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was, without a doubt, the biggest party ever thrown in a NASA Ames Research
Center aircraft hangar. One evening in April, as electronic band Telefon
Tel Aviv twiddled and blurbled away, thousands of beglittered, oddly coiffed
people danced to celebrate the launch date of Soviet cosmonaut Yuri Gagarin,
the first man in space.
It was hard to tell the NASA employees from the rave kids, since, in an
homage to space science, many of the dancers were clad in lab coats and
flight jumpsuits. Pete Worden, director of the center, who took the stage
around midnight urging the crowd to "party like it's 1961,"
appeared to be wearing a wizard outfit. And when the band decamped from
the cable-strewn stage so that NASA planetary scientist Chris McKay could
tell them all how to hunt for life on Mars, everyone stopped dancing long
enough to listen.
McKay was a grad student when Viking landed on Mars in 1976 and sent back
news that although many of the necessary components for life were there,
life itself wasn't. He has devoted his entire career to finding out whether
Viking was wrong. What he wants to discover on Mars, McKay told a rapt
crowd, is a "second genesis" proof that life arose independently
in more than one place in the universe. "Life," he specified,
"but not as we know it."
When McKay started his career, that kind of talk was the province of Trekkies
and tinfoil-hat wearers. Now it's a serious science, and you can hardly
talk to anyone in the field of what's now called astrobiology without
them tipping their hat to McKay's pioneering work.
"For a long time I was sort of a voice in the wilderness," McKay
muses a few weeks later from the comparative calm of his office at NASA
Ames in Mountain View. But in the mid-'90s, he says, three watershed events
hinted that scientists might be on the verge of unpacking some of the
universe's more enduring mysteries: The Hubble Space Telescope began beaming
back pictures from deep space; researchers identified, for the first time,
a planet outside our solar system; and scientists published a paper claiming
they'd found traces of life in a Mars meteorite that had smashed into
Antarctica. Even though that claim was later debunked, McKay recalls that
these events whetted public interest and convinced NASA to fund research
into how and where life could begin. "That's when astrobiology became
flavor of the month," he says. "That's when I no longer had
to start my lectures with explaining why NASA was looking for the origin
In fact, astrobiology has been the flavor of the last decade, particularly
here in the Bay Area where UC Berkeley, San Francisco State, and NASA
Ames Research Center have led the field in trying to answer the kinds
of mind-boggling questions prompted by the search for life in space. Is
our planet an aberration, a warm spot in a cold universe or is
life practically inevitable if you throw the right chemicals together?
If there's other life, what's it like? Where does it live? Is it related
to us? Why doesn't it ever call or write?
The simplest answer could be that we are indeed all alone.
That's the "Rare Earth" hypothesis, put forth by professors
Donald Brownlee and Peter Ward from the University of Washington. Their
2000 book, Rare Earth: Why Complex Life Is Uncommon in the Universe,
argues that our planet is the happy beneficiary of an extremely unusual
chain of circumstances that made the rise of intelligent life possible,
and which is unlikely to be repeated again.
Earth lucked into being born at the right part of the galactic disc in
the right orbit around the right kind of star, and just happens to be
of the right size and composition to have an atmosphere that can support
carbon-based life. It also has many traits that allowed not only life's
genesis, but its continued survival: protective magnetic fields, useful
plate tectonics, and the stabilizing influence of a large moon, to name
a few. While microbial life might be common throughout the universe, the
authors argue, animal life isn't.
Some astrobiologists consider this a flawed argument, overly based on
a terrestrial understanding of what life requires. When you consider the
vastness of space, they say, Earth isn't likely to be that special. But
the only way to prove the Rare Earthers wrong is to go out and find some
aliens, an enormous task.
Astrobiology is an untidy field as it is, encompassing everything from
galactic evolution to the evolution of microbes. By necessity, it is interdisciplinary
it has attacked its core queries with the tools of astrophysics,
biology, chemistry, geology, and paleontology. Yet because astrobiologists
are in the unique position of theorizing about life on landscapes they
will never visit, their explorations must be done by proxy.
Here's the idea: There are places on Earth that make good stand-ins for
other parts of the solar system; the Martian permafrost, say, or the icy
brine of Jupiter's moon Europa. These places are almost unrelentingly
nasty for humans and were once considered lethal to all life. Yet everywhere
astrobiologists have looked on our own planet, life has a toehold. In
some of these forbidding places, it is thriving.
Work over the last decade has greatly expanded our notion of where organisms
might be found, and has fed a growing conviction that life, with its resiliency
and adaptability, is probably very common in the universe. Yet the proof,
McKay says, will be in the Petri dish: "It's like the Europeans wondering
if there was an edge to the Earth or if there were dragons in the Sargasso
Sea. The only way to find out was to go look."
We are now tantalizingly close to getting that look. UC Berkeley researchers
have built a Mars life-detection chip they believe is up to a million
times more sensitive than Viking's instruments. Researchers at Cal and
NASA Ames who study life in extreme environments have provided a game
plan for where to look for life in our solar system. And the Bay Area's
famed planet-hunting team led by Cal astronomer Geoff Marcy has trained
its telescopes on nearby stars and found increasing evidence that small,
rocky planets like ours are common. The team recently announced that it
had even found a planet with water, the number one prerequisite for life
as we know it.
Yet despite the field's banner decade, NASA's recent and highly controversial
U-turn in mission priorities, which emphasizes a return to the moon instead
of exploring deeper space, has sucked the wind from astrobiology's sails.
NASA funding for its astrobiology program was cut in half this year, with
no prospect of reinstatement any time soon. At the same time, several
long-anticipated space missions to seek evidence of life in our solar
system, and habitable planets outside of it, have been scrapped. It's
an agonizing time for some of the field's top researchers. They've come
so close to finding answers, yet remain so far.
The Case for Mars
NASA's plan to return to the moon went over like a lead brick with astrobiologists,
many of whom deride it as having little scientific value we've
already got plenty of moon rocks. The agency's next priority, a manned
expedition to Mars, has a few more supporters, among them Chris McKay.
His top three reasons we might find life on Mars: It used to have liquid
water, it has the chemicals necessary for life, and its cold, dry, low-pressure
atmosphere is essentially a giant freezer vacuum that would have preserved
samples nicely. "I really want to find aliens," he says, "even
if they are little, green, microscopic, and dead."
That may well be the best-case scenario for Mars. If life started there,
it didn't evolve very far. Anything still living would likely be buried
in the polar permafrost or deep under the surface, where it's protected
from the arid climate and surface radiation. More likely, McKay says,
it's long dead. But that's okay, since death proves life: Dead tissue
is different than organic matter that never lived. Better yet, it leaves
That's why McKay found himself in Chile's Atacama Desert with UC Berkeley
chemist Richard Mathies two summers ago. Mathies has designed a life-detection
chip he believes can pick up where Viking left off, even if Mars is pretty
much a ghost planet.
The Atacama is the driest, and therefore most Martian, place on Earth.
It gets one millimeter of rain a year, and even that, Mathies says, is
"one night when the fog came in." It is so dry that McKay once
thought his instruments were broken because they hadn't recorded any moisture
in two years.
The aridity, and the soil's chemical reactivity, which is similar to that
observed by Viking on Mars, makes the Atacama incredibly popular with
astrobio types wanting to test-drive prototypes. If your equipment can't
find life in the Atacama, good luck finding it anywhere.
To get there, Mathies says, you drive toward the Andes until the terrain
completely drains of life. "There's no twigs, no little bugs, no
ants crawling, nothing," he says. "It's just nothing."
Any microbial life that's managed to survive there is hiding out in the
soil, beneath a gypsum crust that has likely not been disturbed in a hundred
thousand years. Hack into it, and see if anyone's home.
The hacking is important Mathies believes one of the flaws of the
Viking landers, as well as the Mars Rovers that were able to churn up
a few centimeters of soil by grinding their wheels, was that they looked
only near the surface. His chip, the Mars Organic Analyzer, is scheduled
to fly on the 2013 ExoMars mission sponsored by the European Space Agency.
The mission should be able to drill two meters below the Martian surface,
a depth at which Mathies believes life would have been sheltered from
the climate and radiation. His 2005 trip to the Atacama showed that although
surface life was barely detectable, it was another story once they dug
under the crust. "Go to a shielded environment, bam!" he says.
"You get a whole bunch more."
Mathies' microfluidic chip is a thing of beauty, a transparent glass and
plastic disc ten centimeters across, woven with a delicate labyrinth of
channels. Soil samples are propelled through the channels using a system
of water and tiny pneumatic pumps and valves. A linked-in computer analyzes
the samples and would transmit results back to Earth.
But how, exactly, will Mathies know if he's found alien life, especially
if it's really bizarre? And what is life, anyway?
You'd think there'd be a concise, universally accepted answer to the latter
question, but there isn't. After all, we've only seen one sprawling example
of life. Even though Earth is teeming, its organisms are all thought to
be descended from the same source, all part of the same tree of life.
At best, astrobiologists usually agree on some working guidelines
that life reproduces, consumes energy, and evolves but even these
criteria, they point out, describe what life does, not what it is.
This has produced a sort of "We'll know it when we see it" attitude
in the field, and even that is iffy. Selective pressures on other planets
could have pushed evolution in directions we can't even imagine, and scientists
have to struggle against their Earthcentric biases. For example, Mathies
says, you wouldn't want to go to Mars and sample for DNA, because what
if Mars life doesn't have DNA? "One of the hard things about structuring
an experiment that looks for life is that if you make your hypothesis
too specific you may not find it," he says. "And if you make
it too general, you may not learn anything."
Yet scientists do believe there are some themes the cosmic creation process
is likely to play repeatedly. Earth life is based on the most common chemical
elements in the universe so other life is likely to use them too.
Liquid water seems to be, as one scientist puts it, the "the cosmic
cocktail mixer" that allows biochemistry to occur, and water also
is commonly available. Amino acids are the building blocks of Earth life,
and they form readily in nature, even through nonbiological processes.
They have been found in meteorites, showing that they don't have to originate
Inspired by science Mathies developed while working on the Human Genome
Project, his chip exploits an amino acid quirk particular to Earth life.
In nature, amino acids have two forms that are mirror images of each other:
They can be either "right-handed" or "left-handed."
Nonbiological processes produce an equal mix of these two forms. By contrast,
Earth life uses only left-handed amino acids. As McKay puts it, "Biology
selects; chemistry doesn't."
So if an extraterrestrial specimen has an equal mix of the two forms,
it's not biological. But if its amino acids are uniformly left- or right-handed,
it's nearly a sure sign of life. If they all happen to be right-handed,
well, that's even more exciting it indicates not only life, but
life different from that of Earth, compelling evidence of an independent
This is the sort of scenario that makes McKay light up with glee. He's
already got plans for what we should do if we discover we have neighbors:
unfreeze them by creating global warming on the Red Planet, a sci-fi notion
if ever there was one. "If I found alien life on Mars, a second genesis,
my vote would be to bring it back to life and restore the planet to habitable
conditions habitable for that life form," he says. "My
slogan would be 'Mars for Martians.'"
Even if that meant a planet covered in bacteria?
"Yep," he says. "As long as they're alien bacteria."
But wouldn't that set in motion an evolutionary chain whose endpoint we
can't possibly predict?
"Exactly," McKay responds. "What if three billion years
ago somebody came to Earth and said, 'Oh, nothing here but microbes, hit
the erase button, alt-shift-delete'? We'd be unhappy with that."
Fine, but imagine the equally likely scenario in which the amino acids
are left-handed, like ours. "Then the simplest conclusion is that
they're our cousins, and that Earth and Mars exchanged material and share
a common origin, and the planets Earth and Mars are not any more isolated
from each other biologically than the continents on Earth than Australia
is from North America," McKay says.
After all, we know that meteors can criss-cross between the two planets
some theories even speculate that Earth life originated on Mars,
then flourished here, meaning that we have been the Martians all along.
More tests would be needed to determine whether and how
we map onto one another's trees of life. To McKay, that would be disappointing.
"I would really much prefer we found a second genesis and we just
smashed the Rare Earth hypothesis to smithereens," he says.
Another plot twist to consider if Mars life looks like ours: that we've
contaminated the planet by repeatedly landing on it. Although great pains
are taken to sterilize spacecraft, and Mars' harsh UV radiation is likely
to have killed off any Earth organisms that could have hitched a ride,
it's still a possibility. That's why some people think that if you want
conclusive proof of a second genesis in our own solar system, and a chance
of finding life totally unrelated to ours, you have to look further out
than Mars. Someplace colder, darker, and altogether weirder.
The Case for Europa
UC Berkeley paleontologist and geologist Jere Lipps spent a good deal
of his career planning expeditions to Antarctica to search for life under
the ice, which more or less qualifies him for planning expeditions to
Jupiter's icy moon Europa.
After Mars, Europa is the number two pick of astrobiologists for places
in our solar system that could harbor life. Two of Saturn's satellites
are runners-up: Titan, because of its carbon-rich atmosphere; and icy
Enceladus, where cryovolcanoes shoot geysers of water vapor into space.
But Europa, an iceball slightly smaller than our Moon, is the clear favorite
astrobiologists believe it contains a deep, salty ocean below its
frozen crust. Both the ice and the ocean can make fine habitats, Lipps
You might think ice is dead. Au contraire. "Life loves ice,"
Lipps explains. So long as they don't freeze and can find food, organisms
can flourish, as Lipps observed during his years studying the habitats
of the microorganisms, crustaceans, fish, and sea sponges that make their
home around Antarctica's Ross Ice Shelf.
But, he cautions, there are differences between our own ice-covered oceans
and Europa's. For example, Europa doesn't get much sunlight, so there's
probably not much photosynthesis. Even creatures that live in Earth's
deep seas often depend on a food chain that begins with photosynthetic
creatures. Lipps believes that Europa may have other nutrient sources,
such as chemicals that well up from the ocean floor.
Europa's surface certainly is more hostile than Earth's it bathes
in Jovian radiation, and its surface temperature is estimated at minus
260 degrees Fahrenheit. But the outer few meters of the ice likely shelter
everything below, Lipps says, and while the surface is frigid, the liquid
water below can't get any colder than it gets on our planet. The tides
may generate enough heat to keep Europa's oceans from freezing solid,
and scientists have posited other heat sources that could help sustain
life, such as radiation and thermal vents in the ocean floor.
If there's any life on Europa, it's trapped beneath a giant slab of ice,
and it can't come to the surface without being frozen or irradiated. So
how to detect it? Lipps explains that, because ice is constantly on the
move, you can do paleontology with it just as easily as you can with rock.
On Europa, ice sheets thrust above or below one another, smash together,
and crack apart, pushing things once buried to the surface. The tidal
action of Jupiter also opens rifts in the ice, which let materials well
up from underneath and then freeze along the edges of the cracks. That
these cracks have a distinct reddish-brown discoloration delights astrobiologists
they wonder if this is residue formed by layers of dead bacteria.
The discolorations also are the sort of thing cameras can spot. For the
last several years Lipps has been working with Lockheed Martin on a concept
for a telescope called MIDAS (Multiple Instrument Distributed Aperture
Sensor) that could fly by Europa and take pictures with a resolution of
up to two centimeters from a distance of one hundred kilometers. Lipps'
job is to tell them where to point it. "My search strategy for Europa
is exactly what I would do if I was going out into the Grand Canyon,"
he says to look for broken, exposed areas and places where chaos
in the terrain might have mixed up the layers and tossed up a residue
of biological material. This includes not only the discolored ridges,
but impact craters from meteorites, cliffs formed by clashing ice sheets,
and places where warmer water from below rose to, and then flattened,
the surface ice.
MIDAS is still in the planning stage, and no one knows when, or if, it
might fly. Until recently, most scientists interested in Europa had pinned
their hopes on NASA's planned Jupiter Icy Moons Orbiter, but the project
was scrapped in 2005. Other probes that could penetrate Europa's ice or
chip off bits of it to sample are still in the theoretical stage.
That hasn't dampened anyone's enthusiasm for Europa. "The chemicals
are there," Lipps says. "There are energy sources there. There's
water there, and those three things are what you need for life generally
as we know it on Earth. So that's a good sign, that's why we want to go
Of course, there's a difference between having the right conditions for
life and actually creating it, cautions NASA Ames astrobiologist Lynn
Rothschild. She's an expert in what kind of conditions organisms can put
up with: She has explored Yellowstone hot springs and Kenyan lakes, finding
creatures that live in hot acid baths. She's been to the Bolivian Altiplano
to learn about critters that can withstand intense UV exposure. Recently
she and her research associate Dana Rogov have been studying salinity-loving
microbes that live in the South Bay's Cargill salt flats. These extremophiles
have taught her that the kinds of habitats that can support life are much
more diverse than we once thought. "The chemical and physical conditions
for life, we're increasingly realizing, are not even uncommon in our own
solar system," she says. "One can't help but believe that there
are literally millions of places where life could form."
That said, she points out, "We have yet to make life. We can't even
take a cell that's dead and bring it back to life, and we've got all the
building blocks right there." There's a weird gap in human knowledge
we know what conditions life needs, and once it exists, Rothschild
says, "we have very well-described evolutionary theory to understand
how to go from microbes all the way to an elephant or a human or a sequoia."
But the crucial step in between the animation of life's raw materials
"Maybe we just haven't added the secret ingredient yet or we don't
have the right proportions," she continues. "But say that I'm
wrong, that there is some incredibly difficult step between having the
right chemistry and physics and actually setting something that's alive
in motion then it may not be common at all."
She weighs her expectations for what we might find in our solar system
with similar caution. Unlike McKay, Rothschild would be delighted to find
any life at all, even if it's our evolutionary cousin. (After billions
of years of separation, it has probably developed some interesting kinks.)
And if it's an independent genesis that hasn't, as the Rare Earthers predict,
proceeded much further than pond scum, that's okay, too. "I think
if people are sitting around waiting for Europa to come out and shake
hands, that's really quite silly," she says. "To me, life is
what's exciting. The rest is just details."
In fact, the most exciting part of finding life in our own solar system
may boil down to sheer math. Our star is one of two hundred billion stars
in our galaxy, the Milky Way, which is one of hundreds of billions of
galaxies in the universe. If life originated twice around a single, unremarkable
star, then really, the sky's the limit. "The difference between one
data point and two data points is more than just double," McKay says.
"If we found that life started twice right here in our own solar
system, then that to me would be scientifically convincing evidence that
life is widespread throughout the universe."
If we struggle to investigate even the next planet over, how are we
going to search for life farther away? Answer: with really big telescopes.
Next week, we'll introduce you to the other half of the scientific tag-team
searching for life in the universe. If astrobiologists are figuring out
what kind of neighborhoods life prefers, these planet hunters are looking
for likely street addresses. As they're discovering, there may be many
other places like home.