Chris McKay at MIT – 1997 MA Space Grant Consortium Public Lecture

Chris McKay at MIT – 1997 MA Space Grant Consortium Public Lecture


[MUSIC PLAYING] MODERATOR: The Massachusetts
Space Bank Consortium is a NASA-funded
program whereby we’re trying to distribute
government funds and industry funds to worthy students
and faculty members throughout the
Commonwealth in an attempt to keep the spirit alive
of the importance of space exploration and
spacecraft technology and make sure that the next
generation is able to have some good fun that
those of us who were in the origins of
the space program has had. The members of the Space
Consortium in this state led by MIT and through the
Boston University, the Draper Laboratory, Harvard Tufts,
University of Massachusetts, Wellesley College in Worcester
Polytechnic Institute, newly added this year, the Woods
Hole Oceanographic Institute, and starting this summer,
the Five College astronomy department [INAUDIBLE]
in the Pioneer Valley. We have programs that
involve summer internships, undergraduate research
opportunities, and fellowships. And those who would
like to find out more can find us on the web. The speaker this afternoon,
Christopher McKay, follows in a line of
distinguished earlier speakers beginning with Bill
[INAUDIBLE] in 1990, and most recently Bob
Stevens last year. Chris’s subject, prospects in
the search for life on Mars, is an exciting one to all of us. I was reminded that our
department head in Aeronatuics and Astronautics here
at MIT, Ed Crowley, said this fall what
a wonderful summer it had been because now following
the Allan Hills Satellite– I’m sorry, the Allan
Hills meteorite finding, the possibility
of life on Mars. Ed says, isn’t this wonderful? Now you go to cocktail
parties and everybody wants to talk to you. [LAUGHTER] So we’re– certainly
we’re grateful, not only for the [? finds ?]
but for the favorable public awareness that is associated
with the exciting prospect of life on other planets. Chris McKay is
uniquely qualified to discuss the prospects for
us, for exploration of Mars, with us. And I heard Chris talk about
this on previous occasions, and I assure you,
you’re in for a treat. He received his PhD
in astrogeophysics at the University of Colorado,
went to NASA’s Ames Research Center, where he
has been ever since. He’s a research scientist
in the Space Sciences Division, the recipient of
many prestigious awards, including the
[INAUDIBLE] [? Urey ?] Prize by the
Division of Planetary Sciences in astronomy. In addition to his
interest in geophysics, he has a strong interest in life
sciences, both on this planet and what it tells
you about exobiology, or life outside this planet. This has led him to
work in such cold places as Antarctica, Siberia,
and now Boston. [LAUGHTER] Chris, I’m glad you made
it through the storm. We welcome you to the
Massachusetts Space Bank Consortium. MCKAY: Thanks, Larry. [APPLAUSE] Hey. [? Thanks, Larry. ?]
[? What up? ?] As Larry was telling, I’m going to talk about
today is Mars and the prospects for understanding whether
there was life on Mars. Great, thanks. Let me start by getting the
right end of the view graphs. First, with just
a one word chart. It’s only word chart
I use, I promise, but since I’m from
NASA I’m required to use at least one word chart. I want to motivate what I
do, what I’m interested in. This is a goals of
planetary sciences put together by some
committee a while ago, and it’s the standard stuff. Determine the origin and
evolution the solar system, understand the Earth,
survey the resources. But the one that I
like is one in the box, and in some sense that’s what
I take as my job description, to understand the relationship
between the chemical and physical evolution of the
solar system, the appearance of life. And this is what got me
into planetary science, and this is what I really do. And just so you
know, just last week, when I was doing
my taxes, there’s a little slot this
says occupation, I started writing, to understand
the relationship between– [LAUGHTER] I’ve never been
audited, you know? [LAUGHTER] I think they’re
afraid of what they’ll find when they come and look. Well, suppose that was
your job, to understand the relationship between the
chemical and physical evolution of the solar system
and the origin of life. Obviously, most of your
work would be on Earth. There’s good samples. There’s a good planet here. It’s easy to get to. A lot of lifeforms. But other than the Earth, the
planet that’s the next best is Mars. And so I’m going to talk about
how Mars compares to Earth, how it represents a second
example, possibly, of life, and our understanding
of it as a planet and how we might investigate,
and in particular, where we would go. And I’ll use places
on Earth as analogs, and our study in places like
Earth, very cold, dry places. Like Larry said,
Antarctica, Siberia, and now here at– in Boston. Today– as models. Let’s start with
this image of Mars, which is a ground-based image. And if you go out, Mars
is in the night sky now. You can look through
a small telescope and see the polar caps and
watch them grow and shrink and dark features,
moving north and south. It’s reasonable to
suspect that this would’ve been water, and this
vegetation, and I think that’s what led
to the notion of Mars as the planet most likely
to have life, maybe even civilizations, because of this
comparison with seasonal change on Earth. And partly for that
reason, in ’76, Viking went to Mars, a little
more than 20 years ago. And its mission was
to search for life. As you may remember, it had
a robotic arm to reach out, scooped up some dirt, and
looked to see if there is any microbial life in the soil. We knew enough by then
to know that there was no widespread biosphere
on Mars, no civilization, no forests, anything like that. But there’s still a possibility
that there was microbial life. What did Viking find? I won’t go into detail,
but basically, it found that the soil had some
sort of reactivity, some kind of oxygen, bleach or something. It found that there was no
organics in the soil at all. So the reactivity
is– that’s why the activity was thought to be
caused by some kind of chemical reaction. So it’s not very
interesting from a bio– a life point of view. The results of Viking
really were, it’s dead, Jim. There’s nothing there. Why is Mars so dead? I think the answers– where is the answer? Well, let’s look
at the atmosphere. Just to remind you what the
atmosphere of Mars is like, it’s not [? in ?]
the atmosphere. This is the atmosphere
you’d expect, mostly carbon dioxide, nitrogen, argon. Very similar to the
atmosphere of Venus, very similar to the
atmosphere that Earth had, early in its history. In fact, this is the
kind of atmosphere you’d expect the Earth to have. It’s only recently
that it’s been polluted by the presence of oxygen,
only a billion or two years. Life has been producing
this pollutant oxygen, replacing the CO2. And of course, human
beings, in their wisdom, are getting rid of
this polluting oxygen and bringing back the CO2– [LAUGHTER] –restoring the Earth to
its environmentally-correct condition, which is
this kind of atmosphere, which is what Earth-like
planets should have. So the atmosphere of
Mars is not surprising, and you can see that all
the elements needed for life are here. CO2, nitrogen, water. And in fact, as we talk later
about humans going to Mars, imagine taking this CO2
and taking the C off. You have oxygen,
nitrogen, and those are the components of breathable
air, and here’s water. Basic requirements needed
to sustain humans on Mars are right there in the
atmosphere, ready to get to. So it’s not the atmosphere, per
se, that’s surprising on Mars. What’s surprising is how
thin that atmosphere is. And let me just show you the
Viking results for three Mars years, six Earth years. This is a pressure at
the two Viking sites, slightly different elevation. And the pressure’s in
units of millibars. As you know on Earth, sea
level pressure is a thousand in these units. So the pressure on Mars
is a hundred times thinner than the pressure on Earth. It’s equivalent to the pressure
about 20 miles high on Earth. This is important
in two respects. First, for humans,
the vapor pressure of water at body temperature,
30 centigrade skin temperature, is about 60
millibars, which means that fluids exposed to Mars
environment at body temperature would start boiling. It’s not recommended, which
is why if you go to Mars, we’ll need spacesuits. From a point of view of
humans, it might as well be the vacuum of space. Also, the triple point
pressure of water is here at 6 millibars. So it says that
water is not going to exist very readily
as a liquid on Mars. On Mars, water is going
to behave the way carbon dioxide does on Earth. As you know, dry ice, if
you take a chunk of dry ice and warm it up, it goes directly
from the solid to the vapor without forming a liquid
phase, which is why it’s called dry ice. On Mars, the pressure
is low enough that water does the same thing. And then fundamentally,
I think that is the answer to the question–
or to the double question, why is Mars so dead and red? I think it’s related. And the question really is
that at the present epoch, there is no liquid water
at any place, at any time. This is a profound observation,
because if we look at life on Earth, life on Earth
is really, essentially, bags of liquid water. That’s what all life
forms on Earth are. There’s some
dormant stages where they can live without
water, but all life in its growing,
reproductive phases, is bags of liquid water. No liquid water, it’s not
surprising that it’s dead. Doesn’t mean there’s
no water on Mars. Here’s my favorite picture
from Viking, showing the surface of the planet. See these white patches? This is water frost. But as I said earlier,
as that ground warms up, it’s going to go
directly into vapor. There’s no point
is there liquid. Well, if that was
the whole story in terms of biology on Mars,
it would be pretty dull. But one of the things
that Viking did find– I’m sure you’re all
familiar with these images showing fluvial features
on Mars, evidence that at one time, Mars
had lots of water. This– the scale on this feature
is some 300 kilometers across, showing fluvial features carving
through the ancient crater terrain. You can see the heavy– heavily the evidence
of craters indicating that this terrain dates back
to the late bombardment, some 3.8 billion years ago. This is, essentially, the– I think these are the
most interesting pictures we have of anything
beyond the Earth, from the point of view of life. We don’t have any
evidence directly of life. We have the next best thing,
which is liquid water. We don’t even have
liquid water, but we have pictures of what
used to be liquid water. So we’re several steps
away, but still, these are the most exciting
pictures that we have from a biological point of
view once we leave the Earth. Now, just as a word
of caution, here’s another interesting
feature, picture, that looks like a fluvial
feature, nice [? oxbows ?] and whatnot. But this is Venus,
and the temperatures were some 600 degrees
when this fluid flowed. So one has to be careful. How do we really know that
these features are water? I won’t go into a lot of
detail, but the morphology of the feature. This is down flow this way, so
it’s a tributary system, not a distributary system,
so it’s unlikely that it’s anything but
a distributed fluid. Candidates, CO2,
water, whatever. Water is the logical one. It’s the only explanation
that really holds water, so to speak. So we’ll take this as
evidence that at one time, there was lots of water on Mars. We have other
indications that Mars was more active in the past,
for example, Olympus Mons. This is volcanoes,
large volcanoes on Mars. This one’s 27 kilometers
high, 500 kilometers across. All indications
are that Mars was an active world at one time. We have not seen any
eruptions at the present time. We have no direct evidence
of current volcanism on Mars, and there’s a lot of
evidence of past volcanism. So it’s interesting. Everything we know about Mars
from the images from Viking would tend to indicate
that it was at one time an active planet and
has become inactive. What was it like
when it was active? Well, I put up this
picture to bring to mind the notion that early in
Mars history when it had water, it might have looked like this. Now, this picture
is actually drawn based on taking the estimates
of the amount of water required to carve the channels. Look at the channels. We know the size
of the channels. Calculate how much
water that is. Extrapolate to the planet. We deduce a layer of water from
that geomorphological argument of 500 meters thick. If you take 500 meters of water
spread over the whole globe, sort of pour it onto
the present topography, sort of like that
Sherwin-Williams ad where they’re pouring
paint over the globe, just let it relax into
the present topography. This is the correct
image that one gets. The northern
lowlands are flooded. Valles Marineris is flooded,
and then the southern highlands [? or ?] [? Tarsus ?]
is above ground. This is a realistic picture. This is a picture– it’s an artist conception
of what Mars was like 3 and 1/2 billion years
ago, might have been like. Sometimes I say,
well, this picture is taken by Hubble, because it
can look backwards in time– [LAUGHTER] –and this is a photograph
of Mars, 3 and 1/2– but you guys know
better than that, so I won’t even try to
convince you of that. Now, when you look
at this picture, I’m sure it must remind you
of the Earth seen from space. The famous– what’s become
essentially a visual icon for the space age, the picture
of the Blue Marble Earth seen from space,
Apollo 17 picture. And that’s really the essential
point in the whole discussion of Mars and what motivates
the interest of Mars, that at one time, there might
have been two blue marbles, Earth and Mars. That’s very interesting. It’s also interesting that
somewhere along the line we lost one of our marbles, and
something went wrong with it. But to me, the most
interesting thing is not that there was
another Earth, per se, but that Earth and Mars
were similar at a time. When early Earth
and early Mars were similar at a time when
early Earth had life. We look at early Earth. We know that it had water,
CO2, atmosphere, volcanism. We know that early Mars
had water, CO2, atmosphere, volcanism. But we know that the
time they were similar was a time when we first see
evidence for life on Earth. And let me go into this in a
little more detail, because I think it’s a very fascinating
story, the early history of the planets. Here is the history of the
Earth and Mars compared. Let’s start with
the Earth forming 4 and 1/2 billion years ago. The moon forming event
somewhere around here, for [? 4.6 ?] or something, but
the Earth is really forming, the surface is stabilizing. The end of the late bombardment,
3.8 billion years ago. So I take that as a birthday
of the Earth, April 1st, 3.8 billion years ago. [LAUGHTER] That’s when the Earth
yesterday– was its birthday. 3.8 billion years ago. And what’s interesting from
a point of view of biology is that we have
evidence for life at 3.8, 3.9 in that form
of chemical fossils. Life selectively takes
carbon-12 over carbon-13 by about a few percent, 2%. And we see that
isotopic signature in sedimentary record. It’s not really hard evidence. It probably wouldn’t stand
up in a criminal trial, but you might get by
with in a civil trial– [LAUGHTER] –in terms of evidence
for life, okay? But– and that’s why I
call it possible life here. And it’s virtually
instantaneous, if not before the end of
the [? end ?] [? late ?] bombardment. Where 3.5, we have
definite evidence. This is beyond a
shadow of a doubt, beyond reasonable doubt,
direct evidence for life at 3.5 in terms of fossil algae. And I’ll show you those images
from those kind of rocks. So this is amazing in that
it shows that Earth forms, and then essentially, possibly
instantly, geologically speaking, where an instant
is 10 million years, life appears on the planet. We can’t reproduce this
in the lab, by the way, and we don’t have a consensus
theory for how it happened. We just have the evidence that
it happened really quickly on Earth. And then what happens,
just to complete the story, as it’s pretty dull for a long
time, we have microbial life, and then eventually oxygen
builds up, multicellular life, and then very recently,
animals, and of course– just to keep perspective, here
is the dinosaur extinctions, just there. And I tried to fit in some
more events like the election last year in there, but it
just doesn’t fit in the scale. So it’s really– this
first half billion years that’s the time period
that’s of interest in terms of life on planets. And in fact, our current
understanding of the biology would suggest that
by 3.5 for sure, all major metabolic
pathways were in place. We had DNA life, DNA-based
life like we have today, with only two major
pathways not yet realized, and that is aerobic respiration,
which we all depend on, and the ability to metabolize
silicon parts like diatoms do. Other than that, the
story is written by 3.5. I call these years, the
first half billion years, the Wonder Bread years. These are the years– you
remember those old commercials? Certainly dates in terms of
what I watched on TV, but it’s– this were the years,
the formative years, when Earth and life are learning
to work and live together. By 3.5, really, it’s
all details after that. Well, let’s go to Mars. This is the same period, 4– 3.5 to 4, when we think
there was water on Mars. And why do we think that? It’s because the fluvial
channels interlace the ancient crater terrain. It’s very convenient that the
surfaces in the solar system are time-stamped. There was a big giant time
stamping a 3.8 billion years ago called the ancient crater– the end of the
heavy bombardment. We look at the lunar highlands. We’re seeing material–
we’re seeing that timestamp. We’re seeing a surface
that dates back to 3.8 billion years. When we look at Mercury, when we
look at the ancient crater tray on Mars, we see that timestamp. On Earth, that
timestamp has been erased by the very activity
that’s kept Earth alive, but we see it on
Mars, and we see that [? while ?] fluvial
features predominantly are associated in
that ancient terrain. So that tells us that water
flowed during this point, some time before and after. And that’s the time when
life is found on Earth. That is, I think, a
very compelling argument that if Earth and Mars
were indeed similar, and similarity really
means only liquid water. From a biological point of view,
the only thing that matters is liquid water. And I’ll show you
arguments for that. Then– and Earth– life appears quickly
on Earth, then could it have appeared on Mars? That’s the essential
scientific question. Let me answer a
related question, which is Earth and Mars
started off so similar. Why did they take such
different trajectories? Why does– why did Mars go bad? Why do planets go bad? Is it bad schools or
bad neighborhoods? Federal programs? What’s the problem? We have some
understanding of that. We have some theories
for why Earth stayed good and why Mars didn’t,
and they have to do with the carbon cycle. Imagine the early Mars,
early Earth as well, with thick CO2 atmospheres. These atmospheres are required
to keep the planets warm. Now, interestingly,
we can’t consistently explain Mars’ early climate
with a CO2 atmosphere, but nonetheless, let’s take
it that Mars had a thick CO2 atmosphere. The CO2 is not stable in the
presence of water, represented here by these clouds. The water will dissolve the
CO2 to form a weak acid, which will weather silicate
rocks, and that result will be the formation
of calcium carbonate. Now, on Earth,
organisms have made use of this saturation
of calcium carbonate to make shells and other things. But even the absence
of life, if left alone, the CO2 would turn into solid
material on ocean and lake basin floors, chalk
and limestone deposits on the bottom of
ocean and lakes. Well, on Earth,
fortunately, that material is carried by
subduction to depths where temperatures of around
1,100 degrees centigrade, the carbonate turns
back to CO2 and comes bubbling up in arc volcanoes. This is exactly
what’s happening, say, at Cascade Range. The Juan de Fuca oceanic plate
is subducting under the North American continental plate. Those sediments volatilize,
and they come bubbling up, and that’s the gases that are
emanating from the Cascade Range. So the gases coming
out of Mount St. Helens are literally the
recycling of carbon that was deposited
in the Pacific Ocean. So while those gases and
ashes were an inconvenience to the people living
near Mount St. Helens, in terms of the health
of the biosphere, it’s an important
recycling mechanism. Well, on Mars, there there’s
no evidence that this occurs. There’s no evidence
of plate tectonics. We don’t see any rifting, the
spreading centers, I mean. We don’t see any
subduction areas and we don’t have anything
that looks like arc volcanism. So Mars being a
one-plate planet, there’s no way to
recycle the carbonate. So in some simple
sense, we think what happened is
Mars started off with a thick CO2 atmosphere. It formed carbonate deposits. And there’s no way to recycle,
and that was all she wrote. A hundred million
years later, everything got cold and everybody died. So in some simple
sense, we think this explains the differences
between the two planets. That early period
of Mars’ history, this period of half a
billion years between 4 and 3 and 1/2 billion, that’s the
period that we’re interested. That’s when Viking should
have landed on Mars. Viking was 3 and 1/2
billion years late. It wasn’t NASA’s fault, but
we get the blame anyway. 3 and 1/2 billion years late. We have other
evidence that suggests that Mars was very different
early in its history as well, and this is the
meteorite evidence. I want to talk briefly about it. We have meteorites on
Earth that came from Mars. How did they get here? Well, it’s represented
in this picture. What we think happens is
stuff slams into the planets. A good example is
look at the night sky and there’s comet
Hale-Bopp, racing through the solar system. Fortunately, it’s
missing all the planets. It’s missing Earth
in particular. But if it wasn’t missing them–
there’s always a finite chance it would hit– it could slam with enough
force to knock material in– with velocities exceeding
escape velocity, and the stuff would
never fall back down onto the planet that was hit. And it could go into a
solar orbit, and millions of orbits later, by
some random chance, it could hit another planet come
slamming into the atmosphere. And it would be found. In this particular case,
we find them in Antarctica. Well, it’s not the
meteorites have some sort of perverse
attraction for Antarctica the way tornadoes do for trailer
parks or anything like that. [LAUGHTER] It’s just that in
Antarctica, it’s very easy to
recognize a meteorite because a big white sheet,
and the only way a black rock can get on that
sheet is literally falling down from the sky. Well, so we have
on Earth 12 rocks, a dozen rocks, that we
think came from Mars. This is a very nice
diagram by Jim Gooding that shows how these rocks
form four classes of rocks. There’s the S, N, and C rocks. 11 of the 12 rocks fall
into these three classes. And what I’m plotting here–
what Jim plotted here is the age– the crystallization age of the
rock, when the rock formed, versus a estimate of the
depth below the surface at which it formed. So you can see that
the S, N, and C types, which is 11 of the
12, are all fairly young, 200 million years for the S type
and only about a billion years for the N and C type. These are young rocks. They formed recently on Mars,
and were then kicked into orbit and came to Earth. And then there’s one
rock, a famous rock now, that was found in Antarctica,
that formed 4 and 1/2 billion years ago on Mars. Well, these 11 are all
consistent with this planet that’s cold, with oxidizing
water, and no organics stable. These are all consistent
with the Mars we see today, and we’re telling
us that it looks like Mars has been the way
it is today for at least a billion years, a cold,
dry desert world, probably lifeless on the
surface, at least. But this one is not consistent
with that kind of environment, and it’s consistent with a
warm, reducing conditions with organic compounds,
stable, again indicating Mars went through
some very deep change in its environmental conditions
from an environment that was much more conducive to life. [? When ?] [? is ?]
[? it? ?] Let me just do sort of a parenthetical discussion
here about how do we know these rocks came from Mars? Because it’s often
an interesting point. And I’ll just go over the
evidence briefly on that. This is– the logic
takes two steps. One is that all these
rocks, 12 rocks, came from the same place. And that’s based on– primarily on oxygen isotopes,
and I just illustrate that here with a diagram that
shows the oxygen isotopes of different meteorites. And they cluster
in certain classes and the SNCs form a
distinct class right there, as you can see. This is oxygen-17 to
16, oxygen-18 to 16, and ocean water would
be 0, 0 on this plot, which would be right
around about there. So you could see these form– each different meteorites
tend to form a distinct class or line on this plot. And there’s a distinct
cluster there, the SNC, that tells us that these all
came from the same parent body. They all came from
the same place. [? This ?] [? doesn’t ?] told
us that they’ve come from Mars. It just tells us they
come from the same place. But what’s interesting,
and the way we figure out that
they came from Mars is one of these types,
and particularly this one, the Elephant Hills
79001 was analyzed by a variety of people,
including Bob [? Pepin ?] in Minnesota. And they found in that meteorite
bubbles of air, bubbles of gas. And those bubbles of
gas are exactly the same as the gas on Mars as
analyzed by Viking. This is the Mars
air in a log plot, and this is the gas in
the S-type meteorite. And the identity function
would be the solid line. And here are the
points, and the size and the circles
of the error bar. So you can see that over a range
of nine orders of magnitude, the gas in this
bubble is exactly like the gas in this
meteorite on Mars, which formed 200
million years ago. And this is not like
the gas anywhere else. It couldn’t be. This is not Earth air,
Venus air, Pluto air, or anything else. This is definitely a signature
that these things came from Mars, and particularly
the argon-36 to 40 ratio is different
than anywhere else. And it would’ve been different
earlier in Mars’ history. So what it tells
us is two things. One is that Mars’ atmosphere
hasn’t changed much, at least over 200 million
years, and that this rock came from Mars, and therefore all
12 of them came from Mars. So that’s the basic logic of why
we think they came from Mars. Now, of course, the famous
one is this Allen Hills 85001, in which interesting
features were found that look like that,
little, tiny, nondescript ovals. And the possibility
was raised that these are direct evidence of fossils. Now, I want to
make a distinction between the
geochemical evidence we had from the meteorites,
this meteorite in particular, that Mars was a
warmer, wetter place, and then this evidence that
there might have been fossils. This evidence is, I think, weak. It certainly can’t be
proven wrong readily, but it’s not very convincing
evidence of past life. But the evidence
of the meteorite that it was warm and
wet is much more robust. So they’re not
necessarily the same. Why is this evidence weak? I think partly
because these fossils are so ambiguous in terms
of evidence for life. They’re very small. Typical scale is about
10 nanometers across, which is very small compared
to microbial life on Earth. And they’re just nondescript,
little oval shapes. Let’s compare that
to the evidence we have on Earth for fossils. The earliest, oldest evidence
for life on Earth is– this is a picture of that. This is rocks that are 3
and 1/2 billion years old. This is the oldest evidence we
have for life on this planet. And these are from Australia. This is from work of
[? Bill ?] [? Scharf ?] and his colleagues. And this is a rock. It’s actually picture of a rock. This shows sort of a
lasagna-like shape feature. What it is a microbial
mat, organisms living in a mat on a shoreline
or an ancient lake, and then successive waves
or years, mat builds up, and it forms a
layered structure, and then it’s
solidified and lithified and it forms this characteristic
shape, stromatolitic shape. And within these structures,
we can find micro fossils. This is a direct
picture A and panel A, and this is a line
representation of it. And we can see, we can
lay down a modern filament of cyanobacteria,
blue green algae, and show that
they’re very similar. This is very good evidence
for biological processes, and in fact for photosynthesis. Not just for biology,
but for photosynthesis, for complete microbial
mat communities on Earth at 3.5 billion years ago. And we can even make
a plausible argument that these are
cyanobacterial mats. So it’s much better argument
than we have for life on Mars. So the one question I
want to now turn to is, if we want to go to Mars, if
we want to get better evidence, how do we do it? How would we do it? Well, I think the
answer is we’re going to have to go to Mars. It’s sort of a
standard sales pitch. The first rock is free. The second one
costs $500 million. [LAUGHTER] So how– where are we
going to go on Mars to buy this $500 million rock? Well, the first
thing you might say is we’ll go to the same
place where this Allan Hills rock came from and get
another one, get a better one. Well, people have identified– Nadine Barlow at Central Florida
has identified a place where this rock could have come from. She thinks it comes from
this crater right here, based on the fact that here is
a spot in the ancient crater terrain. The scale here is about
200 kilometers across. So these are large
craters, old craters. But there’s one here, a fairly
young crater, only about 10, 15 million years old, consistent
with the age of ejection for the Allan Hills rock. It’s slightly oval, indicating
a side or a glancing impact, which is consistent with a
higher efficiency for ejecting material. So this could be it. Maybe the thing to do is
to direct our sample return mission to land
right in that crater, drill down, and pull up, and
bring back another rock just like the one we got. Well, maybe that’s
not a good idea, because we might find just like
the one we’ve got, only more. We haven’t resolved the
question any better. Are there better places
to search for life than this type of material? I think there could be. And so I want to develop
a logic for a place where I think would be the
best place to search for evidence of
past life on Mars. And this logic is based on
going on places on Earth which are very Mars-like. So what is the most
Mars-like place on Earth? It’s the dry valleys
of the Antarctic. Let me show you. This is a Landsat photograph
looking down in the Antarctic. The scale here is
about 300 miles across. This is Ross Island,
this island here. This is Mount Erebus, the
active volcano in Antarctica. This is the main United States
station, McMurdo station. And you can see this
icebreaker track coming in carrying in Cheerios and milk
and other important supplies for the base there. But the reason we’re– the
region we’re interested in is this region here,
the dry valleys. This is the coldest,
driest place on Earth. The mean annual temperature
is minus 20 centigrade, and the precipitation
here is tiny compared to the amount
of snow we have outside. It averages only
snow, only snow, and it averages about 2
centimeters equivalent water a year, which is– which is, for example, 20 times
drier than the Gobi Desert. This is an extremely dry,
extremely cold environment. Needless to say, in
this environment, there’s hardly anything alive. In fact, looking down in
these valleys, it’s lifeless. No birds, no
insects, no anything. It’s dead as a doornail. I always take a doornail
with me just to be sure. Dead as a doornail. But on the floor
of these valleys, there’s a big sheet of ice. Here’s [? it, ?] about
5 kilometers across. A big sheet of ice. That’s not surprising. This is– I mean, the annual
temperature, minus 20, ice is not surprising. But what’s surprising is that
underneath that sheet of ice, there’s water. So what we do is we go down
there and we melt a big hole in that ice. It turns out it’s about a little
bit less thick than this room. It varies, but we melt a hole
through the ice, about that big a hole, by heating up
some ethylene glycol and pumping it through
some copper coils. As it melts down, we’ve
got a [INAUDIBLE] sump pump that just sits on it
and sprays the water out on the ice surface. We get the hole
through, and then we take some nonessential
federal employees– [LAUGHTER] –which we have a lot of. Tie them to a rope
and lower them down. Say, what do you
find down there? Well, what we find down there
in the water underneath this ice is that there’s algae there. There’s life there, the
same sort of cyanobacterial mats that we think
populated the early Earth. So here in the most Mars-like
environment on Earth we find liquid water that’s
persisting all year round. Some of these lakes can be
30 meters deep or deeper underneath, now,
relatively thin ice covers, persisting all
year round with life in it. Well, this is pretty amazing. And the first question
that we tried to address was, well, how can there be
liquid water environment where the mean annual
temperature is minus 20? And how can the
life survive there? And then what does this
tell us about Mars? So we tried to develop
models of this. And I won’t bore you
with the details, but I’ll just
quickly go through, as sort of a fun
sophomore physics exercise in thermodynamics. There’s energy sources. There’s sunlight coming in. There could be geothermal heat. It’s not very important. Turns out the geothermal
heat in this area is the global average, some 70
milliwatts per square meter, nothing to write home about. Sunlight comes through, enough
to photosynthesize, about 1% transmission. 10 to the minus 2, 10 to
the minus 3, but not enough to be appreciable heat source. It turns out the heat source is
the summer melt. What happens is that, indeed, the mean
annual temperature is minus 20. Let me show you a plot
of the temperature out– throughout the
year at a site like this. This is a summer,
winter, summer. Summer, the sun’s shining. January, it’s quite warm. Temperatures can be a few
degrees above freezing, which for Antarctica is very warm. And then when winter
comes, the sun goes away. It gets very cold. Indeed, the average is minus 20. But what’s important
here is that in summer, for a couple days each
year, the temperature climbs above freezing. When that happens, go
back to this picture. You might have noticed it. When that happens,
the water, the ice in these glaciers surrounding
the valleys melts and the water flows down as
liquid water into– underneath the ice cover. And what is it–
when water is melted, it has the latent heat of
fusion, which for water is enormous, 80 calories per gram. And in order for the– that water to freeze, it has
to release that latent heat, and that latent heat has to
be conducted through the ice cover. And it’s that
light and heat that forms the energy source
that keeps the lake liquid. So what’s essential
for understanding this environment is that the
temperature, not that the mean annual is below freezing,
but that the temperature gets above freezing for a
little bit each year. The mean annual temperature
determines the thickness of the ice, of course, because
that determines the barrier. What it can do to
the thermodynamics is very simple, because
the ice-water interface is at 0 degrees, by definition. The mean annual is minus 20. Heat is being lost
by conduction. Energy comes in, sunlight. That’s negligible. Geothermal heat, negligible. This is the latent heat flux. And you can very simply
integrate that and soften the thickness of the ice. And sure enough, it
works in Antarctica. We can then model it on Mars
and say, how long could lakes like this persist on Mars? And indeed, we
could show that long after the rest of the
planet is dead, frozen, cold like Antarctica, there
could be ice covered lakes like the Antarctic, down to mean
annual temperatures on Mars, down to minus 35. We’ve done some
simple climate models that suggest that
this time period could be on the order of
half a billion years. So life could have existed
in ice-covered lakes on Mars, like in Antarctica,
half a billion years after the rest of the
planet would have been dead. Are there lakes on Mars? Can we find spots where
there would have been lakes? Well, let me show you my
favorite spot on Mars. This is a canyon, Hebes Chasma
in the Valles Marineris canyon system near the equator. Hebe was one of
the Greek pantheon. And this is her canyon. And in the middle
of the canyon, it’s a– you see the scale bar here. It’s several hundred
kilometers long on the order of a
hundred kilometers wide. It’s got– in the middle of
the canyon, there’s a plateau, and if you look
carefully, you can see that the plateau has
laminations on the side. We think that this
canyon was full of water and that this plateau is
sediments that were deposited, possibly carbonate sediments,
that were deposited when that canyon was full of water. There’s evidence that suggests
that this whole region experienced extensive
groundwater flow, as water drained from Tharsis
through this region down onto the northern plains. So there’s reason to think
there is extensive groundwater flow in here, would have
been filled with a lake. This deep canyon would have
been filled [? with. ?] The lake was a relatively
thin ice cover, even as temperatures on Mars
got down below minus 20, down to minus 35. There might have been
life in this lake. What we’d like to do is land
in the middle of this plateau, drill down to see if
there’s any fossils. And there’s two reasons here. One is a lake is a
good place to live. As I showed you
in the Antarctic, long after the rest
of the environment became too dry
and cold for life, there might have
been life in a lake. A lake, an ice covered-lake,
would’ve been a good place to live on a cold planet. But even more important,
a lake is a good place to die because if
something dies in the lake, it can get buried and
preserved in the sediments. Those river features I showed
you might have had water, and it might have been
great places to live, but it’s not clear that they’re
great places to find fossils. And I often drive
this point home by telling the story of
going to Los Angeles, which I don’t recommend. But if you do go to Los Angeles,
to visit the La Brea Tar Pits. Here’s this big tar
pits, and there’s all sorts of fossils of saber
tooth tigers and wolves. And you think, why did
they live in tar pits? Well, they didn’t
live in tar pits. It’s just that tar pits
is where evidence of them were preserved. The same challenge is
going to be on Mars. It’s not enough to find a
place where there is life. We have to find a place where
the evidence of that life is preserved. And in this case,
nature has been kind to us in that a lake bed,
I think, provides both examples. It provides an environment which
would have supported life long after the average,
and it also provides an excellent environment
for preserving evidence of that life as fossils. Unfortunately, they won’t let
us land anywhere near this lake. You look at, for example, the
[? aero-lift ?] on Pathfinder. It’s 160 kilometers. That’s about like that,
you’ve got a reasonable chance of hitting a 5 kilometer
cliff and rolling down. And the project manager
doesn’t like that. So they want us to find a lake
bed that’s easier to get to, one that’s near an airport
or something like that. [LAUGHTER] So we’ve been
trying to find that, and we think we’ve got one. And that’s this one right here. This is our practical site. This is a lake, Gusev Crater,
in the southern ancient cratered highlands. You can see from
the scale bar it’s about 100 kilometers across. There’s a river, Ma’adim
Valles, that flowed in. And we think these
sediments are off– basically deposited when
this canyon– crater was full of water. We think this was a crater lake,
with deep sediments deposited when it was full of water. And it’s much
smoother and flatter. No cliffs here. Easy target. Land in the middle of the Rover. Drive around, head down, cross
the shoreline, go up the creek. We could be up the
creek on Mars and find what we’re looking for. So this is our
current best example. And now I want to– so this will be– I want to emphasize a
point that in both cases, what we’re searching
for is fossils. This is what was in the
Allan Hills meteorite, if we believe it. This is what we find
on rocks on Earth, 3 and 1/2 billion years ago. And this is what
we’d be searching for in these ancient lake. That’s fossils,
basically footprints. We don’t actually find
the organism itself. We find the footprints. So I want to make the case
now that that’s not enough. That would be interesting,
and it would make my day. It would make my
decade if we found really good fossil
evidence of life on Mars, but it’s not
enough, and it’s not the end of the story
in that we want to be able to find
something that we can compare to life on Earth. And I want to illustrate this
with a very interesting graphic that was published
in the Journal of Irreproducible Results,
which is a comparison of apples and oranges. People say you can’t
compare apples and oranges– [LAUGHTER] –but in fact, you have to
compare apples and oranges. If you want to understand the
broader category of fruit, you have to compare
apples and oranges. In fact, you’d also want to
compare bananas, and even tomatoes, which,
legally, are vegetables, but biologically,
they’re fruits. You want to compare them all. And this is the point. On Earth, we only have apples
in terms of life, or oranges. Well, we only have one. If you look at
life on Earth, you see that it’s all
the same stuff. It’s all genetically related. We have one example
of life on Earth. This is the 16S
ribosomal RNA tree of life from Carl Woese showing
the main families of life. These are the eukaryotes,
animals, plants, mushrooms, and all those sorts
of things are up here in the green branch. And then the bacteria form
two branches, the eubacteria and the archaeobacteria. All life on Earth is related. There’s no reason, a
priori, why this had to be. We could have mapped
out the tree of life and found that there are
two distinct trees, two separate genesis
of life on Earth that have learned
to live together. Ha, ha, right? But it’s not. It’s only one. If there was somebody
else, we ate them. They’re gone. [LAUGHTER] All that’s left is
one example of life. And this is a profound– it’s what’s called the
unity of biochemistry. All life on Earth has the same
DNA, RNA code, the same 20 left-handed amino acids. It’s all the same. Well, this is what I
mean by one data point. If we want to understand
life as a general phenomenon, we’ve got to be able to
get life from somewhere else and sequence its ribosomal
RNA, if it’s even got it, look at its amino acids. Fossils are not enough. We need actual bodies. We need to be able–
something that’s alive or something that’s dead, but
still preserved organically. Well, there’s a possibility
that the life could be survive– still survive on Mars. Not on the surface. It’s way too dry. But maybe under– deep
under the surface, there might be a magma source
associated with ground ice forming liquid water and
providing an energy source. For example, hydrogen and
CO2, for which methanogens could be the basis
of an ecosystem. And we’re now finding these
on Earth, interestingly. So this diagram actually was
published about six years ago. And since then, people
are now finding these kind of systems completely
isolated from the surface of the Earth, subsurface
microbial ecosystems. Many microbial ecosystems
on Earth that we think of as being isolated are not. For example, the deep
sea vents, because they rely on oxygen from the upper
atmosphere– from the surface. But we’re now finding ones
that are truly anaerobic, chemoautotropic systems in
the subsurface on Earth. There’s been at least one. And so it’s possible that
deep underground on Mars, life is still there. We can dig it up, drag it here,
and analyze it, and see if it maps onto our tree of life. Why would we care about it? Why was it possible
that it might just map onto another diagram here,
is that, as I was saying, Earth and Mars were habitable
early in their history when there was a lot
of meteorite impact, and there could have
been extensive exchange of meteorites between the
two planets at that time, during the late
heavy bombardment. And we know, or we think,
that there was life at Earth– on Earth at that time. So the planets, early
in their history, might literally
been swapping spit and sending microorganisms
back and forth. We’re learning that maybe the
planets are not biologically isolated the way we
thought they were. And so it could be that we go
to Mars and find the organisms. Maybe they’re still
alive, and they’re just another branch on the
eubacterial or archaeobacterial tree. Well, I don’t think
it’s actually likely that we’ll find
subsurface life on Mars. I think it’s highly unlikely. But I think there’s another way
we might get at this question by actually finding the remains
of frozen Martian organisms. And that’s, again, based
on a terrestrial example. In this case, it’s the
Siberian permafrost. Here in Siberia is some of the
oldest frozen ground on Earth. This is the Kolyma region. There’s a river here, the Kolyma
river that flows, cutting away this permafrost. And I’m showing you here. This is the active
zone, first meter or so, which thaws each summer. But below that is the
permanently frozen ground. This ground has been frozen
for 3 and 1/2 million years. We know the age from geomagnetic
reversals in the sediments, and we know it’s been
permanently frozen from the geomorphology
of these ice wedges. These are solid ice wedges here. And what we do is we get
with our Russian colleagues, go back away from that
cliff, and drill down into the permafrost. And we drill without
drilling fluids, which is done because the
drill would get stuck readily if you do that, but
it allows us to drill with sterile technique, so
that the core we pull out, the inside of that core,
is uncontaminated, still frozen and clean. We break it open,
look for organisms. We find that there’s still
viable bacteria frozen in this ground for 3
and 1/2 million years. 3 and 1/2 million years
frozen and still there. Temperature is minus 10. Well, what does
that imply for Mars? Well, Siberia,
frozen in the ground, minus 10, 3 million years. Question, then. Is there freeze-dried
life on Mars? Well, on Mars, we need it to
be frozen for 3 billion years. Well, billions and millions. They sound alike, but there’s
actually a big difference– [LAUGHTER] –between them, a
factor of 1,000. Tell that to your congressman. But it’s also a
lot colder on Mars. It’s minus 70
instead of minus 10. That’s 60 degrees colder. Well, you could do sort of
a handwaving argument that says that the Q10 of biological
degradation at low temperatures is about 3. In other words, it would change
in reactivity rate for every 10 degrees. Drop in temperature is about 3. 60 degrees in temperature. 3 to the 6 very niftily
turns millions into billions, and you could argue
that if life can survive being frozen for 3
million at minus 10, then it could survive
being frozen for 3 billion at minus 70. And we’ll dig up these
frozen Mars organisms from the south polar region,
and they will be alive. Well, the answer turns
out to be no, not because of this thermodynamic argument. Thermodynamics works
in their favor, but because of radiation. Last year we were in Siberia. And I’ll never go again, because
the [? Aeroflot ?] airlines are really coming apart and– seriously. But after we drilled
a hole, we lowered a specially constructed
Geiger counter just to measure the naturally
occurring radioactivity. And this is windblown
sediment in origin. There’s nothing
particularly dangerous here in terms of concentrations
of [? radionuclides ?] but just the naturally-occurring
uranium, thorium, potassium, just crustal average
abundances, part per million, generate radioactivity here such
that a lethal dose of radiation is accumulated in
about 10 million years. If you were to lie in this
permafrost settlement for 10 million years, you
would be dead, for sure. [LAUGHTER] Frozen or not. And while on Earth we’re looking
at survival for 3 millions, it’s not a big problem. We’d expect some
radio selectivity among the microorganisms,
but we wouldn’t expect it to be sterile. But on Mars, where
the crustal abundances of these radioisotopes is
going to be roughly the same, organisms preserved
for 3 billion will have accumulated hundreds
of lethal doses of radiation. They will be dead
as doornails, again. We’ll have that same
doornail in our pocket, and they’ll be dead. Which actually, might
be a good thing. We’re digging up Martian
organisms, warming them up. Who knows what they’d be like? We might be glad
that they’re dead. They’ll be dead, but
they’ll still be there. Their proteins, if they’ve got
proteins, will still be intact. We can grind them up and
run them through a GC and see if they’ve got the same
20 amino acids that we have. We could sequence
their ribosomal RNA, if they even got ribosomes. If they’ve got proteins,
they should have ribosomes. We could compare
them biochemically. We could get a lot further
in our understanding of life than we would just
by having a fossil, because we’d actually have an
organism that we could examine. And so I argue that finding
a fossil would be exciting, but there will be exciting
things to do after that as well that will address
fundamental questions. Let me now turn a little
bit to the missions that are coming
up, just to remind you some of the exciting
things that we have in store. Right now, this is actually a
photo of Mars Observer, which didn’t make it to Mars,
but its reconstructed copy will be on– reaching Mars
later this year, on July 4th. Pathfinder will land, the
little Rover that will go out. Neither of these will really
address the kind of questions I’ve been talking about. Mars Observer will
indeed give us better imaging of
the planet, and so we could do more refined analysis
and more detailed speculation about lakes and places that
we might want to go to. Ultimately, we’ll want
to go to such a place, and the idea now is to construct
a Rover, maybe something like this [INAUDIBLE],, maybe
a derivative of the Sojourner Rover. But this will be the first
time to really direct some of these questions,
land on an ancient lake bed, with something, some kind
of arm that can drill down, or some kind of drill that could
go down and pull up a sample and see if there’s carbonates
and organic material, and maybe even fossils tied in. But I argue that ultimately,
they’re– the questions here are big enough and the problem
is deep enough that this is going to be what
humans do when they go. And so this is– I’ve become an advocate
of human exploration, because I think humans bring a
unique skill to this problem. And the only way I can
describe it is by analogy, and it’s an imperfect
analogy, I realize. But suppose you find
yourself standing in front of a crowd
of a hundred people or so, like in this
room, and one of them happen to be, say, your
mother sitting in the middle. You’d be very instantly
able to pick that face out, that familiar face out of this
whole sea of unfamiliar faces. It’s just something
that we’re intrinsically capable of doing,
recognizing patterns and biological systems. Another example is you have
too little black animals. One’s a dog, and one’s a cat. How can you tell the difference? Well, it’s very easy. If you’re a human,
you know right away. Somebody once suggested a task. You throw a stick. The one that runs
after the stick is a dog, and the one that looks
at you like you’re crazy is the cat. [LAUGHTER] But we as humans are
very, very capable of doing that kind
of recognition. And yet it would be very
hard, at least for me, to imagine programming
a machine to make that kind of
recognition or to make that kind of differentiation. So I argue, and I met without
a real hard justification, that humans bring a unique skill
to the recognition of life, even on Mars, and that that
will be their major contribution and their major task to
the exploring of Mars. And let me take off from
that, if humans go to Mars, set up research bases,
they’ll certainly– as is imagined here– be rather self-sufficient. Their oxygen will come from
the CO2 in the atmosphere and the nitrogen for buffer
gas for breathable air will come from the atmosphere. Water will come
from the atmosphere. They’ll be fairly
self-sufficient out of necessity from Earth. And that, I think, leads to
the question of the long term future. What is the long-term
future of Mars? What does it hold? And it also goes back to water. I’ve been arguing that Mars
is a planet with a past, a steamy, wet past. We have some ideas of how
it got to the present. We’re interested in who
is alive in the past. But does Mars have a future? Could we bring it back to life? Could we do CPR on
this dead planet? Well, what would be required? The first order what
you one would have to do is warm up the planet. But we know how to
warm up planets. We’re doing that on Earth. [LAUGHTER] And in fact, if we would produce
the same sort of gases methane, ammonia, nitrous oxide,
chlorofluorocarbons, put them on Mars at part
per million levels, which is a little bit more than
we’re doing on Earth, but it’s in the right direction. We could imagine bringing Mars–
warming Mars up, bringing it back to the thick CO2
life-supporting atmosphere it once had, introducing life from
Earth and going from there. Mars is the only planet that
this is really feasible on, I think. Simple back of the envelope
calculations like shown here. [LAUGHTER] Applied to any of the
other planets like Venus, just– it’s just ridiculous. This is what you have
to do to spin Venus up, if you are so inclined. And it’s just ridiculous. Mars, for one reason or another,
is very close to the conditions one would like, and
we have evidence that it once had water,
maybe a biosphere. That could be a
blueprint for a future. Let me stop there on this
very speculative end, not that the rest of the
talk wasn’t speculative, but by comparison. [CHUCKLES] And maybe we have
time for a few questions. [APPLAUSE] MODERATOR: Questions
for Dr. McKay? [INAUDIBLE] [? Professor ?]
[? Crowley? ?] AUDIENCE: I want to
push on you, personally, the most speculative
comment about sending humans in headfirst arouses
a lot of enthusiasm and might even arouse some
congressional support. I would never
[? attribute ?] [INAUDIBLE] [LAUGHTER] I would make two comments. One is, do you really believe
that considering the fraction of the GDP which we have
to collect from the coffers to [? conduct ?] such an issue
compared to how many unmanned missions, unpiloted missions,
you could send for the same amount of money, A. And B,
you would strengthen the case for this if you [? brought me ?]
the evidence that [? Harris ?] [? and Schmidtt ?] brought back
significantly better examples of lunar material
than the other– MCKAY: 60 or whatever,
[INAUDIBLE] [? astronauts? ?] AUDIENCE: Nine people? MCKAY: Yeah. AUDIENCE: Or 11
people who [INAUDIBLE] the surface, because
in fact, he was the human who had all that
processes [INAUDIBLE].. MCKAY: Right, right. Well, let me answer the second
question first, especially since I’ve forgotten
the first one. You’ll have to remind me. [LAUGHTER] Which is that he was
only looking for rocks. We’re searching for
fossils and life, and the task is a
little more complex. So I’m not sure it’s
a fair comparison. But the first question
was, does it really make sense to involve humans? And I think you can
answer that in two ways. One way is that humans
do bring, I think, capabilities that are useful
in this particular task. I think the other way to answer
it is that science is not the only reason we go to Mars. And I think that when we– science is one of
the things humans do, and it’s certainly one of
the things we’ll do on Mars. But from my point
of view, there’s broader reasons
for going to Mars. And those reasons all
tie to human exploration. So I think human
exploration is– is– I wouldn’t
say is inevitable, but I think it’s intrinsic. It’s intrinsic. It’s just part of the way we do
things, exploration, adventure, whatever you want to call it. So I resist the calculus that
says how much bits per dollar can you get with robotic mission
versus how many bits per dollar or how many papers
per dollar could you get if you send humans? I think that there’s
more to life than just papers and scientific journals. I don’t know what it is yet,
but I’m sure it’s out there. [LAUGHS] And so I– and I think that that
argument is an argument that will– that I think has some merit
outside scientific circles, with Congress and with
the public, that there’s more to the reasons we go
to Mars than just science. And I– to touch
on part of them, is in some sense
what I’m saying here. Does Mars have a future? I think one of the key
questions about Mars is, is it potentially a
site for human activity? Is it potentially
a planet that we could imagine a large
human presence on, at some point in the future? That is not just a
scientific question. That is a question
that deals with, what do we imagine our role
as a civilization or our role as beings? And so I realize it’s
kind of a mushy answer, but that’s the best I can do. I can’t– if one were
decide that only science was the criteria and that was
all that we were interested in, then I would think that
certainly we could do much better, much more, much faster
with just robotic probes. And we could riddle the planet
with sample return holes and bring them back
for analysis on Earth for the cost of a
human exploration. But that’s not the calculus. MODERATOR: [INAUDIBLE] AUDIENCE: I understand that
Viking did not find any evidence for organics,
but is the upper limit for the [? organics ?]
[? at the ?] [? Viking ?] [? site ?] consistent with
the Allan Hill meteroite? In other words, if you
took the meteorite– MCKAY: Right. And commutated it into dust. AUDIENCE: [INAUDIBLE]. MCKAY: Yeah. AUDIENCE: Distributed
it [? around– ?] MCKAY: Right. AUDIENCE:
[? Would the Viking have ?] [? found the ?] [? evidence ?]
[? for organics? ?] MCKAY: Yeah, that’s
a good question. The limits– I know
the limits on Viking. I don’t know what the equivalent
concentration in meteorites are, but it’s pretty low. The limits on Viking
were parts per billion in the heavy organics
in the soil material. I believe that the
concentration of the meteorite is higher than that, but
I’m not 100% sure of that. I know that if you just look at
the meteoric in-fall on Mars, the rate at which organics
should be coming down from just stuff falling
onto the surface of Mars, then you would have expected
Viking to have seen something. And so there must
be some agent that’s actively destroying organics
on the surface of Mars. Not based on the Allan
Hills meteorites, but based on meteorites
falling on Mars, [? carbonations, ?] meteorites,
or whatever falling on Mars. Doesn’t have to be a
very powerful agent, but it has to be an agent
there destroying organics. MODERATOR: Professor
[? Caravan? ?] AUDIENCE: Yeah. I can understand the scientific
scenario of understanding Mars, but this business of
re-engineering it is a little different, [? don’t you ?]
[? think? ?] The question is, what’s the time scale for that,
and is there any chance that humans would be around
long enough to pull it off? MCKAY: Well, that’s
a good question. And I might be able to find
a chart here that answers it, in that it’s hard to
understand, to predict, what the scale would be. But one can do a simple
calculation in which– just look at the initial
and final states, sort of a delta H change
in [INAUDIBLE] required to go from an initial
and final state, and then calculate what’s the
only logical energy source, which is sunlight. So I did this calculation. Just take an initial
state and a final state, sort of cold and
dry, warm and wet, and calculate the mass involved
in the change in energy, the delta H, and
then just divide that by the solar
constant on Mars, because that’s the only
realistic energy source that we have available to harness. And so that number– if that number is 10
to the 8, well, go home and think of something else. But that– no, those
numbers aren’t 10 to the 8. Those numbers are
1, of order 1, which means that with
perfect efficiency, you could use every
single photon, you could undergo these
changes in a year. Well, obviously you can’t
have perfect efficiency, but the efficiency for,
say, greenhouse effects can be quite high. They can be on the
order of a few percent if we were to introduce parts
per million of these gases on Mars. They could– efficiency for
trapping solar energy could be on the order of
a few percent, which means that on timescales
of hundred years or so, Mars could be warm and quite
pleasant compared to today. Wouldn’t be breathable,
but it would be warm. The one place where this
calculation doesn’t auger well is down here, when you
talk about making oxygen. Then the scale is 17 years. But if you look
at the only way we know how to do that
on a global scale, is with self-replicating
machines called plants, their efficiency on Earth,
which presumably is maximized, because they’ve been working
on this for millions of years, is 10 to the minus
4, then you get a number that’s way out
there, a time of 5 years. So this is the only
way I can answer that. It’s not a prediction. It’s just an energy
efficiency calculation. MODERATOR: Yes? AUDIENCE: Let’s assume that we
would be able to manage to get an atmosphere that’s somewhat
thicker and has a CO2 content like [INAUDIBLE],, maybe even
by using some of the CO2 that’s [INAUDIBLE]– MCKAY: Absorbed. AUDIENCE: –into the rocks. Wouldn’t the same thing
happen that happened– MCKAY: Yep. AUDIENCE: –10
billion years ago, because the basic
cycles are not in place? MCKAY: Yep, yep. We’re not going to
start plate tectonics– AUDIENCE: [INAUDIBLE] MCKAY: –on Mars. AUDIENCE: [INAUDIBLE] lost– MCKAY: Yep. Yeah. Eventually it’ll go back,
and our estimate for how long that took is about 10
to the 8 years, 10 to 7, 10 to the 8 years. So what I view it is you’re
spreading the mortgage payments out over 10 to
the 7, 10 to the 8 year. Now, that’s short compared
to the lifetime of a planet, but it’s long compared to
congressional funding cycles– [LAUGHTER] –or even lifetimes. It’s even long compared
to a civilization. So I think that– and
maybe 10 to the 8 years, somebody else will have a
good idea for what to do next. So I think it’s– yeah, we don’t solve the
problem for all time, but nothing is
solved for all time. Even Earth is not
habitable for all time. I mean, we’re a
middle-aged planet. At best we’ve got another– as long to live as we’ve lived,
maybe even less, depending on your belief in
those scenarios for CO2 and solar luminosity. So nothing lasts
forever, despite what you’ve heard on the radio. [CHUCKLES] MODERATOR: [INAUDIBLE] AUDIENCE: You said
it was unlikely that we would find
subsurface life on Mars. Could you say a little
bit more about– MCKAY: Well, I
think it’s unlikely, and I base– this
is a gut feeling. We have no data that
argues against it. I base it on two to
intuitive senses. One, if we look at Mars,
we don’t see any evidence of recent activity. Granted, the SNC meteorites
indicate volcanism 200 million years ago. That’s yesterday,
geologically speaking. Maybe there’s subsurface
heat, but subsurface heat isn’t enough. We need subsurface heat
and subsurface groundwater, and we need chemical production. It just looks like there’s
too many ifs, geologically. Biologically, it means we have
to postulate a biosphere that can sustain itself, that can
solve recruitment and dispersal problems. You know, one geothermal
site goes off. How is it going to
get to the other one? That sort of issues. Over billions of
years, it just– my sense of it is no. Now, people with all the same
data say that their sense of it is yes, it’s worth looking for. So that’s just the what– just
the differences of opinion. AUDIENCE: Does that
mean, then, that you feel that the forward
decontamination problem is not an issue? Unless [? some people are trying
to ?] load up a spacecraft with [? fossils? ?] MCKAY: Well, the forward
contamination problem is a big issue, because
if we go to Mars we might see a signal
that’s biological, that’s due to something
we carried with us, which would cause a big
problem in future missions. So suppose we went
to Mars with an oven to analyze volatiles that took
a sample and heated it up, and that sample was– that oven was contaminated. And we saw a signature of
reduced gases coming out. And that would be a disaster,
because that would then– masses– bureaucratic machinery
would kick in and say, evidence for life. Everybody stop. We’ve got to worry about
this, when it’s really just contamination from Earth. So I think that the forward
contamination problem is mostly to– it’s mostly just doing
things properly and cleanly. It’s the same thing in a
lab, aseptic techniques, so you don’t culture yourself
or your E. coli in terms of your experimental results. Now, I’m advocating
forward contamination on purpose, later on, where you
don’t accidentally bring gunk with you. You purposely bring
gunk with you. So it’s a different
point of view. AUDIENCE: [INAUDIBLE] much
harder on a manned mission. MCKAY: Controlling it is much
harder on human exploration, but it’s not impossible. We do biological collection with
aseptic technique all the time. Biologists have been doing
it for– field biologists has been doing it for centuries. It doesn’t take a
rocket scientist. It takes a biologist. [LAUGHTER] MODERATOR: Melissa? AUDIENCE: [INAUDIBLE]
What do you think– have you thought about
any ethical reasons behind [INAUDIBLE] behind transforming
another planet when [INAUDIBLE] [? trying ?]
[? to fix ?] [INAUDIBLE].. MCKAY: Right. No, that’s a good point. There’s two points there. One is just as– expenses in space versus
expenses on Earth. And I would apply that logic to
the whole federal budget, not just the space program, which
is a trivial fraction of it. There’s a lot of things which
I think we shouldn’t be buying and should be building
better schools instead. That’s one issue. The other issue is, do we
really want to go to a planet and change its natural
course of affairs? And I’ve only been answering
the question of how. I’m just doing numbers here. Now we come to the
question of should? Should we? Is this something we’d
really want to do? And it really boils
down to what do we think is important
in the environment? The environment,
per se, or the fact that the environment
has life in it? On Earth, there’s
no distinction. It’s the generate case, because
the environment on Earth is biological. Every corner of the
Earth is connected to some biological component. On Mars, that–
there’s a splitting in that [? the generative ?]
is not the same. There’s a distinct
difference between a– between a biosphere and
an environment on Mars. So now I’m speaking just
my own personal opinion. I vote for life. I’m a admitted, now,
life chauvinist. I think life’s a
great thing, and I think if we could spread
life beyond Earth, that would be a good thing to do. Just a personal opinion. It’s not official
NASA policy yet. But I’m working on it. [LAUGHTER] AUDIENCE: [INAUDIBLE] change
Mars before we fix Earth, or– MCKAY: I don’t think
it’s a compare– I don’t think it’s either or. I think what we might
learn about Mars, information will be relevant
to maintaining Earth. I think we have assumed
as a species management responsibilities for Earth,
whether we like it or not. And so we have to take a
course in planet management, and I think most of that course
is going to be studying Earth, but occasional field trips
to other planets, I think, are in order. And I think Mars
will tell us a lot. And if we try to build
a biosphere on Mars, I think that lesson
will be very useful. I remember years ago building
a motorcycle from parts, and that was a profound lesson
in how that motorcycle worked. It didn’t work when
I tried to start it after I built it, by the way. [CHUCKLES] Which
is another lesson. But I think studying Mars
will be part of learning to manage the Earth. It’s not an alternative. I don’t think it’s– that they’re in that
relationship at all. We just don’t have any
choice to manage the Earth. AUDIENCE: Chris,
one of the missions that you didn’t talk about
was the 1998 [INAUDIBLE] MCKAY: Polar. AUDIENCE: [INAUDIBLE] land in
the southern layer terrain. You said, high– MCKAY: Right. AUDIENCE: –latitude and it’s
go gas and chemical analyzers on it. And are the sensitivities
of that instrumentation germane to making the
kind of measurements that you talked about for
[? the pole ?] [INAUDIBLE]?? MCKAY: That’s an
interesting instrument. The [? TIGA ?] instrument
on Mars ’98 will land. It’s about 70 degrees
south, in the polar terrain. The polar terrain
isn’t the best place to search for
evidence of past life because it’s relatively young. So it’s not in the– it’s not– my understanding
of the material they’ll sample is that they’re
probably seeing stuff that’s on the order of 10 to the
6, 10 to the 7 years old, so it’s not really going
back into the ancient stuff. We’d really want to
drill down, I think, deep enough that we’re
below the annual wave, and probably deep
enough that we’re below the obliquity wave,
so changes in obliquity. So really, deep down, to
get old stuff that’s been frozen for billions of years. But the [? TIGA ?] instrument
may find something, and it’s an example where
forward contamination matters. If it sees [? and it’s ?]
evolved gases, methane, and that turns out to be
something that they cooked, that they brought with them, a
piece of [? Billboy’s ?] Pizza or something, you know, that’s
going to be a big problem. AUDIENCE: [INAUDIBLE] thinking
about the [? sterilization. ?] MCKAY: Well, sterilization
isn’t required, I think. It’s just clean, cleanliness. Clean room technique. I think that’s the
protocols on ’98 are adequate for
forward contamination. MODERATOR: Well, Chris, before
I let you go and give you a [? small ?]
[? presentation, ?] let me just make one announcement. For those members of my
undergraduate seminar who were here, would you please
move down a bit to the front? We’ll have a brief informal
discussion with Professor McKay and I’ll let you
sign in for the day. MCKAY: And a quiz. MODERATOR: I told
the rest of you– I told you an hour ago you’re
in for an exciting time. I underestimated even what
Chris would produce for us. This certificate– it says
certificate of appreciation. That’s an understatement. Chris, you did a
wonderful job, and we’re– MCKAY: Thanks, Larry. MODERATOR: –delighted
[INAUDIBLE].. MCKAY: My pleasure. [APPLAUSE]

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