a given scientist’s career span. Thus, some scientists who were “right” never lived to see their vindication; Alfred Wegener, a German geologist who first articulated the evidence for continental drift early in the last century, was widely considered a crank during his lifetime. Only after the sea-floor had been mapped and sampled after World War II did we have the evidence that the continents had moved relative to each other.

Neil Tyson’s third motivator is still with us. We call it “Science” and it is a key driver for many social activities, including and especially for space exploration. The current focus of the Mars program is the Search for Life, a goal many scientists believe should be the motivator for the entire space program. Some pursue this idea with an intensity I can only describe as “religious” – it is there and we will find it!

Cathedral building is alive and well in the 21st century.

People can do field work better than robots

The discussion at Space Politics got me thinking about the scientific value of human spaceflight.  Although there are many reasons for humans to go into space, I also believe that humans bring unique and non-duplicative skills to scientific exploration as well.

Last time, I discussed how the capabilities and experience of the Apollo missions led to a revolution in our understanding of the history of both Moon and Earth and gave new insight into the process of evolution and in turn, our origin.  In this post, I want to look ahead to the value humans bring to future exploration, particularly to the scientific exploration of the Moon and their critical role in lunar return, resource development and ultimately, settlement.

A common article of faith in many academic and space circles is that robotic spaceflight is the preferred method of scientific exploration.  Many famous space scientists (including James Van Allen and Carl Sagan) preached the superiority of unmanned missions to human ones.  Indeed, many phenomena in space (such as plasmas and magnetic fields) cannot be sensed directly by humans or in some cases (e.g., detecting the tenuous lunar “atmosphere”), the presence of people interfere with the property being measured.  I agree that some scientific activities cannot or should not be done by people.  But in other areas of science, human presence is not merely beneficial, it’s critical.

The Moon is a natural laboratory where we will answer critical scientific questions.  The “field” is the world in its natural state, where the phenomena we study are on display and where we learn the key facts that permit us to reconstruct past processes and histories.  Field work is not merely a matter of picking up rocks or taking pictures.  It is the conceptual visualization of the four-dimensional (three spatial dimensions plus time) make-up of planetary crusts.

A good example of the differences in capabilities between humans and robots is illustrated by the experience with the Mars Exploration Rovers (2003-present).  These  machines have traversed many kilometers of terrain, examined and analyzed rock and soil samples, and mapped the local surface over the course of five years.  Many gigabytes of data have been returned by these rovers, giving us an unprecedented view of the martian surface and its geology.  They are truly marvels of modern engineering.

Yet after all this exploration, we are unable to draw a simple geological cross section through either of the two MER landing sites.  We do not know the origin of the bedded sediments strikingly shown in the surface panoramas, whether they are of water-lain sedimentary, impact, or igneous origins.  We don’t know the mineral composition of rocks for which we have chemical analyses; such information is crucial to determine processes and origins.

After five years of Mars surface exploration, we do not know things about the field site that a human geologist could determine after an afternoon’s reconnaissance.  In contrast, we have an incredibly detailed conceptual model, albeit incomplete, of the geology and structure of each of the Apollo landing sites.  The longest stay on the Moon for these missions was three days, most of which was spent inside the Lunar Module.

A robotic rover can be designed to collect a sample, but it cannot be designed to collect the correct sample.  Field work involves posing and answering conceptual questions in real time, when emerging models and ideas can be tested in the field.  It is a complex and iterative process; we sometimes spend years at certain field sites on the Earth, asking and answering different and ever more detailed scientific questions.  Our objective in the geological exploration of the Moon is knowledge and understanding.  A rock is just a rock, a piece of data.  It is not knowledge.  Robots collect data, not knowledge.

It has been argued that planetary exploration robots are controlled by people so human intelligence guides the robot explorer.  Having done both types of exploration in the field on Earth, I contend that remote teleoperated robotic exploration is no substitute for being there.  All robotic systems have critical sensory limitations – important sensory aspects as resolution, depth of field, and peripheral vision.  They have even greater limitations in physical manipulation, an extremely important aspect of field work, where picking a sample, removing some secondary over coating and examining a fresh surface is an important aspect of work in the field.  The makers of the MER rovers recognized this need by including the RAT (Rock Abrasion Tool) to create fresh surfaces; it became worn down and unusable after a short period of operation.

Ultimately, we need both people and machines to explore the Moon and other planets.  Each has their appropriate skill base and limits.  Machines can gather early reconnaissance data, make preliminary measurements, and do repetitive or exhaustive manual work.  But only people can think.  And thinking – and acting and working based upon the results of that thinking – is what field work is all about.