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TEDGlobal 2010

Dimitar Sasselov: How we found hundreds of potential Earth-like planets

July 15, 2010

Astronomer Dimitar Sasselov and his colleagues search for Earth-like planets that may, someday, help us answer centuries-old questions about the origin and existence of biological life elsewhere (and on Earth). Preliminary results show that they have found 706 "candidates" -- some of which further research may prove to be planets with Earth-like geochemical characteristics.

Dimitar Sasselov - Astronomer
Dimitar Sasselov works on uniting the physical and life sciences in the hunt for answers to the question of how life began. Full bio

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Double-click the English subtitles below to play the video.
Well, indeed, I'm very, very lucky.
00:15
My talk essentially got written
00:18
by three historic events
00:20
that happened within days of each other
00:22
in the last two months --
00:24
seemingly unrelated, but as you will see,
00:27
actually all having to do with
00:29
the story I want to tell you today.
00:31
The first one was actually a funeral --
00:33
to be more precise, a reburial.
00:36
On May 22nd, there was a hero's reburial
00:38
in Frombork, Poland
00:41
of the 16th-century astronomer
00:43
who actually changed the world.
00:46
He did that, literally,
00:48
by replacing the Earth with the Sun
00:50
in the center of the Solar System,
00:53
and then with this simple-looking act,
00:55
he actually launched a scientific
00:58
and technological revolution,
01:00
which many call the Copernican Revolution.
01:02
Now that was,
01:05
ironically, and very befittingly,
01:07
the way we found his grave.
01:10
As it was the custom of the time,
01:12
Copernicus was actually
01:14
simply buried in an unmarked grave,
01:16
together with 14 others
01:19
in that cathedral.
01:21
DNA analysis,
01:24
one of the hallmarks
01:26
of the scientific revolution
01:28
of the last 400 years that he started,
01:30
was the way we found
01:33
which set of bones
01:35
actually belonged to the person
01:37
who read all those astronomical books
01:39
which were filled with leftover hair
01:42
that was Copernicus' hair --
01:44
obviously not many other people
01:46
bothered to read these books later on.
01:48
That match was unambiguous.
01:50
The DNA matched,
01:52
and we know that this was indeed
01:54
Nicolaus Copernicus.
01:56
Now, the connection between
01:58
biology and DNA
02:00
and life
02:02
is very tantalizing when you talk about Copernicus
02:04
because, even back then,
02:06
his followers
02:08
very quickly made the logical step
02:10
to ask: if the Earth is just a planet,
02:12
then what about planets around other stars?
02:15
What about the idea of the plurality of the worlds,
02:18
about life on other planets?
02:20
In fact, I'm borrowing here from one of those
02:22
very popular books of the time.
02:24
And at the time,
02:26
people actually answered that question
02:28
positively: "Yes."
02:30
But there was no evidence.
02:32
And here begins 400 years
02:35
of frustration, of unfulfilled dreams --
02:38
the dreams of Galileo, Giordano Bruno,
02:41
many others --
02:44
which never led to the answer
02:46
of those very basic questions
02:48
which humanity has asked all the time.
02:50
"What is life? What is the origin of life?
02:52
Are we alone?"
02:54
And that especially happened in the last 10 years,
02:56
at the end of the 20th century,
02:59
when the beautiful developments
03:01
due to molecular biology,
03:03
understanding the code of life, DNA,
03:05
all of that seemed to actually
03:07
put us, not closer,
03:09
but further apart from answering
03:11
those basic questions.
03:13
Now, the good news.
03:16
A lot has happened in the last few years,
03:18
and let's start with the planets.
03:20
Let's start with the old Copernican question:
03:22
Are there earths around other stars?
03:25
And as we already heard,
03:28
there is a way in which
03:30
we are trying, and now able,
03:32
to answer that question.
03:34
It's a new telescope.
03:36
Our team, befittingly I think,
03:38
named it after one of those dreamers
03:40
of the Copernican time,
03:42
Johannes Kepler,
03:44
and that telescope's sole purpose
03:46
is to go out,
03:48
find the planets that orbit
03:50
other stars in our galaxy,
03:52
and tell us how often do planets like our own Earth
03:54
happen to be out there.
03:57
The telescope is actually
04:00
built similarly to
04:02
the, well-known to you, Hubble Space Telescope,
04:04
except it does have an additional lens --
04:06
a wide-field lens,
04:09
as you would call it as a photographer.
04:11
And if, in the next couple of months,
04:13
you walk out in the early evening
04:15
and look straight up
04:17
and place you palm like this,
04:19
you will actually be looking at the field of the sky
04:21
where this telescope is searching for planets
04:24
day and night, without any interruption,
04:27
for the next four years.
04:29
The way we do that, actually,
04:32
is with a method, which we call the transit method.
04:34
It's actually mini-eclipses that occur
04:37
when a planet passes in front of its star.
04:39
Not all of the planets will be fortuitously oriented
04:41
for us to be able do that,
04:44
but if you have a million stars,
04:46
you'll find enough planets.
04:49
And as you see on this animation,
04:51
what Kepler is going to detect
04:54
is just the dimming of the light from the star.
04:56
We are not going to see the image of the star and the planet as this.
04:59
All the stars for Kepler are just points of light.
05:02
But we learn a lot from that:
05:05
not only that there is a planet there, but we also learn its size.
05:07
How much of the light is being dimmed
05:10
depends on how big the planet is.
05:12
We learn about its orbit,
05:15
the period of its orbit and so on.
05:17
So, what have we learned?
05:19
Well, let me try to walk you through
05:22
what we actually see
05:25
and so you understand the news
05:27
that I'm here to tell you today.
05:29
What Kepler does
05:31
is discover a lot of candidates,
05:33
which we then follow up and find as planets,
05:35
confirm as planets.
05:37
It basically tells us
05:39
this is the distribution of planets in size.
05:41
There are small planets, there are bigger planets, there are big planets, okay.
05:44
So we count many, many such planets,
05:47
and they have different sizes.
05:50
We do that in our solar system.
05:52
In fact, even back during the ancients,
05:54
the Solar System in that sense
05:57
would look on a diagram like this.
05:59
There will be the smaller planets, and there will be the big planets,
06:01
even back to the time of Epicurus
06:04
and then of course Copernicus
06:06
and his followers.
06:08
Up until recently, that was the Solar System --
06:10
four Earth-like planets with small radius,
06:12
smaller than about two times the size of the Earth --
06:15
and that was of course Mercury,
06:18
Venus, Mars,
06:20
and of course the Earth,
06:22
and then the two big, giant planets.
06:24
Then the Copernican Revolution
06:26
brought in telescopes,
06:28
and of course three more planets were discovered.
06:30
Now the total planet number
06:32
in our solar system was nine.
06:34
The small planets dominated,
06:36
and there was a certain harmony to that,
06:38
which actually Copernicus was very happy to note,
06:40
and Kepler was one of the big proponents of.
06:43
So now we have Pluto to join the numbers of small planets.
06:46
But up until, literally, 15 years ago,
06:49
that was all we knew about planets.
06:52
And that's what the frustration was.
06:54
The Copernican dream was unfulfilled.
06:56
Finally, 15 years ago,
06:59
the technology came to the point
07:01
where we could discover a planet around another star,
07:03
and we actually did pretty well.
07:06
In the next 15 years,
07:09
almost 500 planets
07:11
were discovered orbiting other stars, with different methods.
07:13
Unfortunately, as you can see,
07:16
there was a very different picture.
07:19
There was of course an explanation for it:
07:21
We only see the big planets,
07:23
so that's why most of those planets
07:25
are really in the category of "like Jupiter."
07:27
But you see, we haven't gone very far.
07:30
We were still back where Copernicus was.
07:33
We didn't have any evidence
07:36
whether planets like the Earth are out there.
07:38
And we do care about planets like the Earth
07:40
because by now we understood
07:43
that life as a chemical system
07:45
really needs a smaller planet
07:48
with water and with rocks
07:50
and with a lot of complex chemistry
07:52
to originate, to emerge, to survive.
07:54
And we didn't have the evidence for that.
07:57
So today, I'm here to actually give you a first glimpse
08:00
of what the new telescope, Kepler,
08:02
has been able to tell us in the last few weeks,
08:05
and, lo and behold,
08:08
we are back to the harmony
08:10
and to fulfilling the dreams of Copernicus.
08:12
You can see here,
08:15
the small planets dominate the picture.
08:17
The planets which are marked "like Earth,"
08:19
[are] definitely more than
08:22
any other planets that we see.
08:24
And now for the first time, we can say that.
08:26
There is a lot more work we need to do with this.
08:28
Most of these are candidates.
08:31
In the next few years we will confirm them.
08:33
But the statistical result
08:35
is loud and clear.
08:37
And the statistical result is that
08:39
planets like our own Earth
08:42
are out there.
08:44
Our own Milky Way Galaxy is rich in this kind of planets.
08:46
So the question is: what do we do next?
08:49
Well, first of all, we can study them
08:52
now that we know where they are.
08:54
And we can find those that we would call habitable,
08:57
meaning that they have similar conditions
09:00
to the conditions
09:02
that we experience here on Earth
09:04
and where a lot of complex chemistry can happen.
09:07
So, we can even put a number
09:10
to how many of those planets
09:13
now do we expect our own
09:15
Milky Way Galaxy harbors.
09:17
And the number, as you might expect,
09:19
is pretty staggering.
09:21
It's about 100 million such planets.
09:23
That's great news. Why?
09:26
Because with our own little telescope,
09:28
just in the next two years,
09:30
we'll be able to identify at least 60 of them.
09:32
So that's great because then
09:35
we can go and study them --
09:37
remotely, of course --
09:39
with all the techniques that we already have
09:41
tested in the past five years.
09:43
We can find what they're made of,
09:45
would their atmospheres have water, carbon dioxide, methane.
09:47
We know and expect that we'll see that.
09:50
That's great, but that is not the whole news.
09:54
That's not why I'm here.
09:57
Why I'm here is to tell you that the next step
10:00
is really the exciting part.
10:03
The one that this step
10:06
is enabling us to do is coming next.
10:08
And here comes biology --
10:11
biology, with its basic question,
10:13
which still stands unanswered,
10:16
which is essentially:
10:18
"If there is life on other planets,
10:20
do we expect it to be like life on Earth?"
10:22
And let me immediately tell you here,
10:25
when I say life, I don't mean "dolce vita,"
10:27
good life, human life.
10:29
I really mean life
10:31
on Earth, past and present,
10:34
from microbes to us humans,
10:36
in its rich molecular diversity,
10:38
the way we now understand life on Earth
10:41
as being a set of molecules and chemical reactions --
10:44
and we call that, collectively, biochemistry,
10:47
life as a chemical process,
10:50
as a chemical phenomenon.
10:53
So the question is:
10:55
is that chemical phenomenon universal,
10:57
or is it something
11:00
which depends on the planet?
11:02
Is it like gravity,
11:04
which is the same everywhere in the universe,
11:06
or there would be all kinds of different biochemistries
11:08
wherever we find them?
11:11
We need to know what we are looking for
11:13
when we try to do that.
11:16
And that's a very basic question, which we don't know the answer to,
11:18
but which we can try --
11:21
and we are trying -- to answer in the lab.
11:23
We don't need to go to space
11:25
to answer that question.
11:27
And so, that's what we are trying to do.
11:29
And that's what many people now are trying to do.
11:31
And a lot of the good news comes from that part of the bridge
11:34
that we are trying to build as well.
11:37
So this is one example
11:40
that I want to show you here.
11:42
When we think of what is necessary
11:44
for the phenomenon that we call life,
11:46
we think of compartmentalization,
11:49
keeping the molecules which are important for life
11:52
in a membrane,
11:55
isolated from the rest of the environment,
11:57
but yet, in an environment in which
11:59
they actually could originate together.
12:01
And in one of our labs,
12:04
Jack Szostak's labs,
12:06
it was a series of experiments
12:08
in the last four years
12:10
that showed that the environments --
12:12
which are very common on planets,
12:14
on certain types of planets like the Earth,
12:16
where you have some liquid water and some clays --
12:19
you actually end up with
12:22
naturally available molecules
12:25
which spontaneously form bubbles.
12:27
But those bubbles have membranes
12:30
very similar to the membrane of every cell
12:33
of every living thing on Earth looks like,
12:36
like this.
12:39
And they really help molecules,
12:41
like nucleic acids, like RNA and DNA,
12:43
stay inside, develop,
12:46
change, divide
12:48
and do some of the processes that we call life.
12:50
Now this is just an example
12:53
to tell you the pathway
12:55
in which we are trying to answer
12:57
that bigger question about the universality of the phenomenon.
12:59
And in a sense, you can think of that work
13:03
that people are starting to do now around the world
13:06
as building a bridge,
13:08
building a bridge from two sides of the river.
13:10
On one hand, on the left bank of the river,
13:13
are the people like me who study those planets
13:16
and try to define the environments.
13:19
We don't want to go blind because there's too many possibilities,
13:21
and there is not too much lab,
13:24
and there is not enough human time
13:27
to actually to do all the experiments.
13:29
So that's what we are building from the left side of the river.
13:31
From the right bank of the river
13:34
are the experiments in the lab that I just showed you,
13:36
where we actually tried that, and it feeds back and forth,
13:39
and we hope to meet in the middle one day.
13:42
So why should you care about that?
13:45
Why am I trying to sell you
13:48
a half-built bridge?
13:50
Am I that charming?
13:52
Well, there are many reasons,
13:55
and you heard some of them
13:57
in the short talk today.
13:59
This understanding of chemistry
14:01
actually can help us
14:03
with our daily lives.
14:05
But there is something more profound here,
14:07
something deeper.
14:09
And that deeper, underlying point
14:11
is that science
14:15
is in the process of redefining life
14:17
as we know it.
14:20
And that is going to change
14:22
our worldview in a profound way --
14:24
not in a dissimilar way
14:27
as 400 years ago,
14:29
Copernicus' act did,
14:31
by changing the way
14:33
we view space and time.
14:35
Now it's about something else,
14:37
but it's equally profound.
14:39
And half the time,
14:41
what's happened
14:43
is it's related this kind of
14:45
sense of insignificance
14:47
to humankind,
14:49
to the Earth in a bigger space.
14:51
And the more we learn,
14:53
the more that was reinforced.
14:56
You've all learned that in school --
14:59
how small the Earth is
15:01
compared to the immense universe.
15:03
And the bigger the telescope,
15:05
the bigger that universe becomes.
15:07
And look at this image of the tiny, blue dot.
15:09
This pixel is the Earth.
15:12
It is the Earth as we know it.
15:14
It is seen from, in this case,
15:16
from outside the orbit of Saturn.
15:18
But it's really tiny.
15:21
We know that.
15:23
Let's think of life as that entire planet
15:25
because, in a sense, it is.
15:27
The biosphere is the size of the Earth.
15:29
Life on Earth
15:31
is the size of the Earth.
15:33
And let's compare it to the rest of the world
15:35
in spatial terms.
15:38
What if that
15:40
Copernican insignificance
15:42
was actually all wrong?
15:45
Would that make us more responsible
15:47
for what is happening today?
15:49
Let's actually try that.
15:51
So in space, the Earth is very small.
15:53
Can you imagine how small it is?
15:56
Let me try it.
15:58
Okay, let's say
16:00
this is the size
16:02
of the observable universe,
16:04
with all the galaxies,
16:06
with all the stars,
16:08
okay, from here to here.
16:10
Do you know what the size of life
16:12
in this necktie will be?
16:14
It will be the size
16:17
of a single, small atom.
16:20
It is unimaginably small.
16:22
We can't imagine it.
16:24
I mean look, you can see the necktie,
16:26
but you can't even imagine seeing
16:28
the size of a little, small atom.
16:30
But that's not the whole story, you see.
16:33
The universe and life
16:36
are both in space and time.
16:38
If that was
16:41
the age of the universe,
16:44
then this is the age of life on Earth.
16:46
Think about those oldest living things on Earth,
16:50
but in a cosmic proportion.
16:53
This is not insignificant.
16:55
This is very significant.
16:58
So life might be insignificant in size,
17:00
but it is not insignificant in time.
17:03
Life and the universe
17:07
compare to each other like a child and a parent,
17:09
parent and offspring.
17:12
So what does this tell us?
17:14
This tells us that
17:16
that insignificance paradigm
17:18
that we somehow got to learn
17:20
from the Copernican principle,
17:22
it's all wrong.
17:24
There is immense, powerful potential
17:26
in life in this universe --
17:29
especially now that we know
17:31
that places like the Earth are common.
17:33
And that potential, that powerful potential,
17:37
is also our potential,
17:40
of you and me.
17:42
And if we are to be stewards
17:44
of our planet Earth
17:46
and its biosphere,
17:48
we'd better understand
17:50
the cosmic significance
17:52
and do something about it.
17:54
And the good news is we can
17:56
actually, indeed do it.
17:58
And let's do it.
18:00
Let's start this new revolution
18:02
at the tail end of the old one,
18:04
with synthetic biology being
18:07
the way to transform
18:09
both our environment
18:11
and our future.
18:13
And let's hope that we can build this bridge together
18:15
and meet in the middle.
18:17
Thank you very much.
18:19
(Applause)
18:21

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Dimitar Sasselov - Astronomer
Dimitar Sasselov works on uniting the physical and life sciences in the hunt for answers to the question of how life began.

Why you should listen

Dimitar Sasselov is an astronomer who explores the interaction between light and matter. He studies, among other things, extrasolar planets, and he's a co-investigator on NASA's Kepler mission, which is monitoring 100,000 stars in a three-year hunt for exoplanets -- including Jupiter-sized giants. Sasselov watches for exoplanets by looking for transits, the act of a planet passing across the face of its star, dimming its light and changing its chemical signature. This simple, elegant way of searching has led to a bounty of newly discovered planets.

Sasselov is the director of Harvard's Origins of Life Initiative, a new interdisciplinary institute that joins biologists, chemists and astronomers in searching for the starting points of life on Earth (and possibly elsewhere). What is an astronomer doing looking for the origins of life, a question more often asked by biologists? Sasselov suggests that planetary conditions are the seedbed of life; knowing the composition and conditions of a planet will give us clues, perhaps, as to how life might form there. And as we discover new planets that might host life, having a working definition of life will help us screen for possible new forms of it. Other institute members such as biologist George Church and chemist George Whitesides work on the question from other angles, looking for (and building) alternative biologies that might fit conditions elsewhere in the universe.

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