L o n e l l
y
P l a n e t s
The Natural Philosophy of
Alien Life
D A V I D G R I N S P O O N
For my parents
Evelyn Betsy Grinspoon
and
Lester Grinspoon
with love and gratitude
Penetrating so many secrets,
we cease to believe in the unknowable.
But there it sits, nevertheless, calmly licking its chops.
—H. L. MENCKEN
Contents
Epigraph
iv
Foreword: It Came Out of the Sky
viii
Preface
xx
P A R T I
H I S T O R Y
1
1 Spirits from the Vasty Deep
3
2 Plurality of Worlds
19
3 A Wobbly Ladder to the Stars
34
4 The Planets at Last
51
P A R T I I
S C I E N C E
6 7
5 The Greatest Story Ever Told
69
6 Earth Birth
88
7 Life Itself
97
8 Childhood
115
9 So What?
135
10 The Lives of Planets
150
11 Venus and Mars
167
12 Growing Up with Europa
191
13 Enter the Exoplanets
205
vii
Contents
14 Exobiology: Life on the Fringe
221
15 Astrobiology
237
16 Is It Science Yet?
252
17 Living Worlds
266
P A R T I I I
B E L I E F
2 8 7
18 SETI: The Sounds of Silence
289
19 Fermi’s Paradox
310
20 Have You Seen the Saucers?
334
21 Cons, Piracies, Conspiracies
358
22 Believing Is Seeing
374
23 The Immortals
389
24 Astrotheology
408
Notes on Sources and Suggestions for Further
Reading
417
Index
423
About the Author
Praise
Other Books by David Grinspoon
Credits
Cover
Copyright
About the Publisher
Foreword:
It Came Out of the Sky
We are all in the gutter, but some of us are looking at the stars.
—Oscar Wilde
On a tranquil late afternoon in early January 2004, the sky split open
and an alien ship dropped out. In a tired, rusty desert land where noth-
ing more than a dust devil had stirred for a hundred million years, the
monotony was shattered and a thundering, glowing ball of light rushed
toward the ground. Suddenly, at about two hundred feet, the visitor
inflated like an angry puffer fish, growing to many times its original
size, and then, seconds later, landed with a mighty “whump!” bouncing
as high as a four-story building. After twenty-eight more bounces—
each one raising a fearsome cloud of dust that slowly drifted off—it
came to rest on a desolate, sandy plain scattered with worn and broken
rocks.
Nineteen days later, on the other side of the world, a twin vessel
made a similarly strange, bouncing entrance, rolling to a stop in a small
crater sunk into a vast flat wasteland of salt-crusted rocks sprinkled
with metallic, berrylike spheres. Each visitor quickly began to trans-
form itself, deflating its landing cocoon to reveal a small hibernating
creature within. Extending wheeled legs, mechanical eyes, and other
peculiar sensory limbs, each slowly crawled off its now defunct landing
pod. The Martian arrival had begun.
Back on Earth, just two months later, in late March 2004, hundreds
of scientists pursuing alien life congregated in a hastily constructed
NASA facility in northern California—a colossal white tent with semi-
translucent siding, illuminated by rows of massive searchlights. Armed
government guards checked ID of all who wished to enter. At first
glance it resembled some top-secret X Files–type government installa-
tion, but a peek inside dispelled that impression. Instead of emotionless
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Foreword: It Came Out of the Sky
space-suited functionaries intent on inscrutable experiments, the giant
hall was filled with a motley assortment of nerds (myself among them)
and student nerds-in-training. Fashions ranged from suits and ties to
sandals and shorts. Information-packed posters hung in long rows,
displaying the latest scientific results on “astrobiology”—the study of
extraterrestrial life. A platoon of headsetted journalists, chasing us
around with microphones and cameras, completed the scene. This was
the Third Astrobiology Science Conference, held at NASA’s sprawling
Ames Research Center, spread along the southwestern shore of San
Francisco Bay—a tentful of carbon-based, water-loving, marginally
intelligent organisms gathered on the thin skin of planet Earth, to prog-
nosticate about the possibilities of life beyond.
We had a lot to talk about. NASA’s two Mars Exploration Rovers
had made their spectacular bouncing landings only two months prior
and had already made fantastic discoveries that had recharged and
refreshed the perennial debates about life on Mars.
Of course Mars was all the rage, so I was somewhat surprised, but
delighted, to have been invited to the conference to speak about one of
my pet ideas: “Sympathy for the Devil: The Case for Life on Venus.” It
was fun to play Lucifer’s advocate for the astrobiology community and
attempt to sell Venus’s overlooked charms to this skeptical but far-
reaching audience.
In a speculative field like astrobiology, complacency, overconfidence,
and unsupported consensus are all serious dangers. After all, our field is
still lacking in any actual bona fide extraterrestrial research volunteers.
So outside ideas, however ultimately wrong-headed they may prove,
are welcomed, as long as they can be supported with plausible argu-
ments that don’t break too many of our agreed-upon rules. (What are
these rules? Why do we agree upon them? Should we? Read this book.)
My conjectures about possible microbial life in the clouds of Venus
were deemed to pass this test, and so they were invited into the tent,
joining the more “conventional” notions of life underground—in possi-
ble Martian hot springs and the buried seas of Jupiter’s icy moons. (See
chapters 11 and 12 for more on possible Venusian life.)
This gathering under a tent, though perhaps not nearly as exotic as a
secret government alien research lab, was definitely not your mom’s sci-
ence conference. The two other programs for which
I was enlisted that
week were a panel called “Ethics of Exploration” and a public debate in
which a group of scientists and science fiction writers argued over the
Foreword: It Came Out of the Sky
x
possibility and desirability of “Terraforming Mars” (the future engineer-
ing of Mars to be more like Earth).
Now hold on. Science fiction? Ethics? At a science conference? Yes, if
the science is astrobiology. In addition to the “strictly physical” ques-
tions we wrangle with—such as making life to begin with, transporting
it between worlds, and keeping it alive in a wide range of planetary
environments—questions about life in the universe inevitably spill over
into other realms. Intellectually, astrobiology itself is a rather big tent,
somewhat hastily constructed, in which the Earth, space, and life sci-
ences commingle with wild speculation, a dash of philosophy, and even
a splash of spirituality.
The most eagerly awaited moment of the weeklong conference came
Tuesday afternoon, when Steve Squyres, principal scientist for the Mars
rovers, gave us an update on the activities of his two little Martian robot
geologist puppies, Spirit and Opportunity. There was an air of celebra-tion at this session, as a community that has known recent and repeated
failure enjoyed a great success. This cockamamie bouncing–on–air bags
landing scheme had worked once before with the Sojourner rover in
1997, but we all had a lot more riding on this attempt than just the
equipment. During the weeks prior to the landings, there had been
a palpable nervousness, fueled by the fact that we still weren’t sure
what went wrong with our last attempt to land on Mars in 2000
and tempered somewhat by the thought that this time we were sending
two identical, carefully tested rovers and at least one of them ought to
work.
This time they both did. Each survived the bouncy landing without
a hitch, and at the time of the Astrobiology Science Conference, each
was inching across one of the thousand unexplored deserts of Mars,
scratching and poking among the ruddy dirt and ancient rocks, shaking
loose buried secrets, snapping pictures all the while.
Squyres—rail-thin, angular, and as always sporting jeans over cow-
boy boots—was looking very bright-eyed for someone who’d been liv-
ing on Martian time for the last three months. As far as I could tell, he
hadn’t changed a bit since we first crossed paths in the summer of 1978
as students at Cornell. I ran into him in the hallway before his talk, and
though at that moment he was the coolest person in the solar system,
he didn’t act with one ounce of self-importance. He recounted the latest
rover findings and the fun he was having, as if he were just an old col-
league at a meeting telling me about his latest pet project. Which he
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Foreword: It Came Out of the Sky
was, but . . . his pets were on Mars, and they were on the move. Steve
took the stage, to thunderous applause, meant for the triumphant little
robots as well as for their driver. These are the moments we live for. It is
thrilling to be back on Mars.
He began with a spirited recap of the rovers’ initial forays on Mars
and a preview of their possible futures. Then he got right to the good
stuff—the possible stuff of life on Mars. What had we found? When I
think about it I still get so excited I can hardly talk—or type. All my
life, and my professional career, I’ve been enthralled with the possibil-
ity that through planetary exploration we can learn something defi-
nite about whether we have living company in the universe beyond
Earth. Well, the universe had just dropped us a big hint. We found
rocks on Mars that were formed of sulfate salts. The only way we
know of to make that kind of rock is through the evaporation of salty
seas from a place that must have been soaking wet for significant peri-
ods of time.
Why are we so hyped-up about finding sea-formed rocks on Mars?
Well, as far as we know at present, life needs water. On Earth, where
there is water there is life. Over the last few decades, circumstantial evi-
dence had been building for large quantities of surface water in the
Martian past. Orbital photographs revealed shapes strongly suggestive
of watery rivers and lakes. Yet, there has always been the nagging possi-
bility that we were searching so hard for signs of the familiar that we
were misinterpreting the photos and maps, mistaking the action of lava,
wind, ice, or some other unknown carver for the work of our beloved
water. But the rocks don’t lie. Now, at last, we’ve sampled the ground
itself, and the evidence is no longer circumstantial. We’ve found the
smoking gun (which in this case is a dripping Super Soaker) of past hab-
itability. We now know there was other wet ground, beyond the Earth,
in our solar system. Right next door. Buckets of rain once ran like salty
tears over the face of our little red brother Mars. This discovery proves
that Mars is indeed an important place for astrobiology exploration—a
place where many kinds of Earth life could once have survived—so why
not Martians? The idea that we might really find fossils of bygone crea-
tures on the Red Planet can no longer be regarded as far-fetched.
Among other things, this will be a major shot in the arm for our
desires and plans for future missions, providing the encouragement
(and most likely the funding) we need to keep going, to send new
machines there that can look for fossils or chemical traces of past life.
Foreword: It Came Out of the Sky
xii
Soon we will want to return Martian samples to Earth. With the right
Mars rocks in our own laboratories, we will be able to more defini-
tively test the idea that life once graced our red planetary neighbor.
The raised prospect of new missions to—and from—Mars height-
ened the exigency of our ethical discussions, topics that just a year ago
seemed more academic. How much should we care about—and spend
to guard against—the possibility that we might contaminate Mars with
microbes from Earth, or even the slight but disquieting chance that we
could bring something back from Mars that might enjoy snacking upon
our own biosphere? John Rummel, NASA’s planetary protection officer,
was at the conference, addressing these issues.
Does the news that Mars once had the conditions for life increase the
threat of contamination? Perhaps not. Many of us believe that what-
ever biology once graced this rusty world disappeared long ago, along
with the sputtering geology and the evaporating seas. The Mars rovers
are wandering places where almost nothing has happened in uncount-
able eons. Seen up close, these landscapes verify our belief that the sur-
face of Mars is incredibly ancient. There is nothing in the new photos
to suggest any recent action, beyond the frequent bursts of dusty winds.
Most of the geological activity is long gone, leaving a surface freeze-
dried, ossified, and sculpted in places into bizarre forms not see
n on
Earth, because you couldn’t find a place on our planet that has been left
to the wind alone for a billion years. The rovers haven’t found much
that changes our views of present-day circumstances on Mars. Their
biggest discoveries are about conditions in the deep past, including the
enticing possibility of ancient life.
Even the finding of once-soggy ground, as spectacular as it is, is not
revolutionary. It doesn’t overturn our current notions about Mars—in
fact, it confirms them. Yet, while the rovers were grabbing all the atten-
tion, about a week before the conference, another report had come in
from Mars that could have truly revolutionary implications. The
European Space Agency’s Mars Express, which arrived in Mars orbit
on Christmas Day 2003, had caught a whiff of something in the air.
Something that didn’t belong there. Something that might indeed be a
sign of life there today. The announcement received much less press
attention than the rovers, which, after all, were taking cool pictures. On
board the orbiter, an infrared spectrometer—which precisely dissects
the radiation leaking from the planet into a million distinct colors—had
detected a most unexpected trace gas in the Martian air. Feeble signs of
xiii
Foreword: It Came Out of the Sky
methane had been found on Mars. Methane is CH4, a carbon bonded
to four hydrogens.
Chemically, it is out of place in an atmosphere like that of Mars,
which is composed almost completely of carbon dioxide (CO2). Finding
methane on Mars is like finding a gazelle strolling unnoticed through a
pack of hungry lions.
To me this announcement was shocking, and it seemed even more
unreal than any of the strange postcards sent home by the rovers. I used
to say that methane on Mars would be one finding that could change my
mind about that planet being a perfectly dead world. Why? Because as
life evolves on a planet, the atmosphere evolves along with it. Chemically,
the two become intimately coupled. On Earth, the oxygen we breathe,
the protective ozone layer, and, yes, the trace of methane in the air are all
chemical by-products of 4 billion years of biology. Life in turn has
molded its chemistry to cleverly utilize the atmosphere pervading our
world. It may be this way on all planets with life and air. If so, then a
close study of a planet’s air will always reveal life or the lack of it.
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