how we tweak our climate models. Remember, early on, the Sun was
significantly dimmer than it is now, and this makes the problem harder
to solve. We’re working on it, but we haven’t yet found a way to melt
Mars. Maybe we’re missing something. The other nagging problem is
that we can’t find the carbonate rocks that should be common on the
planet everywhere if it once enjoyed a watery climate.
Even given these puzzling discrepancies with the wet-Mars theory, it
seems nearly inescapable that Mars had liquid water flowing in the
*A cautionary aside: In the early nineties Magellan found many riverlike features on Venus. Since conditions on Venus are far too hot for liquid water, this possibility was never seriously considered, so we’ve dreamed up exotic liquids, such as carbon-rich lavas, that might flow under Venusian conditions as easily as water does here. No one anticipated the existence of such strange materials before the observations required that we think them up.
Venus and Mars
187
past. But running water today? In some of the coldest, most shadowed
places? It seems wrong.
Several clever theories have been proposed to explain how the gullies
could form without violating the laws of chemistry and physics. For
instance, maybe the runny stuff is actually liquid CO2. If you pressurize
CO2 to many times the surface pressure on Mars, it condenses into a
liquid. Liquid CO2 might exist in pressurized underground channels,
sometimes breaking out and spraying onto the surface, causing loose
material to run downhill and forming the gullies. Or maybe an under-
ground heat source is pumping water around, or maybe the water is in
some exotic mix with frozen carbon dioxide, giving it the right fluid
properties.
Now that the cat has been let out of the bag and the president has
gone back to bed, we are all free to gleefully theorize about these
recent-looking flow features on Mars. Fresh surface water, if con-
firmed, would mean that, by the currently accepted rules, Mars should
have life. It makes Mars, not Europa, Jupiter’s watery moon, the most
accessible place to test our “water = life” paradigm. It also emboldens
those who urge manned—I’m sorry, “peopled”—missions to Mars in
the near term, since an accessible water supply would make it that
much easier for us to live off the land.*
S A M E A S T H E O L D M A R S ?
There is a cyclical quality to our ideas about Mars. Like pilgrims seek-
ing tears on a stone Virgin, we are ready to announce, at the least
provocation, that we see water running there still. For over a hundred
years now, the watery channels of Mars have reappeared in different
forms. So, when MGS scientist Ken Edgett excitedly exclaimed at the
press conference, “This is not your mother’s Mars!” I thought, “No,
but it might be my grandmother’s.”
I am not convinced that the gullies are evidence for surface water on
Mars today, but they’ve sure shown us that things are happening there
that we don’t understand. Mars, viewed with unprecedented detail in
the MGS camera, has once again showed us new sides of its personality.
*One of Asimov’s best SF stories, “The Martian Way,” involves the struggles of Martian colonists to achieve water independence from imperialist Earth. They achieve this in the end by mining water from the rings of Saturn.
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While the hints of current water flow remain provocative and puzzling,
less controversial are numerous features providing the best evidence yet
that flowing water really did affect much of the surface in the distant
past. Numerous old impact craters and other topographic depressions
contain subtle deposits that look like dried-up lakes. Perhaps most
striking is the wide occurrence of terrain made of layered, sedimentary
rocks. With the improved clarity of the MGS cameras, the layered
structures that have been there all along jump out at us.
These deposits look familiar to terrestrial geologists, and for that
matter to any terrestrials who have visited the Grand Canyon or any
number of places where the layered structure of sedimentary rock dom-
inates the landscape. Such thick tableaux of layered rocks have been
laid down over extended periods of geological time, usually by liquid
Image unavailable for
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Venus and Mars
189
water. Though some have proposed that on Mars these layers could
have been built up out of wind-borne sediments, they look exactly like
sedimentary rocks on Earth that we know were laid down beneath
shallow seas of water. More recently still, the Mars Odyssey spacecraft, which arrived at Mars in October 2001, has revealed vast fields of permafrost, frozen water mixed with dirt, in large areas surrounding both
poles. The Red Planet may once have been blue.
But was it ever green?
Jonathan Eberhart, the superb writer who covered planetary explo-
ration for Science News and was a fixture at our conferences for years
until he retired in the early nineties, was also known to many as an excel-
lent singer/songwriter. We had fun rocking out together at some planetary
meetings in the eighties: Jonathan sang and played piano, I played guitar,
planetary geologist Dave Pieri played bass, and Kelly Beatty, the editor of
Sky and Telescope, played drums. It was the ultimate geek jam, a regular planetary Nerdstock. Jonathan’s song “Lament for a Red Planet” is an
ode to all the lost visions of a vibrant, comfortable, and living Mars from
the past of science and science fiction. I first heard him sing it in the press-
room at the Jet Propulsion Laboratory the week of the Viking 2 landing
on Mars. In a deep, sea-shanty voice, he sang:
Ten thousand times a hundred thousand dusty years ago,
Where now extends the Plain of Gold did once my river flow;
It stroked the stones and spoke in tongues and splashed against
my face,
Till ages rolled, the sun shone cold on this unholy place.
Your ochered cliffs and rusted sands stand regal and serene,
But oh my wan and wasted world, I miss your blues and greens.*
When it comes to life on Mars, we’ve got a feeling we can’t hide. Our
intuition that Mars holds life is strong, recurrent, and seemingly imper-
vious to data. Every time we learn a new way that Mars is deadly, it
represents only a temporary setback for this stubborn belief, until we
can invent new ways that Mars might, after all, live on. This pattern
suggests that our persistent belief fulfills needs that go beyond scientific
evidence. Decade after decade, both before and during the space age,
*Jonathan’s album Life’s Trolley Ride, which has this song, is available from Folkways Records. Sadly, Jonathan passed away in 2003.
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our science has been swayed by this hope. The more we learn, the more
likely that we won’t get fooled again, but if we ever do discover life on
Mars, one of the lessons might be that we should trust our intuition
about these things. The picture of Mars that is emerging from our latest
missions of exploration is oddly re
miniscent of Percival Lowell’s dying,
dried-out world. Gone are the canal builders, but visions of rebel bacte-
ria colonies holding out in some underground cave will be much harder
for our science to rout out. The deeper we probe, the deeper they seem
to retreat into the bowels of the planet.
As my planetologist friend (and former office mate at NASA/Ames)
Kevin Zahnle, a keen observer of the scientific condition, wrote in 2001
in Nature, “The most interesting information remains right at the limit
of resolution. . . . Always life on Mars seems just beyond the fields that
we know.”
Growing Up with Europa
12
All these worlds are yours—except Europa.
Attempt no landings there.
Image unavailable for
—ARTHUR C. CLARKE’S 2010: Odyssey Two
electronic edition
Image unavailable for
Lime and limpid green the sound
electronic edition
resounds the icy waters underground.©
—SYD BARRETT,
Astronomy Domine
T H E T R I A L S O F G A L I L E O
So far our search for alien life isn’t going too well. Although we cannot
count Venus or Mars out yet, neither looks as promising—at least for
our kind of life—as many believed when we began exploring. But from
this we do not conclude that the universe is lifeless.
We’re not capable of reaching such a conclusion—logically or emo-
tionally. In this sense, aliens are like gods. No scientific result would
convince us that alien life does not exist. Yet, the opposite—proof posi-
tive of life on another planet—would be accepted by everyone except
those yahoos who think the lunar landing was faked.* The hopes and
faith we place in our dreams of alien life are not in any danger of being
dashed by science. At worst, they will be displaced at the pace of our
exploration. At best, they will be confirmed in a dramatic discovery of
something unmistakably alive.
*If you are one of those yahoos, I apologize for my insensitivity.
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Our reluctant letting go of warm oceans on Venus and Mars simply
forced us to broaden our definitions of habitability. We widened our
search, traveling ten times farther afield to other worlds, which seem,
on the surface, even more exotic.
Just the idea that there are other worlds has been a difficult and
painful concept to get into our little carbon-based skulls. Galileo was
the first to actually find any new worlds, and look what happened to
him. Recently our search for life has taken us back to the site of that
first decisive Copernican battle: Jupiter’s Galilean moons.
We know them as the four lovers of Jupiter: Io, Europa, Ganymede,
and Callisto.* It only took us four hundred years to progress from dis-
covery to exploration. Now, we’ve launched ships to cross wider seas
and explore Galileo’s new worlds. Out there we’ve found unforeseen
wonders that feed our hopes for a new revolution of Copernican pro-
portions. Could we possibly find confirmation, among the moons of
Jupiter, of our suspicion that we are not alone in the universe?
Our first good look came in 1979 when the two Voyager spacecraft
whipped through the Jupiter system, frantically snapping pictures as
they sped by. It all happened fast; each Voyager, with no way of slowing
down, spent just two days in the vicinity of Jupiter and its moons
before being gravitationally flung back out into the void toward a ren-
dezvous with Saturn.
In the summer of 1979 I was a space-freak college freshman with a
way-cool summer job: assistant to the Voyager Imaging Team at the Jet
Propulsion Laboratory (JPL) in Pasadena during the Voyager 2 Jupiter
encounters. When I wasn’t running off to Grateful Dead shows, I was
closeted in a big, air-conditioned cubical building with the men and
women who had planned and built these early ships of deep space,
delighting in every new picture as the expanding, approaching dots
became worlds. It was then that Galileo’s four strange moons first took
on their distinct personalities: the manic volcanic face of Io; the dark
lines winding like turnpikes across Europa’s bright, icy landscapes; the
densely grooved terrain of Ganymede; and the ancient, icy, cratered
surface of Callisto.
I will never forget the heart-stopping moment when the first close-up
pictures of Europa arrived on Earth. On the morning of July 9, we—the
imaging team and assorted students, assistants, and hangers-on—were
*Jupiter is bisexual. There is a lot of him to love.
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193
stuffed into a small, dimly lit room, staring up at a dark screen in com-
munal, nervous anticipation. It was as if we were all riding along on the
spaceship and gathered together to stare out of a porthole near the
bow, awaiting our first glimpse of an unknown shore. A film crew from
Cosmos was crammed in there as well, adding to the suspenseful air.*
As the face of Europa began to appear on the screen, slowly, in thin,
vertical strips, gasps of disbelief erupted from this crowd of generally
reserved scientists. Never before and never since has our knowledge of
another world taken such a great leap in a few brief revelatory
moments.
Our theories predicted an ancient, dead, cratered landscape on the
small ice-planet. Instead, we saw a smooth, bright surface crisscrossed
by strange dark lanes. The immediate impression was of a fresh, active
world. At first nobody spoke. The appearance of Europa was so truly
unexpected that no one, in a room full of verbose rocket scientists,
could offer anything intelligent. The first to speak was Carl Sagan:
“Percival Lowell was right!” he exclaimed. “Only, the canals are on
Europa!”
While they’re not canals, those enigmatic markings might be signs
pointing to life. This took a while to sink in. The Voyagers’ trajectories
were not optimized for Europa viewing. Each ship had a date with
Saturn that dictated its hurried path through the environs of Jupiter.†
On a flyby you only get one chance, so coverage of Europa was spotty
and incomplete. We saw only half the planet in photos taken from
thousands of miles away, leaving us with only imagination and theories
to fill in what we could not glimpse.
We had to wait nearly two decades to get back to Jupiter. During that
time I finished college, moved out West, toured with a reggae band, cut
off my Afro, and became a comparative planetologist funded by NASA.
In 1989, the year I got my Ph.D., a spacecraft bearing Galileo’s name
was launched toward the moons that he had first seen on a cold
January night in 1610.
Even before its launch, Galileo was a hard-luck spacecraft. Always at
the edge of disaster, it has at times seemed jinxed. The spacecraft has
*I actually appear briefly here in the television show: I’m the skinny geek sporting an improbably huge Afro, wide-eyed in the back of the room.
† Voyager 1’s path through the system four mont
hs earlier had not permitted any close-up pictures of Europa.
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followed a tortuous path and faced trials that rival those of the man for
whom it’s named. Budget-cutters in Congress threatened repeatedly to
cancel the mission. Protesters tried to derail the launch over concerns
about the fifty pounds of plutonium that it carried for power at Jupiter.
In December 1986, the Challenger blew up, killing seven brave explor-
ers and shutting down the space shuttle program for three years.
Galileo had been slated for the very next launch.
The irrepressible craft finally made it off the ground in October
1989. Upon reaching deep space, its twelve-foot-diameter main
antenna, folded tight for launch, was supposed to spread open like a
metallic beach parasol. But when the moment came, it just sat there,
stuck stubbornly in the folded position. Ground controllers tried to jar
it loose by running its motor in various stop-and-start sequences. They
tried spinning the spacecraft in hopes that it would fling itself free.
Months went by, and increasingly desperate efforts failed to open the
umbrella, which we needed to establish a communications link between
Jupiter and Earth. Gradually the reality set in that it would not open.
The main antenna, vital portal for all the riches expected at Jupiter,
remained in a crumpled-up, completely useless configuration for the
entire mission. Imagine the frustration. We had the most sophisticated
spacecraft ever built finally sailing toward Jupiter, able to photograph
the mysterious moons in unprecedented detail, but we had no way to
send the pictures homeward.
Houston, we had a problem.
NASA engineers marshaled all of their legendary, save-the-day inge-
nuity and found solutions. A puny “low-gain” antenna, not designed
for this kind of work, was pressed into service—a little like finding that
your new high-speed modem is dead and being forced to settle for two
tin cans and a piece of string. The expected rushing stream of data was
reduced to a feeble drip. The mission never fully recovered from the
main-antenna failure, but clever work-arounds, combined with
Galileo’s stubborn longevity, allowed us to get 10 percent of the origi-
nally planned pictures of Jupiter and its moons.
After suffering enough technical glitches to give the most even-
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