Lee Billings - Five Billion Years of Solitude: The Search for Life Among the Stars

CURRENT

Published by the Penguin Group

Penguin Group (USA) LLC

375 Hudson Street

New York, New York 10014

USA | Canada | UK | Ireland | Australia | New Zealand | India | South Africa | China

penguin.com

A Penguin Random House Company

First published by Current, a member of Penguin Group (USA) LLC, 2013

Copyright 2013 by Lee Billings

Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech, and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying with copyright laws by not reproducing, scanning, or distributing any part of it in any form without permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA

Billings, Lee, author.

Five billion years of solitude : the search for life among the stars / Lee Billings.

pages cm

Includes bibliographical references and index.

ISBN 978-0-698-13768-4

1. Life on other planets. 2. Extrasolar planets. I. Title.

QB54.B54 22013

576.8'39dc23 2013017672

While the author has made every effort to provide accurate telephone numbers, Internet addresses, and other contact information at the time of publication, neither the publisher nor the author assumes any responsibility for errors or for changes that occur after publication. Further, publisher does not have any control over and does not assume any responsibility for author or third-party Web sites or their content.

To Mike and Pam, Bruce and Jo, Melissa,

and all those with the courage to keep looking up

T his story properly begins 4.6 billion years ago, with the birth of our solar system from a cloud of cold hydrogen and dust several light-years wide. The cloud was but a wisp from a much larger mass of primordial gas, a stellar nursery manufacturing massive stars destined to explode as supernovae. One by one, the giant stars popped off like firecrackers, ejecting heavy elements that sizzled with radioactivity as they rode shock waves through the murk like so much scattered confetti. One of those enriching shock waves may have compressed the cloud, our cloud, in its passage. The cloud became dense enough for gravity to seize control, and it collapsed in on itself. Most of its material fell to its center to form a hot, simmering protostar. Eventually, the protostar gained enough mass to kindle a thermonuclear fire at its core, and the Sun began to shine. What was left of the cloud settled around the newborn star in a turbulent, spinning disk of incandescent vapor.

Microscopic grains of metal, rock, ice, and tar rained out from the whirling disk as it slowly cooled. The grains swirled through the disk for millennia, occasionally colliding, sometimes sticking together, gradually glomming into ever-larger objects. First came millimeter-scale beads, then centimeter-scale pebbles, then meter-scale boulders, and finally kilometer-scale orbiting mountains called planetesimals. The planetesimals continued to collide, forming larger masses of ice, rock, and metal that grew with each impact. Within a million years, the planetesimals had grown into hundreds of Moon-size embryos, protoplanets that through violent collisions grew larger still, until they became full-fledged worlds.

After perhaps one hundred million years of further collisions, the embryos in the inner solar system had combined to make Earth and the other rocky planets. The inner worlds were likely bone-dry, their water and other volatiles blowtorched away by the intense light of the newborn Sun. In the outer solar system, freezing temperatures locked the volatiles in ice. The ices provided more-solid construction material, allowing the cores of Jupiter and the other outer planets to rapidly form and sweep up lingering gas within the disk in only a few million years. As they grew, the giant planets created zones of instability where embryos could not assemble, leaving behind pockets of primordial planetesimals and bands of shattered rock and metal. These remnants are the asteroids. The giant planets also catapulted many icy planetesimals far out into the solar hinterlands, to drift in the dark out beyond the orbit of present-day Pluto. When jostled by perturbing planets, galactic tides, or close-passing stars, those icy outcasts fall back toward the Sun as comets.

Finally, sometime between 3.8 and 4 billion years ago, a complex, chaotic, hazily understood series of gravitational interactions between the giant planets stirred up most of the outer solar system, sending barrages of asteroids and comets hurtling sunward to pound the dry, rocky inner worlds. This event is called the Late Heavy Bombardment, and was the last gasp of planet formation. We observe its effects in the cratered surface of the Moon, and also in the rain that has eroded its geographic scars from our own planetmuch of Earths water seems to have arrived during the Bombardment, express-delivered from the outer solar system. Afterward, Earths crust had partially melted, and its original atmosphere had been mostly swept away. But as those first torrential rains fell from the steam-filled sky, our planet gained the gift of oceans. Slowly, the Earth cooled, and gas-belching volcanoes gradually replenished the atmosphere. Soon, perhaps uniquely of all the new-formed worlds of the solar system, ours would somehow come alive.

Slightly less than four billion years later, I was four years old, standing with my mother, father, and sister in our backyard in Jasper, Alabama. It was January 1986, shortly after sunset. My father had built a small bonfire, and we clustered around it against the evening chill, roasting marshmallows as the stars came out overhead. Lower in the sky, just above the treetops, a soft white smear was barely visible. It was Halleys comet, passing near Earth on its trip around the Sun. I remember asking whether I could visit it. I had recently seen the 1974 film adaptation of Saint-Exuprys The Little Prince , and, like the small boy living on an asteroid in the story, I, too, wanted to fly through space to see all the solar systems strange places. Maybe someday, the answer came. Weeks later, I and the rest of a generation of children would learn that space travel is no fairy tale, watching as NASAs space shuttle Challenger broke apart on its way to orbit.

I didnt know then that Halleys comet would not be coming back until far-off 2061, and I was much too young to feel the weight of that date. The comet didnt feel it, eitherwhen it returned, it would be practically unchanged. I, on the other hand, would be nearing my eightieth year on Earth, if I was so lucky. With a great deal more luck, my parents would see it through centenarian eyes.