"When the history of the last fifty years can be viewed in a more balanced perspective, some of its most inspirational highlights will surely be the major space projects--often international in scope--that have voyaged to distant planets, extended our cosmic horizons, and deepened our understanding of Earth's place in the wider universe. This fascinating and finely written book chronicles the peak achievements in this grand exploratory endeavor, showing that credit is due to the cutting-edge technology as well as to visionary science."--Martin Rees, Trinity College, University of Cambridge, and Astronomer Royal

"Until we build the starship Enterprise, our efforts to boldly seek out new worlds will depend on mechanical surrogates. This book gives voice to their exploits--adventures not equaled since the great Age of Exploration four centuries ago. The flood of imagery sent back by these craft has revealed--for the first time--a universe of uncanny beauty, terrifying desolation, and inspiring promise. Surely, this is the most wondrous legacy of our generation."--Seth Shostak, SETI Institute

"Dreams of Other Worlds interweaves cutting-edge science, popular culture, and history, using each mission as a springboard to launch into what are sometimes quite unexpected directions. There is really nothing else quite like this book out there."--Michael A. Strauss, Princeton University

"In writing that is clear, engaging, and at times almost lyrical, Dreams of Other Worlds provides deep treatments of these important space missions and their cultural relevance. Scientifically attentive readers will gain a great deal from this book."--Stephen P. Maran, author of Astronomy for Dummies

"Dreams of Other Worlds traces the history of ideas about the cosmos from the Greeks to the latest space missions. Exciting to read and accessible to lay readers, this book offers inspiration and intriguing speculations in addition to facts."--Larry Esposito, author of Planetary Rings

"When the history of the last fifty years can be viewed in a more balanced perspective, some of its most inspirational highlights will surely be the major space projects--often international in scope--that have voyaged to distant planets, extended our cosmic horizons, and deepened our understanding of Earth's place in the wider universe. This fascinating and finely written book chronicles the peak achievements in this grand exploratory endeavor, showing that credit is due to the cutting-edge technology as well as to visionary science."--Martin Rees, Trinity College, University of Cambridge, and Astronomer Royal

"Until we build the starship Enterprise, our efforts to boldly seek out new worlds will depend on mechanical surrogates. This book gives voice to their exploits--adventures not equaled since the great Age of Exploration four centuries ago. The flood of imagery sent back by these craft has revealed--for the first time--a universe of uncanny beauty, terrifying desolation, and inspiring promise. Surely, this is the most wondrous legacy of our generation."--Seth Shostak, SETI Institute

"Dreams of Other Worlds interweaves cutting-edge science, popular culture, and history, using each mission as a springboard to launch into what are sometimes quite unexpected directions. There is really nothing else quite like this book out there."--Michael A. Strauss, Princeton University

"In writing that is clear, engaging, and at times almost lyrical, Dreams of Other Worlds provides deep treatments of these important space missions and their cultural relevance. Scientifically attentive readers will gain a great deal from this book."--Stephen P. Maran, author of Astronomy for Dummies

"Dreams of Other Worlds traces the history of ideas about the cosmos from the Greeks to the latest space missions. Exciting to read and accessible to lay readers, this book offers inspiration and intriguing speculations in addition to facts."--Larry Esposito, author of Planetary Rings

Dreams of Other Worlds

The Amazing Story of Unmanned Space Exploration

PRINCETON UNIVERSITY PRESS

Contents

CHAPTER 1

Introduction

Someone who "missed" the late part of the twentieth century, perhapsby being in a coma or a deep sleep, or by being marooned ona desert island, would have many adjustments to make upon rejoiningcivilization. The largest would probably be the gallopingprogress in computers and telecommunications and informationtechnology. But if their attention turned to astronomy, they wouldalso be amazed by what had been learned in the interim. In thelast third of the century, Mars turned from a pale red disk as seenthrough a telescope to a planet with ancient lake beds and subterraneanglaciers. The outer Solar System went from being frigid anduninteresting real estate to being a place with as many as a dozenpotentially habitable worlds. They would be greeted by a cavalcadeof exoplanets, projecting to billions across the Milky Waygalaxy. Their familiar view of the sky would now be augmentedby images spanning the entire electromagnetic spectrum, revealingbrown dwarfs and black holes and other exotic worlds. Finally,they would encounter a cosmic horizon, or limit to their vision,that had been pushed back to within an iota of the big bang, andthey would be faced with the prospect that the visible universemight be one among many universes.

This book is a story of those discoveries, made by planetaryprobes and space missions over the past forty years. The word"world" means "age of man" in the old Germanic languages, andthat proximate perspective took centuries to expand into a universefilled with galaxies and stars and their attendant planets. Themissions at the heart of this narrative have not only transformedour view of the physical universe, they've also become embeddedin culture and inspired the imagination—this book is also a storyabout that relationship. But people were dreaming of other worldslong before the space program and modern astronomy.

Almost nothing written by Anaxagoras has survived, so we canonly imagine his dreams. He was born around 500 BC in Clazomenaein Ionia, a bustling port city on the coast of present-day Turkey.Before he moved to Athens and helped to make it the intellectualcenter of the ancient world, and long before he was sentencedto death for his heretical ideas, we can visualize him as an intenseand austere young man. Anecdotes suggest someone who was farremoved from the concerns of everyday life. He believed that theopportunity to understand the universe was the fundamental reasonwhy it was better to be born than to not exist.

Anaxagoras' mind was crowded with ideas. Philosophy is basedon abstraction—the power to manipulate concepts and retain aspectsof the physical world in your head. He believed that the Sunwas a mass of fiery metal, that the Moon was made of rock likethe Earth and did not emit its own light, and that the stars werefiery stones. He offered physical explanations for eclipses, for thesolstices and the motions of the stars, and for the formation ofcomets. He thought the Milky Way represented the combined lightof countless stars. We imagine him standing on the rocky Ionianshore at night, with starlight glittering on dark water, gazing upinto the sky and sensing the vastness of the celestial vault. Thedreams of such a powerful and original thinker were probably suffusedwith the imagery of other worlds.

This is speculation. As with most of the Greek philosophers, andespecially the pre-Socratics, very little of their writing has comedown to us unaltered. Typically, there are only isolated fragmentsand commentaries, sometimes by contemporaries and often writtencenturies later. Each historical interpreter added their own predilectionsand biases; the result is a view of the original ideas seenthrough a gauzy veil. Modern scholars pore over the shards andoften come up with strikingly different interpretations. Anaxagorasthought that the original state of the cosmos was undifferentiated,but contained all of its eventual constituents. The cosmos was notlimited in extent and it was set in motion by the action of "mind."Out of this swirling, rotating mixture the ingredients for materialobjects like the Earth, Sun, Moon, and planets separated. Althoughthe nature of the animating agent is not clear from his writings,Anaxagoras was the first person to devise a purely mechanical andnatural explanation for the cosmos, without any reference to godsor divine intervention. His theory sets no limit to the scale of thisprocess, so there can be worlds within worlds, without end, eitherlarge or small. A case can be made that he believed that our worldsystem is not unique, but is one of many formed out of the initialand limitless mass of ingredients.

Radical ideas often come with a price. For daring to suggestthat the Sun was larger than the Peloponnese peninsula, Anaxagoraswas charged with impiety. He avoided the death penalty bygoing into exile in Asia Minor, where he spent the remainder ofhis life. Pluralism—the idea of a multiplicity of worlds, includingthe possibility that some of them harbor life—had antecedents inwork by Anaximander and Anaximenes, and in speculation passeddown by the Pythagorean School. But Anaxagoras was the first toembed the idea in a sophisticated and fully fledged cosmology. Bythe time of the early atomists Leucippus and Democritus, pluralityof worlds was a natural and inevitable consequence of their physics.There were not just other worlds in space, but infinite worlds,some like this world and some utterly unlike it. It was a startlingconjecture.

The next two thousand years saw the idea of the plurality ofworlds ebb and flow, as different philosophical arguments werepresented and were molded to accommodate Christian theology.The pluralist position was countered by the arguments of Plato,and particularly Aristotle, who held that the Earth was unique andso there could be no other system of worlds. European cultureswere not alone in developing the idea of plurality of worlds. Babyloniansheld that the moving planets in the night sky were hometo their gods. Hindu and Buddhist traditions assume a multiplicityof worlds with inhabiting intelligences. For example, in one myththe god Indra says, "I have spoken only of those worlds within thisuniverse. But consider the myriad of universes that exist side byside, each with its own Indra and Brahma, and each with its evolvingand dissolving worlds." In cultures around the world, dreamers'imaginations soared. The Roman poet Cicero and the historianPlutarch wrote about creatures that might live on the Moon, andin the second century CE, Lucian of Samosata wrote an extraordinaryfantasy about an interplanetary romance. A True Story wasintended to satirize the epic tales of Homer and other travelers,and it began with the advisory that his readers should not believea single word of it. Lucian and his fellow travelers are depositedby a water spout onto the Moon, where they encounter a bizarrerace of humans who ride on the backs of three-headed birds. TheSun, Moon, stars, and planets are locales with specific geographies,human inhabitants, and fantastical creatures. This singular work isconsidered a precursor of modern science fiction.

For more than a millennium it was dangerous in Europe to espousethe idea of fully fledged worlds in space with life on them.Throughout medieval times, the Catholic Church considered itheresy. There was an obvious problem with this position: if Godwas really omnipotent, why would he create only one world?Thomas Aquinas resolved the issue by saying that although theCreator had the power to create infinite worlds, he had chosennot to do so, and this became official Catholic doctrine in a pronouncementof the Bishop of Paris in 1177. Nicolas of Cusa sorelytested the bounds of this doctrine. In 1440, he produced a bookcalled Of Learned Ignorance where he proposed that men, animals,and plants lived on the Sun, Moon, and stars. He furtherclaimed that intelligent and enlightened creatures lived on the Sunwhile lunatics lived on the Moon. It's said that friendship with thePope shielded him from repercussions, and he went on to becomea cardinal.

Giordano Bruno was less fortunate. The lapsed Dominicanmonk had deviated from Catholic orthodoxy in a number of ways,but his espousal of the Copernican system, which displaced theEarth from the center of the universe, brought him extra scrutiny.He believed that the stars were infinite in number, and that eachhosted planets and living creatures. Bruno was incarcerated forseven years before his trial and was eventually convicted of heresy.13 A statue in the Campo de' Fiori in Rome marks the placewhere he was burned at the stake in 1600 as an "impenitent andpertinacious heretic." Religion had cast an ominous shadow overthe idea of the plurality of worlds.

The same year Bruno was put to death, a twenty-nine-year-oldmathematician named Johannes Kepler, an assistant to TychoBrahe, was working with data that would cement the Copernicanmodel of the Solar System. As he published his work on planetarymotion in 1609, he dusted off a student dissertation he had writtensixteen years earlier, where he defended the Copernican idea byimagining how the Earth might look when viewed from the Moon.Kepler elaborated on his youthful paper and added a dream narrativeto turn it into a sophisticated scientific fantasy: Somnium.Kepler was inspired by Lucian and Plutarch's earlier work, but unlikethem, and unlike the mystic Bruno, he was a rational scientistwho wanted to realistically envisage space travel and aliens. Hisnarrative is rich with comments on the problems created by accelerationand varying gravity. The geography and geology of theMoon are realistically rendered. He even speculates on the effect ofthe physical environment on lunar creatures, foreshadowing Darwinand Lyell. Kepler had every reason to take refuge in a dream.He was frail and bow-legged, covered in boils, and was cursedwith myopia severe enough that he would never see the celestialphenomena he enunciated so elegantly. Somnium was known toJules Verne and H. G. Wells, and it's a crucial step in the progressiontoward rational speculation about other worlds.

The Copernican revolution was not a single event; it was a seriesof realizations over a period of a century that the cozy idea ofEarth as a singular place at the center of the universe was wrong.Displacing the Earth into motion around the Sun was the firstwrenching step, but another was recognizing that the Earth wasone of many worlds in space. The Copernican principle is morethan just a cosmological model; it's a statement that the Earth isnot in any central or favored position in the universe. A heuristicthat extends from the work of Copernicus is the principle of mediocrity,which goes much further by supposing that there's nothingspecial or unusual about the situation of the Earth, or by extension,the fact that humans exist on this planet. That is of course acentral tenet of modern astrobiology, but four hundred years agoit was a radical idea.

The Scientific Revolution recast the debate over the plurality ofworlds. Within months of Kepler's dream piece, Galileo pointedhis telescope at the Moon and affirmed it as a geological world,with topography similar in scale to the Earth. He also showedthat Jupiter had orbiting moons and that the Milky Way resolvedinto points of light that seemed to be more distant versions of thebright stars. The word world was no longer confused with kosmos;it meant a potentially life-bearing planet orbiting the Sun or,hypothetically, a distant star. Speculation about life on the Moonbecame routine, almost mundane. However, theology and philosophystill colored the debate in several ways. One theologicalconcept was the principle of plenitude—everything within God'spower must have been realized, so inhabited worlds should beabundant. Another was the strong influence of teleology—purposeand direction in nature that implies a Creator, who would surelynot have gone to the trouble of creating uninhabited worlds.

For a long time, scientific arguments could do no more than supportthe general plausibility of the plurality of worlds. Telescopescould easily track the motion of stars and planets, but gaining aphysical understanding was much more challenging. The blurringeffect of Earth's atmosphere prevented astronomers from resolvinganything smaller than continent-sized surface features on anySolar System body other than the Moon. Even the nearest starsare a hundred thousand times farther from us than the size of theSolar System. In addition, planets do not emit their own light, soastronomers must gather the hundred million times dimmer lightthat they reflect from their parent stars. Three centuries of improvementsin telescope design after Galileo yielded only two newplanets, a dozen or so moons, and no success in detecting worldsbeyond the Solar System.

And so the dreamers held sway. Many of them were groundedin science so they advanced the Copernican idea that our situationin the universe was not special. One striking work from the beginningof the Age of Enlightenment was Conversations about thePlurality of Worlds by Bernard de Fontenelle, published in 1686.He wrote about intelligent beings inhabiting worlds beyond theEarth, and incorporated the biological argument that their characteristicswould be shaped by their environment. Fontenelle alsofollowed Galileo's lead by writing in his native language, French,rather than the scholarly language of Latin, and he was forward-lookingin having a female protagonist and explicitly addressingfemale readers. A much later high-water mark was On the Pluralityof Habitable Worlds by Camille Flammarion, which reacheda wide audience in 1862. By the early twentieth century, scientificspeculations and fictional accounts of worlds beyond the Earthproliferated, but technology and research weren't able to addresssuch conjectures. There's an unbroken thread between earliestGreek thinkers and more recent explorations of science fictionwriters. Anaxagoras was a visionary, but it would probably havetaken his breath away to know that one day we would actuallyvisit other worlds.

* * *

Isaac Newton's Mathematical Principles of Natural Philosophy, athree-volume masterwork published in 1687, is a landmark in thehistory of science. Principia, as it is known, laid down the foundationsof classical mechanics and gravitation. Tucked away inone of the volumes is the drawing of a cannonball being launchedhorizontally from a tall mountaintop. This "thought experiment"sustained the dreams of space travel for nearly three centuries. October4, 1957 was a pivotal moment in the history of the humanrace; on that day a metal sphere, no bigger than a beach ball andno heavier than an adult, was launched into orbit. The worldwas transfixed, and amateur radio operators monitored Sputnik'ssteady "beep" for three weeks until its battery expired. Withintwo years the Soviets had crashed a probe into the Moon—the firstmanmade object to reach another world—and the Space Age wasin full flight. Humans have never been any farther than the Moonbut we've sent our robotic sentinels through most of the Solar Systemand slightly beyond.

For the universe beyond our backyard in the Solar System, wehave no direct evidence and we cannot gather and analyze physicalsamples. The data are limited to electromagnetic radiation. Newtonimproved on Galileo's simple spyglass with a design for a reflectingtelescope. All research telescopes are now reflectors. In understandingdistant worlds, the complement to direct explorationwith spacecraft is remote sensing with telescopes. A succession oflarger and larger telescopes over the past century have now expandedour horizons, and extended the Copernican revolution.We know that we orbit a middle-aged, middle-weight star, one of400 billion in the Milky Way, which is one of 100 billion galaxiesin the observable universe. The pivotal moment in the remote sensingof distant worlds happened on October 6, 1995, when MichelMayor and Didier Queloz announced that they had discoveredthe first planet beyond the Solar System. We're now "harvesting"Earths from deep space, and our dreams have moved on to thenature of life that might be found there.
(Continues...)Excerpted from Dreams of Other Worlds by Chris Impey, Holly Henry. Copyright © 2013 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.