Extreme Environments and the Search for Water
IS EARTH THE ONLY PLANET IN OUR SOLAR SYSTEM WHERE LIFE EXISTS?
AND, BY THE WAY, WHAT IS LIFE?
chapter head: LIFE DEFINED
IN THIS VIDEO, WE'LL HEAR LIFE DEFINED, AND DISCOVER HOW TO LOOK FOR IT...
chapter head: EXTREME SURVIVORS
WE'LL SEE THAT IN THE PAST FEW YEARS WE'VE FOUND LIFE SURVIVING IN PREVIOUSLY UNEXPECTED PLACES...
chapter head: HABITABLE ZONES?
AND WE'LL LOOK FOR HABITABLE ZONES ON THE OTHER PLANETS AND MOONS OF OUR SOLAR SYSTEM...
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program 7
LOOKING FOR LIFE
Extreme Environments and the Search for Water
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chapter head: LIFE DEFINED
MOST OF US HAVE A PRETTY GOOD IDEA OF WHAT LIFE IS...
A PARROT, OR A PENGUIN, A SLOTH OR A SEAL, IS CLEARLY ALIVE.
A FLOWER IN THE FOREST... A CACTUS IN THE DESERT, THEY'RE ALSO LIVING.
BUT RESEARCHERS LOOKING FOR LIFE ACROSS THE UNIVERSE HAVE TO COME UP WITH A MORE SOPHISTICATED DEFINITION.
name title:
CHRIS CHYBA
Carl Sagan Chair for the Study of Life in the Universe, SETI Inst. / Stanford
I would say that life as we know it means three things.
TITLE: LIQUID WATER
It means life based on liquid water, almost all life on Earth is 80 or 90 percent liquid water by mass.
TITLE: "BIOGENIC" ELEMENTS
It means life based on a set of certain elements, sometimes called biogenic elements, most famously carbon, but also nitrogen, oxygen, sulfur, phosphorous, and there's a long list of others.
TITLE: ENERGY SOURCE
And it means an energy source. Life requires an energy source because life has to create and maintain order and you need energy to do that.
So when I say "life as we know it," I mean life that's based on water, life that's based on carbon, and some other elements, and life that requires a source of free energy.
WHEN WE TURNED OUR TELESCOPES TO THE HEAVENS AND LOOKED FOR LIFE, OUR FIRST THOUGHTS WERE TO SEEK CREATURES LIKE THOSE WE KNEW DOWN HERE ON EARTH.
title: PERCIVAL LOWELL 1856-1916
PERCIVAL LOWELL LOOKED AT MARS... THOUGHT HE SAW CANALS, AND INFERRED AN ALIEN CIVILIZATION THAT BUILT THESE CHANNELS TO BRING WATER ACROSS DRY DESERTS TO THIRSTY CITIES.
AND IN THE 20TH CENTURY, WHEN THE VIKING SPACECRAFT SHOWED US LANDFORMS THAT LOOKED A LITTLE LIKE A HUMAN FACE, TABLOID NEWSPAPERS AND OTHERS RUSHED TO CLAIM MORE PROOF OF LIFE ON MARS.
IN REALITY, LOWELL'S CANALS WERE THE RESULT OF TELESCOPIC DISTORTION...
title: courtesy Malin Space Science Systems / NASA
AND THE FACE ON MARS, AS MORE RECENT IMAGES FROM GLOBAL SURVEYOR SHOW, IS REALLY WIND-BLOWN ROCK.
IF WE WANT TO LOOK FOR LIFE, WE HAVE TO BE ABLE TO RECOGNIZE IT EVEN WHEN IT DOESN'T LOOK LIKE LIFE AS WE KNOW IT…
name title:
KEN NEALSON
Director, Center for Life Detection
JPL, NASA / Caltech
NEALSON:
Can we develop methods that would detect life, even if it wasn't made of the same stuff that it is on Earth and even if it were fundamentally different? Uh, by doing this we turn the search for life into a physics and chemistry and statistics problem, rather than just a biology problem.
SO WHAT ARE THE UNIVERSAL FEATURES OF LIFE, APART FROM HOW WE DEFINE IT DOWN HERE ON EARTH?
title: WHAT IS LIFE?
NEALSON:
...what might be the fundamental features of life?
Life uses energy. What are the sources of energy on a planet? Can we look at the ways that energy moves around?
Uh, life makes products some of which are gases, some of which are liquids, some of which are solids.
Uh, if we found those products when they shouldn't be there, Sherlock Holmes-as we all have to be-would start to claim there must've been life here, or maybe its still there.
title: WHERE IS LIFE?
CHYBA
As far as we know, life is a planetary phenomenon. That is, life as we know it is going to live on either a planet or a moon, a satellite of another planet.
...it's not out of the question that there could be an ecosystem that lives entirely in the atmosphere of a planet like Jupiter or Saturn, but you know if you look at the Earth, life exists almost everywhere where there's liquid water on the Earth. But there seems to be, as far as we know, there seems to be no entirely airborne form of life.
ONE OF CHRIS'S SCIENTIFIC COLLEAGUES PUTS IT THIS WAY: WHY ARE EARTH'S CLOUDS NOT AS GREEN AS GRASS, AS FULL OF LIFE AS RAINFORESTS?
CHYBA:
...it seems like there are limitations probably on how long you can stay suspended in the atmosphere. In any case it looks as though atmospheres are bad places to find life. So probably worlds like Jupiter and Saturn don't have life on them.
A CANAL OR GIANT CITY ON ANOTHER PLANET WOULD BE A SURE SIGN OF LIFE.
OR IF THAT FACE WERE REAL, WE'D KNOW FOR SURE.
title: BIO-SIGNATURES
BUT IN THE ABSENCE OF THAT KIND OF SIGN, WE HAVE TO LOOK FOR WHAT NEALSON CALLS "BIO-SIGNATURES"-OTHER SIGNS OF LIFE.
NEALSON:
Most of you have seen bio-signatures like this. Uh, they're called fossils. This particular one is from the Green River formation in Wyoming ...and you can see there is no question that this is a bio-signature. This is proof of former life on this planet. If we found a rock like this on Mars or anywhere we would be overjoyed. But what about the other side of the rock? Believe it or not, this is a bio-signature too. But in this case, we need to look at in at very high resolution and see the bacterial bodies and other things that might be preserved in a rock like this.
So, as you get to more primitive life which is what life was like on Earth for the first 2 and a half billion years, the bio-signatures become less and less obvious and the challenge becomes more and more.
We don't imagine that every planet or move would have advanced and structural intelligent life and you don't want to miss it if it looked like Earth did 2 billion years ago. What we want to do is develop "bio-signatures" that would never miss life no matter what the form that its in.
SOMETIMES WHAT SEEMS TO BE A BIO-SIGNATURE MAY BE, AT BEST, AMBIGUOUS.
TAKE THE FAMOUS MARTIAN METEORITE, ALH 84001.
IT WAS FOUND BY AN NSF-NASA RESEARCH TEAM LIKE THIS ONE, OUT ON THE BLUE ICE FIELDS OF ANTARCTICA.
THEN RESEARCHERS AT NASA'S JOHNSON SPACE CENTER SHOCKED THE WORLD WITH AN ANNOUNCEMENT THAT THEY BELIEVED THESE SQUIGGLY SHAPES WERE LIKELY MARTIAN MICROBES, FOSSIL RELICS OF A TIME WHEN MARS WAS MORE HOSPITABLE THAN TODAY.
OTHERS SAID THESE FORMS WERE JUST TOO SMALL FOR ANY KIND OF LIFE, AND QUESTIONED WHETHER SOME OF THE APPARENT SIGNS OF LIFE ENTERED THE ROCK AFTER IT FELL ONTO THE ANTARCTIC ICE...
ON ALL THESE MATTERS, THE SCIENTIFIC JURY IS STILL OUT...
SKEPTICS USED TO SAY THAT LOOKING FOR LIFE BEYOND EARTH WAS A SCIENCE WITHOUT A SUBJECT.
BUT IN THE PAST 2 DECADES DISCOVERIES DOWN HERE ON EARTH HAVE PROVED THAT LIFE AS WE THOUGHT WE KNEW IT WAS NOT THE ONLY KIND OF LIFE THERE IS, EVEN HERE ON OUR OWN PLANET.
chapter head: EXTREME SURVIVORS
NEALSON:
I'm a micro-biologist by training and my field has changed almost 180 degrees, almost completely turned upside down in the last 20 years. Uh, because of the discovery of what we might call extreme environments and the organisms that live there. I have an example of one of those extreme environments here.
This is a rock from the bottom of the Pacific, from the hydro-thermal vents. The water coming out that forms these rock formations is on the order of 300 degrees centigrade... and can remain liquid because of the high pressures at the bottom of the ocean.
As it comes out and starts to cool down, it's full of chemicals that allow microbes to live in this environment, even when it's hotter than boiling.
TITLE: EXTREMOPHILES
Uh, these are called extremophiles. And the discovery of such extremophiles that could live at a hundred centigrade or higher, completely changed the way we viewed life on this earth and spurred a lot of research into other extremophiles.
WE'VE FOUND LIFE NOT JUST IN EXTREME HEAT, BUT ALSO IN EXTREME COLD.
EARTH'S SOUTH POLE IS NEARLY 2 MILES HIGH IN ELEVATION AND SURROUNDED BY HUNDREDS OF MILES OF EMPTY ICE.
JUST A FEW YEARS AGO, THE TEXTBOOKS SAID THAT APART FROM HUMANS WITH OUR POWERFUL TECHNOLOGY, NOTHING COULD LIVE HERE.
BUT THEN IN 1999, RESEARCHERS DISCOVERED THESE MICROBES HAPPILY LIVING IN THE ICE, TAKING IN ENERGY, REPRODUCING AND DOING ALL THOSE THINGS WHICH PLANTS OR PENGUINS DO IN MORE CLEMENT PLACES, AND WHICH ARE CHARACTERISTIC OF LIFE.
HOT... COLD... WHAT ABOUT DEEP DOWN BELOW EARTH'S SURFACE?
CHYBA:
What we have learned about life on Earth in the last decade or so is that life doesn't only live at the surface. There is a so-called deep biosphere on the earth. Life can live miles underground. And in fact it looks as though there is as much life underground in terms of total mass of living things as there is in all the life on the surface, and that includes, in fact that's dominated by trees. Trees make up well over 90 percent of all the biomass on the life of the earth. So it's kind of a staggering picture if you think about life living underground, which is exclusively microbes once you get below the upper few feet. There's nothing but microbial life underground. And yet all those single-celled organisms add up to as much mass as is present in all the forests on the surface of the earth.
If it is the case as it apparently is from the Earth that life can exist in a deep biosphere, then you have to ask, could there be worlds where there is no liquid water at the surface but would still harbor life because that life is living underground?
And... probably... the answer to that question is yes.
NEALSON:
What we've discovered is that virtually any environment that allows liquid water to be there, will be compatible with life... that life has a way of inhabiting every place that has liquid water on this planet.
WHAT WE'VE LEARNED FROM THESE EXTREME SURVIVORS HERE ON EARTH OPENS OUR MINDS TO NEW POSSIBILITIES AS WE LOOK FOR LIFE IN OTHER PLACES IN OUR SOLAR SYSTEM.
chapter head: HABITABLE ZONES?
AS WE CONSIDER THE OTHER WORLDS OF OUR SOLAR SYSTEM, WHAT ARE THE BEST PLACES TO LOOK FOR LIFE?
NEARLY EVERYONE AGREES THE FIRST RULE IS... "FOLLOW THE WATER."
CHYBA:
Well, obviously a world like the Earth would be ideal, but we're it in our solar system. There is no other planet with liquid water at the surface, certainly not with liquid water oceans ...and that means that to look for life elsewhere in our solar system, we have to look for places that are as much like the Earth as we can find.
So what are those places? Well, first and foremost there's Mars. We know that liquid water existed on Mars early in its history and it appears that there are still short-lived environments at the surface of Mars where water can briefly exist. It doesn't last long because the Martian atmosphere is too thin and water boils off right away, but for short periods of time you can still have liquid water flowing at the surface of Mars.
So you can imagine life having begun at the surface of Mars and then retreated into the subsurface as the surface freeze-dried. So Mars is the best candidate.
AS WE'VE SEEN, VENUS LOST ALL ITS WATER...
AND IF LIFE CAN'T EASILY EXIST IN GAS GIANT PLANETS, DOES THAT MEAN OUR SEARCH FOR LIFE HAS "RUN DRY"?
NOT EXACTLY...
NEALSON:
We need to broaden our perspectives and think about uh, some of the other abodes for life. A good example is Jupiter with a series of moons that are on the order of the size of Mars some of them, they're very large habitats for life.
CHYBA:
The next most interesting place is Europa, one of the big moons of Jupiter. Europa is an ice-covered world that almost certainly has an ocean underneath of that ice, and when I say an ocean, I mean an amount of water that's probably double the amount of water in all of the Earth's oceans. That's potentially a great habitat for life.
What we don't know is whether there are the sorts of energy sources available in that ocean either to fuel life if it exists or for life to have begun there. But the high probability that there's liquid water on Europa makes it the other important place to go in our solar system to look for life.
BEYOND JUPITER LIES SATURN, TO BE EXPLORED BY THE CASSINI SPACECRAFT STARTING IN 2004.
IT TOO HAS GIANT MOONS, ONE OF WHICH HAS ASTROBIOLOGISTS-SCIENTISTS WHO LOOK AT LIFE IN THE COSMIC CONTEXT-VERY ANXIOUS FOR THE NEW RESULTS...
CHYBA:
Titan has an atmosphere in which we know that organic molecules are being produced. That's intriguing, but the surface of Titan is very cold, minus 180 degrees centigrade, so there can't be liquid water at the surface for any length of time. Even so, it's not out of the question that there might be subsurface water on Titan...
So if I were looking for life in our solar system, I would begin with Mars and Europa, because in both those cases we have good evidence for liquid water, even if not yet quite yet definitive proof... And I might even think about Titan first of all ....and at least in the case of Titan, we have evidence for the sort of carbon-based organic molecules that we also know are important for life.
NEALSON:
...we have to remember that life doesn't require abundant water, it just requires enough to sustain itself.
20 years ago I dismissed organisms that could grow at 100 degrees C and I was wrong.
So I think we have to keep an open mind in this business when we're looking for life especially on planets with different gravity and magnetic fields and other properties than Earth.
FOR MILLENNIA, HUMANS HAVE LOOKED UP TO THE SKIES AND SPECULATED ABOUT THE POSSIBILITY OF LIFE BEYOND EARTH.
NOW WE HAVE THE TOOLS AND TECHNIQUES, NEW SPACECRAFT AND NEW SCIENTIFIC CONCEPTS, THAT JUST MIGHT ENABLE US TO FIND OUT...
STAY TUNED... SUCCESS IN LOOKING FOR LIFE MIGHT PERHAPS BE JUST AROUND THE CORNER...
