>> From the Library of Congress in Washington, DC.
[ Silence ]
>> Jennifer Harpster: Good afternoon.
I'm Jennifer Harpster, a reference and research specialist
for the Science, Technology and Business Division here
at the Library of Congress.
I'd like to welcome you to today's program, "Exotic Earths:
Exploring Planets Around Other Stars."
This program is the third program in the 2013 series,
presented through a partnership between my division
and NASA Goddard Space Flight Center.
This is the final lecture in our spring series.
But please don't despair, our fall series will begin in September
with hurricane researcher Owen Kelly,
who will talk about discovering hot towers in hurricanes.
It is my pleasure to introduce today's speaker, Dr. Avi Mandell,
a research scientist with the Planetary Systems Laboratory
at Goddard.
Dr. Mandell received his bachelor degree in physics and astronomy
at Vassar College, and his doctorate in astronomy and astrophysics
from Pennsylvania State University.
He has worked his way up through the ranks at Goddard,
having begun his career while he was a graduate assistant,
and then received a postdoctoral fellowship.
Currently as a research scientist, he is also a guest lecturer
in the education physics department at Catholic University.
His series of lectures are on the origin of planet formation.
The idea of distant planets with the potential
to host a completely independent and exotic origin
for life has fascinated him since his graduate work at Penn State.
And his research interests have expanded
to also encompass the formation and the evolution of planetary systems.
He has developed both modeling and observational techniques
to study protoplanetary disks and planets at infrared wavelengths.
You could find Dr. Mandell's published articles
in academic publications, as well as a number of articles
in Popular Astronomy magazines.
Today's lecture will take us on an exciting journey from the discovery
of the first planet orbiting a sunlit star, through current efforts
to decipher the atmospheric structure
and composition of exotic planets.
So let's get to exploring planets around other stars,
and please join me in welcoming Dr. Avi Mandell
to the Library of Congress.   [Applause] Thank you.

>> Dr. Avi M. Mandell: Thank you all for coming,
and I want to thank the Library of Congress
for inviting me to come do this talk.
So today I'm going to be talking about the discovery of exoplanets,
and the potential discovery
for earthlike exoplanets in the near future.
This here is just an artist representation
of what a planet might look
like from a great program by National Geographic.
But I want to tell you right now, not to spoil things,
that we're not taking pictures like this of exoplanets event [phonetic].
I want to start, though,
with a quote that really has inspired me for a long time.
It's good, it's by Carl Sagan, who is really an icon for a lot of us
in planetary science and astrobiology, which is the study
of life in the universe, because he really popularized the idea
that science and the study of the universe
and the cosmos could be something more than just an academic pursuit
for people in ivory towers and academic institutions.
It could be something that inspires all of us to think bigger
than ourselves and to be good stewards of the world around us.
So this quote, "Somewhere something incredible is waiting to be known,"
is a great motivating statement.
Every day when I'm sitting in my office sometimes struggling
with the work I'm doing, trying to make that next discovery,
I think about the idea
that something somewhere is waiting to be known.
And this talk is going to be about one of these questions
that really motivates me, "How will the discovery
of a distant world teaming with life change our perspective
of our own planet and of ourselves?"
If you think about it, discovering a planet out there
with a brand new origin
of life never before seen will really give us a new place
in the universe, will hopefully encourage us to think
of our own planet and ourselves as something new and different
that we might not have thought about before.
So I'm going to start by really laying the groundwork
by charting the path using an equation --
a famous equation called "the Drake equation," first postulated
by Frank Drake in 1967 where he was really doing a thought experiment
about how we might be able to discover civilizations and a number
of civilizations out there in the universe.
So you start with the fraction of planets that actually develop life,
and then you go onto think about the fractions of planets
that develop intelligent civilizations.
Eventually the fraction of civilizations
that develop a detectable technology because really
of course we're thinking about the detectable civilizations
in our galaxy right now.
And finally you have to factor in the length of time
that the civilization survive, because a civilization can grow
and develop and become detectable, and then suddenly it will be snuffed
out and be undetectable from that period on.
So factoring in all these pieces you can get down to this question of,
"Can we find intelligent life in the universe?"
Now, I like to break these up into things that are measurable today
in this moment, from what we know.
And as I said, we already know our stars,
so that's not really a question.
The thing we're really striving for are these 2 factors of then fraction
of stars with planets and the fraction of number of planets
that might be able to support life.
But I sort of like to put out this warning, you know, to this equation
that these final 4 factors are almost unmeasurable and unknowable,
because especially today with our sample size of 1 planet
that has evolved and developed life, it's pretty hard to put any types
of constraints on these types of factors,
because we're really just going to have to take guesses.
And you can actually go out there on the internet --
I encourage you if you're really interested in these questions,
go out and find an online calculator of the Drake equation,
just put that into Google and you'll actually be able to play
with these numbers yourself and try to calculate
and determine what N would be under some reasonable
or more optimistic estimates of some of these other perimeters.
And so for this talk, though, I'm going to be talking
about what we're actually studying and looking for in these --
are these extra solar planetary systems.
So where we are today; so this was back in September of 1995,
the known exoplanets, confirmed main sequence planets over time.
And as you can see, well these blue dots aren't actually anything.
You can see there were no planets discovered in September of 1995.
If you think about it, I know this is sort of a funny slide,
but this is less than 15 years ago; 15 years.
Now, if you think about it, if you have kids who have grown up,
they might have been born after this date.
We didn't know about any planets before this date.
Of course, there are a lot of people who thought they knew about aliens
out there in the universe.
[Laughter] But these are -- as I said, also a little bit unmeasurable
from a quantitative sense.
And so we like to think about real planetary systems.
So I want to talk about how we started this quest and this --
of discovery for exoplanets.   I call this "Exoplanet 101."

This strategy called "precision radio velocity," or it's called
"the Doppler method," was really -- is still really the workhorse,
and was the method first used to discover planets around other stars
around other main sequence stars.
And so this is sort of an animation showing how it works.
The idea is that you break light from the star
that you're observing this central star, into its different colors,
and as a planet goes around the star, that central star moves
in concert with that planet.
So they basically do a do-si-do process.
You can see that they're on opposite sides of their orbit,
and the spectrum of light, the colors shift back
and forth as the star moves.
You're not detecting the planet at all, you're only detecting the star,
watching the star move as if you had a dark unseen companion pulling
on you as you go around in a circle
if you can imagine a kid swinging you in a circle,
that's what going on, the planet is swinging the star
around in a circle here.
So this has been used for, you know, decades and decades
to study stellar systems, stellar binary systems,
but we didn't have the precision to do it for exoplanets until 1995.
The other thing that we didn't really realize was that the signal
of these exoplanets would actually be extremely much,
much stronger than we might have expected,
because the planets we found are very,
very close to their parent star.
And if you could think about it, the closer the planet,
the stronger the gravitational tug,
and the more motion will be placed on that central star.
So these guys here were the first discoverers of exoplanets,
and some people think they are just waiting in line for their chance
at the Nobel Prize in physics
because this discovery really revolutionized what we know
about planetary systems.
But for the longest time, especially this group here in the US --
this is the European group, and this group in the US,
they labored really in obscurity.
They were building their instruments and testing them
and they were finding them, improving them,
but no one really believed that they would be able to do anything
on planets for the longest time because the idea was
that the signals of a Jupiter-like planet would be so small
because it was so faraway from its parent star,
way out in the distances of the solar system
that you could never actually see it.
But once these -- what we call "short period planets" burst
onto the scene -- and I'll talk about that, these guys kind
of became rock stars in the field,
and the rest is history really for them.
So in 1996 we had 6 planets.
This was the first confirmed radio velocity planet, 51 Peg b.
And I want to point out here the scale.
Here we have astronomical units,
so Earth is at 1 astronomical unit here, and Jupiter is at 5,
and Mercury is here at around .4, moving indoors in our solar system.
And this is mass of the planet, so Jupiter and Jupiter mass.
And this is 1 Jupiter mass, and then Earth is
down here below at .003 Jupiter masses.
So you can see that the first planet was pretty big,
close to a Jupiter mass planet,
but more importantly it is extremely close to its parent star,
far inside the orbit of Mercury in our own solar system.
And so this is what was completely unexpected,
the idea that giant planets, the planets the size of Jupiter
or even larger could be orbiting their parent stars basically
within what we think about as the sublimation zone
where atmosphere should be completely destroyed
by the blasting heat of their star.
So that confounded scientists for quite a while,
and is still confounding scientists to some respect.
But the surveys at that point started really looking hard for more
of these and they were finding some more planets,
especially these ones a little bit farther out were more serendipitous,
but quickly the surveys started to produce large numbers
of these short period planets inside the orbit of Jupiter
and even inside the orbit of Earth.
In 2000 there was 38 planets in the year 2000.
So only 4 years later they had more
than 6 coupled there in number of planets.
So in 2000 the first transiting exoplanet was discovered.
And I want to talk about what a transiting exoplanet is.
This is my second slide on Exoplanet 101.
A planetary transit is when a planet actually goes
in front of its parent star.
And this is -- if you think about the geometry of a planetary system,
this is a kind of unusual event because the planet's orbit has
to be exactly aligned with our line of sight
as we're observing this star, right?
If it's slightly up or slightly down, the planet won't actually go
in front of its star in our line of sight.
And you won't actually see anything.   So only a small fraction

of exoplanets actually transit their parent star.
So you have to look at a large number of stars to discover these.
But in 2000 they were able to discover the first planetary transit
or part of one as it dipped in.
And these are the first 2 discoverers
of transits in '99 and 2000.   And as I'll talk about now,

planetary transits have become a second workhorse,
a real huge discovery space for exoplanets.
And we're even improving
and increasing our discoveries using transits today.
>> [Inaudible]?   >> Dr. Avi M. Mandell: Yes.

>> Your graph up there is just that the [inaudible] on the bottom --
>> Dr. Avi M. Mandell: Yes.   >> -- wiggled.

It doesn't go straight across.   Why is that?

>> Dr. Avi M. Mandell: Yes.
This can be -- in this animation I'm not sure exactly what they were
trying to get at.
My idea is that they were actually trying to show
that it's a noisy curve, that you actually have noise on top
of your straight curve, and it will dip and wiggle and you'll have
to be able to correct for that type of thing.
But there are actual physical phenomena that cause these curves
to not be exactly perfectly straight.
For example, star spots on the parent star --
I think everyone has seen on pictures of our own sun,
solar pictures the dark spots on the star when there's less light coming
from the star that will change the brightness of the system,
and so you'll see some dips and wiggles.
But that's more of a rare phenomenon.
You wouldn't see it all over the curve -- the place.
But it was a good question, excellent question.
Anymore questions so far?   Okay, we're doing all right?

Good. So in 2000 we had 38 planets.   2005 we had 155 planets.

2008 we had 260 planets.
2012, as of last year, you see this plot, this was done in March
of last year, 570 known exoplanets.   And today we have more than 700.

Only a year later we've doubled,
added almost 200 more planets to this count.
Or so we're now into a regime
where finding planets is not new, is not unusual.
And we're really starting to be able to do statistics,
interesting questions about those 2 perimeters that I talked
to you about, the frequency of planets around stars,
and the frequency of earthlike planets around stars.
So in this plot, again, we have astronomical units on the bottom
and mass on the left here.
But I also want to point out that we have an eccentricity scale.
Now eccentricity, the word "eccentricity" refers to the --
how elliptical an orbit is.
If you think about planets in our solar system,
they're on very circular orbits in our own solar system.
Earth and Jupiter would be all the way down here
in the dark blue on this plot.
But comets and cometary bodies are very elliptical.
They go in and out in these long orbits, long narrow orbits.
And so they would have ellipticities [phonetic] [phonetic] all the way
up here at the top.
So you can see a number of these planets are really more
like giant planetary comets in these systems zooming in and out as close
as possible to the parent star, and then zooming all the way
out to near the orbit of Jupiter.
Other ones are extremely circular, and you can see there's this clump
of very circular planets down here.
We think these planets have actually --
their orbits have been circularized by interactions with the parent star
and so that's why they're all very dark blue.
But this dark -- this circle around the central dot,
these are transiting planets, while these other dots
out here are the planets that have only been detected using
radio velocity.
So you can see kind of the complement
between the two methods radio velocity is able
to find these more distant long-period planets,
while transits are very good
at finding all the planets very close to their parent star.
So right now we're working with the Kepler Telescope,
which is a transiting telescope to fill out a lot of this space,
and I'll talk about Kepler coming up.
But the interesting thing about transits and radio velocity is
that you can actually give you different information about planets.
Transits, if you can imagine back to that video here --
let's see if -- there we go.
This method gives you the radius of the planet, if you can imagine that,
because as the planet goes across the star
by determining the difference in the size of the planet versus the size
of the star, you can determine the radius of the planet.
While the radio velocity method -- going back again here,
this method gives you the mass of the planet, because it's based
on the gravitational tug of that planet around the central star,
and gravity is a function of mass of objects.
You have more gravity if you're massive.
And so by combining these 2 methods,
you can actually determine the density of a planet.
If you can observe it both as a transiting planet
and a radio velocity planet,
you can actually constrain both the mass and the radius.
And therefore, if anyone remembers back
from their 12th grade physics class,
radius and mass gives you the density of an object.
And so here we're plotting mass and radius,
and then in color we have density where Earth is here
at around 5 grams per centimeter cubed,
while Saturn is the lightest planet in our own solar system.
And it has a density less than water.
Water has the density of 1 gram per centimeter cube.
So Saturn is extremely light and gaseous.
And so the planets we found range quite a bit
from extremely under-dense, even less dense than Saturn, these dark,
dark blue points, all the way down through some extremely dense --
even as dense as iron, a completely iron planet here.
And some of these look more like Earth where they might be rocky,
combination of rocky, iron and some gas or liquid.
And you can actually put quantitative limits on this
by drawing the curves that you would expect for a planet made completely
of iron here, completely of rock, and completely of water,
and then made completely of hydrogen or hydrogen
and helium here in these curves.
And so this gives you a general guideline.
All these planets are planets just like the rocky planets
in our own solar system, the terrestrial planets,
made mostly of rock, metal and water,
and some small gaseous atmosphere, while these planets
up on this line are like the giant planets in our solar system,
like Jupiter and Saturn, and even Uranus and Neptune
up in this region up here.   Yes, question.

>> Are these like graphs available [inaudible]?
>> Dr. Avi M. Mandell: These graphs are not available on the website.
This whole -- this will be on YouTube.
You can check it out there,
but you can actually put these graphs together yourself, again,
and I would suggest, again,
if you're interested there's something called "exoplanets.org."
And it's an award-winning exoplanet data website which has access to all
of this data and allows you to basically easily --
kind of like you do, you know, just toggling switches on the internet,
easily plot out some of these same categories
and do this type of exploration.   >> [Inaudible].

>> Dr. Avi M. Mandell: Sure, okay thanks.
>> Okay.
>> Dr. Avi M. Mandell: So I want to move
onto how we're making these discoveries today.
And a lot of them are being made by the Kepler Space Telescope.
You may have heard about Kepler.   It was launched in 2009.

And since then in the last 4 or 5 years it has really revolutionized,
again, after the radio velocity revolution now comes the transit
revolution of exoplanets.
Because we're able to look at 150,000 stars constantly.
On 30-second intervals we take exposures of these 150,000 stars,
and we download the data and we're able to watch over years and years
to see, look for these dips as the planets go
in front of their parent stars.
So just to go back, this is the field, the giant field
in the Cygnus Constellation here.
It's just a bunch of camera CCD's just placed and staring
at this giant field of view.   And you can see all the planets

that have been discovered all over this field.
They range from giant planets all the way
down to even earth-sized planets today.
And we've discovered more than 3,000 of them in the last 5 years.
This was downloaded -- I got this number yesterday, last night,
but it could have changed by today.   It literally changes day to day,

and it's a pretty fast-moving and interesting field.
So I want to talk more about Kepler because it's really sort
of settled a lot of the statistical information
that we now know about exoplanets.
As of January this was the range of planets that we were finding,
very few, very large planets.
Jupiter and even larger planets are actually quite rare
around these stars.
It's much, much more likely to find planets of the Neptune
and smaller sized planets around stars out there.
This plot is slightly biased towards Neptune,
compared to earth-sized planets, because they're easier to find.
If you think about it, a bigger planet is easier to see that dip
of light, and so there's some bias in the observations here.
But overall it's showing that small planets, Earth --
1 to 2 Earth radii, if you think about it we're only talking
about radii because of this transit, 1 to 2 earth radii are very,
very common around stars.
And a recent work -- and this is literally in 2013 here,
has tried to look only at planets within 50 days, which we have,
so 50-day orbit, a period of 50 days around their parent star,
and to get a very complete assessment of this FP,
remember I talked about this, this frequency of planets,
this planet-star fraction.
And specifically from 1 to 14 earth radii it looks like 8%
of stars have an earth-sized or slightly larger
than earth-sized planet around them.
So almost 1 in 10 stars have an earthlike planet.
And if you think about the 250 billion stars in our galaxy,
that is a lot of earthlike planets.
Now, remember, this is only within a period of 50 days.
And Mercury, for example, has a period of 88 days.
So we're still within the orbit of Mercury.
These are not planets that could host life,
they're most likely extremely rocky, or extremely hot dense planets.
But either way, this is a very, very interesting result.
And to take it another way, this is, again, from Kepler.
Here we're looking at the actual orbital period of the planets,
and remember our orbital period around the sun is 365 days, right?
So we would be all the way out here,
right here on this earth radius line.
And so we're finding tons of planets in here the size and even smaller
than Earth, much smaller than Earth with the Kepler Space Telescope.
But we haven't yet reached out to earthlike, as in the distance
from the star of our Earth.
But you can see this region is very under-populated,
compared to the density of Earth and Neptune like planets
around their parent star.
So I want to talk about some of these smaller planets.
This is the main question that really plagues us right now
in exoplanet studies, "Are these planets more like mini-Neptunes
where they're icy with big giant ice and gas envelopes, or super-earths,
more earthlike where they're mostly made of rock with little, you know,
thin shells of an atmosphere around them?
And so we can start looking at this by, again,
comparing these curves of mass to radius.
Remember, I showed this before, and getting a density and comparing it
to models of what Earth would look like, or a 100% water world,
where you are completely made of ice and water, and then of course worlds
of more hydrogen or helium up here at the top.
And you can see these planets are really falling
into what you might think of as an earthlike earth composition planet.
They're rocky, they probably have some water in them,
some of them more than others, but really a lot
of these planets we're finding are very similar to the densities
that we would expect for earthlike planets.
This is -- all these planets, Kepler 11, are actually in 1 system,
all within 50 -- a period of 50 days.
So they're all extremely close
and they're all rocky to Neptune-like planets.
And there's many more interesting systems that are coming out.
As I said, the Kepler 11 system the outer planet I guess is beyond the
orbit of Mercury, but the inner ones, the inner 4 planets are
within the orbit of Mercury here.
So the next question, of course, that comes up is,
"How can we find planets that are more like Earth, more warm and wet,
and not too hot but not too cold?"
We call them "the Goldilocks planets."
And they fit within what we call, "the habitable zone," and it's kind
of a hokey term, but it caught on very fast
when it was first introduced in the '80s,
this idea of this Goldilocks zone between where water boils
at a surface temperature of more than 100 degrees Celsius,
and where water freezes in the outer region.
And for different stars, hotter stars have a habitable zone
that is larger and farther out than their --
than smaller stars which have habitable zones
that are closer in, in this picture.
And so we can start placing all of these Kepler planets
in context of their habitable zone.
This is the Kepler 22 System, which was discovered after Kepler 11,
and for a while was our best, best candidate for a habitable planet.
It's a large planet.
You can see in size it's much larger than Earth, within 2 Earth radii
in size, so more like a Neptune, a mini-Neptune size.
But can see it fits right inside the inner edge
of the star's habitable zone here.
Earth, you can see, is slightly more central to our own habitable zone,
but Kepler 22 is almost certainly --
has a surface temperature that would be able
to maintain liquid water on the surface.
So this was the first real mind-blowing discovery with regard
to earthlike planets that came out of Kepler.
The problem is that the planet is large enough that the density
of the atmosphere is high, and so the pressure that you would feel
on the surface of the planet under this thick,
thick atmosphere would be so large
that you most likely would not have any type
of extent life beyond postful [phonetic] microbial,
more submicrobial life on this planet.
But the temperature would be pretty nice and cozy.
So there are a couple other systems that have recently been announced.
This was only in the last 2 to 3 months
that these planetary systems were announced.
Kepler 62 has a very small habitable zone.
It's a small K type star, much dimmer than our own star.
But here they fit 5 planets all within,
and 2 inside the habitable zone and 3 more
in the very inner regions of the system.
So this system finally starts to look a bit like our own solar system
where we have some planets in the habitable zone,
or close to the habitable zone, and some planets in tier to that.
So this system may have formed in a very similar way
to planets in our own system.
The planets are slightly larger than our own terrestrial planets,
but especially 62F here, is getting down,
as you can see, to the size of Earth.
And it's firmly within the habitable zone.
So there was a press release I think only about a month ago
on this planet and where they had a whole news conference with models
and discussions of what this planet might look like.
Now, that is -- I wanted -- if you go out and read about it,
and I suggest you should, I want you to take it
with a bit of grain of salt.
As a layperson looking at this, scientists love
to hypothesize way beyond what the data actually tells us.
So they love to talk about blue skies and raindrops
and all of this other stuff.
But really from Kepler all we get is the radius of the planet,
and the period of the planet.
And so we can tell where it is in the system and the expected size,
but we can't tell anything more about the composition,
the amount of atmosphere, so forth and so on.
So I think it's very exciting, but we're going to need
to find planets that are closer to us.
These planets are so far away that we can't follow up with them.
The key about Kepler is that it looks
for planets throughout the galaxy in a pencil beam.
It basically stares, if you can imagine.
Imagine looking down your block at home, right, and you're standing
in your front lawn and you're looking
down your block along the road, you can see your neighbor's yard,
which is nice and close, and may have kids playing in it,
but if you have a long block, you could also see all the way
down to the store at the end where you can't --
you don't know what's going on in that store.
All you can maybe see is the door opening and closing.
And that's the idea with Kepler is a lot
of these planets you can see them, you can detect them,
but they're so far away that you can't actually learn what they're
made of, or what the planet looks like.
Here's one more system that's very favorable that's come out of Kepler.
The Kepler 69 System has 169C, also just slightly larger than Earth,
in the very interior part of the habitable zone.
So we're starting to make a menagerie here,
a collection of possible earthlike, literally Earth temperature
and slightly larger than earth-sized planets from the Kepler Telescope.
And this was the whole goal of Kepler,
was to find earthlike planets.   Now, unfortunately for all of us,

Kepler has had a bit of an accident recently.
One of the reaction wheels that really drives the precise pointing
that Kepler needs failed on the last month.
And so Kepler at this point is hobbled severely
in its pointing accuracy, and can't really do the precision measurements
that it needs to at this point to find more
and more distant earthlike planets like this.
And so NASA is still trying to determine what
to do with the telescope.
It's in a bit of a holding pattern right now.
But for the moment, this is what we have from Kepler.
And there's much more data to be analyzed from previous years,
but Kepler is in a decline, is in its last legs,
and we may be saying goodbye to it pretty soon.
So what comes next?
Well, the real question we'd like to do is we'd like to learn
about the atmospheres of earthlike planets,
and of course of larger planets as well.
And to do this the main and the most well-documented
and most robust method for doing this is using the transit method
again, but actually examining the light as it comes
through the outer atmosphere of the planet.
And you can see here as the planet goes across, it has that thin shell
of an atmosphere around it,
and the light from the star will actually filter
through like a dirty windshield, filter through the atmosphere
of the planet and arrive at our telescopes.
And the difference in absorption
through the atmosphere will tell you something about the composition
and size of the different molecules and atoms in that atmosphere.
If you look in regions of colors of light, where water is absorbed,
if you think about it, different molecules have different absorption.
A good way to describe this is if you're in the swimming pool, right,
and you look up at light it has a blue tinge to it,
and that's because you're getting scattering from the water molecules
between you and the light.   If you're in the infrared,

the reason that the infrared is actually very bright to our eyes
when we put on infrared goggles is because water molecules absorb
and emit extremely well in the infrared, and that's why plants
and other objects with a lot
of water look very bright in the infrared.
And so water and methane, and lots
of these other molecules can be detected
in the atmospheres of transient planets.
Now, we're not able to do this with many planets yet, because they're --
as I said, the Kepler planets are far too far away.
So the goal now is to find super-earths, or earthlike planets
that are close enough to us.
And this planet GJ1214B was the first super-earth
that was discovered close enough to actually do these observations.
It's around a very, very dim M-type star.
These M-type stars are much, much smaller than the sun,
more than a 10th -- less than a 10th the size of our sun.
And so it's actually much easier
to find smaller planets around smaller stars.
If you think about it, as a planet moves in front of its star
if its star is smaller, then
that means the planet makes a bigger signal in front of that star.
And so you're able to look at the light and break it
up into different colors and actually tell the difference
between a sunlight composition where we have lots of molecules,
and a 100% water atmosphere where your atmosphere is only made
of water, and no nitrogen, no hydrogen, nothing else.
You can actually see a huge difference in the transit depth,
as in how big a planet looks to you depending
on what the planet is made of.
The problem is that with our current level
of technology these measurements are still extremely hard.
I'm counting up all the measurements made
since this planet was discovered in 2009, and the problem is
that you can see that they're kind of all over the map right now.
You can see they have a huge scatter, lots of uncertainty
in a lot of these measurements, and even the best ones are kind
of uncertain whether they're seeing absorption features for molecules,
or whether they're flat like the 100% water-rich atmosphere.
But it looks like right now that we may be seeing one
of these water planets, a planet made completely of ice and water
in a very thin water-rich atmosphere,
and a very dense water-rich surface layer.
So this is the first planet we're able to do this with,
and we're hoping to find more planets in the future,
and with future missions.   The main mission to do this type

of work is the James Webb Space Telescope.
James Webb is the future of space astronomy at NASA.
I mean, if any of you actually work in the federal government,
and I'm sure many of you do, you may have been party to some
of the discussions on the Hill that have gone on about James Webb.
James Webb is an $8 billion telescope,
developed over the last 35 years and expected to launch in 2018,
but it is extremely, extremely complicated.
It is -- let me show you some of these pictures.
It is at least 3 times larger than the Hubble Mirror,
and made of a collection of beryllium-covered segments
that all have to fold out like a giant peddle once the telescope is
in space.
So it's an extremely complicated complex telescope to build,
and it's had a lot of controversy as the budgets have overrun,
and NASA administrators have trekked back
and forth defending the telescope's importance over and over again.
But we're almost there.
We're within about 5 years now of the launch of the James Webb.
And the reason that it will be so important for this type of work is
that we will actually be able to discover
around habitable super-earths.   Super-earths in the habitable zone

of their parent stars will actually be able
to detect molecules like water and CO2.
Right now the planets we can look at are so hot, 500 Kelvin,
which is on the order of, you know, something like 700 degrees Celsius,
so extremely hot temperatures where you would never have water
on the surface of the planet.
James Webb will be able to look at habitable planets,
and actually investigate their atmospheres
for what they're made of.
So I want to then talk about strategy number 3
for discovering planets, which is called "corona graphic imaging."
And the reason this is so important is that if we ever want
to actually image an earthlike planet, we're going to have
to use this method rather than the transit method;
because the transit method only takes an indirect measurement
of the planet's atmosphere.
A direct image, as you see over here, actually shows you a pinprick
of light around the star where the planet is.
And you can actually watch the planet orbiting.
The problem is that this method as well is extremely complex.
And I won't really go into the details here, but I just wanted
to give you an understanding of the multiple optical complexities
in a telescope designed to take this type of image.
You have to block out the central star extremely well in order
to see the tiny little dot of a planet here next
to the blinding spotlight of the star.
So it's a -- again, people at NASA and elsewhere,
at universities are working extremely hard to make this work.
And so far there's been some successes.
We've been able to discover Jupiter mass planets
around some nearby stars.
These are only in the last 3 to 4 years
that we've been able to do this effectively.
This is really the sort of standard bearer right now
of directly imaged planets.
There's a 4-planet system directly imaged around the Star HR8799.
These planets are way beyond the distance of Jupiter.
You can see here the scale bar shows you 20 astronomical units.
Saturn is at a distance of 10 astronomical units.
So these planets are way beyond the reaches
of our own solar system and theirs.
But it shows you that multiple planets can really be imaged
with this method.
The problem, though, is that earthlike planets,
if you take a look at this box,
earthlike planets are an acquired technology to be 10,000 times better
than our current technology for making these images.
So right now we're really limited to the best and brightest,
the largest planets at the farthest distances from their parent star
in order to make these measurements.
So we're moving forward, but there's still a long way to go.
And I want to leave you here with a slide that really sort of shows us
where we hope to go in the next 15 or 20 years, possibly 30 years,
depending on how the federal budget shakes out,
to measure the atmosphere on a living planet.
And the first thing I'm going to sort of show you are the timeline
of exoplanet discovery to date.
This shows you the major launches of space telescopes from NASA.
First the Hubble was launched in 1990, the Spitzer,
and then the Kepler Telescope was launched in 2009,
and finally we hope JWST.
But within this exoplanets have really marched in lock step
with the launches of these telescopes.
The first exoplanet was found in '95,
and then the first transiting exoplanet in 2000, the first light,
directly imaged light from an exoplanet was in 2005.
And finally the first spectrum
of the super-earth I just showed you was taken in 2012.
And the first earth-sized exoplanets were found by Kepler in 2012.
And so the question is, "What comes next?"
We found habitable planets but we need
to find habitable earth-sized exoplanets,
and we need to find them nearby to take a spectrum
of a habitable planet, sometime hopefully after JWST launches.
But really we need to move forward into the 2020s and the 2030s
to think about what comes after JWST.
I know it's really funny to think about a telescope
that isn't even built yet, but thinking about what comes after it.
But NASA we sort of think long-range like this, "What do you really need
in a telescope to image and take a spectrum
of a habitable earthlike planet to discover what the molecules are?"
JWST was planned and re-orchestrated before we even knew
that exoplanets existed.
This planet -- this telescope took 35 years to plan,
so even before Hubble launched they were already planning JWST,
but we didn't even know that exoplanets existed at that point.
So the next generation telescope should really be planned
to take an image like this.
[Laughter] Of course this is not real.
Don't take a picture and put this on YouTube or Twitter.
But this is what we would hope to see is the blotted out spot
of the star with a pale blue dot, just that side of the system.
These other white spots would be --
are actually a realistic image of what the dust
in an earthlike planetary system --
we have a large amount of dust in our own system
and it's a major problem, but you can still see this pale blue dot
that Carl Sagan very famously discussed when thinking
about what Earth would look like.
But a spectrum of Earth also is required really
to understand what the atmosphere is made of.
This is a spectrum on our own Earth here.
This yellow curve is the thermal emission at 300 Kelvin R
at the temperature of our own Earth,
basically about 40 degrees -- 35 degree Celsius.
So the planet emits thermal infrared absorption net --
we're talking about the thermal infrared portion
of the spectrum here, but there's huge absorption on top of this
for molecules like water, and methane, and then carbon dioxide.
These are the main absorbers in our atmosphere.
And then you can see very interesting absorbers
like ozone in our atmosphere.
Ozone is a key marker of life on Earth, because the only thing
that can create ozone is molecular oxygen.
And the only thing that can create molecular oxygen is life on Earth.
In the early parts of Earth's history there was no oxygen.
For billions of years there was no oxygen on Earth.
It was a fully carbon-dioxide and methane dominated atmosphere,
with a lot of water from the planet.
And methane created by bacteria, methanogen
and methanic methane emitting bacteria were producing quite a bit
of methane in the very early periods of Earth's history,
in the 2 billion years of Earth's history.
But once you have plants and algae developing
around 2.7 billion years ago, that's when you developed ozone
and molecular oxygen in our atmosphere.
And so these, we call these molecular features "biomarkers"
in the spectrum of a planet.
They indicate a strong indication that there is living, breathing,
as you might say, life on the surface
of that planet, changing its atmosphere.
And so this is what we hope to take in the next 20 to 30 years
to build a telescope that can really tell us --
really sniff for the evidence of life in the atmosphere
of planets around other stars.
And so I finally leave you with the question, "Where will you be
when we find these planets," because it's really going
to revolutionize our whole picture of our place in the cosmos
and what life on Earth really means to the universe.
So I thank you very much.
I'll open the floor to questions [phonetic].
[ Applause ]
>> Jennifer Harpster: [Inaudible] I want to remind you to try to --
>> Dr. Avi M. Mandell: Yes, repeat the question.
>> Jennifer Harpster: -- [overlapping].
I'm sure we have lots of questions.   Yes; questions?

>> Dr. Avi M. Mandell: Yes?
>> What are we talking about as far as [inaudible] we're looking
at light, there may have been light and no longer is [inaudible]?
>> Dr. Avi M. Mandell: Yes; so the question is with the distance
of the stars that we're looking at, that we're observing,
there's a period of time it takes for the light actually reach Earth.
And so what we're actually looking at, what we're actually detecting
or observing has actually happened in the past, because planets
that are light years away from us have --
we're seeing them years in the past.
And so the closest stars, which are the ones that we'll actually be able
to search for the smallest and most earthlike planets,
are only on the order of 30 to 50 to 100 light years away from us.
So there could have been a catastrophe
that has destroyed the planet or even life on the surface
in the last 30 to 100 years,
but most likely we're seeing the planet almost
in essentially real time in a geologic sense.
We're not seeing it millions or billions of years in the past.
Kepler, on the other hand, does see planets that are on the order
of 10,000 light years away from us.
And so those planets there may have been significant change
in the planet's surface in that time.
But the ones that we'll actually be searching for life
on are the nearest ones
and therefore the ones most closest to our present day.

Yes.
>> Can you talk a little bit about [inaudible]?
>> Dr. Avi M. Mandell: Yes; so that's a --
that's for bringing up pulsar timing.
I left it out because I'll describe a little bit
about what pulsar timing is.
The question was, "Can you describe the method
of planet detection called 'pulsar timing,
and compare it to other methods?"
First of all, pulsar is a name for a neutron star,
which is a star similar to what a black hole is at the very end
of its lifetime of a star or after it has gone into a supernova
or a planetary nebula phase and has crunched
down into a very dense neutron-rich, very small star.
And pulsar timing is what happens is neutron stars actually emit radio
waves due to their extremely strong magnetic fields.
And so they emit a very directed beam of radio waves focused
by their magnetic fields in a certain direction.
And because they spin like this,
it's almost like a lighthouse going around, if you would imagine being
on a ship in the ocean and seeing the lighthouse beam hit you
and then go away, and come back and hit you, the radio waves
from pulsars do the same thing.   And they're extremely regular,

literally down to nanoseconds changing over time.
And similar to the way radio velocity works,
if a pulsar is moving towards you or away from you,
those timing will actually change significantly just
through the motion of the pulsar moving.
And so pulsars timing is even more accurate than radio velocity
and finding small planets orbiting the stars.
The reason I didn't bring it up in this discussion mostly is
because pulsar timing is restricted, naturally, as you can imagine,
to finding planets around pulsars.
And pulsars are extremely inhospitable environments
for planets.
If the planets are there, they're most likely planets
that were either formed before the star went supernova,
and then sort of made of debris leftover, or they actually formed
from debris after the supernova occurred,
and formed into planets after that.
And so they are most likely sort of rubble leftover around the star
that does not produce any other light besides this radio light.
And so there will definitely not be locations
where you can imagine having planets or anything
like planets in our own solar system.
But I want to say that -- and I omitted this, and anyone who works
on pulsars would like to state this,
that pulsar planets are actually the first planets discovered
in 1992 around any star.
They are concretely confirmed through pulsar timing
in '92 a full 3 years before radio velocity was able to make it work.
And the problem is that actually pulsar planets are not very common.
There's not -- there's maybe only 2
or 3 systems known of pulsar planets.
So they're very hard to find.   Yes, question.

>> Can you speak about the possibility
of finding life on other worlds?
What kind of criteria are you using --
is being used to define what we view as life [inaudible]?
>> Dr. Avi M. Mandell: Excellent question; yes, so the question was,
"As we're thinking about detecting life on other planets,
we really have to go back, all the way back
to the fundamental question, and again, this is why it sort
of gets exciting about thinking about these ideas is,
'What do we mean by life?
What is the definition of life?'" And now on Earth of course,
you know, it's this question of, "Well,
you know life when you see it," right?
That's sort of the classic response is, "Oh,
I'll know it when I see it."
Well, on Earth that's a very easy response to make,
because we have life teaming around us, and a lot of the characteristics
of life are very common of all different life forms
that almost all -- every life form uses DNA, there's a question
about what that can mean, but life forms on Earth use DNA,
we use proteins, we have cells, so forth and so on.
So all of these types of definitions work very well
for life forms on Earth.
But if you think of a brand new origin for life
on a different planet with no relation to Earth,
you may think of life forming with extremely different characteristics.
And Carl Sagan was a big proponent of thinking outside the box on this.
He thought of life forms made of silicon.
He thought of life forms of giant balloons floating
in the atmospheres of Jupiter like planets.
So you can think really far outside the box
about what life might look like,
but really the question I think comes not what life might be
like out there, which is a very fun question to ask,
but as a scientist we really ask, "How do you define
and characterize the criteria for saying you have discovered
or met the criteria for finding life on another planet?"
And with this you really have to think
about what are the detectable signatures of life forms
as we know it, and as we can imagine.
And so people have come up with things like respiration,
converting one molecule or a collection of molecules
into other molecules to produce energy in your body.
That may be a process that's completely separate
from the functional form of a life form.
Or possibly entropy, a negative entropy grading
where a construct has been formed that it would not be formed
out of randomness in an environment.
No matter what that construct looks like, if you can see
that that is something that would not be randomly formed you could
construe that as something that was built and organized by life.
But you can see that these questions get very murky.
Now, a question that I love to pose to kids that I talk to
and my kids especially is, "Let's say you were an alien looking
down at Earth, and you saw cars moving around on our roads, right?
Would you consider these cars to be life forms on Earth," right?
Right; well they move, they have motion, they actually take
in products and give out respiration products, they have internal organs,
they have apparent -- a purpose in their motions.
So of course, you know, when you got
to the surface you might realize they lacked other reasonable
expectations for life, but it's very, very difficult
to separate some processes that may look and appear to be lifelike,
and aren't really lifelike.   And so the whole field

of astrobiology right now is spending a lot of time thinking
about what might be the most likely.
But the problem is we are really stuck
with our own anthropocentric views of what life would like.
As I said, ozone or oxygen, which is a clear signal of life
on Earth may be a completely non-biological process
on some other planet.
And so we have to try to think outside the box,
but yet stay grounded in what we know
about the scientific process of life forms and life.
So excellent question; yes.
>> I had a quick question to follow up.
Is there a focus on searching for planets or in [inaudible]?
>> Dr. Avi M. Mandell: Yes.
There's always a focus on nearby stars,
mostly because they're the best targets
and astronomers are very pragmatic people.
And they say, "Well, let's look at the best stuff first
and then move onto other stuff."
The problem with nearby stars is there are several --
well one is that our telescopes,
our big telescopes aren't actually designed
to study these blazingly bright nearby stars, they were designed
to study distant, distant galaxies.
And as an astronomer I can tell you it's very hard
to tell a telescope committee, "Let me take your giant telescope
and stare it at a giant spotlight in the sky and potentially burn
out your whole instrumentation."   So it's actually going to --

it's been a real struggle to convince people
that we can actually do this with big telescopes.
There are other problems such as nearby stars are scattered all
over the sky, so you have to do what are called "all sky surveys."
And they also move quite quickly,
proper motion because they're close to us.
But one of the most exciting discoveries
in recent years was the discovery of a potential planet
around Alpha Centauri B. So it's --
Alpha Centauri is actually a triple system,
and 2 of the stars are on a close binary.
And one of those stars appears to have almost an earth-sized planet
and a 3-day orbit around that star.
It hasn't been fully confirmed yet, and so, you know,
if these things take years to really sort of put to bed,
but that was the first real idea that we'd maybe find planets very,
very close to our own solar system.
Of course, to get there is a whole different question
and a whole different talk that I could give
at a different time, but we are searching so.
>> Jennifer Harpster: I have time for like maybe one more question.
>> Dr. Avi M. Mandell: One more question in the back?
>> [Inaudible] my question is about does NASA or are you aware


2090 to succeed [overlap conversation].
>> Dr. Avi M. Mandell: I hope before then.
I might be dead.   [Laughter]

>> [Inaudible] going on, or the day after when [inaudible]?
>> Dr. Avi M. Mandell: Yes, yes; I mean,
that's a very interesting question.
So of course I can't speak for DARPA or the defense industry on this,
but I can tell you that there are protocols in place if something
like a signal from an extraterrestrial intelligence for --
of course the problem is when you get, you know, an announcement
like this from a scientist or a group of scientists, or even,
you know, a ton of places, you really have
to spend a lot of time verifying this.
You know, really big claims require really extraordinary verification.
And so it would be a long period of verifying
that this was actually what we thought it was.
But it's very different than something like, you know,
a movie like "Independence Day," where the aliens show
up on your doorstep and you've really got
to make a split-second decision.
With this one you're a passive observer of another planet.
And so the question of, you know, what we do as a society is more
of a long-term question of how we react from a philosophical,
and scientific, and theological, and emotional, and military --
yes, though, as I said, traveling to these places or having that --
unless they show up on our doorstep we're not really going there anytime
soon, so.
>> Jennifer Harpster: And I'd like to remind you we do have some books
and some guides outside if you're interested
in this topic and want to learn more.
And we welcome you to the science and business reading room
where you can discover some of that stuff.
>> Dr. Avi M. Mandell: And of course ask me questions afterwards.
I'll be standing around for a little bit.
>> Jennifer Harpster: Yes; but we've got -- okay.
Oh, yes.
>> Dr. Avi M. Mandell: I mean, for a few moments.
>> Jennifer Harpster: We had some technical problems in the beginning.
>> Dr. Avi M. Mandell: Oh, okay.
>> Jennifer Harpster: We're going to have to redo the beginning,
but you guys [inaudible].   >> Dr. Avi M. Mandell: Oh, okay.

We're going to --   >> Jennifer Harpster: [Inaudible].

[Laughter]
>> Dr. Avi M. Mandell: Nice, nice, thanks.
>> This has been a presentation of the Library of Congress.