Understanding the Poles of Earth, the Moon, and Mars

Christopher Rapley

National Museum of Science and Industry, London, England

INTRODUCTION

Al Gore, on the inside front cover of his book Inconvenient Truth displays a familiar image (Figure 6.1). He points out that it is the most published image of anything, Earth in particular, that you will come across. It’s a photograph that was taken on December 7, 1972, by the astronauts on the last Apollo mission, Apollo 17, soon after the astronauts had left Earth orbit. It’s an impressive photograph because it’s one of the very few where the Sun is behind the camera so you see a fully illuminated globe. It’s also impressive from the point of

FIGURE 6.1 Earth from Space. SOURCE: Courtesy of NASA. Available at http://apod.nasa.gov/apod/ap010204.html.

FIGURE 6.1 Earth from Space. SOURCE: Courtesy of NASA. Available at http://apod.nasa.gov/apod/ap010204.html.

view of those of us interested in the poles, particularly the Antarctic, because as you look carefully you’ll see that the picture was taken well out of the equatorial plane of the planet and you can see Antarctica quite prominently at the bottom of the globe.

Quite honestly, you could devote the whole of this paper to simply discussing the many facets of this image. It should be pointed out that in spite of the best efforts to discover life on other planets, we have not actually done that yet. In order to understand this object, you not only need geologists and physicists and chemists, but you need biologists. The sort of green color you can see on Africa is, of course, due to biology. To fully understand this image you also need economists, technologists, sociologists, and what have you. You need to assemble all of these scientists together to understand this object because it operates blissfully unaware that we’ve divided it into little pieces and studied them separately. We need to recognize that its various components, the atmosphere, the ocean, the ice, the biology, the humans, all interact in hugely complex non-linear ways.

It can be argued that Earth is, as far as we know, the most complex object in the universe and therefore a really worthy object of our study, not least because it happens to be our home. It’s a puzzle to me that more Earth images were not taken on the Apollo missions. Figure 6.2 is one of the relatively few photographs of Earth that were taken by the Apollo astronauts. This lack of Earth images is a bit puzzling until one accepts that the whole point of the Apollo program was to leave Earth and to get to the Moon, which was therefore the focus of everybody’s attention.



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Understanding the Poles of Earth, the Moon, and Mars Christopher Rapley National Museum of Science and Industry, London, England INTRODUCTION view of those of us interested in the poles, particularly the Antarctic, because as you look carefully you’ll see Al Gore, on the inside front cover of his book Incon- that the picture was taken well out of the equatorial enient Truth displays a familiar image (Figure 6.1). plane of the planet and you can see Antarctica quite He points out that it is the most published image of prominently at the bottom of the globe. anything, Earth in particular, that you will come across. Quite honestly, you could devote the whole of It’s a photograph that was taken on December 7, 1972, this paper to simply discussing the many facets of this by the astronauts on the last Apollo mission, Apollo 17, image. It should be pointed out that in spite of the soon after the astronauts had left Earth orbit. It’s an best efforts to discover life on other planets, we have impressive photograph because it’s one of the very few not actually done that yet. In order to understand this where the Sun is behind the camera so you see a fully object, you not only need geologists and physicists and illuminated globe. It’s also impressive from the point of chemists, but you need biologists. The sort of green color you can see on Africa is, of course, due to biology. To fully understand this image you also need econo- mists, technologists, sociologists, and what have you. You need to assemble all of these scientists together to understand this object because it operates blissfully unaware that we’ve divided it into little pieces and studied them separately. We need to recognize that its various components, the atmosphere, the ocean, the ice, the biology, the humans, all interact in hugely complex non-linear ways. It can be argued that Earth is, as far as we know, the most complex object in the universe and therefore a really worthy object of our study, not least because it happens to be our home. It’s a puzzle to me that more Earth images were not taken on the Apollo missions. Figure 6.2 is one of the relatively few photographs of Earth that were taken by the Apollo astronauts. This lack of Earth images is a bit puzzling until one accepts that the whole point of the Apollo program was to leave Earth and to get to the Moon, which was therefore the FIGURE 6.1 Earth from Space. SOURCE: Courtesy of NASA. focus of everybody’s attention. Available at http://apod.nasa.gov/apod/ ap010204.html. 1

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2 FORGING THE FUTURE OF SPACE SCIENCE • Nations should collaborate, • Coordinated research expeditions using stan- dardized instruments and methods would give a bigger bang for their collective buck, • Observations should be over at least one annual cycle, and • Observations should be a synchronized. This showed great foresight for its time, but it has remained the basis of all the international collaboration on terrestrial, and if you like, space research that has followed. There were 12 nations involved, undertaking a total of 12 expeditions to the Arctic and 3 to the Southern Ocean and the Antarctic. Fourteen meteorological stations were operated and there was a wide range of science undertaken: polar meteorology, atmospheric electricity, geomagnetism, auroral studies, ocean cur- FIGURE 6.2 The Moon with a red dot indicating where Apollo rents, tides, ice motion, and so on. All benefited from 17 landed. SOURCE: Moon image courtesy of P.-M. Heden of this joint collective standardized approach. Vallentuna, Sweden. The Second International Polar Year The red dot shows roughly where Apollo 17 was heading. It got there a few days after that photograph Fifty years later there was a second International Polar was taken. Then on December 14, 1972, we reached Year, organized by the World Meteorological Orga- the end of the heroic age when Gene Cernan and Jack nization, which had also been involved in the earlier Schmitt lifted off from the Moon. Just in the same event. Forty nations participated with 40 Arctic observ- way that the exploration of Antarctica had its heroic age, this remains the end of the heroic first age of lunar exploration. What is particularly interesting is that the first hu- man landing on the Moon took place just under 12 years after the launch of the Soviet Union’s Sputnik 1, which was launched on the fourth of October 1957, heralding the start of the space age that we all celebrate today. THE FIRST INTERNATIONAL POLAR YEAR Sputnik 1 was part of the International Geophysical Year (IGY; 1957 to 1958), which had it’s origins in something that had happened considerably earlier, in the 1880s. The first International Polar Year (1882 to 1883) was proposed by George Neuymeyer but was actually developed, although not completely executed F IGURE 6.3 A model of the beachball-sized Sputnik 1. because he did not live to see it completely, by an SOURCE: Courtesy of NASA National Space Science Data Austrian naval lieutenant, Karl Weyprecht. He devel- Center. Available at http://nssdc.gsfc.nasa.gov/planetary/ oped the principles of the International Polar Year as image/sputnik_asm.jpg. follows.

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 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS ing sites. The United States established the first inland Furthermore, the establishment of: Arctic research stations, so beginning the penetration of the Antarctic for research purposes. Meteorology, • The scientific committees for Antarctic research, including the “jet stream” and ionospheric studies were SCAR, and for ocean research, SCOR, the subjects of a lot of the effort. The initiative was not • World data centers, quite as successful as it might have been because it took • COSPAR, place during the Great Depression, and there simply • World Climate research programs, and was not the financing available for it to be anymore • The International Geosphere-Biosphere than it was. program all have their origins in the IGY. The International Geophysical Year Basically, all of the international coordinated Twenty-five years later, after World War II, and with Earth-system science that you see today owes its origins the huge surge of technological and scientific advance to this historical thread. Of course, another extremely that that stimulated, it was decided that it would be a important outcome of the IGY was the Antarctic Treaty good idea to have a third International Polar Year. This system. The nations with land claims in the Antarctic, grew to become the International Geophysical Year. It particularly those with disputed land claims, agreed to was organized by the World Meteorological Organi- set them aside during the period of the IGY. They then zation and by the International Council of Science, or decided that “if we can do it for a couple of years why Scientific Unions (ICSU) as it was in those days, and don’t we do it in perpetuity,” and indeed that is the way involved 67 nations and 8,000 stations; 12 nations went that the government of the Antarctic was established. to the Antarctic and set up 40 stations, mainly around This joint government now involves 34 nations and the coastline. Eighty thousand scientists and volunteers has been an extraordinary successful, if slightly arcane, were involved and a very broad range of science was way of managing a major part of the planet, which is addressed. reserved for peace and science. It took place, of course, in the shadow of the Cold IGY made the news. The public was aware of it. War, but it fostered that wonderfully creative mix of It was a very exciting time, not least because of the both international cooperation and rivalry that stimu- beginning of space age and the birth of space research. lated huge amounts of progress. Some examples of what However, it was also a time when the public took a emerged from the IGY are: greater interest, at least for a short while, in science and what science can do. • The discovery of the Van Allen belts, • The first measurements of the thickness of the EARTH OBSERVATION Antarctic ice sheet—thickness in nature, if you like, of the Antarctic ice sheet, and The beginning of what many people recognize as • Establishment of the first Arctic and Antarctic quantitative Earth observation started with SEASAT permanent bases and research programs, which have in 1978. This was followed by a whole series of other endured since. satellites which have provided us with a unique view of Earth. To use a term coined by Hans-Joachim Schelln- huber at the Potsdam Institute for Climate Impact Research, we can now view Earth through a “macro- scope” (Figure 6.5). Just as you use microscope to study something that is very small compared with you, you FIGURE 6.4 The official logo can use a macroscope to study something that is very o f the 1957–1958 Internation - large compared with you. Earth is that object. al Geophysical Year. SOURCE: With the convergence of the ground tracks at polar Courtesy of International Council for Science, World Meteorological orbiting satellites at the poles, not only do you get a Organization Joint Committee.

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 FORGING THE FUTURE OF SPACE SCIENCE been removed the ocean and the atmosphere are far better coupled than they would otherwise be. Quite a lot of that heat comes back out again. However, it is not entirely obvious which way this will work out. It is the difference of two large numbers, but it does turn out that by and large the ice-albedo feedback does have its affect, and this is why we have seen this extra warming in the polar regions. However, because you get this amplification in the polar regions, the system amplifies the noise as well as any systematic signal. It’s not at all obvious that you would detect climate change or human-induced climate change more easily in the polar regions than in the tropics. The signal to noise ratio issue is not fully resolved. However, if there are impacts of humans on the planet, they will have a big impact in the polar regions. THE ARCTIC FIGURE 6.5 A model of a macroscope. Figure 6.6 shows the sequence of satellite-derived minimum-Arctic-sea-ice measurements that extends from the summer minimum of 1979 through to the fantastic view of what is going on over the whole Earth summer minimum of 2005. Despite the large amount if you build the right instruments and put them on the of inter-annual variability, it can be seen that there right satellites, but you also get a spectacularly good has been a steady decline of about 25 percent over view of what is going on in the polar regions. that period. In 2005 there was bit of a dip, and people What have we learned from this? It is a combina- speculated about whether they’re seeing an accelera- tion of the work done by all of the scientists involved tion of the loss of sea ice, especially because of a rather in the space-Earth observation initiatives over the past dramatic decline in the multi-year ice. The thicker ice three decades and also all of the work that has gone on that survived several annual cycles was noted, but in the ground and in the atmosphere using ships, aircraft 2006, measurements were back up on the curve again, and research stations. What we have learned is that and then last year (2007) there was an extraordinary human-induced climate change is real and serious. decrease. If you’re looking for a dramatic non-linear effect The previous minimum of 5 million square kilo- of warming, then watching a piece of ice melt is pretty meters is shown on the right in Figure 6.7. The 2007 dramatic, and in a warming world, ice retreats. It does minimum of 4 million square kilometers is shown on not necessarily have to melt, at least not initially, but it the left. This is an excellent example of what satellite can slide off into the ocean and do things and then melt data can tell us. at its leisure; so ice retreats. Now one of the things that The image in Figure 6.8 was taken by passive you often hear is that the polar regions see an amplifi- microwave instrument. You can see the pole with a cation of global warming, and this is true. The fastest sort of black hole where there is no observation and warming spots on the planet are in Alaska, Siberia, and you can clearly see Greenland. You see the ice melting the Antarctic Peninsula. At least in part, this is because back to the minimum, and if you know where to look, as you melt white ice or snow, it reveals dark ocean or the northwest and northeast passages open up in a way land, so instead of reflecting away 80 percent of the that is quite unprecedented. Somebody decided to see incoming solar heat or light, you absorb it. if they could sail a sailing boat through the Northwest One thing to bear in mind is that for half the year Passage last year, and they found themselves in the in the polar regions it is dark, and if the ice cover has

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 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS F IGURE 6.6 Arctic sea ice summer minimum extent. SOURCE: Courtesy of National Snow and Ice Data Center. Pacific without having seen a single piece of ice. That blue on the right. Trying to get ships through these is a measure of the dramatic change that has been seen. passages was something that the British Navy and oth- The Northwest Passage is marked in yellow on the left. ers struggled to do for the best part of 50 years. This The Northeast Passage, which still required a little bit is a good thing for those who wish to transport goods of ice breaking to get through last year, is marked in during these brief summer months, and in South Korea FIGURE 6.7 Average arctic sea ice extent for September 2007 (left) and September 2005 (right). National Snow and Ice Data Center.

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 FORGING THE FUTURE OF SPACE SCIENCE FIGURE 6.8 Envisat ASAR mosaic of the Arctic Ocean for early September 2007. S OURCE: Courtesy of European Space Agency. the shipyards are building vessels for this purpose. On between 1996 and 2005. It is making a significant the other hand, it’s not such a good thing if you’re a contribution now to sea level rise, which previously polar bear or if you’re a frontier person whose livelihood was dominated by thermal expansion and the melting depends on having sea ice to fish from or to catch seal of glaciers. from. Synthetic Aperture Radar has proved to be one Floating sea ice, if it melts, does not change sea of the most extraordinary of instruments available level. Archimedes would have understood that. Up on to the remote sensing community and has absolutely the Greenland ice sheet, the area of summer melting transformed our ability to monitor the movement of has increased in size and progressed steadily north- ice. However, a new weapon has arrived in our armory wards. The summer melt area has increase dramati- recently and that is the extraordinary capacity to mea- cally over the time period during which the area has sure the gravity field, and indeed the changes—very, been monitored by satellites. This surface melting is very subtle changes—in gravity due to the changing not just a few little puddles that get your feet wet. distribution of the ice mass, or indeed the loss of ice in These are torrents of water that can make their way this particular case. down through the ice sheet, lubricate the underside of The graph shown in Figure 6.9, derived from it and indeed cause it to accelerate in its gravitational gravity data obtained by the Gravity Recovery and extrusion towards the periphery of the continent and Climate Experiment (GRACE) mission (twin satel- the ocean. There has been some increased snowfall in lites launched in March 2002 that are making detailed the interior in Greenland, but not enough to compen- measurements of Earth’s gravity fields) show the rate sate for this increased acceleration. The ice discharged of change of mass of the Greenland ice sheet—quite by melting and sliding has increased dramatically an extraordinary feat.

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 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS Apr 2002 - Sep 2007 73.250 Kangerdludssuaq glacier Helheim glacier FIGURE 6.9 Rate of change of mass from GRACE. SOURCE: Courtesy of Isabella Velicogna and John Wahr, Cooperative Institute for Research in Environmental Sciences and Department of Physics, University of Colorado, Boulder. 6.09 from IGY_Paris_Rapley.eps THE ANTARCTIC a succession of ice shelf collapses all due to human- induced global warming, combined with an effect of Let us look at the Antarctic now. One of the things that the ozone hole. has happened in the past 15 years is that the “Wester- Whether or not you accept that, there is no doubt lies” (prevailing winds in the middle latitudes between that there has been warming, and that 90 percent of 30 and 60 degrees latitude, blowing towards the poles) the glaciers on the peninsula are in retreat. The ecology have increased in intensity around the Antarctic. It is also changing. For example, penguin colonies and has also been noted that the place that has warmed the distributions are shifting in response, indicating that fastest around the planet (2½ degrees or more) in the there is a major upheaval going on. However, one thing last 40 years is the Antarctic Peninsula. Indeed, there that can be done when an ice shelf has collapsed is take has been a study that indicates that these things are a research ship into where it was, get some samples of connected. With the intensification of the Westerlies, the sediment from underneath it, and try and figure there have been a greater number of events where out whether it had collapsed in the past. When that warm winds make it over the Antarctic Peninsula, and has been done, it has been found that the northern

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 FORGING THE FUTURE OF SPACE SCIENCE most ice shelves had collapsed perfectly naturally in a had been weakened by melt ponds on its surface that climatic fluctuation 3,000 to 5,000 years ago. However, had broken up its structure and fabric. when it comes to the Larsen ice shelf which collapsed If you look at these pictures of the Wilkins ice shelf in 2002, allowing sediment to be removed from that that were taken by a research aircraft just a week or so area of the continental shelf, it was found that that ice ago (Figure 6.11), you’ll see that it seems to have suf- shelf had been in place for at least 10,000 years and fered a different sort of fracture. It will be very interest- probably longer. Warming is reaching locations it has ing to see what the glaciologists make of this. They are not reached before. flying along a fracture between two major pieces, but One of the things that the Larsen ice shelf collapse look at these extraordinary perfect pieces of ice shelf did for us was resolve a long-standing dispute amongst that have broken almost at right angles and with almost glaciologists as to whether these ice shelves provide a plain “R” cracks. back pressure obstructing the flow of the feed glaciers. In Figure 6.12, the area circled in red is part of the Monitoring the behaviors of those feed glaciers after West Antarctic ice sheet, the so-called Amundsen Sea the Larsen B collapse indicated that this was in fact Embayment. Radar altimetry has show us for some the case. Just a month ago on the western side of the while that the drainage basins marked H and G are peninsula the Wilkins ice shelf suddenly lost a very discharging ice very dramatically. The green colors substantial segment of ice. Almost exactly a month show a substantial loss of ice. Notice that over in east ago, the ice was still in place. One day later, an almost Antarctica there are a couple of other areas that are explosive collapse of the ice took place, and it is now discharging ice as well. drifting off to sea. The thing about the Wilkins ice It turns out that those areas have a very substan- shelf is that it is 5 degrees of latitude further south than tial volume of ice sitting on rock below sea level. The Larsen B. This suggests the warming is penetrating yet West Antarctic is a marine ice sheet (Figure 6.13); it further south. is ice that is sitting on rock up to 2 kilometers below Figure 6.10 is a high resolution image of these huge sea level, which means this is a substantial hydrostatic blocks of ice moving out to sea. Interestingly Larsen B uplift, trying to lift it off the rock. It is very heavy, so that uplift is not winning at present. As that ice begins to slide, it is apparent that the very-high-pressure water FIGURE 6.10 The Larsen ice shelf as seen by MODIS on Febru- FIGURE 6.11 Wilkins ice shelf. SOURCE: Courtesy of the ary 23, 2002. SOURCE: NASA/Goddard Space Flight Center and Scientific Visualization Studio. British Antarctic Survey.

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 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS Using Interferometric Synthetic Aperture Radar, you can see where major discharges are taking place around the Antarctic. It has been said that the increased snowfall on the Antarctic domes, the high parts of the ice sheet, would compensate for some of the losses. In- deed that has been assumed by the Intergovernmental Panel on Climate Change, up until now. Interestingly, the radar altimeter data which seemed to show the effect are a bit in dispute. It is a very tough measurement to make, because the changes are so small. Something like 70 ice cores taken over the whole of that area showed no change in snowfall over the last 50 years at all. It seems that a compensating mechanism may not be taking place. It’s still an unresolved issue. Now consider, what would be the consequence of that continuing discharge running its course? The Amundsen Sea Embayment is a very difficult area to FIGURE 6.12 Radar altimeter data. SOURCE: D.J. Wingham, A. Shepherd, A.6.12 and G.J. Marshall, Mass balance of the Muir, with red circle.eps reach, and indeed it was not until Carl Herb at the Antarctic ice sheet, Phil. Trans. Royal Soc. (Lond) A, 364:1627– National Science Foundation deployed some C130s 1635, doi: 10.1098/rsta.2006.1792, 2006. Courtesy of Dun- to put in major fuel dumps that the British Antarctic can Wingham, Earth Sciences, University College London. Survey and the University of Texas managed to get into the area a couple of years ago. They flew 30,000 kilometers of flight lines with two Twin Otters with at the ground line can begin to force its way in, under ice penetrating radars on board and produced a map the ice sheet. of the underside of the ice sheet. This showed that the What we do not know, because we do not have ice accessible for discharge is equivalent to a one and a the physics to put into the models, having never seen a half meter, mean sea level rise. Of course, the whole of marine ice sheet collapse before, is whether this retreat the West Antarctic ice sheet would raise sea level by 5 will come to a halt, or whether it will continue until all meters if it melted. The area that is currently discharg- of the ice that could discharge has discharged. Indeed, ing; if it continued to do so, it would raise sea level by if that were to happen, how long would that take? one and a half meters or thereabouts. FIGURE 6.13 Schematic diagram of the West A ntarctic ice sheet. SOURCE: W AIS Science a nd Implementation Plan , NASA Conference Publication 3115, Volume 1, September 1995, available at http://neptune.gsfc.nasa.gov/wais/ documentation/toc.html. Courtesy of NASA.

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100 FORGING THE FUTURE OF SPACE SCIENCE How quickly could that happen? The discharge that we are seeing at present is of the order of a half a millimeter a year, sea level equivalent. Even if that ac- celerated, even if that doubled, we would still be talking about 1,000 years before that one and a half meters was delivered, all things being equal. The ice sheet model simply can not tell us, because the ice dynamics is not properly included, and there are even numerical issues about modeling the ice sheet near the ground inline. Just looking at what is going on at present: there is what appears to be a slow acceleration of sea level rise that has been running at about 1.8 millimeters a year during the last century (Figure 6.14). It is now about 3 millimeters a year. If we look at what has happened since the last ice age, there was a 9,000-year sustained period where sea level was rising at about one meter per century, and there were a couple of bursts that were substantially faster than that (Figure 6.15). Of course, sea level was stable for about 3,000 years. Whether or not the pres- FIGURE6.15 from IGY_Paris_Rapley.eps 6.15 Past Sea Level Rise 1 m/C for 9000y 2–5 m/C ent configuration of ice sheets could deliver a meter bursts? NOTE: Mwp, meltwater pulse. SOURCE: Reprinted bitmap image by permission from Macmillan Publishers Ltd: Nature (R.G. per century or whether, because the warming that we Fairbanks, A 17,000-year glacio-eustatic sea level record: influ- are imposing, is at a rate 100 times faster than any- ence of glacial melting rates on the Younger Dryas event and thing in the natural system—or at least if it follows deep-ocean circulation, Nature 342, 637–642, doi:10.1038/ the rate at which we are injecting carbon dioxide into 342637a0, 1989) Copyright 1989). the atmosphere—is an open question. Just how quickly could this happen? A few years ago, if I had discussed the flooding of London, I would have been concerned to be accused of alarmism. Increasingly these days, serious people are taking the threat very seriously. INTERNATIONAL POLAR YEAR In order to try and sharpen up on the answers to some of these questions, such as how much, how quickly, what is going on, the International Polar Year was established by ICSU and the World Meteorological Organisation, F IGURE 6.14 Annual averages of the global mean sea level (mm). SOURCE: N.L. Bindoff, J. Willebrand, V. Artale, A, encompassing a wide variety of sciences. Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. It involves 63 nations, 50,000 individual partici- Levitus, Y. Nojiri, C.K. Shum, L.D. Talley, and A. Unnikrishnan, pants, and some 229 projects, of which 170 are science Observations: Oceanic Climate Change and Sea Level. In Cli- based and 58 are for education and outreach. It has mate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the resulted in more than $300 million in new funding Intergovernmental Panel on Climate Change (S. Solomon, D. worldwide. IPY has a complex structure covering the Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, Arctic, the Antarctic, land, ocean, atmosphere, ice, and H.L. Miller, eds.), Cambridge University Press, Cambridge, United Kingdom and New York, N.Y., USA, 2007.

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101 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS people, and so on. As is to be expected, it has a major space component. One of the most ambitious projects being un- dertaken is called GIIPSY, the Global Interagency IPY Polar Snapshot Year. This is an attempt to get a comprehensive series of “snapshots” by planning and synchronizing IPY satellite acquisition data requests, ultimately resulting from approved IPY projects. Figure 6.17 provides an indication of the satellites that can be brought to bear to study the polar regions. Not shown is the CryoSat mission, scheduled for launch in 2009, which will provide a new view on the cryosphere. IPY set itself the task of leaving a legacy that changes the way polar science is executed. GIIPSY FIGURE 6.16 International Polar Year 2007–2008 SOURCE: will be a major contribution to this task. Courtesy of International Council for Science, World Meteoro- logical Organization PRIC Presentation.eps 6.17 Joint Committee. bitmap image Ai rcraft and in-situ METOP Aqua & Sounders and GP R DMSP T erra GRAC E S ystems SSMI ADM-Aeolus AMSR-E AV HRR MO DIS / AS TER AS CAT ERS-2 Envisat IceSat SMOS RA DA RSAT AS AR M ERI S / A -ATSR GOC E SP OT -4 ALOS HRVIR / V GT PA LS AR P RIS M / A VNIR-2 H f FIGURE 6.17 Global Inter-agency International Polar Year Polar Snapshot Year, the IPY 2007–2008 Snapshot. SOURCE: Courtesy of International Council for Science, World Meteorological Organization Joint Committee. 6.18 GIIPSY_Program_Oct_06.eps bitmap and vector combined

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102 FORGING THE FUTURE OF SPACE SCIENCE ture ranges, from minus 143 degrees centigrade in the depths of the martian polar winter through to as much as 20, maybe even 25, degrees centigrade in the hot summer, with a mean of about minus 63 degrees cen- tigrade. Clouds, fog, and frost all exist on the planet as do surface winds of about 400 kilometers an hour. There is also evidence (relic water flows) that there was free-flowing water on the surface of the planet in the past. Interesting questions therefore abound such as What was Mars like before? and What caused it to change? Mars has an obliquity very similar to Earth. If obliquity is important then, that matching between the two planets simplifies our understanding or our ability to understand. Given the above, a lot of the Mars science has to do with “following the water” and also “following the carbon dioxide.” Indeed, it is interesting to note that the north polar cap, about 1,000 kilometers in diameter, FIGURE 6.18 NASA’s Hubble Space Telescope took this close- has substantial water ice, up to 1.8 kilometers thick; up of Mars when it was just 55 million miles away on Decem- with the seasonal carbon dioxide frost there, up to a ber 18, 2007. SOURCE: Courtesy of NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (Cornell University), and meter thick. M. Wolff (Space Science Institute, Boulder). In Figure 6.19 you can see in these two images of the north polar cap taken one martian year apart, a very substantial difference from one season to another, or if MARS you like, one annual cycle to another. It is also apparent that the dust cover is critical, because blowing dust onto The martian year is 1.9 times that of Earth. Its at- the ice, whether it’s carbon dioxide or water, changes mosphere has only one percent of the surface pressure its albedo, and that will change its ability to absorb or of Earth’s, is 95 percent carbon dioxide, and includes reflect heat. trace amounts of oxygen and water. Surface tempera- FIGURE 6.19 The north polar cap of Mars in summer. SOURCE: Courtesy of NASA/JPL/MSSS.

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10 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS FIGURE 6.20 Terrain differences of the polar caps of Mars: south “Swiss Cheese” (left) and North Pits (right). SOURCE: Courtesy of NASA/JPL/MSSS. 6.21 left and right combined.eps FIGURE 6.21 South p olar cap of Mars, summer 2000. NASA P hoto ID PIA02393. SOURCE: Courtesy of NASA/JPL/MSSS. Interestingly, there are quite substantial differences permanent, although it varies in thickness. It is cur- between the north polar cap and the south polar cap. rently estimated that there is sufficient ice (water ice) in They have quite different long-term histories, and the this polar cap that, if you melted it all, would cover the morphological features of their ice are substantially planet to a depth of 11 meters, i.e., a very substantial different. store of ice. In Figure 6.20, note the so-called “Swiss Cheese” A number of spacecraft have provided different appearance of the south polar cap and the very pitted sorts of data concerning the martian polar regions. nature of the north polar cap. For instance we have MARSIS data, from the sub- The south polar cap possesses water ice (Figure surface radar sounder on the Mars Express space- 6.21) plus a substantial carbon dioxide ice that seems craft which has allowed us to measure the thickness

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10 FORGING THE FUTURE OF SPACE SCIENCE FIGURE 6.22 Map of the thickness of the s outhern polar layered deposits of Mars from MARSIS and MOLA surface topogra- phy. SOURCE: Courtesy of NASA/JPL/ASI/ ESA/University of Rome/MOLA Science Team/USGS. of these polar caps and indeed map that thickness (Figure 6.22). So, what can we learn from such data? Obviously trying to understand the behavior of Mars itself is a scientific challenge. However, given that there is cur- rently no evidence of biological activity, we are then talking mainly about dynamics and physics. The next major spacecraft event will be arrival of the Phoenix spacecraft a little bit later this year (May 25, 2008). It is actually scheduled to land on the edge of the northern polar ice cap and start to perform some tests, drilling down into the ice. THE MOON After the Apollo program ended, the United States rather lost interest in the Moon. The Russians com- pleted their initial program of lunar rovers, orbiters, FIGURE 6.23 The Moon. SOURCE: Courtesy of P.-M. Heden of Vallentuna, Sweden.

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10 UNDERSTANDING THE POLES OF EARTH, THE MOON, AND MARS FIGURE 6.24 Earth-set high-definition image shot onboard the KAGUYA. SOURCE: Courtesy of Japan Aerospace Exploration Agency and NHK (Japan Broadcasting Corporation). the atmosphere are firmly on, or indeed accelerating landers, and sample return missions in 1976. There was above, the business as usual curve. If we do not take then an extended hiatus in lunar missions. action to stabilize these emissions at acceptable levels, The 1990s saw a rekindled interest, and missions temperature-projection models indicate the potential have been flown by the United States, Japan, the for a severe future a century from now and a planet European Space Agency, and recently by China and which is completely transformed, with major social India. These last two nations have used such missions implications. to demonstrate technological skills and capabilities. This is not the whole story. The global climate NASA’s Lunar Reconnaissance Orbiter will begin system is a complex interconnected non-linear system, to tell us a little bit more about the Moon, including capable of going through major reorganizations. A case whether or not water ice really does exist in shaded in point: there is a 50 degrees centigrade temperature spots at the poles, and if so, how much there is.1 It will differential between the equator and the poles, and also be looking for safe landing sites for future crewed that, combined with the angular momentum effects or missions, locating potential resources, characterizing coriolus effects of being on a rotating planet, is what the radiation environment, and demonstrating new determines the flows of the fluids, the atmosphere, technologies. and the ocean. It’s interesting to note that because of the amplification of warming at the poles (by a factor CONCLUSION of 2 or more), at some point, one would reach a situa- tion where that temperature differential has been very Coming back to Earth, we need to remember that, in substantially changed. Whether there would be a major spite of all the rhetoric, carbon dioxide emissions into non-linear reorganization, is something about which we need to be a little concerned. 1The LRO was launched on June 18, 2009.

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10 FORGING THE FUTURE OF SPACE SCIENCE The image in Figure 6.24 was taken from lunar serious the prospect of global climate change really is. orbit by the Japanese SELENE spacecraft. It was im- To quote Socrates (ca. 450 B.C.): “Man must rise above ages of Earth such as this one that arguably crystallized Earth—to the top of the atmosphere and beyond—for in humanities mind the finite nature of the planet, its only thus will he fully understand the world in which limited resources and the need to take care of it. This he lives.” image, I think, should also inspire us to consider how

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