fanfare that they had found tiny fossils in one of these Mars rocks. That same day, the president released an announcement praising the scientists, gushing about the significance of the discovery, and calling for a
summit meeting to reassess our space goals.
What they had actually found were several separate oddities in the
rock, none of which individually offered proof of life, but all of which,
they felt, collectively pointed toward a signature of ancient Martian
biology. These signs included organic molecules, strange carbonate
deposits similar to those made by bacteria on Earth, and a few other
chemical clues possibly suggestive of a biological origin. However, what
really made a splash at the press conference were the pictures: photomi-
crographs of tiny, segmented, wormlike structures that, you have to
admit, do look like little creatures.
Everyone loves aliens—Martians especially. The fossils made news all
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over the world. Plans for a series of new Mars missions, already in the
works, were recast as an effort to find signs of life. Suddenly all NASA
science was given a more biological spin. Astrobiology was born, amid
surging scientific interest in the possibility that Mars might contain
signs of past, or even present, life.
Mars today, on the surface, is a dead world: freeze-dried, geologically
static, and irradiated daily with lethal ultraviolet.* The entire planet is
covered with red dust that has been blowing in the winds, sandblasting
every canyon, rock, and crater for eons. Mixed into this dry dust is, we
think, a deadly brew of strong oxidizing chemicals such as hydrogen
peroxide, which so eagerly attacks organic molecules, plundering car-
bon, that we use it on Earth to kill germs. Although Mars once flowed
with water, the Red Planet ran dry billions of years ago.
However, visions of life on Mars are centuries old, and astrobiolo-
gists still dare speak of them. From orbit we observe valleys carved by
ancient rivers and floods, and find hints of a bygone but familiar, com-
*Mars has nothing like Earth’s ozone layer, which is all that stands between us and the sun’s deadly UV rays.
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forting, and life-sustaining flow. We imagine life that has receded into
underground oases where the waters of Mars may yet run. What is it
about Mars, or about us, that induces these recurring dreams?
Though, after Earth, Mars is the planet most intensely studied by
humans, we are still having a hard time figuring it out. You’d think
after sending forty-two spacecraft to Mars (and counting), eighteen of
which have actually succeeded in sending back pictures or information,
we’d have more definite answers. But while we have superb, detailed
pictures of the entire planet, it remains cloaked in mystery. Despite its
proximity and our relatively unobscured view of the surface, Mars has
always been hard to see clearly.
Our powerful hopes for Mars, combined with great practical limita-
tions on our knowledge, have seduced us down many blind alleys and
dead ends. Every new, more detailed look gives us, along with greater
clarity, new sources of confusion. Mars messes with our minds. It is a
shape-shifter, revealing a different age and personality with each new
look.
Through our naked eyes we see a willful bright red orb strutting
through the passive starry backdrop. This confident march and its
bright sanguineous glow have made Mars the macho warrior star of all
the best and bloodiest splatter myths (and an equal number of lame
movies).
Viewed with telescopes the warrior morphed into a shimmering fuzz
ball with intriguing linear features that were either barely discernible or
not there at all depending on who was looking. Shifting dark patches
and seasonal polar caps suggested some dynamic presence.
From space, first photographed from fifty-nine hundred miles out by
Mariner 4 in 1965, it was a barren, cratered lunar landscape, disap-
pointingly old and dead. Then, global views from Mars orbit showed a
more varied and promising world of giant, extinct volcanoes, ancient
flood patterns, sculpted canyons, and active wind streaks. Yet, captured
with cameras landed on the surface, in five places so far, it is a desolate
desert landscape with piles of rusty rocks and dusty dunes.
So, is Mars dead or alive? Right now I’m not talking biology. I’m
asking whether, geologically, Mars is alive in the sense that its big sis-
ters, Earth and Venus, are: hot on the inside and active on the outside.
In contrast, puny Mercury and our punk little Moon are cold and
solid. If planets are made of butter, Earth and Venus are room-
temperature soft, but Moon and Merc were left in the freezer. Their
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surfaces are rigid, immobile shells. They have been dead for billions of
years.
Photographs of Mars from space show a world that is in many
respects intermediate between the opposite extremes of Earth and
Moon.
This Viking orbiter mosaic is one of my favorites, because it illus-
trates the dual character of Mars: static and dead on the inside, effer-
vescent and shifting on the outside.
A southern hemisphere densely packed with giant impact craters
betrays a frightfully ancient planetary surface. These are scars left from
the early, intense bombardment that ravaged the solar system when all
were young worlds. Like the Moon, Mars has large surface areas pock-
marked by that primordial pounding. That we can still easily see the
damage from this early epoch puts severe limits on the level of subse-
quent surface activity. Whatever action has been going down on the
surface of Mars for most of its time, 4 billion years of it has been insuf-
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ficient to fill in those holes. Mars is a world that has been largely inac-
tive throughout most of solar system history.
Geologically, Mars is only a shadow of its youthful self. At least in
terms of internally generated geological activity, driven by the libera-
tion of interior heat, like that which builds mountains and makes new
crust on the Earth, Mars is long gone. It’s been dead now for much
longer than it was ever alive.
W I N D S O F C H A N G E
Look again at the above Viking orbiter mosaic. Mars is a rusted old
hulk of a world. Yet, on the edge of the planet, at the border between
the deep red of Mars and the deeper black of space, you can see a fea-
ture that clearly shows this is not the Moon or Mercury. There, an
indistinct bright swath reveals an atmosphere thick enough to scatter
light and hold aloft clouds and hazes. What’s more, if you’ve got the
attention span to watch Mars over days and months, you will see
movement down there. Breezes blow. Dust swirls. Features are buried
and unburied again. Storms gather and clouds rol
l by. Polar caps grow
and shrink with the changing seasons. All is not quiet on the Martian
front, yet these changes are all caused by the motions and transforma-
tions of the atmosphere, fueled by the heat of the sun.
Global movements of gas and ice do cause some geological activity.
Glaciers freeze and thaw, carving channels and loosening rock.
Underground deposits of permafrost expand and shrink in the polar
regions. Mobile deposits of ice mixed with rocks cause “rock glaciers”
to flow. Landslides tumble down slopes softened by the seasonal freez-
ing and thawing. In all these ways the effects of the changeling atmo-
sphere go more than skin deep. Geology on Mars today is driven by the
sun, not by heat from the planet’s interior.
Earth’s surface gets it from both sides—from above and below. The
internal heat induces most of the local geology (earthquakes, mountain
building, volcanoes) that wipes out older surfaces. Earth’s solar-driven
atmosphere and hydrosphere constantly erode landforms from above.
On Mars, weather is very much a factor, but Mars today is not both-
ered by internally generated activity. Clearly, it wasn’t always this way.
Looking down at Mars from orbit, we can see that in the past it was more
like Earth and Venus. We see widespread and varied volcanoes that once
erupted, and giant faults that once caused mighty Marsquakes. Magnetic
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patterns in the ancient southern hemisphere hint at the past operation of
something like plate tectonics. But these are all relics of ancient history.
That we can easily see these structures, still exposed on the surface despite
billions of years of dusty storms, is a further reminder of just how incred-
ibly quiescent the planet has been for most of its existence.
A dead surface continually sculpted by a lively atmosphere is the dual
personality of Mars today. The cryogenically preserved corpse of
Martian geology, continually kicked around by its active atmosphere,
can seem animated at first glance, but the body is cold and its soul long
departed. The lively nature of the air currents and the shifting patterns of dust had many astronomers believing that we were seeing something
alive, right up until the return of the Mariner 4 photos provided a cold slap, awakening us to a new Mars. But the old Mars, some believe, may
be there still, buried just beneath the dusty surface, and we are doing
our best to find it. Recent pictures from the Mars Global Surveyor
spacecraft have hinted that there may be life in the rusty old cadaver
after all.
M E E T T H E N E W M A R S
I first became aware that something new was up in early June 2000
when I heard from a colleague, a trusted senior scientist not given to
hyperbole or idle speculation, that the cameras on Mars Global
Surveyor ( MGS for short) had “seen something” on Mars, that it was being kept secret and that “the president has been briefed.” A few
quick phone calls to some friends at NASA revealed that something
really had been found, the White House had indeed been informed, and
those who actually knew something—the scientists on the MGS camera
team—were the only ones not talking.
What could possibly merit this kind of treatment? Keeping important
scientific findings secret until publication is not unusual, but the White
House briefing conjured up images of saucers landing in the Rose
Garden. Naturally, speculation on the Net spun quickly into orbit.
Active volcanic hot springs, tracks left by migrating Mars bunnies, or
signs of crashed spacecraft were some of the putative discoveries being
batted about by space and conspiracy enthusiasts.
Had they actually found life on Mars? That seemed quite unlikely for
two reasons. First, whatever it was had apparently been seen from
orbit. What we do know about Mars strongly suggests that any life to
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be found there will be hiding underground, protected from the lethal
radiation showering the surface. Second, if life really had been found,
then the prolonged secrecy would be irresponsible, fanning the ready
flames of government conspiracy theories and general mistrust of sci-
ence. Yet a cool new picture of some rocks or sand dunes would hardly
merit an Oval Office audience.
Short of alien pyramids, a rock face with the likeness of Elvis, or an
invading fleet heading our way, what could be behind the secrecy and
the high-level briefings? With a little thought many of us quickly con-
cluded that the big secret must have something to do with water. The
current mantra of astrobiology is “follow the water”—i.e., water = life.
A finding somehow indicating the presence of liquid water on Mars
today, or in the recent past, would be big news. This seemed the only
reasonable choice for all the fuss surrounding the secret new discovery.
It was interesting to watch the rumor mill spin into hyperdrive,
spurred on by the hungry media monster. I began to get calls from local
and national newspaper reporters about a week before the official
announcement, asking if I’d heard anything. When I said, “Only
rumors, but I don’t really know anything,” they would always ask me
to speculate on what I had heard, and I would explain why I thought it
must be some sign of water on the surface. What happened next was
revealing, but not about Mars. News articles reported the discovery of
water on Mars based on the speculation of scientists like me who didn’t
actually know anything but had reached this conclusion simply because
we could not think of anything else that fit the profile of secrecy and
hype. A reporter from USA Today called and implored me to speculate
on the possible implications should the speculations of other scientists
about published rumors prove to be true.
Such was the pressure to break the story in a timely fashion that sev-
eral supposedly reputable news organizations published “scoops” from
“inside sources” that proved to be completely false. Both MSNBC and
BBC news ran a story reporting pools of standing water seen oozing
from the bottom of the giant canyon Valles Marineris.
After the publication of these first false stories from “unnamed
sources at NASA,” the official release of the discovery was abruptly
moved forward a week. Clearly, someone had decided that when it
comes to Martian mysteries, too much anticipation is not a good thing.
There was a real danger that the significance of the actual discovery
would be buried in a dust storm of dramatic speculation.
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At a hastily arranged press conference, MGS scientists showed stun-
ning new pictures portraying their discovery: photos of numerous
places with fresh-looking gullies running downhill, apparently seeping
from the sides of steep cliffs. Many of these appear to flow out over
sand dunes, demonstrating that the flow features are younger than the
dunes (which are, themselves, presumably young, because dunes are
ephemeral things). At several locations ar
ound the planet where the
gullies were found, some liquid has apparently been recently seeping
out of the ground onto the surface of Mars. “Recently,” in this context,
means less than a million years ago, and possibly last week. “Some liq-
uid” probably means water.
These photographs are astounding, unsettling, and provocative. The
second most amazing thing about them is simply that they look so
hauntingly familiar. Here are close-ups of the face of Mars* looking
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*Not to be confused with the face on Mars, which I’ll discuss in chapter 21.
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more like someplace you hiked one spring in Utah than an alien planet.
The most amazing thing about them is the implication of recent water
flow.
Most scientists see Mars as a good place to look for fossils from the
good old days, long ago when the nights were warmer and the rivers
flowed. Most do not expect to find life there today, but also admit that
we cannot rule it out. Now, however, MGS has photographed several
different places where it looks as if water might still be running. If there
really is liquid water near the surface of Mars today, it truly does
change the equation, shifting the odds in favor of present life.
But, here’s where it gets strange: the sites where we see the seepage are
among the places you would least expect to find flowing water, because
they are, even by Martian standards, so damn cold. (This is not summer
in San Francisco—we’re talking one hundred degrees below freezing.)
We do not see them anywhere near the equator, and not on the warm,
Sun-facing slopes. Paradoxically, these features seem to shy away from
the Sun, preferring frigid, high latitudes and shadowed slopes. This does
make one wonder if perhaps there isn’t some other substance, liquid at
these temperatures, mimicking the action of flowing water.
All over Mars, we see ancient channels, rivers, and dried-up ponds
and we think, “Water!” Since such features could not form under the
present climate, we conclude that the climate has changed, that Mars
used to be warmer and wetter, more like Earth.* This idea has a couple
of major problems that we tend to sweep under the dust. One is that it
is difficult to get the surface of Mars to stay above freezing no matter
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