Science Goes to the Moon and Planets: Celebrating 50 years since the IGY

Wesley T. Huntress, Jr.

Geophysical Laboratory

Carnegie Institution of Washington

INTRODUCTION

This year marks the fiftieth anniversary of the International Geophysical Year (IGY). The IGY was organized by an international council of scientists in 1955 and set to begin on July 1, 1957. It was the largest international scientific endeavor ever undertaken, and it actually went on for about 5 years. The significance of the IGY to the space age is that both the United States and the Union of Soviet Socialist Republics (USSR) proposed to orbit satellites of Earth as part of the IGY. Both succeeded and opened the door to space. The scientific exploration of space began as an element of the IGY.

After the launch of Sputnik on October 4, 1957, and the first U.S. satellite, Explorer, almost 4 months later, the United States established its civilian space agency, NASA, on October 1, 1958. The U.S. National Academy of Sciences had already established its Space Science Board, now named the Space Studies Board, in June 1958 to advise federal agencies on research in space. In commemoration of the IGY, the opening of a new age of space science, and the establishment of NASA and the Space Studies Board, it seems very appropriate now to reflect back on these past 50 years, how far we have come, and where we want to go.

A LITTLE HISTORY

A little more than 50 years ago we had no space program at all. But we did have a vision. Americans had been treated to a dream of space travel authored by Werner Von Braun in magazine articles and on television programs. In 1952, Collier’s magazine began a series of articles about Von Braun and his vision for putting a space station in orbit around Earth and using it as an assembly point to send spaceships first to the Moon and then to Mars. The articles were filled with fabulous paintings by Chesley Bonestell illustrating how all of this would be done (Figure 3.1). It was science fiction brought to reality. The articles were thrilling. And shortly afterwards Walt Disney, who had an immensely popular weekly show on television, made animated movies based on the Collier’s articles that brought it all to life for American audiences.

The first Collier’s article outlined in technical detail and in brilliant illustrations how man would conquer space with new rockets and space stations—written by experts with considerable respect. The second issue showed how we would get to the Moon. It all seemed fantastic but at the same time credible, and a fair amount of it actually came true. We even dreamed in the mid-1950s of going to Mars—the planet foremost and most mysterious in the mind of man—and the third article in Collier’s in 1954 showed how we could do it.

It was not just a U.S. dream either. The Russians also had dreams to go to the Moon and Mars—visions contemplated by Sergei Korolev, the hidden rival in the Soviet Union to Von Braun in the United States. The USSR built its own version of the Saturn V, the N1, but could not make it succeed. After realizing in 1969 that they had lost the race to the Moon, the Russians countered with robotic rovers and sample return mis-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 41
Science Goes to the Moon and Planets: Celebrating 50 years since the IGY Wesley T. Huntress, Jr. Geophysical Laboratory Carnegie Institution of Washington INTRODUCTION Werner Von Braun in magazine articles and on televi- sion programs. In 1952, Collier’s magazine began a This year marks the fiftieth anniversary of the In- series of articles about Von Braun and his vision for ternational Geophysical Year (IGY ). The IGY was putting a space station in orbit around Earth and using organized by an international council of scientists in it as an assembly point to send spaceships first to the 1955 and set to begin on July 1, 1957. It was the largest Moon and then to Mars. The articles were filled with international scientific endeavor ever undertaken, and fabulous paintings by Chesley Bonestell illustrating it actually went on for about 5 years. The significance how all of this would be done (Figure 3.1). It was sci- of the IGY to the space age is that both the United ence fiction brought to reality. The articles were thrill- States and the Union of Soviet Socialist Republics ing. And shortly afterwards Walt Disney, who had an (USSR) proposed to orbit satellites of Earth as part immensely popular weekly show on television, made of the IGY. Both succeeded and opened the door to animated movies based on the Collier’s articles that space. The scientific exploration of space began as an brought it all to life for American audiences. element of the IGY. The first Collier’s article outlined in technical detail After the launch of Sputnik on October 4, 1957, and in brilliant illustrations how man would conquer and the first U.S. satellite, Explorer, almost 4 months space with new rockets and space stations—written later, the United States established its civilian space by experts with considerable respect. The second is- agency, NASA, on October 1, 1958. The U.S. National sue showed how we would get to the Moon. It all Academy of Sciences had already established its Space seemed fantastic but at the same time credible, and a Science Board, now named the Space Studies Board, fair amount of it actually came true. We even dreamed in June 1958 to advise federal agencies on research in in the mid-1950s of going to Mars—the planet fore- space. In commemoration of the IGY, the opening most and most mysterious in the mind of man—and of a new age of space science, and the establishment the third article in Collier’s in 1954 showed how we of NASA and the Space Studies Board, it seems very could do it. appropriate now to reflect back on these past 50 years, It was not just a U.S. dream either. The Russians how far we have come, and where we want to go. also had dreams to go to the Moon and Mars—visions contemplated by Sergei Korolev, the hidden rival in the A LITTLE HISTORY Soviet Union to Von Braun in the United States. The USSR built its own version of the Saturn V, the N1, A little more than 50 years ago we had no space pro- but could not make it succeed. After realizing in 1969 gram at all. But we did have a vision. Americans had that they had lost the race to the Moon, the Russians been treated to a dream of space travel authored by countered with robotic rovers and sample return mis- 1

OCR for page 41
2 FORGING THE FUTURE OF SPACE SCIENCE FIGURE 3.1 American dreams—Collier’s magazine covers in 1952 and 1954 illustrating Werner von Braun’s dreams of spaceflight. 3.01 magazines collage.eps SOURCE: Reproduced with permission of Bonestell Space Art. sions to the lunar surface—perhaps not as dramatic After Apollo, the political will in the United States as astronautics walking on the surface, but certainly evaporated. In 1972 the United States abandoned the just as scientifically valuable, demonstrating the utility Apollo program and the future promise of lunar bases and excitement of robots traveling beyond Earth and and human flights to Mars. The human space explora- exploring the surface of new worlds under control of tion enterprise retreated to Earth and was resigned to humans on Earth. remain in Earth orbit. We did set foot on the Moon almost exactly as While human space exploration languished after Von Braun had originally envisioned, but not on Mars. 1972, robotic exploration flourished (see Figures 3.3, 3.4, 3.5, and 3.6), and that has kept our dreams alive. Humans may not have exploded out into the solar sys- tem, but our robots certainly have. We have leapt off the surface of our home planet and sent robotic exten- sions of our eyes, ears, noses, arms, and legs to the far reaches of the solar system. Our robotic explorers go where we cannot go because of the limitations of our bodies, and they go where we cannot yet go because of the limitations of our own vision and will. Since the abandonment of human exploration of space beyond Earth, robotic spacecraft have surveyed the solar system from Mercury to beyond Pluto; orbited Venus, Mars, Jupiter and Saturn; and landed on the Moon, Venus, Mars, and Titan to show us the bizarre surfaces of exotic new worlds. In 1957 these places could only be imagined, and traveling to them was in the realm of science fiction. Today, the solar system has FIGURE 3.2 Beginning of the Space Age—the launch of Sput- nik on October 4, 1957. SOURCE: Courtesy of RKK Energia. become our backyard.

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS FIGURE 3.3 The Moon (USA/Apollo 15). SOURCE: Courtesy of NASA. WHY DO WE EXPLORE SPACE? Humans have an inborn imperative to explore and to understand. Exploration and the drive to make Why do we find spaceflight so compelling? Because new discoveries and to learn about what we do not exploration is part of what we are as human beings. understand are qualities that have allowed humans to We have cultural, scientific, political, and economic survive on Earth. Human beings strive to know and incentives to explore space. to understand what surrounds them. By exploring the unknown, humans gain security and dispel fear of the unknown, of what is beyond. This survival mechanism is encoded in our genes. We use the challenge of exploration to advance and to learn, to improve our scientific and techno- logical skills for survival, to sustain our human experi- ence, and to progress. We also exploit the adventure of exploration to provide hope for the future. This is particularly important for our youth, who need to be given a positive vision for their future and inspiration toward achievement. The development of powered flight and global air transportation in the 20th century created new eco- nomic opportunities and ultimately connected societies all over the planet. So too will the exploration of space FIGURE 3.4 Venus (USSR/Venera 13). SOURCE: Courtesy of create new economic opportunities in the 21st cen- Don P. Mitchell of Redmond, Washington.

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE can be accomplished by nations working together, and thereby each gains security by cooperating in a chal- lenging enterprise where there are no risks to national sovereignty. Space is a place to be utilized by Earth, by the humans of Earth, not by any one nation. SCIENTIFIC EXPLORATION: WE ARE COMPELLED The exploration of space is a noble human enterprise with roots in the exploration of our own planet in the 20th century. At the beginning of the 20th century we were exploring the unknown polar regions of our own planet with ships and men. At the end of the 20th century we were exploring the Moon and beyond with spacecraft, robots, and men. Science has been a partner in all of this. We have now stepped upon the Moon and sent robotic spacecraft on flights past every planet in the solar system. We have conducted orbital reconnais- sance of four planets and two asteroids (soon to be five planets and four asteroids); landed on two planets, an asteroid, and a moon of Saturn; and we have conducted roving expeditions on both the Moon and Mars. We are compelled to explore the Moon and the solar system because it is there that we will find answers to fundamental questions humans have been asking themselves as long as we can remember—questions about our own origins and destiny. Questions such as FIGURE 3.5 Titan (ESA/Huygens). SOURCE: Courtesy of How did we come to be? and What will happen to us ESA/NASA/JPL/University of Arizona. in the future? and Are we alone in the universe? The progress we have made in space science over these past 50 years has brought us to the point where we dare voice these big questions, because we believe now that they tury in ways that we cannot anticipate today. Spurred can be answered through the scientific exploration of by the advent of the space age in the late 1950s, the space. These human questions can be recast as scien- investment in science and technology by the United tific challenges—goals to be achieved in the course of States, a relatively young country, drove a half-century exploring space. And from these scientific goals, plans of unprecedented wealth and prosperity. Science and can be formulated for both robotic and human explor- technology are the greatest engines of economic growth ers, including the destinations and the exploration in America, and this has become obvious to the rest of objectives for each. world as new nations open up their own roads to the How did we come to be? This is a question that Moon and beyond. approaches the contemplation of existence. Even so, In our complex world of national interests and astronomers can address the question by determining barriers, the exploration of space can and should be a how the universe began and evolved; learning how global enterprise. Space exploration is an adventure of galaxies, stars, and planets formed; and searching for and for humankind, not for any nation in particular. It is Earth-like planets around other stars. And when we the perfect place for nations to cooperate, because space find Earth-like planets, are they habitable or even is new, unbounded, and open. Achievements in space

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS FIGURE 3.6 Mars (USA/Spirit Rover). SOURCE: Courtesy of NASA/JPL. inhabited? The answers require large and complex space notion that we should be alone; others are fearful of telescope systems made possible by human construc- the potential for other life “out there.” Most scientists tion and servicing in space. We need to find out how see the possibilities and are overwhelmed by the notion Earth developed its biosphere and whether these same that the universe might be teeming with life, at least processes ever occurred on other planets in our solar microbial life and perhaps even intelligent forms. We system. This requires research on life here on Earth will find the answer by searching for life in the most and extensive exploration of other planets in our solar system where there may have been another chance for life, such as Mars and Europa. What will happen to us in the future? Every human wonders about the future. One form of this question asks if there is any threat to us from space, especially from Earth-crossing asteroids. The answer will come from surveys of the Earth-crossing asteroid popula- tion in space and space missions that determine their c omposition and structure. Another form of this question asks what future humans have in traveling to and living on other planets. Is our species destined to populate space? Ultimately I believe the answer is yes, and it will happen through exploring space and utiliz- ing the resources we find in the most promising places out there. Are we alone in the unierse? Every human being FIGURE 3.7 The Moon and Mars beyond—the two most wants to know the answer to this question. We are exciting places for human and robotic exploration. SOURCE: compelled to find its answer. Some find comfort in the Courtesy of Donald Parker and Jeff Beish.

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE promising places in the solar system, such as Mars and nation, first a virtual one through robotic missions and Europa, and by looking for signs of life on planets out- the internet, and ultimately for humans a permanent side the solar system with space telescopes. exploration outpost and then a tourist destination. So how do we go about all this? Where do we go in the solar system, and what do we do there to try Science On and About the Moon and answer these questions? Let’s start with the Moon. It’s not the only place we need to go, but it’s close, it’s The Moon is a solar system history book, a “Rosetta right there in our sky and a convenient trip of only a stone,” providing a template for deciphering and un- few days. derstanding the history and evolutionary processes of the terrestrial planets. Due to its lack of atmospheric weathering and geological activity, the surface of the WHAT GOOD IS THE MOON? Moon is a repository of information from the earli- We probably would not have a space program if it was est epochs of solar system history. Impact-generated not for the Moon. samples of the early Earth, Venus, Mars, and asteroids may lie on the surface, and samples of lunar mantle If God wanted man to be become a space-faring spe- material may also be exposed as a result of large im- cies, He would have given [us] a Moon. pacts. The ancient rocks on the Moon may represent —Krafft Ehricke, Saturn V rocket engineer our best hope of directly sampling the material from A bit facetious perhaps, but well crafted and on the which the Earth–Moon system formed. We can also mark. The Moon has been dominant in our sky since determine the impact flux of asteroids and comets on before the dawn of man. It is another planet large in Earth over time using the cratering record preserved our sky, demanding attention, drawing our eye and on the Moon. Material from the solar wind trapped curiosity. And without it, man may never have looked and buried in the lunar surface can also elucidate the so questioningly at the sky and generated the interest history of the Sun. in going to the Moon and beyond. Comet impacts over the eons may have resulted in The Moon is a destination for scientific explora- an accumulation of water ice in permanently shaded tion. There is much we still do not know about the regions at the poles. Some studies have suggested that Moon, even after Apollo. It is an archeological site there may be as much as 10 billion tons of water in the for understanding solar system history, especially the polar regions, potentially a valuable source of oxygen earliest phases where the evidence has been wiped out and rocket propellant for future human outposts on on Earth. It is also a close-by platform for conducting the Moon. Finally, the Moon may represent a potential science, a natural scientific outpost from which to ob- resource for commercial exploitation. There have been serve the rest of the solar system, the Sun, Earth, and proposals to export lunar resources for use on Earth, as the universe. well as proposals to use lunar-generated energy and to The Moon is the first step into deep space for use the Moon for education, entertainment, or space any nation’s space enterprise. It is a nearby planetary tourism. destination for flexing the technological muscles of The Moon has also been proposed as a platform any country’s young space enterprise. It is also a way for astronomical telescopes. The most compelling of station to exploring deep space. It can become the new these is a low-frequency radio telescope on the far side Antarctica, a place for nations to cooperate in peaceful where interference from the overwhelming background exploration and to develop the trust needed to proceed of commercial radio broadcast traffic is eliminated. together in international deep space exploration. The Moon is potentially a commercial destina- Origin of the Earth–Moon System tion. The possibilities have been raised for developing resources, including materials and energy to use locally The Moon contains a 4.5 billion year old record of the on the Moon, to support further space exploration, or origin of the Earth–Moon system. Apollo and other perhaps even for export to Earth. The Moon will at lunar missions have only scratched the surface of what some point in the next 50 years become a travel desti- the Moon can tell us about the history of the inner solar

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS critical function, and there remains a trade-off on the capabilities of lunar robots with human operators on Earth versus human lunar field geologists. Impact History of the Earth–Moon System The Moon has recorded the history of impact bom- bardment since its solidification shortly after the for- mation of the solar system (Figure 3.9). It is a “witness plate” that can provide the statistics on impacts that must have occurred on Earth, but whose evidence has been erased by Earth’s turbulent tectonic activity. This lunar impact record extends to time periods earlier than the origin of life on Earth, so that the chaotic disruptions caused by impacts on Earth can be used to understand the life forming process on early Earth. There are meteorites from the Moon found on Earth, and there is every reason to suspect that the inverse is also true. It is possible that material blasted from Earth in its early years rests now on the lunar surface—stones containing secrets to the first billion years of Earth’s history just waiting to be picked up. We FIGURE 3.8 The Earth–Moon pair is unique. It is the only have evidence from the oldest rocks available on Earth major twin planet in the solar system, and Earth is the only that life had already arisen more than 3.5 billion years planet with a surface ocean and life. SOURCE: Courtesy of ago at the end of the Hadean eon and the beginning NASA/JPL. of the Archean eon. Perhaps the clues we need to this early age are waiting to be identified and retrieved on system. There remain some key elements and isotopes that have not been measured and that are necessary for fully understanding the Moon’s thermal and volcanic history and for making an accurate assessment of the resource potential of the Moon. We need to explore and sample more of the diverse regions of the Moon we have not yet visited. We need samples from the lunar mantle that may await us in the deep basins on the Moon. We need to determine the interior structure and composition of the Moon in greater detail than we know today. This can be accomplished with an in situ network of seismic stations and heat flow measurements distributed around the surface. And the determination of absolute ages of lunar minerals is a requirement for understanding the history of the Moon and its rela- tionship to Earth. These measurements now require FIGURE 3.9 The Moon has a unique ability to record his- analysis by ultra-sensitive, highly complex, and mas- tory. The lunar surface may harbor meteorites from Earth’s first billion years, transported to the Moon by large impacts. The sive instruments in Earth laboratories with extensive lunar soil contains embedded solar wind particles; the ancient sample preparation by human laboratory technicians. stratigraphic record exposed on the Moon may reveal a his- W hile sample return can be done robotically, sample tory of the luminosity and state of the Sun over time. SOURCE: selection and characterization on the lunar surface is a Courtesy of NASA.

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE A Platform for Observatories the Moon. Samples of Earth ranging back into the late Hadean could tell us a lot about the early atmosphere, The far side of the Moon, in permanent shadow from ocean, surface, and climate when life was first evolving Earth, is the perfect location for a radio telescope. It on the planet. would be possible to emplace very simple and extremely In addition to assessing the effects of bombardment long, narrow antennas on the far side of the Moon that on Earth’s environment in the Hadean, the post-mare would have unparalleled spatial resolution on the sky cratering record on the Moon can yield information on with extreme sensitivity. Antennas that are kilometers other critical phases of the evolution of life on Earth. in length and deployed from very small roll-up pack- There is evidence that Earth periodically receives large ages are easy to envision. They could be operated re- impacts, and these have been linked to mass extinctions. motely and serviced by humans. They could be used to This hypothesis cannot be tested on Earth, but it can examine solar radio emissions and emissions from the be tested on the Moon by a careful examination of its planets, map emissions from Milky Way objects, and cratering record. look back into time just after the Big Bang when stars Finally, the Moon preserves a record of the most had yet to form. recent impact history of the Earth–Moon system. There are also notions to place optical telescopes on There has been an increased awareness of the potential the Moon. The advantages are that there is no atmo- for future large impacts by Earth-approaching asteroids sphere to distort images and filter out large portions of and comets. The time scale for such impacts is a strong the electromagnetic spectrum, and there is a cold, dark function of size, and current statistics are not as accurate sky for 14 days (except at the poles where permanent as the potential threat dictates they should be. There is night can exist). However, there are significant chal- a growing program for the identification, orbit determi- lenges to emplacing large telescopes on the Moon, nation, and monitoring of Earth-approaching objects including mitigation of lunar dust, the local atmosphere in order to provide advance warning of any threat to near a human-occupied base, large thermal excursions the planet, but more accurate statistics are required between lunar day and night, and the large propulsion to complement the observational techniques. These requirement for the repeated trips into and out of the statistics could be determined by deciphering the late lunar gravity well that will be needed for construction cratering history of the Moon from samples of a large and servicing. number of post-mare craters. Resources: Materials and Energy for A Record of the Ancient Sun Space and Earth The Sun propels enormous amounts of material into The Moon’s regolith contains resources that might be space in the form of hot tenuous plasma known as the useful for processing into materials and consumables solar wind. The solar wind is a sample of the composi- for supporting human explorers on the Moon or for tion of the surface of the Sun. As the Sun burns hydro- sustaining exploration of space beyond the Moon, or gen in its interior over time, it produces new elements perhaps even for export to Earth. These prospects have and isotopes that migrate to the surface and are expelled been buoyed recently by the discovery that there may be in the solar wind. The solar wind impacts the Moon water ice in permanently shadowed regions at the lunar and is trapped in regolith material, which is well pre- poles. The distribution, form, and amount of any such served on the Moon. Age dating of lunar stratigraphy ice in the polar regolith must be understood before the with atomic and isotopic analysis of the implanted solar potential for supporting human exploration can be fully wind in these layers can be used to determine the past evaluated. This assessment can be accomplished first history of solar luminosity as well as to predict its future from lunar orbit followed by in situ measurements on evolution. This information will help us understand the the surface and at depth to characterize these potential past climate of Earth over the entire time that life has deposits in detail. In addition to assessing the value of existed on our planet. these deposits for oxygen and fuel production, they

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS have scientific value in their potential to unravel the history of volatiles in the inner solar system. In addition to the possibility of usable quantities of water ice at the poles, there may be other useful volatiles implanted in lunar dust grains, such as hydrogen from the solar wind. It may be possible to extract oxygen and metals from lunar rocks and regolith to use for life support, propulsion, and construction. Solar energy is another resource that could be har- vested on the Moon. While storage batteries would be required to survive the long lunar night, solar power plants could be placed in polar locations where there is permanent sunlight. The problem then becomes transmission of that power to other regions where it is needed. This energy could also potentially be exported to cis-lunar space or even back to Earth. Exploration: Becoming a Space-faring Species FIGURE 3.10 Astronaut Eugene Cernan drilling a core sample on the Moon. SOURCE: Courtesy of NASA. In addition to its intrinsic science value and its potential importance as an observational platform and a resource node, the Moon is a stepping stone into the so- lar system. The Moon is a natural space station, already Beyond the Moon in Earth orbit, providing a benign environment with In the long run, the Moon is but one of many exciting one-sixth gravity for human utilization and explora- places to visit in the solar system. Our robotic spacecraft tion. The proximity of the Moon suggests its potential have free reign of the entire solar system, while humans as a training ground for human exploration of space. will be limited to Earth’s vicinity, including the Moon, The Moon is a place to learn the skills we need to live in the immediate future. The ultimate goal for human off-planet, to explore planetary surfaces, to learn the spaceflight should be to visit Mars in the next 50 years, respective roles of robots and humans, to develop the but there are two other places for humans and their means to live as much as possible with local resources, accompanying robots to visit between the Moon and and to confront the societal and psychological impacts Mars: one in near-Earth space just beyond the Moon, of confined living in a hostile, alien environment far the Sun–Earth Libration Point L2 (SEL2), and the from Earth and home. other just beyond Earth space, a near-Earth asteroid. W hile the Moon may seem to be a “been there, done that” destination for the American public, the rest of the world has a “go there, do that” attitude, and SUN-EARTH LIBRATION POINT L2: many nations with emerging space programs have the A PLACE THAT IS NOT A PLACE Moon in their sights. There will be a renaissance in In 1772, the French mathematician Joseph L. Lagrange lunar scientific exploration in the next several decades showed that there are five positions of gravitational that the United States will not want to miss. The pull e quilibrium in a rotating two-body gravity field. of the Moon to emerging space programs around the Three of these Lagrange points—also called “libration world can be a catalyst for a new era in space explora- points”—are situated on a line joining the two attract- tion—one of international cooperation instead of the ing bodies, and the other two form equilateral triangles rocket-rattling days of the Cold War and national with these bodies. Figure 3.11 shows a total of seven breast-beating in the days since. libration points located in Earth’s neighborhood, five

OCR for page 41
0 FORGING THE FUTURE OF SPACE SCIENCE FIGURE 3.11 Libration points in the vicinity of Earth. SOURCE: Courtesy of NASA. of which derive from the Earth–Moon gravitational Moon all lie in the same general direction and are far system and two which derive from the Sun–Earth away. There is no obscuration from a local platform. system. Although the collinear points are unstable, The entire sky is accessible all the time. There is no dust very little propulsion is needed to keep a spacecraft at to contaminate mirrors and clog mechanisms. There is or near one of these points for an extended period of a continuous source of solar power for uninterrupted time. This unique gravitational balance and consistent observations. Because of these advantages, the next geometry makes the libration points very important generation of space telescopes is targeted for SEL2 locations in space-exploration architecture. In particu- beginning with the James Webb Space Telescope. lar, the Sun–Earth L2 point is the ideal location for It is conceivable to construct extremely-large- space telescopes, and it is an excellent stepping-stone to aperture telescopes at SEL2 because there is no gravity more distant destinations. Sun–Earth L1 is an excellent to distort mirrors or impede pointing operations. It vantage point for solar telescopes and for viewing the is also possible to fly multiple telescopes in forma- entire sunlit hemisphere of Earth. tion, their mirrors optically linked by laser metrology, The Sun–Earth Libration Points L1 and L2 to provide unfilled dispersed apertures with sizes of (SEL1 and SEL2) are located at the very edge of kilometers or more. Such large sizes can provide spec- Earth’s gravitational influence in the solar system. From tacular, unprecedented resolution on the sky. With such there, you would literally fall off Earth’s gravitational multiple telescope systems it will be possible to survey field into the solar system beyond. For this reason it the universe across the entire spectrum and look back would make an excellent staging point for astronauts at the universe to the beginning of time. It will be pos- traveling beyond Earth–Moon space into the rest of the sible to observe the process of planetary system forma- solar system. The disadvantage relative to Earth–Moon tion around young stars and to search for terrestrial libration points is that the Sun–Earth libration points planets around more mature stars. We can search for are farther away and would take more travel time to evidence of life in the spectra of the extra-solar planets reach. That extra time may be worth it, however, since we find, and multiple aperture systems may ultimately SEL1 and SEL2 are energetically inexpensive points be capable of imaging Earth-like planets around other to reach in space, taking much less energy than getting stars. Imagine a time when humanity will be treated to into lunar orbit or reaching the Earth–Moon libration the first image of an Earth-like planet around another points where the Moon’s gravitational field must be star. That image will have an even larger effect on the countered. human consciousness than did the first global image of SEL2 is an ideal vantage point for space telescopes Earth taken from space by Apollo 8 in 1968. (Figure 3.12). It is a thermally benign environment. Such large, complex systems would probably be There are no temperature changes caused by day–night most cost effective if constructed and serviced by astro- cycles like those on Earth or the Moon. Viewing con- nauts at SEL2 or at a servicing waypoint in one of the straints are minimized because the Sun, Earth, and Earth–Moon libration points closer to Earth. SEL2 is

OCR for page 41
1 SCIENCE GOES TO THE MOON AND PLANETS FIGURE 3.12 Multiple space telescopes flying in formation, positioned at SEL2, and coherently linked optically through laser metrics, may someday be able to resolve and image Earth-like planets around nearby stars. SOURCE: Courtesy of NASA. a relatively benign and low-risk destination for human spaceflight. Its unique location at the edge of Earth’s gravitational influence makes it an energy-efficient starting point for missions to deep space. Having de- veloped the capability to travel to SEL2 for telescope construction and servicing, astronauts could use SEL2 to construct and service spacecraft to be staged from here for journeys to more distant destinations. SPACE ROCKS Near-Earth objects (NEOs), also known as near-Earth asteroids, are nearby remnants of planetary formation FIGURE 3.13 Itokawa, a near-Earth asteroid several city and represent valuable storehouses of information on blocks long, visited and sampled by the Japanese Hayabusa the origin of the solar system. Their structure and spacecraft now returning its cargo to Earth. SOURCE: Courtesy composition may hold clues to important scientific of JAXA.

OCR for page 41
2 FORGING THE FUTURE OF SPACE SCIENCE questions about the history of the solar system. In addi- exploration just enough to greatly reduce the risk of the tion, since they pose by far the most significant impact Mars missions to come. In addition, development of the threat to Earth, an understanding of their diversity and capability for human operation on and near NEOs, in their physical characteristics could someday be vital advance of the discovery of any specific impact threat, to averting a potential global disaster. These objects could turn out to be a wise investment. impact Earth regularly, with mean times between col- lisions dependent on size—larger objects fall much less MARS IS FOR ROBOTS AND HUMANS often simply because there are fewer of them. There are recent and dramatic impact scars on Earth, including Virtually ever since it was discovered, the planet Mars the 50,000-year-old crater near Winslow, Arizona, and has been special to humankind. For centuries it has the massive blow down scar of the 1908 Tunguska event been a centerpiece for much of our scientific specula- (probably a comet impact) in Siberia. tion and imagination, and it has been explored in the The primary properties of composition and bulk space age more intensively than any other body in the density must be determined in order to understand solar system except Earth. NEO structure, the nature and severity of possible Mars is the most Earth-like planet in the solar impact threats, and the efficacy of various mitigation system and almost certainly had a warmer and wet- strategies. NEOs also represent substantial mineral ter environment early in its history, with flowing and resources in space relatively near Earth. Because NEOs standing water on its surface. Mars may have developed have very low gravity, transportation of these resources life, and while its surface appears lifeless today, an early to other locations can be done relatively inexpensively. biosphere may have survived at depth where liquid wa- These resources could be used for in-space operations or ter might still exist. Mars is the most accessible place may have commercial potential for export to Earth. in the solar system where we can search for evidence of While most of the scientific exploration of NEOs an independent origin of life. From Mars we can learn can be done robotically, NEOs are ideally situated about the origin and history of an Earth-like planet that to provide an important stepping-stone for human has taken a different path in planetary evolution. By missions to Mars. A mission to an NEO provides an comparing the geological and climatological histories opportunity to exercise many of the required human of Earth and Mars, we will gain clues to what it takes transportation elements for Mars in a relatively low- to construct a habitable planet and how that habit- risk manner. NEOs are relatively easy to reach, with ability may be sustained or lost over time. All of these lower energy requirements than achieving lunar orbit objectives share a common thread—water. When in in many cases, but require longer flight times on the the planet’s history did liquid water exist? Where was order of 6 months to a year. Their locations and physi- it and where is it now? In what form (rain, rivers, lakes, cal characteristics will stretch the capabilities of human and oceans)? How much? FIGURE 3.14 Mars has a history. The history of Mars can be read in sedimentary layers like these at the Opportunity rover landing site. SOURCE: Courtesy of NASA/JPL/Cornell.

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS There is evidence that Mars had more habitable outbreaks of such aquifers in the past. Global remote climates in its past and has undergone climatological sensing and sounding can identify potential aquifers cycles, linked to orbital and obliquity changes, that where there might be subsurface ice or water that can episodically may have produced a warmer and wetter be reached with in situ exploration using additional surface environment. There is every reason to believe sounding and drilling. A source of liquid water would that 4 billion years ago the surface environments of the be a key resource for establishing a human outpost two young planets, Earth and Mars, were very similar on Mars. when life first arose on Earth. So by extension, there is a fair possibility that life may have arisen on Mars at that Was There or Is There Life on Mars? time. If there was life on the young Mars, there may be fossil indications of that life to be found. If life has On Earth, wherever there is liquid water there is life, survived and still exists today, then it is hidden below and the same may be true of Mars. Mars may have the surface of Mars where liquid water and sources of developed an independent origin of life early in its chemical energy may still be found. history when it was warmer and wetter, and that life By exploring the geological and climatological his- might have survived at depth where liquid water may tory of Mars, we are examining the evolution of another remain. Mars is therefore a most compelling place to Earth-like planet. The knowledge to be gained will help answer the question, Did life ever arise elsewhere in us to understand how terrestrial planets are built and the solar system? how they evolve, how a habitable environment can be Life requires a source of liquid water (only a dab established and maintained, how that environment can will do), a source of energy, and a source of chemical evolve to become biological, and what the prospects materials. Life is not particular about what it “eats” and may be for other habitable planets in planetary systems seems able to adapt to whatever chemical energy source around other stars. is available. Life on Earth can exist on hydrogen, carbon dioxide, hydrogen sulfide, iron, manganese, and host of other energy sources, so that martian life could do the Where Is the Water? same on mineral deposits and gases escaping from the The key to exploring Mars is to “follow the water.” interior. But liquid water is an absolute requirement. Scientific results from robotic missions show that the The search for extant life should therefore focus on history of martian water and the distribution of its areas where surface mineralogy and subsurface sound- repositories are strongly coupled to the geological and ing indicates a concentration of ice, and perhaps water, climatological histories of the planet. Water has been at accessible depths below the surface. Sites where a major erosional force on the planet in the past; its volatiles are escaping, particularly with some reduced features are written all over Mars. Water has also been components such as hydrogen and methane, would be a major climatological force during the history of the particularly exciting. planet. There is enough water locked up in the seasonal Likewise, the search for past rather than extant polar caps today to cover the surface of Mars to a depth martian life is the search for locations of past liquid of 20 to 30 meters. Water is a major element in pres- water on the planet. Tectonic activity on the planet ent day martian weather. While present in only trace will likely have left samples on the surface with some amounts, the atmosphere is quite often fully saturated fossil evidence of past biological processes. This fos- with water. There are hidden reservoirs of ice, and sil evidence could be in the form of characteristic perhaps water, in the subsurface, evidenced by seepage elemental distributions, isotope ratios, organic residue channels in cliffs and crater walls and the strong near- and perhaps even microfossil morphologies in carefully surface signals of ice seen by orbiting neutron detectors selected rock samples. Finding such evidence can be and radar sounders. The layered polar deposits probably accomplished with an orderly procedure starting with contain as much as 20 to 50 percent water ice. a search from orbit for a set of promising sites, fol- Liquid water in extensive aquifers could exist be- lowed by an in situ examination of the identified sites low the surface, and there is evidence of catastrophic to certify which is most suitable, and finally concluding

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE with in-depth study at one more particularly promising sary of the space age, 50 years from now, humans will site to include very detailed local geochemical examina- have walked on Mars. tion, drill samples, and perhaps even sample return to Earth, depending on in situ measurement capability at BEYOND MARS that time. For its scientific value as well as for its enduring Beyond Mars lies the outer solar system, land of the place in human consciousness, Mars is the ultimate giant planets Jupiter, Saturn, Uranus, and Neptune. destination for humans in the next 50 years. Until that And fencing off the outer solar system from the inner time, robotic missions will play an important role in lays the asteroid belt, with Mars at its inner boundary defining the activities of human explorers, character- and Jupiter beyond its outer boundary. These regions izing the martian environment, searching for potential beyond Mars are out of reach for human exploration in resources, and emplacing assets on the surface. the next 50 years, but they have been and continue to be The ongoing U.S. Mars Exploration program has regions explored by our robotic spacecraft. Fifty years maintained a continuing presence at Mars since 1997. ago at the onset of the IGY, and even after the launch U.S. and European spacecraft operating in orbit and the of Sputnik, it might have seemed that the Moon and Mars rovers Spirit and Opportunity operating on the the nearest planets, Mars and Venus, might be attain- surface are still making discoveries, one after another, able, but we have explored well beyond them. We have that add to the impression of a once-wet Mars and a ventured throughout the entire solar system with our place ever more interesting for further exploration. spacecraft, and the adventure continues. At this writing, Mars beckons. There will be a day when humans a U.S. spacecraft is on its way to the innermost planet, will join our robots on the surface of the fourth planet Mercury. Europe has spacecraft in orbit about Venus from the Sun. The first stop may be the Moon, with a and Mars, Japan and China have spacecraft orbiting layover at an asteroid, and perhaps a stop at one of the the Moon, with India and the U.S. to follow. Japan has moons Phobos or Deimos. But on the 100th anniver- a spacecraft returning from a near-Earth asteroid, and FIGURE 3.15 Is Mars a place for humans? Map of near-surface ice from the Mars Odyssey mission. To understand the potential for past or present life and the future habitability of Mars, we must determine the history of water and its form, amount, and distribution on the planet. SOURCE: Courtesy of Los Alamos National Laboratory.

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS the United States has a spacecraft on the way to two main belt asteroids. The United States has two orbit- ers and two rovers at Mars, with another lander on the way, the U.S./European Cassini spacecraft continues to orbit Saturn, and the U.S. New Horizons spacecraft is on its way to Pluto-Charon and the Kuiper Belt. Asteroids Japan’s Hayabusa spacecraft approached the surface of Itokawa to within a few feet and activated its sampling system. It is returning from its trip and hopefully will land a sample of the asteroid on Earth in 2010. The U.S. Dawn spacecraft is on its way to two of the largest main belt asteroids, Vesta and Ceres, where it will orbit each in turn to carry out the first ever comprehensive investigation of such bodies. Jupiter and the Galilean Moons Beyond the main asteroid belt lies massive Jupiter with its large Galilean moons. There seems little doubt after the Galileo orbiter mission that Callisto, Ganymede, and Europa harbor subsurface oceans, but their fluidity, depth, and extent are unknown. The most intriguing is ice-covered Europa with surface manifestations of a more mobile fluid underneath (Figure 3.19). If there FIGURE 3.16 Mars: What might we find? Not these. SOURCE: is an ocean beneath this ice, then it is sustained by H.G. Wells, The things that live on Mars, Cosmopolitan, March heat flow from the interior of Europa, quite likely by 1908. Illustration by William R. Leigh. FIGURE 3.17 Microbes living in rocks deep within Earth. SOURCE: Courtesy of NASA.

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE tectonic processes that might also bring mineralogical nutrients into the ocean. On Earth, this is a recipe for life. There are plans in the United States and Europe for sending a robotic spacecraft to investigate the Galilean satellites in more detail and in particular to orbit Europa and investigate the depth and extent of its subsurface ocean. Saturn and Titan Beyond Jupiter lies perhaps the most magnificent and spectacular planet in the solar system, ringed Saturn. The Cassini spacecraft now orbits Saturn— FIGURE 3.18 Microbes living on ice in Antarctica. SOURCE: investigating the planet, its atmosphere, magneto - Courtesy of Philippa Uwins, the Discovery Team, and the Queensland University of Australia Centre for Microscopy and sphere, rings, and retinue of moons. While Jupiter has Microanalysis. four large Galilean moons, Saturn has seven somewhat FIGURE 3.19 E uropa and its subsurface ocean. SOURCE: Top: Courtesy of NASA/JPL/DLR. Bottom: Courtesy of NASA/JPL. 3.19 collage.eps

OCR for page 41
 SCIENCE GOES TO THE MOON AND PLANETS smaller icy moons and one giant moon, Titan, which is larger than the planet Mercury. Titan is the only moon in the solar system with a thick atmosphere. Shortly after it arrived at Saturn, the Cassini space- craft dispatched the European Huygens spacecraft to Titan, where it entered the atmosphere, floated down on a parachute, and landed on Titan’s surface. Cassini continues to make close passes at Titan, examining it with its cameras, spectrometers, and imaging radar. Titan’s surface and atmosphere show strong analo- gies to Earth, although it is much colder—near 93 K at the surface where methane plays a similar role on Titan that water does on Earth. Photolysis of methane leads to an atmosphere loaded with organic aerosols and hydrocarbon clouds. There are clear signs of hy- FIGURE 3.20 Huygens image of Titan’s surface from 8 km drocarbon rain and mist near the surface with coastal altitude showing coastal-like deltas flowing into dark plains. deltas very similar to Earth’s that open onto dark flat SOURCE: Courtesy of ESA/NASA/JPL/University of Arizona. plains resembling oceans in appearance. These plains appear episodically to become covered with liquid hydrocarbon. Huygens landed on such a plain, and its Pluto-Charon, the Kuiper Belt, and Comets instruments indicated that the surface seems to have the consistency of a mud wet with methane and other Launched in January 2006, the New Horizons space- hydrocarbons. The Cassini radar has returned images craft will arrive in the vicinity of the dwarf double of large lakes of hydrocarbon fluid in the polar regions planet Pluto-Charon in July 2015, returning data and of Titan (see Figure 3.21). Titan has indeed turned high-resolution images of one of the largest members of out to be a fascinating place and may hold clues to the the Kuiper Belt of icy dwarf objects at the fringe of our earliest chemistry on Earth that enabled the origin of solar system. It will proceed onward to visit at least one biology on our planet. other yet unidentified member of the Kuiper Belt. FIGURE 3.21 Cassini orbiter radar image of Titan at a northern latitude showing dark hydrocarbon lakes. SOURCE: Courtesy of NASA/JPL.

OCR for page 41
 FORGING THE FUTURE OF SPACE SCIENCE The Kuiper Belt is the storehouse of comets that It is the Moon that first intrigued us and drew us into occasionally get perturbed through close encounters space, next is Mars, and finally it is the notion that we and are thrown inward towards the Sun where they are not alone, that somewhere out there is a planet like make their spectacular appearance with large halos of our own, a planet with life on it, and perhaps a civiliza- gas, dust, and ionized curved tails. We have even sent tion—galactic neighbors with whom we can share the our spacecraft to intercept these objects, returning data glory of the universe. and images on flybys, one returning samples after flying through the coma of Wild 2, and another impacting WE’VE COME A LONG WAY Tempel I to examine the resulting plume for clues to IN THE LAST 50 YEARS its composition and structure. It is amazing how far we have come since we began this adventure 50 years ago, from confinement on Earth to Beyond Our Own Solar System spacecraft on their way to the very extreme boundaries Beyond our solar system, one day we will find another of the solar system and beyond. We have walked on Earth-like planet in the sights of our space telescopes, the Moon and will again. We will eventually walk on a blue dot circling another star, with oceans, continents, Mars. And in the meantime we will continue to explore and signs of life. This will be one of the most enduring and make new discoveries with our robotic spacecraft, products from space exploration in the 21st century, just extensions of our human senses, that can go where no as that first image of our own planet from Apollo 8 is human can ever go and where we have not yet seen fit one of the most enduring products of the 20th century. to send them.

OCR for page 41