0:00:00.943,0:00:02.364
I'm really glad to be here.

0:00:03.015,0:00:04.703
I'm glad you're here,

0:00:04.727,0:00:06.560
because that would be a little weird.

0:00:07.460,0:00:09.565
I'm glad we're all here.

0:00:10.303,0:00:13.156
And by "here," I don't mean here.

0:00:14.831,0:00:15.981
Or here.

0:00:16.728,0:00:17.880
But here.

0:00:17.904,0:00:19.054
I mean Earth.

0:00:19.627,0:00:23.570
And by "we," I don't mean[br]those of us in this auditorium,

0:00:23.594,0:00:25.064
but life,

0:00:25.088,0:00:26.537
all life on Earth --

0:00:26.561,0:00:31.943
(Laughter)

0:00:32.280,0:00:34.271
from complex to single-celled,

0:00:34.295,0:00:36.619
from mold to mushrooms

0:00:36.643,0:00:38.021
to flying bears.

0:00:38.045,0:00:39.411
(Laughter)

0:00:41.736,0:00:43.245
The interesting thing is,

0:00:43.269,0:00:46.300
Earth is the only place[br]we know of that has life --

0:00:46.324,0:00:48.201
8.7 million species.

0:00:48.660,0:00:49.914
We've looked other places,

0:00:49.938,0:00:52.035
maybe not as hard[br]as we should or we could,

0:00:52.059,0:00:53.986
but we've looked and haven't found any;

0:00:54.010,0:00:56.286
Earth is the only place[br]we know of with life.

0:00:57.318,0:00:58.592
Is Earth special?

0:00:59.591,0:01:02.045
This is a question I've wanted[br]to know the answer to

0:01:02.069,0:01:03.323
since I was a small child,

0:01:03.347,0:01:05.379
and I suspect 80 percent[br]of this auditorium

0:01:05.403,0:01:08.411
has thought the same thing[br]and also wanted to know the answer.

0:01:08.879,0:01:11.046
To understand whether[br]there are any planets --

0:01:11.070,0:01:13.348
out there in our solar system or beyond --

0:01:13.372,0:01:14.830
that can support life,

0:01:14.854,0:01:18.051
the first step is to understand[br]what life here requires.

0:01:18.575,0:01:22.138
It turns out, of all of those[br]8.7 million species,

0:01:22.162,0:01:24.360
life only needs three things.

0:01:25.032,0:01:27.884
On one side, all life[br]on Earth needs energy.

0:01:27.908,0:01:31.393
Complex life like us derives[br]our energy from the sun,

0:01:31.417,0:01:33.518
but life deep underground[br]can get its energy

0:01:33.542,0:01:35.264
from things like chemical reactions.

0:01:35.288,0:01:37.439
There are a number[br]of different energy sources

0:01:37.463,0:01:38.706
available on all planets.

0:01:39.400,0:01:40.556
On the other side,

0:01:40.580,0:01:43.285
all life needs food or nourishment.

0:01:43.741,0:01:48.215
And this seems like a tall order,[br]especially if you want a succulent tomato.

0:01:48.239,0:01:49.955
(Laughter)

0:01:49.979,0:01:53.045
However, all life on Earth[br]derives its nourishment

0:01:53.069,0:01:55.099
from only six chemical elements,

0:01:55.123,0:01:58.127
and these elements can be found[br]on any planetary body

0:01:58.151,0:01:59.487
in our solar system.

0:02:00.537,0:02:03.764
So that leaves the thing[br]in the middle as the tall pole,

0:02:03.788,0:02:05.742
the thing that's hardest to achieve.

0:02:05.766,0:02:07.658
Not moose, but water.

0:02:07.682,0:02:10.463
(Laughter)

0:02:11.285,0:02:13.079
Although moose would be pretty cool.

0:02:13.103,0:02:14.261
(Laughter)

0:02:14.285,0:02:19.820
And not frozen water, and not water[br]in a gaseous state, but liquid water.

0:02:20.748,0:02:23.201
This is what life needs[br]to survive, all life.

0:02:23.680,0:02:27.016
And many solar system bodies[br]don't have liquid water,

0:02:27.040,0:02:28.676
and so we don't look there.

0:02:28.700,0:02:31.693
Other solar system bodies[br]might have abundant liquid water,

0:02:31.717,0:02:33.052
even more than Earth,

0:02:33.076,0:02:35.526
but it's trapped beneath an icy shell,

0:02:35.550,0:02:37.811
and so it's hard to access,[br]it's hard to get to,

0:02:37.835,0:02:40.554
it's hard to even find out[br]if there's any life there.

0:02:41.475,0:02:44.470
So that leaves a few bodies[br]that we should think about.

0:02:44.494,0:02:46.923
So let's make the problem[br]simpler for ourselves.

0:02:46.947,0:02:50.288
Let's think only about liquid water[br]on the surface of a planet.

0:02:50.312,0:02:53.268
There are only three bodies[br]to think about in our solar system,

0:02:53.292,0:02:55.874
with regard to liquid water[br]on the surface of a planet,

0:02:55.898,0:03:00.724
and in order of distance from the sun,[br]it's: Venus, Earth and Mars.

0:03:01.265,0:03:04.637
You want to have an atmosphere[br]for water to be liquid.

0:03:04.661,0:03:07.039
You have to be very careful[br]with that atmosphere.

0:03:07.063,0:03:10.475
You can't have too much atmosphere,[br]too thick or too warm an atmosphere,

0:03:10.499,0:03:13.404
because then you end up[br]too hot like Venus,

0:03:13.428,0:03:15.165
and you can't have liquid water.

0:03:15.189,0:03:19.142
But if you have too little atmosphere[br]and it's too thin and too cold,

0:03:19.166,0:03:21.190
you end up like Mars, too cold.

0:03:21.865,0:03:24.340
So Venus is too hot, Mars is too cold,

0:03:24.364,0:03:25.528
and Earth is just right.

0:03:25.552,0:03:29.027
You can look at these images behind me[br]and you can see automatically

0:03:29.051,0:03:31.648
where life can survive[br]in our solar system.

0:03:32.296,0:03:33.896
It's a Goldilocks-type problem,

0:03:33.920,0:03:36.410
and it's so simple[br]that a child could understand it.

0:03:37.452,0:03:38.632
However,

0:03:39.450,0:03:42.378
I'd like to remind you of two things

0:03:42.402,0:03:45.356
from the Goldilocks story[br]that we may not think about so often,

0:03:45.380,0:03:47.476
but that I think are really relevant here.

0:03:48.056,0:03:49.206
Number one:

0:03:50.311,0:03:53.103
if Mama Bear's bowl is too cold

0:03:53.833,0:03:55.841
when Goldilocks walks into the room,

0:03:56.642,0:03:58.785
does that mean it's always been too cold?

0:03:59.825,0:04:03.093
Or could it have been just right[br]at some other time?

0:04:03.650,0:04:07.331
When Goldilocks walks into the room[br]determines the answer

0:04:07.355,0:04:08.687
that we get in the story.

0:04:09.114,0:04:10.844
And the same is true with planets.

0:04:10.868,0:04:12.894
They're not static things. They change.

0:04:12.918,0:04:14.660
They vary. They evolve.

0:04:14.684,0:04:16.727
And atmospheres do the same.

0:04:16.751,0:04:18.453
So let me give you an example.

0:04:18.477,0:04:20.479
Here's one of my favorite[br]pictures of Mars.

0:04:20.503,0:04:23.634
It's not the highest resolution image,[br]it's not the sexiest image,

0:04:23.658,0:04:25.161
it's not the most recent image,

0:04:25.185,0:04:28.679
but it's an image that shows riverbeds[br]cut into the surface of the planet;

0:04:29.320,0:04:31.904
riverbeds carved by flowing, liquid water;

0:04:33.515,0:04:38.401
riverbeds that take hundreds or thousands[br]or tens of thousands of years to form.

0:04:38.425,0:04:40.043
This can't happen on Mars today.

0:04:40.067,0:04:42.548
The atmosphere of Mars today[br]is too thin and too cold

0:04:42.572,0:04:44.713
for water to be stable as a liquid.

0:04:44.737,0:04:49.085
This one image tells you[br]that the atmosphere of Mars changed

0:04:49.109,0:04:51.141
and it changed in big ways.

0:04:51.714,0:04:56.523
And it changed from a state[br]that we would define as habitable,

0:04:56.547,0:05:00.137
because the three requirements[br]for life were present long ago.

0:05:01.049,0:05:03.117
Where did that atmosphere go

0:05:03.141,0:05:05.961
that allowed water[br]to be liquid at the surface?

0:05:05.985,0:05:09.332
Well, one idea is it escaped[br]away to space.

0:05:09.356,0:05:12.023
Atmospheric particles[br]got enough energy to break free

0:05:12.047,0:05:13.700
from the gravity of the planet,

0:05:13.724,0:05:16.413
escaping away to space, never to return.

0:05:16.437,0:05:19.125
And this happens with all bodies[br]with atmospheres.

0:05:19.149,0:05:20.321
Comets have tails

0:05:20.345,0:05:23.602
that are incredibly visible reminders[br]of atmospheric escape.

0:05:23.626,0:05:27.035
But Venus also has an atmosphere[br]that escapes with time,

0:05:27.059,0:05:28.719
and Mars and Earth as well.

0:05:28.743,0:05:31.711
It's just a matter of degree[br]and a matter of scale.

0:05:32.092,0:05:34.768
So we'd like to figure out[br]how much escaped over time

0:05:34.792,0:05:36.908
so we can explain this transition.

0:05:36.932,0:05:39.543
How do atmospheres[br]get their energy for escape?

0:05:39.567,0:05:41.698
How do particles get[br]enough energy to escape?

0:05:41.722,0:05:44.907
There are two ways, if we're going[br]to reduce things a little bit.

0:05:44.931,0:05:46.082
Number one, sunlight.

0:05:46.106,0:05:49.518
Light emitted from the sun can be absorbed[br]by atmospheric particles

0:05:49.542,0:05:51.256
and warm the particles.

0:05:51.280,0:05:53.388
Yes, I'm dancing, but they --

0:05:53.412,0:05:54.883
(Laughter)

0:05:55.693,0:05:57.605
Oh my God, not even at my wedding.

0:05:57.629,0:05:59.121
(Laughter)

0:05:59.145,0:06:02.148
They get enough energy[br]to escape and break free

0:06:02.172,0:06:04.672
from the gravity of the planet[br]just by warming.

0:06:04.696,0:06:07.858
A second way they can get energy[br]is from the solar wind.

0:06:07.882,0:06:12.908
These are particles, mass, material,[br]spit out from the surface of the sun,

0:06:12.932,0:06:15.336
and they go screaming[br]through the solar system

0:06:15.360,0:06:17.145
at 400 kilometers per second,

0:06:17.169,0:06:19.763
sometimes faster during solar storms,

0:06:19.787,0:06:22.509
and they go hurtling[br]through interplanetary space

0:06:22.533,0:06:24.979
towards planets and their atmospheres,

0:06:25.003,0:06:26.628
and they may provide energy

0:06:26.652,0:06:28.780
for atmospheric particles[br]to escape as well.

0:06:29.182,0:06:31.151
This is something that I'm interested in,

0:06:31.175,0:06:32.888
because it relates to habitability.

0:06:33.378,0:06:36.510
I mentioned that there were two things[br]about the Goldilocks story

0:06:36.534,0:06:39.518
that I wanted to bring to your attention[br]and remind you about,

0:06:39.542,0:06:41.781
and the second one[br]is a little bit more subtle.

0:06:41.805,0:06:44.593
If Papa Bear's bowl is too hot,

0:06:46.180,0:06:49.414
and Mama Bear's bowl is too cold,

0:06:51.057,0:06:54.168
shouldn't Baby Bear's bowl be even colder

0:06:55.081,0:06:56.877
if we're following the trend?

0:06:58.195,0:07:00.507
This thing that you've accepted[br]your entire life,

0:07:00.531,0:07:03.601
when you think about it a little bit more,[br]may not be so simple.

0:07:04.513,0:07:08.541
And of course, distance of a planet[br]from the sun determines its temperature.

0:07:08.565,0:07:10.831
This has to play into habitability.

0:07:10.855,0:07:13.785
But maybe there are other things[br]we should be thinking about.

0:07:13.809,0:07:15.425
Maybe it's the bowls themselves

0:07:15.449,0:07:18.505
that are also helping to determine[br]the outcome in the story,

0:07:18.529,0:07:19.829
what is just right.

0:07:20.765,0:07:23.630
I could talk to you about a lot[br]of different characteristics

0:07:23.654,0:07:24.805
of these three planets

0:07:24.829,0:07:26.398
that may influence habitability,

0:07:26.422,0:07:29.016
but for selfish reasons related[br]to my own research

0:07:29.040,0:07:32.628
and the fact that I'm standing up here[br]holding the clicker and you're not --

0:07:32.652,0:07:33.658
(Laughter)

0:07:33.682,0:07:35.791
I would like to talk[br]for just a minute or two

0:07:35.815,0:07:37.112
about magnetic fields.

0:07:37.715,0:07:40.247
Earth has one; Venus and Mars do not.

0:07:40.825,0:07:43.948
Magnetic fields are generated[br]in the deep interior of a planet

0:07:43.972,0:07:47.689
by electrically conducting[br]churning fluid material

0:07:47.713,0:07:50.618
that creates this big old magnetic field[br]that surrounds Earth.

0:07:50.642,0:07:53.038
If you have a compass,[br]you know which way north is.

0:07:53.062,0:07:54.556
Venus and Mars don't have that.

0:07:54.580,0:07:56.494
If you have a compass on Venus and Mars,

0:07:56.518,0:07:57.914
congratulations, you're lost.

0:07:57.938,0:07:59.841
(Laughter)

0:07:59.865,0:08:01.905
Does this influence habitability?

0:08:03.175,0:08:04.477
Well, how might it?

0:08:05.024,0:08:07.628
Many scientists think[br]that a magnetic field of a planet

0:08:07.652,0:08:10.047
serves as a shield for the atmosphere,

0:08:10.071,0:08:13.426
reflecting solar wind particles[br]around the planet

0:08:13.450,0:08:15.265
in a bit of a force field-type effect

0:08:15.289,0:08:17.989
having to do with electric charge[br]and those particles.

0:08:18.362,0:08:21.989
I like to think of it instead[br]as a salad bar sneeze guard for planets.

0:08:22.013,0:08:24.292
(Laughter)

0:08:24.962,0:08:28.343
And yes, my colleagues[br]who watch this later will realize

0:08:28.367,0:08:30.911
this is the first time in the history[br]of our community

0:08:30.935,0:08:33.214
that the solar wind has been[br]equated with mucus.

0:08:33.238,0:08:34.888
(Laughter)

0:08:36.978,0:08:40.453
OK, so the effect, then, is that Earth[br]may have been protected

0:08:40.477,0:08:41.646
for billions of years,

0:08:41.670,0:08:43.520
because we've had a magnetic field.

0:08:43.544,0:08:45.723
Atmosphere hasn't been able to escape.

0:08:45.747,0:08:47.854
Mars, on the other hand,[br]has been unprotected

0:08:47.878,0:08:49.720
because of its lack of magnetic field,

0:08:49.744,0:08:51.696
and over billions of years,

0:08:51.720,0:08:53.900
maybe enough atmosphere[br]has been stripped away

0:08:53.924,0:08:56.517
to account for a transition[br]from a habitable planet

0:08:56.541,0:08:58.207
to the planet that we see today.

0:08:59.059,0:09:02.048
Other scientists think[br]that magnetic fields

0:09:02.072,0:09:04.235
may act more like the sails on a ship,

0:09:04.958,0:09:09.995
enabling the planet to interact[br]with more energy from the solar wind

0:09:10.019,0:09:13.291
than the planet would have been able[br]to interact with by itself.

0:09:13.315,0:09:15.806
The sails may gather energy[br]from the solar wind.

0:09:15.830,0:09:18.496
The magnetic field may gather[br]energy from the solar wind

0:09:18.520,0:09:21.764
that allows even more[br]atmospheric escape to happen.

0:09:21.788,0:09:24.042
That's an idea that has to be tested,

0:09:24.066,0:09:25.951
but the effect and how it works

0:09:25.975,0:09:27.126
seems apparent.

0:09:27.150,0:09:28.301
That's because we know

0:09:28.325,0:09:31.400
energy from the solar wind[br]is being deposited into our atmosphere

0:09:31.424,0:09:32.575
here on Earth.

0:09:32.599,0:09:35.004
That energy is conducted[br]along magnetic field lines

0:09:35.028,0:09:36.376
down into the polar regions,

0:09:36.400,0:09:38.536
resulting in incredibly beautiful aurora.

0:09:38.560,0:09:41.216
If you've ever experienced them,[br]it's magnificent.

0:09:41.240,0:09:43.246
We know the energy is getting in.

0:09:43.270,0:09:46.303
We're trying to measure[br]how many particles are getting out,

0:09:46.327,0:09:49.365
and if the magnetic field[br]is influencing this in any way.

0:09:50.722,0:09:53.102
So I've posed a problem for you here,

0:09:53.126,0:09:54.672
but I don't have a solution yet.

0:09:54.696,0:09:55.972
We don't have a solution.

0:09:56.702,0:09:59.059
But we're working on it.[br]How are we working on it?

0:09:59.083,0:10:01.381
Well, we've sent spacecraft[br]to all three planets.

0:10:01.405,0:10:02.881
Some of them are orbiting now,

0:10:02.905,0:10:05.977
including the MAVEN spacecraft[br]which is currently orbiting Mars,

0:10:06.001,0:10:09.533
which I'm involved with[br]and which is led here,

0:10:09.557,0:10:11.366
out of the University of Colorado.

0:10:11.390,0:10:13.672
It's designed to measure[br]atmospheric escape.

0:10:14.022,0:10:16.496
We have similar measurements[br]from Venus and Earth.

0:10:16.953,0:10:18.618
Once we have all our measurements,

0:10:18.642,0:10:21.517
we can combine all these together[br]and we can understand

0:10:21.541,0:10:24.958
how all three planets interact[br]with their space environment,

0:10:24.982,0:10:26.144
with the surroundings.

0:10:26.168,0:10:29.690
And we can decide whether magnetic fields[br]are important for habitability

0:10:29.714,0:10:30.872
or not.

0:10:30.896,0:10:33.161
Once we have that answer,[br]why should you care?

0:10:33.185,0:10:34.485
I mean, I care deeply ...

0:10:36.128,0:10:38.134
And financially as well, but deeply.

0:10:38.158,0:10:40.000
(Laughter)

0:10:40.763,0:10:42.681
First of all, an answer to this question

0:10:42.705,0:10:44.808
will teach us more[br]about these three planets,

0:10:44.832,0:10:45.992
Venus, Earth and Mars,

0:10:46.016,0:10:48.927
not only about how they interact[br]with their environment today,

0:10:48.951,0:10:50.878
but how they were billions of years ago,

0:10:50.902,0:10:52.964
whether they were habitable[br]long ago or not.

0:10:52.988,0:10:54.632
It will teach us about atmospheres

0:10:54.656,0:10:56.651
that surround us and that are close.

0:10:57.127,0:10:59.311
But moreover, what we learn[br]from these planets

0:10:59.335,0:11:01.356
can be applied to atmospheres everywhere,

0:11:02.485,0:11:05.398
including planets that we're now[br]observing around other stars.

0:11:05.422,0:11:07.177
For example, the Kepler spacecraft,

0:11:07.201,0:11:10.409
which is built and controlled[br]here in Boulder,

0:11:10.433,0:11:13.718
has been observing[br]a postage stamp-sized region of the sky

0:11:13.742,0:11:14.989
for a couple years now,

0:11:15.013,0:11:17.241
and it's found thousands of planets --

0:11:17.265,0:11:20.178
in one postage stamp-sized[br]region of the sky

0:11:20.202,0:11:24.291
that we don't think is any different[br]from any other part of the sky.

0:11:24.815,0:11:26.625
We've gone, in 20 years,

0:11:26.649,0:11:30.686
from knowing of zero planets[br]outside of our solar system,

0:11:30.710,0:11:32.463
to now having so many,

0:11:32.487,0:11:35.626
that we don't know[br]which ones to investigate first.

0:11:37.269,0:11:38.729
Any lever will help.

0:11:40.539,0:11:44.123
In fact, based on observations[br]that Kepler's taken

0:11:44.147,0:11:46.276
and other similar observations,

0:11:46.300,0:11:47.469
we now believe that,

0:11:47.493,0:11:52.192
of the 200 billion stars[br]in the Milky Way galaxy alone,

0:11:52.786,0:11:57.390
on average, every star[br]has at least one planet.

0:11:58.819,0:12:00.322
In addition to that,

0:12:00.346,0:12:06.047
estimates suggest there are somewhere[br]between 40 billion and 100 billion

0:12:06.071,0:12:09.403
of those planets[br]that we would define as habitable

0:12:11.139,0:12:12.551
in just our galaxy.

0:12:14.590,0:12:16.627
We have the observations of those planets,

0:12:16.651,0:12:19.135
but we just don't know[br]which ones are habitable yet.

0:12:19.159,0:12:22.765
It's a little bit like[br]being trapped on a red spot --

0:12:22.789,0:12:23.960
(Laughter)

0:12:23.984,0:12:25.216
on a stage

0:12:26.178,0:12:29.740
and knowing that there are[br]other worlds out there

0:12:31.042,0:12:33.818
and desperately wanting to know[br]more about them,

0:12:35.174,0:12:39.108
wanting to interrogate them and find out[br]if maybe just one or two of them

0:12:39.132,0:12:40.742
are a little bit like you.

0:12:42.244,0:12:44.803
You can't do that.[br]You can't go there, not yet.

0:12:44.827,0:12:48.820
And so you have to use the tools[br]that you've developed around you

0:12:48.844,0:12:50.139
for Venus, Earth and Mars,

0:12:50.163,0:12:52.976
and you have to apply them[br]to these other situations,

0:12:53.000,0:12:57.696
and hope that you're making[br]reasonable inferences from the data,

0:12:57.720,0:13:00.838
and that you're going to be able[br]to determine the best candidates

0:13:00.862,0:13:03.261
for habitable planets[br]and those that are not.

0:13:04.139,0:13:06.854
In the end, and for now, at least,

0:13:06.878,0:13:09.665
this is our red spot, right here.

0:13:10.376,0:13:13.712
This is the only planet[br]that we know of that's habitable,

0:13:13.736,0:13:16.927
although very soon we may[br]come to know of more.

0:13:16.951,0:13:19.687
But for now, this is[br]the only habitable planet,

0:13:19.711,0:13:21.013
and this is our red spot.

0:13:21.976,0:13:23.396
I'm really glad we're here.

0:13:24.507,0:13:25.682
Thanks.

0:13:25.706,0:13:28.793
(Applause)