0:00:11.724,0:00:14.324
Okay, this is going to be[br]so much fun!

0:00:14.359,0:00:15.359
(Laughter)

0:00:15.443,0:00:16.864
I'm really glad to be here.

0:00:17.515,0:00:19.203
I'm glad you're here,

0:00:19.227,0:00:21.060
because that would be a little weird.

0:00:21.960,0:00:24.065
I'm glad we're all here.

0:00:24.803,0:00:27.656
And by "here," I don't mean here.

0:00:29.624,0:00:30.774
Or here.

0:00:32.528,0:00:33.680
But here.

0:00:33.704,0:00:34.854
I mean Earth.

0:00:35.827,0:00:39.770
And by "we," I don't mean[br]those of us in this auditorium,

0:00:41.294,0:00:42.764
but life,

0:00:42.788,0:00:44.237
all life on Earth --

0:00:44.261,0:00:49.041
(Laughter)

0:00:49.080,0:00:51.071
from complex to single-celled,

0:00:51.095,0:00:53.419
from mold to mushrooms

0:00:53.443,0:00:54.821
to flying bears.

0:00:54.845,0:00:56.211
(Laughter)

0:00:58.536,0:01:00.045
The interesting thing is,

0:01:00.069,0:01:03.100
Earth is the only place[br]we know of that has life --

0:01:03.124,0:01:05.001
8.7 million species.

0:01:05.459,0:01:06.714
We've looked other places,

0:01:06.738,0:01:08.835
maybe not as hard[br]as we should or we could,

0:01:08.859,0:01:10.786
but we've looked and haven't found any;

0:01:10.810,0:01:13.086
Earth is the only place[br]we know of with life.

0:01:14.118,0:01:15.392
Is Earth special?

0:01:16.391,0:01:18.845
This is a question I've wanted[br]to know the answer to

0:01:18.869,0:01:20.123
since I was a small child,

0:01:20.147,0:01:22.179
and I suspect 80 percent[br]of this auditorium

0:01:22.203,0:01:25.211
has thought the same thing[br]and also wanted to know the answer.

0:01:25.679,0:01:27.846
To understand whether[br]there are any planets --

0:01:27.870,0:01:30.148
out there in our solar system or beyond --

0:01:30.172,0:01:31.630
that can support life,

0:01:31.654,0:01:34.851
the first step is to understand[br]what life here requires.

0:01:35.375,0:01:38.938
It turns out, of all of those[br]8.7 million species,

0:01:38.962,0:01:41.160
life only needs three things.

0:01:42.532,0:01:45.384
On one side, all life[br]on Earth needs energy.

0:01:45.408,0:01:48.893
Complex life like us derives[br]our energy from the sun,

0:01:49.817,0:01:51.918
but life deep underground[br]can get its energy

0:01:51.942,0:01:53.664
from things like chemical reactions.

0:01:53.688,0:01:55.839
There are a number[br]of different energy sources

0:01:55.863,0:01:57.106
available on all planets.

0:01:57.800,0:01:58.956
On the other side,

0:01:58.980,0:02:01.685
all life needs food or nourishment.

0:02:02.141,0:02:06.615
And this seems like a tall order,[br]especially if you want a succulent tomato.

0:02:06.639,0:02:08.354
(Laughter)

0:02:08.378,0:02:11.445
However, all life on Earth[br]derives its nourishment

0:02:11.469,0:02:13.499
from only six chemical elements,

0:02:13.523,0:02:16.527
and these elements can be found[br]on any planetary body

0:02:16.551,0:02:17.887
in our solar system.

0:02:18.937,0:02:22.164
So that leaves the thing[br]in the middle as the tall pole,

0:02:22.188,0:02:24.142
the thing that's hardest to achieve.

0:02:24.166,0:02:26.058
Not moose, but water.

0:02:26.082,0:02:28.863
(Laughter)

0:02:29.685,0:02:31.479
Although moose would be pretty cool.

0:02:31.503,0:02:32.661
(Laughter)

0:02:32.685,0:02:38.227
And not frozen water, and not water[br]in a gaseous state, but liquid water.

0:02:38.448,0:02:40.901
This is what life needs[br]to survive, all life.

0:02:41.380,0:02:44.716
And many solar system bodies[br]don't have liquid water,

0:02:44.740,0:02:46.376
and so we don't look there.

0:02:46.400,0:02:49.393
Other solar system bodies[br]might have abundant liquid water,

0:02:49.417,0:02:50.752
even more than Earth,

0:02:50.776,0:02:53.226
but it's trapped beneath an icy shell,

0:02:53.250,0:02:55.511
and so it's hard to access,[br]it's hard to get to,

0:02:55.535,0:02:58.254
it's hard to even find out[br]if there's any life there.

0:03:00.675,0:03:02.720
So that leaves

0:03:04.085,0:03:06.029
a few bodies that we should think about.

0:03:06.094,0:03:08.523
So let's make the problem[br]simpler for ourselves.

0:03:08.547,0:03:11.888
Let's think only about liquid water[br]on the surface of a planet.

0:03:11.912,0:03:14.868
There are only three bodies[br]to think about in our solar system,

0:03:14.892,0:03:17.474
with regard to liquid water[br]on the surface of a planet,

0:03:17.498,0:03:22.324
and in order of distance from the sun,[br]it's: Venus, Earth and Mars.

0:03:22.865,0:03:26.237
You want to have an atmosphere[br]for water to be liquid.

0:03:26.261,0:03:28.639
You have to be very careful[br]with that atmosphere.

0:03:28.663,0:03:32.075
You can't have too much atmosphere,[br]too thick or too warm an atmosphere,

0:03:32.099,0:03:35.004
because then you end up[br]too hot like Venus,

0:03:35.028,0:03:36.765
and you can't have liquid water.

0:03:36.789,0:03:40.742
But if you have too little atmosphere[br]and it's too thin and too cold,

0:03:40.766,0:03:42.790
you end up like Mars, too cold.

0:03:43.465,0:03:45.940
So Venus is too hot, Mars is too cold,

0:03:45.964,0:03:47.128
and Earth is just right.

0:03:47.152,0:03:50.627
You can look at these images behind me[br]and you can see automatically

0:03:50.651,0:03:53.248
where life can survive[br]in our solar system.

0:03:53.896,0:03:55.496
It's a Goldilocks-type problem,

0:03:55.520,0:03:58.010
and it's so simple[br]that a child could understand it.

0:04:00.052,0:04:01.232
However,

0:04:02.050,0:04:04.978
I'd like to remind you of two things

0:04:05.002,0:04:07.956
from the Goldilocks story[br]that we may not think about so often

0:04:07.980,0:04:10.076
but that I think are really relevant here.

0:04:10.656,0:04:11.806
Number one:

0:04:12.911,0:04:15.703
if Mama Bear's bowl is too cold

0:04:16.433,0:04:18.440
when Goldilocks walks into the room,

0:04:19.242,0:04:21.385
does that mean it's always been too cold?

0:04:22.425,0:04:25.693
Or could it have been just right[br]at some other time?

0:04:26.250,0:04:29.931
When Goldilocks walks into the room[br]determines the answer

0:04:29.955,0:04:31.287
that we get in the story.

0:04:31.714,0:04:33.444
And the same is true with planets.

0:04:33.468,0:04:35.494
They're not static things. They change.

0:04:35.518,0:04:37.260
They vary. They evolve.

0:04:37.284,0:04:39.326
And atmospheres do the same.

0:04:40.550,0:04:42.252
So let me give you an example.

0:04:43.176,0:04:45.178
Here's one of my favorite[br]pictures of Mars.

0:04:45.203,0:04:48.334
It's not the highest resolution image,[br]it's not the sexiest image,

0:04:48.358,0:04:49.861
it's not the most recent image,

0:04:49.885,0:04:53.379
but it's an image that shows riverbeds[br]cut into the surface of the planet;

0:04:54.520,0:04:57.104
riverbeds carved by flowing, liquid water;

0:04:59.115,0:05:04.001
riverbeds that take hundreds or thousands[br]or tens of thousands of years to form.

0:05:04.025,0:05:05.643
This can't happen on Mars today.

0:05:05.667,0:05:08.148
The atmosphere of Mars today[br]is too thin and too cold

0:05:08.172,0:05:10.313
for water to be stable as a liquid.

0:05:10.337,0:05:14.685
This one image tells you[br]that the atmosphere of Mars changed,

0:05:14.709,0:05:16.741
and it changed in big ways.

0:05:17.314,0:05:22.123
And it changed from a state[br]that we would define as habitable,

0:05:22.147,0:05:25.737
because the three requirements[br]for life were present long ago.

0:05:27.149,0:05:29.217
Where did that atmosphere go

0:05:29.241,0:05:32.061
that allowed water[br]to be liquid at the surface?

0:05:32.085,0:05:35.432
Well, one idea is it escaped[br]away to space.

0:05:35.456,0:05:38.123
Atmospheric particles[br]got enough energy to break free

0:05:38.147,0:05:39.800
from the gravity of the planet,

0:05:39.824,0:05:42.513
escaping away to space, never to return.

0:05:43.037,0:05:45.725
And this happens with all bodies[br]with atmospheres.

0:05:45.749,0:05:46.921
Comets have tails

0:05:46.945,0:05:50.202
that are incredibly visible reminders[br]of atmospheric escape.

0:05:50.226,0:05:53.635
But Venus also has an atmosphere[br]that escapes with time,

0:05:53.659,0:05:55.319
and Mars and Earth as well.

0:05:55.343,0:05:58.311
It's just a matter of degree[br]and a matter of scale.

0:05:58.692,0:06:01.368
So we'd like to figure out[br]how much escaped over time

0:06:01.392,0:06:03.508
so we can explain this transition.

0:06:05.032,0:06:07.643
How do atmospheres[br]get their energy for escape?

0:06:07.667,0:06:09.798
How do particles get[br]enough energy to escape?

0:06:09.822,0:06:13.007
There are two ways, if we're going[br]to reduce things a little bit.

0:06:13.031,0:06:14.182
Number one, sunlight.

0:06:14.206,0:06:17.618
Light emitted from the sun can be absorbed[br]by atmospheric particles

0:06:17.642,0:06:19.356
and warm the particles.

0:06:19.380,0:06:21.488
Yes, I'm dancing, but they --

0:06:21.512,0:06:22.983
(Laughter)

0:06:23.793,0:06:25.705
Oh my God, not even at my wedding.

0:06:25.729,0:06:27.221
(Laughter)

0:06:27.245,0:06:30.248
They get enough energy[br]to escape and break free

0:06:30.272,0:06:32.772
from the gravity of the planet[br]just by warming.

0:06:32.796,0:06:35.958
A second way they can get energy[br]is from the solar wind.

0:06:36.482,0:06:41.508
These are particles, mass, material,[br]spit out from the surface of the sun,

0:06:41.532,0:06:43.936
and they go screaming[br]through the solar system

0:06:43.960,0:06:45.745
at 400 kilometers per second,

0:06:45.769,0:06:48.363
sometimes faster during solar storms,

0:06:48.387,0:06:51.109
and they go hurtling[br]through interplanetary space

0:06:51.133,0:06:53.579
towards planets and their atmospheres,

0:06:53.603,0:06:55.228
and they may provide energy

0:06:55.252,0:06:57.380
for atmospheric particles[br]to escape as well.

0:06:57.782,0:06:59.751
This is something that I'm interested in,

0:06:59.775,0:07:01.488
because it relates to habitability.

0:07:03.278,0:07:06.410
I mentioned that there were two things[br]about the Goldilocks story

0:07:06.434,0:07:09.418
that I wanted to bring to your attention[br]and remind you about,

0:07:09.442,0:07:11.681
and the second one[br]is a little bit more subtle.

0:07:12.405,0:07:15.193
If Papa Bear's bowl is too hot,

0:07:16.780,0:07:20.014
and Mama Bear's bowl is too cold,

0:07:21.657,0:07:24.768
shouldn't Baby Bear's bowl be even colder

0:07:25.681,0:07:27.477
if we're following the trend?

0:07:28.795,0:07:31.107
This thing that you've accepted[br]your entire life,

0:07:31.131,0:07:34.201
when you think about it a little bit more,[br]may not be so simple.

0:07:35.113,0:07:39.141
And of course, distance of a planet[br]from the sun determines its temperature.

0:07:39.165,0:07:41.431
This has to play into habitability.

0:07:41.455,0:07:44.385
But maybe there are other things[br]we should be thinking about.

0:07:44.409,0:07:46.025
Maybe it's the bowls themselves

0:07:46.049,0:07:49.105
that are also helping to determine[br]the outcome in the story,

0:07:49.129,0:07:50.429
what is just right.

0:07:51.365,0:07:54.230
I could talk to you about a lot[br]of different characteristics

0:07:54.254,0:07:55.405
of these three planets

0:07:55.429,0:07:56.998
that may influence habitability,

0:07:57.077,0:07:59.391
but I would like to talk[br]for just a minute or two

0:07:59.415,0:08:00.712
about magnetic fields.

0:08:01.315,0:08:03.847
Earth has one; Venus and Mars do not.

0:08:04.425,0:08:07.548
Magnetic fields are generated[br]in the deep interior of a planet

0:08:07.572,0:08:11.289
by electrically conducting[br]churning fluid material

0:08:11.313,0:08:14.218
that creates this big old magnetic field[br]that surrounds Earth.

0:08:14.242,0:08:16.638
If you have a compass,[br]you know which way north is.

0:08:16.662,0:08:18.156
Venus and Mars don't have that.

0:08:18.180,0:08:20.094
If you have a compass on Venus and Mars,

0:08:20.118,0:08:21.514
congratulations, you're lost.

0:08:21.538,0:08:23.441
(Laughter)

0:08:23.465,0:08:25.505
Does this influence habitability?

0:08:26.775,0:08:28.077
Well, how might it?

0:08:29.724,0:08:32.328
Many scientists think[br]that a magnetic field of a planet

0:08:32.352,0:08:34.746
serves as a shield for the atmosphere,

0:08:34.770,0:08:38.126
deflecting solar wind particles[br]around the planet

0:08:38.150,0:08:39.965
in a bit of a force field-type effect

0:08:39.989,0:08:42.688
having to do with electric charge[br]of those particles.

0:08:43.062,0:08:46.689
I like to think of it instead[br]as a salad bar sneeze guard for planets.

0:08:46.713,0:08:48.992
(Laughter)

0:08:49.662,0:08:53.043
And yes, my colleagues[br]who watch this later will realize

0:08:53.067,0:08:55.611
this is the first time in the history[br]of our community

0:08:55.635,0:08:57.914
that the solar wind has been[br]equated with mucus.

0:08:57.938,0:08:59.588
(Laughter)

0:09:02.377,0:09:05.853
OK, so the effect, then, is that Earth[br]may have been protected

0:09:05.877,0:09:07.045
for billions of years,

0:09:07.069,0:09:08.920
because we've had a magnetic field.

0:09:08.944,0:09:11.123
Atmosphere hasn't been able to escape.

0:09:11.147,0:09:13.254
Mars, on the other hand,[br]has been unprotected

0:09:13.278,0:09:15.120
because of its lack of magnetic field,

0:09:15.144,0:09:17.096
and over billions of years,

0:09:17.120,0:09:19.300
maybe enough atmosphere[br]has been stripped away

0:09:19.324,0:09:21.917
to account for a transition[br]from a habitable planet

0:09:21.941,0:09:23.607
to the planet that we see today.

0:09:24.459,0:09:27.448
Other scientists think[br]that magnetic fields

0:09:27.472,0:09:29.635
may act more like the sails on a ship,

0:09:30.658,0:09:35.695
enabling the planet to interact[br]with more energy from the solar wind

0:09:35.719,0:09:38.991
than the planet would have been able[br]to interact with by itself.

0:09:39.015,0:09:41.506
The sails may gather energy[br]from the solar wind.

0:09:41.530,0:09:44.196
The magnetic field may gather[br]energy from the solar wind

0:09:44.220,0:09:47.464
that allows even more[br]atmospheric escape to happen.

0:09:47.488,0:09:49.742
It's an idea that has to be tested,

0:09:49.766,0:09:51.651
but the effect and how it works

0:09:51.675,0:09:52.826
seems apparent.

0:09:52.850,0:09:54.001
That's because we know

0:09:54.025,0:09:57.100
energy from the solar wind[br]is being deposited into our atmosphere

0:09:57.124,0:09:58.275
here on Earth.

0:09:58.299,0:10:00.704
That energy is conducted[br]along magnetic field lines

0:10:00.728,0:10:02.076
down into the polar regions,

0:10:02.100,0:10:04.236
resulting in incredibly beautiful aurora.

0:10:04.260,0:10:06.916
If you've ever experienced them,[br]it's magnificent.

0:10:06.940,0:10:08.946
We know the energy is getting in.

0:10:08.970,0:10:12.003
We're trying to measure[br]how many particles are getting out

0:10:12.027,0:10:15.065
and if the magnetic field[br]is influencing this in any way.

0:10:16.422,0:10:18.802
So I've posed a problem for you here,

0:10:18.826,0:10:20.372
but I don't have a solution yet.

0:10:20.396,0:10:21.672
We don't have a solution.

0:10:22.402,0:10:24.759
But we're working on it.[br]How are we working on it?

0:10:24.783,0:10:27.081
Well, we've sent spacecraft[br]to all three planets.

0:10:27.105,0:10:28.581
Some of them are orbiting now,

0:10:28.605,0:10:31.677
including the MAVEN spacecraft[br]which is currently orbiting Mars,

0:10:31.701,0:10:35.233
which I'm involved with[br]and which is led here,

0:10:35.257,0:10:37.066
out of the University of Colorado.

0:10:37.090,0:10:39.372
It's designed to measure[br]atmospheric escape.

0:10:39.722,0:10:42.196
We have similar measurements[br]from Venus and Earth.

0:10:42.653,0:10:44.318
Once we have all our measurements,

0:10:44.342,0:10:47.217
we can combine all these together,[br]and we can understand

0:10:47.241,0:10:50.658
how all three planets interact[br]with their space environment,

0:10:50.682,0:10:51.844
with the surroundings.

0:10:51.868,0:10:55.390
And we can decide whether magnetic fields[br]are important for habitability

0:10:55.414,0:10:56.572
or not.

0:10:57.596,0:10:59.861
Once we have that answer,[br]why should you care?

0:10:59.885,0:11:01.185
I mean, I care deeply ...

0:11:02.828,0:11:04.834
And financially as well, but deeply.

0:11:04.858,0:11:06.700
(Laughter)

0:11:07.463,0:11:09.381
First of all, an answer to this question

0:11:09.405,0:11:11.508
will teach us more[br]about these three planets,

0:11:11.532,0:11:12.692
Venus, Earth and Mars,

0:11:12.716,0:11:15.627
not only about how they interact[br]with their environment today,

0:11:15.651,0:11:17.578
but how they were billions of years ago,

0:11:17.602,0:11:19.664
whether they were habitable[br]long ago or not.

0:11:19.688,0:11:21.332
It will teach us about atmospheres

0:11:21.356,0:11:23.351
that surround us and that are close.

0:11:23.827,0:11:26.011
But moreover, what we learn[br]from these planets

0:11:26.035,0:11:28.056
can be applied to atmospheres everywhere,

0:11:29.185,0:11:32.098
including planets that we're now[br]observing around other stars.

0:11:32.122,0:11:33.877
For example, the Kepler spacecraft,

0:11:33.901,0:11:37.109
which is built and controlled[br]here in Boulder,

0:11:37.133,0:11:40.418
has been observing[br]a postage stamp-sized region of the sky

0:11:40.442,0:11:41.689
for a couple years now,

0:11:41.713,0:11:43.941
and it's found thousands of planets --

0:11:43.965,0:11:46.878
in one postage stamp-sized[br]region of the sky

0:11:46.902,0:11:50.991
that we don't think is any different[br]from any other part of the sky.

0:11:51.515,0:11:53.325
We've gone, in 20 years,

0:11:53.349,0:11:57.386
from knowing of zero planets[br]outside of our solar system,

0:11:57.410,0:11:59.163
to now having so many,

0:11:59.187,0:12:02.326
that we don't know[br]which ones to investigate first.

0:12:03.969,0:12:05.429
Any lever will help.

0:12:07.239,0:12:10.823
In fact, based on observations[br]that Kepler's taken

0:12:10.847,0:12:12.976
and other similar observations,

0:12:13.000,0:12:14.169
we now believe that,

0:12:14.193,0:12:18.892
of the 200 billion stars[br]in the Milky Way galaxy alone,

0:12:19.486,0:12:24.090
on average, every star[br]has at least one planet.

0:12:25.519,0:12:27.022
In addition to that,

0:12:27.046,0:12:32.747
estimates suggest there are somewhere[br]between 40 billion and 100 billion

0:12:32.771,0:12:36.103
of those planets[br]that we would define as habitable

0:12:37.039,0:12:38.451
in just our galaxy.

0:12:40.490,0:12:42.527
We have the observations of those planets,

0:12:42.551,0:12:45.035
but we just don't know[br]which ones are habitable yet.

0:12:45.059,0:12:48.665
It's a little bit like[br]being trapped on a red spot --

0:12:48.689,0:12:49.860
(Laughter)

0:12:49.884,0:12:51.116
on a stage

0:12:52.078,0:12:55.640
and knowing that there are[br]other worlds out there

0:12:56.942,0:12:59.718
and desperately wanting to know[br]more about them,

0:13:01.074,0:13:05.008
wanting to interrogate them and find out[br]if maybe just one or two of them

0:13:05.032,0:13:06.642
are a little bit like you.

0:13:08.144,0:13:10.703
You can't do that.[br]You can't go there, not yet.

0:13:10.727,0:13:14.720
And so you have to use the tools[br]that you've developed around you

0:13:14.744,0:13:16.039
for Venus, Earth and Mars,

0:13:16.063,0:13:18.876
and you have to apply them[br]to these other situations,

0:13:18.900,0:13:23.596
and hope that you're making[br]reasonable inferences from the data,

0:13:23.620,0:13:26.738
and that you're going to be able[br]to determine the best candidates

0:13:26.762,0:13:29.161
for habitable planets,[br]and those that are not.

0:13:30.639,0:13:33.354
In the end, and for now, at least,

0:13:33.378,0:13:36.165
this is our red spot, right here.

0:13:36.876,0:13:40.212
This is the only planet[br]that we know of that's habitable,

0:13:40.236,0:13:43.427
although very soon we may[br]come to know of more.

0:13:43.451,0:13:46.187
But for now, this is[br]the only habitable planet,

0:13:46.211,0:13:47.513
and this is our red spot.

0:13:48.476,0:13:49.896
I'm really glad we're here.

0:13:51.007,0:13:52.182
Thanks.

0:13:52.206,0:13:55.437
(Applause)