Technology Sounds
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Dr. John Holdren: Life is the most complex thing in the known universe.
Just ask anybody in the White House. Abundant on Earth,
hugely successful in colonizing every available
niche. It seems that once started, life is
unstoppable. But does that mean there's life on other planets,
elsewhere in the universe? So far we have not seen signs
of life elsewhere, and not for lack of trying.
Is there other life or traces of former life out there?
Is there now or has there ever been intelligent life
anywhere but on our Earth? With a hundred billion
galaxies, the order of a hundred billion galaxies,
each containing the order of a hundred billion stars, most of which we
now know have their own planets,
the probability of life having evolved elsewhere
seems very, very high. Indeed, on the numbers,
it seems highly likely that intelligent life has
evolved in the universe at some other time, at some other
place, and maybe is out there now.
How will we find out for sure? Tonight, we're going to take you on a
journey from Earth, through the solar system, to planets around
other stars in the search for life.
Let's start with the Earth, and I note that some have asked whether there's intelligent
life on Earth I believe there is, but let me turn
it over now to Gavin Schmidt. Gavin?
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Dr. Gavin Schmidt: Earth is the only example we have
so far of a planet with a biosphere. As we get
further away, Earth shrinks from a recognizably inhabited
place, to a blue dot and then to just a tiny point
in orbit around the sun. The further out we go,
the harder it is to tell that there is life on Earth.
But there has been life on Earth for more than three billion years.
The universe has existed for 13.8 billion years
since the Big Bang, and our solar system has been around for the last
4.6 billion years of those. But
remarkably quickly after the solar system formed and rocky planets
condensed and cooled, there was liquid water on the surface of our
planet. For a planet 4.5 billion years old,
we have evidence of water from only .2 billion years later.
But it took life perhaps another
500 million years to appear. Early life
forms weren't much to look at, but life itself has been here
a long time. We don't yet know how life got started,
there are many theories, but we do know that it got going
under some very challenging conditions.
The sun was 30 percent dimmer than today, but with more
solar flares. There was no oxygen, and therefore
no ozone layer to protect the surface from harsh ultraviolet
rays. But Earth did have the ingredients necessary
to support life. A solvent like water, an energy
source, and abundant nutrients.
For 1.5 billion years, this primitive life survived
in the oceans, protected by the water's opacity.
But around 2.5 billion years ago,
bacteria started to use sunlight directly to fuse
water and carbon dioxide to make sugars, which were then used as food.
But for every molecule of carbon dioxide they used,
and there was a lot of carbon dioxide in the atmosphere,
they released a molecule of oxygen. Those bacteria were followed
by photosynthesizing algae, mosses, and plants.
And eventually, after a number of false starts,
the oxygen built up in the atmosphere until around 500 million years ago,
it got close to present day concentrations, giving a start
to the huge variety of land animals, insects, and
plants we see today. Meanwhile, the
climate was not static. The planet went through cycles of snowballs
and hot houses, driven by plate tectonics, volcanism, greenhouse
gases and impacts. Indeed, it was only
after the last snowball Earth event that set the stage--
that the stage was set for the evolution of multicellular life in the
Edicarian 600 million years ago. The new
species that were rapidly born, evolved and died
changed the planet forever. The surface became completely covered,
you could say infected, infested, with life.
And that life affected the climate, changing the
composition of the atmosphere, the reflectivity of the surface, and the cycling
of water, radically transforming the view from space.
Life co-created the broad
array of special, unique ecosystems and microclimates that
characterize the Earth today, visible even from a million miles away.
But remember, for most of the time
that life existed on Earth, it did not have a land fingerprint,
and the oxygen that we now rely on wasn't detectable
for perhaps half that time. Under those conditions,
or any others in Earth's history, how can we know what would have been
seen from further away? This is where our
understanding of current climates, and of processes that control
composition, clouds and dynamics come into play.
We can simulate the impacts of climate on life, and the impacts of
life on climate at each stage of our planet's history.
Simulations which include the physics of clouds,
oceans, ice, and of atmospheric particles like dust.
We can take those results and then project how those
climates would look from space, from beyond even the solar system.
But we can go further, we can even
simulate the climates of Venus and Mars three billion years ago,
when they were both very different places. Places that
perhaps also had the seeds of life. And Jen can discuss that.
//applause//
Dr. Jen Eigenbrode: If life ever existed in our solar system
then it found a way to adapt to extreme conditions.
Conditions that may be more extreme than what we have on Earth.
I am constantly amazed to find that life has adapted
to every niche, no matter how harsh the environment.
Take for example, the extraordinary springs of Dallol in the
Danakil Desert of Ethiopia. These springs are hot,
salty, rich in heavy metals, and they're
acidic. Microorganisms thrive in these pools,
even the pools of pH less than one. That's more acidic than battery acid.
Life adapted.
Another example, the Atacama Desert in the rain shadow of the Andes
Mountains. It is the driest land desert on Earth. This
Martian-like landscape has been shaped by the wind and salty aerosols
for millions of years. It has been one of the most
challenging places to find evidence of life.
And yet it's there, a few cells here and there. Life adapted.
One last example, and this one really
me, Chernobyl. This diverse life
in this agricultural region is punctuated by the presence of
fungi that live off the radiation from the 1986
meltdown of reactor four. These fungi
use the radiation, the gamma radiation, in the same way
plants use sunlight to grow. Life adapted on Earth.
Could life have arisen and adapted to the extreme
conditions of other places in the solar system?
We're going to find out. We will search for biomolecules,
the organic compounds that make up life, its food and waste products.
We may need to extend that search to other types of signatures,
to build confidence in that detection. We might search for active
cells, and catch extraterrestrial life in action.
We might search for fossilized cells
in ancient rocks and ice. Gavin explained that
Earth is the only known biosphere. However, Mars is a
close neighbor. Although it looks like a rusty,
barren planet today, its history was very similar to Earth's in the beginning.
Did life arise on Mars around the same time that life
arose on Earth? Why are these
two planets so vastly different today?
Both Earth and Mars had a liquid core when they
formed. Movement of this molten iron
generate a magnetic field that shield the atmosphere and surface from being
blasted by ionizing radiation. Earth maintains its
magnetic field, but not so for Mars. Convection of the
Martian core slowed or stopped four billion years ago.
Without the protection of the magnetic field, the powerful solar
wind streaming continuously from the young sun crashed into the
red planet, piling up in front of it like a bow wave of a ship, except in this case,
the wave is charged particles that electrically strip away the
Martian atmosphere. This process continued
for eons regulated by the sun's activity, and slowly stripped
away gases from the volcanoes and the rocks.
With the magnetic field and atmosphere mostly gone, the rocky
surface of Mars was bombarded by ionizing radiation from the
galaxy and the sun. This radiation
comes in the form of photons, such as UV, x-ray,
and gamma rays, as well as charged particles. However, unlike what we experience
here on Earth, all of these forms have an enormous amount of energy.
When ionizing radiation encounters
molecules, it changes them. Radiation damage
to molecules means damage to life and the
signatures that we seek. We know that life
adapts. If life ever existed on Mars,
did it adapt to the harsh radiation environment at or near its
surface? Life has surprised us on Earth and perhaps
life will surprise us on Mars too.
I have spent the last four years exploring Mars through the imagers and the
instruments of the Curiosity rover. We have discovered that Mars is not
really red, it's grey with a rusty skin.
Mars is not really dry, either. Liquid
water on Mars formed rivers, deltas, lakes,
maybe seas. It has been cold and warm, acidic and
alkaline. Its surface and atmospheric chemistry evolved.
It has organic matter and the key nutrients needed
for life. We have only scratched the
surface of Mars and begun to decipher its story.
Did life ever live there? Is there life
on Mars now? And could life live here
in the future? Beyond Mars, we will
search for life in the ocean worlds of the moons of Jupiter and Saturn.
Jupiter has a magnetic field
20.000 times stronger than Earth's. The field
produces a donut-shaped belt around the planet in which charged particles get trapped.
Europa is a water ice-covered ocean
world, and one of great interest as a possible abode for life.
It sits right smack in the middle of Jupiter's magnetic belt,
which means that it is being bombarded by intense amounts of radiation.
Although the Europan surface
is inhospitable, it may offer a glimpse of
the chemistry of what lies beneath. Europa's thick crust
is sufficient for protecting the underlying
global ocean from radiation. And it is hypothesized
that Europa may have hydrothermal vents stemming from its rocky
interior. And if so, these are ideal sites for life,
and they support the potential of life in the ocean.
Now let's go to Saturn, where the moons are embedded in
the rings, where we think life may exist on some of these moons.
Like Europa, Enceladus is an icy
ocean world. And in 2005, the Cassini spacecraft witnessed
geysers of gas arising from the surface. These
plumes are direct conduits to a deep ocean. We might search
for signs of life by flying through these plumes.
And then there's Titan. A rocky moon
with seas of liquid methane and an atmosphere of organic smog.
Titan is drenched in hydrocarbons, and it's cold enough
to freeze most of them. Life as we know it is largely
made of hydrocarbons. Although it may be a stretch of our imagination
to think that life might live here, it is considered
potentially habitable. Did life arise on
Titan? There are
possibilities for extraterrestrial life in our solar system. However, as
Aki will explain, there even more possibilities of life outside of it.
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Dr. Aki Roberge: If we're going to look for life that's really Earth-like, we need to look for planets
around other stars. Exoplanets, for short. When I started
undergrad, we only knew of nine planets in the solar system. Actually, eight
now. //audience laughter// And in grad school we thought exoplanets
would be rare. Twenty years ago we discovered the first planet around another
star. Since that time, we've gone from a few planets in the solar system
to literally thousands of exoplanets orbiting other stars.
And we have only searched a tiny portion of the galaxy with the Kepler
'space mission. We think there's at least one exoplanet
for every star in the galaxy, which would mean over 100 billion planets in the
Milky Way alone. So that's at least 14 planets for every human
on Earth. And the Milky Way is only one of a myriad
of galaxies in the universe. We've found that the planet formation process
is more robust and easy than we thought, and exoplanets
are common. They can form around all different
kinds of stars, even ones not like the sun. There are even planets around binary
stars, just like Tatooine in Star Wars. To our delighted
surprise, exoplanets are not only common, but diverse.
The first planets discovered are unlike anything we have in the solar system.
They are hot Jupiters, massive, gassy planets orbiting closer
to their stars than Mercury orbits our sun.
So in the solar system we have two basic classes of planets. We have
massive gas giants like Jupiter, and small rocky planets like Earth.
But there's all sizes of planets out there. From super Jupiters
to Neptunes, to rocky planets several times more massive
than Earth, all the way down to true Earth-size planets.
So with all this richness of planetary real estate,
it encourages us to start thinking more ambitiously. To search for
those rocky planets that are actually like Earth. We may have
already found some, but we can't actually tell right now what their surfaces are really
like. So as Gavin mentioned, Earth's abundant
surface life makes it unique in the solar system. And this is probably
the only kind of life that we can detect from really far away.
There might be other kinds of life on other kinds of worlds out there, but we
probably won't be able to recognize it. So astronomers are really
focused on finding the true Earth twins out there, and we will look for them
in the habitable zones of nearby stars. So,
the habitable zone is the region around a star where an Earth-like planet
is just the right temperature to have liquid water on its surface, the key ingredient
for Earth life. So for the sun, the habitable zone stretches from
just outside Venus' orbit to Mars. For bigger, brighter stars,
the habitable zone moves out, to cool off, like moving away from a campfire.
And then for smaller, dimmer stars, the habitable zone moves in
to keep the planet warm. Now this spectrum
is how astronomers want to look for life on other worlds. It's the light from the
Earth as if it were really far away, separated by color. Don't panic, we'll go through it.
So this rise in brightness on the
far left is literally our blue sky. And this narrow dip
comes from oxygen, which is produced by plants. These several deep
dips come from water vapor. And then over here is a methane
feature. So methane in our atmosphere
largely comes from bacteria in the guts of our livestock, and in swamps.
So the Earth's atmosphere is full of bio signatures, gases
that wouldn't be present in our atmosphere without life.
Now, the technical challenge of ever seeing something like this is one of the hardest things
scientists have ever thought of trying, and here's why. The Earth is
10 billion times fainter than the sun. So. if the
Luxor Sky Beam, the brightest man-made light in the world, is the sun,
the Earth is four candles on your dinner table. But
astronomers actually observe things that faint all the time. The real problem
is those four candles are sitting right next to the bright lights. If we're
looking at the solar system from 33 light years away, which is not that far,
it's pretty nearby, the separation between the Earth and the sun
.1 arc seconds, or the width of a human hair from the distance of two
football fields. So imagine trying to see those candles if they were right on top of
the Luxor Sky Beam. We have to suppress the light
from the star before we can see the faint blue dot next to it.
There are a couple of different technologies people have come up with to do this. One of
them is a star shade, a gigantic deployed screen that would fly tens of thousands of
kilometers in front of a telescope. You'd be aligned with a star
to block its bright light. But this telescope is a relatively
small one. If we really want to get a spectrum like the Earth
one I showed, we need a bigger telescope. So, NASA has
begun a concept study for a super-duper Hubble called LUVOIR,
which will search for dozens of Earth-like planets and probe their atmospheres.
In addition, it would enable a wide range of general astronomy,
just like Hubble did. With powerful future missions,
we could see the pale blue dot of Carl Sagan's imagining, and have a fighting
chance of finding life out there among the stars. So to
put this grand endeavor into perspective, we turn to Piers.
//applause//
Dr. Piers Sellers: The universe is really big and really old.
Life has been on Earth for about four
billion years. Now we know that in the universe, physics and chemistry
are the same everywhere. A Hydrogen atom here
is just the same as a Hydrogen atom on the other end of the universe.
The laws of physics and chemistry work the same everywhere.
Now we strongly suspect, based on an example of one,
our Earth, that the laws of biology work the same everywhere too.
And by that I mean the laws that Charles Darwin discovered for us.
We think that based on these laws, that
evolution can drive life. To greater complexity,
and ultimately to intelligence. It's the smart thing to do.
Now look at this tree of life. We can see intelligent
animals that we're familiar with. Humans,
elephants, dolphins. These creatures are very
closely related to us. But look over here on the far right.
There's one other intelligence, an invertebrate
intelligence, that evolved completely separately from the rest of us.
They split off from us before brains were even thought of,
when all creatures had were just a few nerve cells.
Octopuses have an intelligence that's comparable to quite a lot of
mammals, and it evolved completely separately.
These guys are like little aliens
living with us on our own planet. If you look at an
octopus, you can see that its brains are actually distributed all over
its body. Most of its brains are in its feet, or in its legs,
and they're connected to the nerve center in its head by a neural
network. It's a distributed intelligence.
But it turns out that they think pretty much the same way that mammals do.
They have a short-term memory and a long-term memory,
they learn, and they get mad. They basically tackle the
business of living in a complex environment the same way that we mammals do.
We think that we understand
how an octopus thinks. So the secret of intelligence
is in the software, it's not in the hardware.
It's very likely that an alien intelligence would be
comprehensible to us in the same way that an octopus'
thoughts are more or less comprehensible to us too.
We should be able to communicate with them if we met them.
So, you'd think there'd be plenty of opportunities for life to evolve
somewhere else, and maybe swing by the Earth, or at least call on the radio.
But we haven't found any alien monoliths,
or beer cans, or cigarette ends,
and we have not heard them tweeting on the radio either.
So, where are they? That's what Johnny von Neumann asked.
Where are they? There are lots of theories about that,
but I'm going to concentrate on the more plausible ones.
First of all, there's the water trap. Maybe the worlds
that have water on them are all ocean, for the most part.
And if that's the case you can't discover combustion, you can't
make metals, so you can't make a radio or a spaceship.
If our dolphin friends lived on an ocean planet, they would be stuck where
they are, in the Stone Age, forever.
We might discover intelligent life here, but they could be incredibly
boring. Talking endlessly about the flavors of different kinds of plankton,
and that sort of thing. Or maybe on a
planet that has dry land but no metals,
same problem. You can't develop a technology.
And how about the difficulty of interstellar travel?
Maybe it's just too hard. It looks like a real challenge for us,
it could be a couple of hundred years before we try that. Maybe it's just too hard.
And then there's the great sci-fi standbys, hostile
races evolve, they wipe out everyone else, that's sort of an ugly end.
I think we should move on quickly, this is meant to be a fun evening.
And then there's another theory, which is that we could be the first.
We could be the first intelligence to evolve
in this part of the galaxy. Someone has to be. We could be
the elder race. So here's a time history of Earth.
When you look at all the time that life has been here. Nearly four
billion years, humans have only been around for a couple of
hundred thousand years, civilization for about 6,000 years,
depending how you count it, and our technical era
only for 200 years. When you look at this picture,
it is obvious that the most likely first alien life forms
that we discover will not be intelligent. They will be somewhere back
here, equivalent to life on Earth during the first three billion years
of evolution. Similarly,
nearby life on an exoplanet is probably plodding its way
up the evolutionary ladder. Remember how long
it took us to get where we are. Where we could even think about life
elsewhere. So, what are the chances
of us finding anything, or anybody, soon?
Here's a timeline of missions for exploring the solar system
with some notional ideas of what we'll be doing in the next
50 years. I think that over the next 30 to 50
years, we will have thoroughly explored every nook and cranny of the solar system,
and seen or determined where there is life here, or past life,
or not. I think there's a good chance we'll nail that one flat.
And then there's a chance of looking for bio signatures
in the atmospheres of exoplanets.
Here's the missions, again, pretty notional, and it's all the 30
to 50-year timeframe, in the future that we could see looking at exoplanets
where we'd be looking for traces of life in their
atmospheres. It turns out
that we Earthlings have the prime real estate in our solar system,
as far as having a habitable environment is concerned.
Most of the rest of the solar system looks like a really tough place to live.
But, you never know. We need to
thoroughly check out our own backyard as well as the planets around other stars.
We'd look like idiots if we failed to check for life
close to home, and failed for lack of trying.
Now back to the beginning. John Holdren's question.
Why do we even care about this stuff? We think it goes
beyond just intellectual curiosity. It's in our nature
because we humans grew up as part of nature, and need to pay attention to it.
I want you to imagine what humans could do in a couple of
hundred years or so. Imagine a probe
from Earth entering the solar system of another star
after a journey of decades, maybe a century.
Note the MSBR logo.
What would it find? My advice to you is eat
healthy, don't smoke, don't jaywalk,
and you might find out. It'd be good to find out we're not alone.
Thank you for your attention.
//applause//