>> Stephanie Marcus:
Hello and welcome.
I'm Stephanie Marcus from
the Science Technology
and Business Division.
I want to take the
opportunity today
to say Happy 60th
Birthday to NASA.
And I only wish that
I were that young.
Today we're going to hear about
eclipses and occultation's
and other shadowy effects.
We are still buzzing about the
eclipse that we had last year,
it was just really
such an amazing kind
of life changing
event for some people.
And of course we're looking
forward to the next one in 2024.
But in the meantime, we've
got a lot of other shadowy,
what does he call
it shadow science.
We have a lot of other
things to learn about.
Test took off finally,
looking for exoplanets.
And we have the best
person to talk about it
because Dr. James Green was
the Chief of Planetary Sciences
and was recently chosen to
be NASA's Chief Scientist;
so he's got some new duties and
it will be really interesting
to hear about that too.
But, not today I suppose.
So Dr. Green got his PhD
at the University of Iowa
and worked there
with Dr. Van Allen.
And then in 1980 he began
his career with NASA
down at the Marshall Space
Flight in Alabama, and then came
to Goddard in 1985 as head
of the National Space
Science Data Center.
And in 2006 he became
Director of Planetary Science.
So that, if you want to
know more you can Google him
because he has quite a long and
detailed history there at NASA,
with many awards and
many achievements.
And of course as Chief
of Planetary Sciences he oversaw
some really cool missions
to Mars and past Pluto, etc. So,
please help me welcome
Dr. Green to the Library.
[ Applause ]
>> Dr. James Green:
Thank you very much.
It's a real pleasure to be here.
I know many of you perhaps had
an opportunity last year to go
to Alex Young's talk prior
to the fabulous eclipse
that occurred across America.
And so here's a follow-up.
We're going to talk about what
we learned during the eclipse.
Not everything that we
learned during the eclipse,
but at least it gives
you an idea
that we can actually do
some really new science.
So, we'll be talking
about that great eclipse.
Then I want to change gears
a little bit and we're going
to be talking about how we use
eclipses to learn new things
about the solar system, and set
ourselves up to learn even more
than our originally planned
for many of our missions.
And then of course
eclipses are one
of the critical ways we
actually find planets
in other solar systems,
so we'll talk
about what we've
learned from that.
So we have a number of
really spectacular sets
of science that we do.
And of course we'll start with
the great eclipse of 2017.
You know what's really
spectacular
about these eclipses,
you know you would think
that we've learned
everything that we need to know
about the sun and that we
can learn from eclipses.
Since they occur
somewhere on this globe
about every 18 months, okay?
But in reality when NASA
goes to eclipse they will go
to a couple sites, they will set
up several sets of experiments
and then they will
execute those experiments.
But the 2017 eclipse
provided us an opportunity
that was just too good to pass
up because we had all kinds
of things that we did
during this eclipse.
If I could say it this way,
NASA really owned this event
in the sense that we did
some really great things.
So, here's a little
animation, of course this cut
across the United States,
what you see are how
the sun would look
at different locations
along the path of totality.
Path of totality
is that red stripe.
We did a lot of work
in terms of analyzing
who in America could have seen
the eclipse, and the results
of that are absolutely
astounding.
154 million America's -
million American adults
since we couldn't survey
kids watched it live, okay?
20 million traveled to see
it, they were in far reaches
of the United States, which
couldn't see any part of it,
but then came - many of them
came to the area of totality.
61 million viewed it either over
the internet, which we supported
or through the TV for which we
had broadcast stations all along
the eclipse path.
And that results in 88% of the
American adults saw the eclipse
in some way, shape
or form, all right?
It's truly a phenomenal event.
It's - for NASA it really
started just before we hit the
shadow hit the United States.
We had planes out.
These planes were
carrying instruments
that will probably end up
on satellites in the future.
And here was a perfect
opportunity
to test their sensitivity as we
look right at various features
of the sun because we can black
out the main light of the sun,
we can see these
fine detailed images.
And so here's a little movie
of the eclipse shadow coming
in over the Pacific as it then
entered the United States.
And then instruments could - to
look at the sun and really look
at a lot of the fine details
of the lower atmosphere.
We observed this eclipse through
the eyes of many telescopes,
from many satellites, and
in many different ways.
So here's an image shot
of our lunar mission,
the lunar recognizance orbiter,
that's orbiting the moon
looked back at the earth
and saw the shadow as it was
crossing the United States.
And what it tells you when you
look at this, how lucky we were
as a nation to be able
to have such a large area
of the United States clear for
us to be able to really look at,
and enjoy the eclipse.
So how many were
in the clear areas?
How many actually had an
opportunity to see it?
So my - my quick look looks
like that's 88% of the audience.
So very - very good.
Nose from spacecraft that were
dedicated to look at the sun,
of course you had to be
along the eclipse path
to see totality.
But many of them of course,
saw different things,
so here's the moon moving
in front of the sun as seen
from one of our major
spacecraft that is looking
at the upper atmosphere
of the sun.
This would be - this
would be the - the Corona.
So this area is really
actually high above the sun.
The surface of the sun,
if you were to put the sun
in this image it would be a
globe that would be smaller
than the edges of
this - of this frame
because this light is coming
from a region that's higher
up in the atmosphere, okay?
And so what we want to do of
course is we want to tease
out what's happening just
above the surface of the sun.
Now from our spacecraft we look
at the atmosphere of the sun,
this is the extended
atmosphere of the sun.
It's called Corona.
And the Corona is as shown
here, this is one of the best
from our spacecraft
that we can do.
So, here's - we have an
occulting disc that we put
in front of it and we make
measurements all the time.
And we see coronal
mass ejections,
we see all kinds of things.
And the light that you're seeing
is actually material that's
leaving the sun.
The sun constantly
outgasses in all direction.
And there's all kinds
of dust that is left in
and around this area
as comets come in
and are disintegrated
by the sun's light.
Some survive, but many don't.
And so this area is
just full of dust.
And that dust enables
the scattering of light
that gives us this image.
So this is really very
low light compared
to the very bright
disc of the sun.
Now if I were to put the actual
globe of the sun on this image,
it would look like that.
So, what we're not seeing is
everything that's below the red
and to the surface of the sun.
And this is really
the atmosphere just
above its surface.
And then it purges into
that - that corona.
And this area is
called the chromosphere,
the atmosphere is
called the chromosphere.
So indeed we want to
be able to look at that
and the eclipses provide the
perfect opportunity to do that.
What we want to do and try to
understand how active the sun is
over time, is to use our massive
compute capability to be able
to really model this area.
It's full of magnetic fields.
These magnetic fields
are very strong,
and they either allow hot
gasses that come up from the sun
to return to the sun, or
to come up from the sun,
go into the corona and then get
accelerated and blast it out.
They also - this region
has all sorts of phenomena
where coronal mass
ejections start.
This is where magnetic fields
close together creating huge
bubbles of atmosphere and
just like your boiling pot,
they become buoyant and
they pop off the globe
and move into the solar wind.
And those bubbles will
go all over the place.
And when they come and hit the
earth it really wreaks havoc
with the earth's magnetic field
and we always receive aurora
during coronal mass ejections.
And so here's our model,
so there's the magnetic field
we modeled before the event.
Here is that upper part of the
atmosphere we called the corona,
and what we want to do is look
below that and then here's a -
here's that brightness
distribution
and polarized light allowing us
to tease out the kind of gasses
that are circulating in
these magnetic fields.
And then that produces
these two images.
One is a model done
in a computer
and the other one is
what everyone saw, okay?
And just to tell you
which one is which,
the lower one is the real one.
And so we're doing quite
well with the modeling.
We're getting there.
If we really have any
hope of understanding
and predicting space
weather, these are the -
the coronal mass ejections and
flares that occur to the sun
that when they are directed
to the earth can actually wreak
havoc on our electronic devices
and even our power grids.
Then this is a fundamental
thing to do.
So we made major progress
in this particular eclipse.
And then of course there's
the absolute beautiful images
that comes from an event like
this, that everyone enjoys.
That was just one of many things
we learned during the eclipse,
but I want to move on and
talk about how we use eclipses
to explore the solar
system and do a variety
of really important
and unique ways.
And if I can start with a
Cassini at Saturn, okay?
Cassini was orbiting
Saturn for about 13 years.
The Saturn has the
beautiful rings
and it was making
unbelievable discoveries.
What we would call
transformational
science discoveries.
And one of these is the
moon Titan, all right?
Titan is a fabulous
moon of Saturn.
This particular moon
is - has an atmosphere.
That atmosphere actually
is twice as dense
as ours on its surface.
It's made mostly of nitrogen and
it has a variety of trace gasses
of methane and ethane
and other gasses.
This body is so big it's
larger than the planet Mercury.
It's larger than a planet
- the planet Mercury.
And if it wasn't orbiting Saturn
and it was orbiting the sun,
we would call it a planet.
I mean this is really
a very special object.
It's special also because
it is the only other body
in the solar system besides
the earth that has liquid
on its surface, and a lot of it.
Okay? But that's not liquid
water; it's liquid methane.
And so water is important
for life.
And the new concept is if
we want to look at places
where there might be alternate
types of life, you need a liquid
as part of the metabolic
process.
We use water in ingesting
food; it helps the process
of extracting the
energy from that food.
And then water is used for
eliminating the waste, okay?
That process is a
fundamental one that's part
of our definition of life.
And so we want to go to places
where there are liquids.
This one in particular
if there's life
on this moon it's got to be very
different than our life, okay?
And there's a whole field of
study called weird life, okay?
That's what they call it.
Call it weird life where they're
studying these alternate types
of life that would use methane
in substitute for water.
So that means that Titan
has a potential for life.
And so we want to protect it.
Another moon that we discovered
which is on the right;
Enceladus is a small moon,
much smaller than Titan.
It's actually only about 300
kilometers in size, on the order
of the width of California
for instance.
And this particular moon we
found really walls of water.
It looked like geysers,
they looked like individual
events that are occurring.
But when we looked at them
up close it's really from -
emanating from these
cracks from Enceladus.
These are literally walls of
water pouring out of the moon
and it does it all the time.
Anywhere in its orbit,
these cracks are active
and the water is pouring out.
It turns out 95% of the water
falls back down on the moon,
but there is a small
percentage that escapes it
and then ends up
orbiting Saturn.
So, because as I mentioned
the importance of water
as it's connected to life,
then this is a moon we
need to protect too.
Now Cassini, when we launched it
we did not develop the planetary
protection procedures necessary
to keep it completely clean,
you know, so it's got human
microbes all over it, all right.
Even though we develop
it in clean rooms
and that it's important to keep
what we call this bio-burden.
This - this human cells
and life off of it.
We recognize that if Cassini
were to crash into one
of these moons it might
affect the potential for life
on these moons in
important ways,
and we just couldn't
afford to let that happen.
So over time, over time it
was brought to my attention
that we have an opportunity
to dispose of Cassini.
Here is a series of
trajectories for Cassini
as you can see in blue.
They're really wild.
Typically we'll orbit
in a plain,
but you can see these
trajectories are
out of the plain and they're
going in different directions.
And there are certain
nodal areas,
there are certain locations
that are like right here
where a whole series of these
orbits cross and that turns
out to be where Titan
ends up at the right place
at the right time, giving
us a gravity assist,
allowing us to change the
orbit, change the velocity
and therefore, really
make a major difference
in - in its trajectory.
And surveying a much broader
part of the Saturn system.
We did that very effectively.
A set of orbits were
calculated that clearly
as shown in the yellow here.
If we could get the
right gravity assist
from Titan we could just go
on the outside of the rings
and then another gravity assist
would put us inside the rings.
In other words between the
cloud tops and the lower -
the first part of the
ring, the lowest part
of the ring closest to Saturn.
This was really exciting
and enabled us then to come
up with a plan that would
allow Cassini to end its life
as its fuel was running
out into Saturn.
And not - and not have the
possibility of it after it ran
out of fuel, hitting
one of these moons,
one of these precious moons.
So that was proposed by the
project and I am the one
that signed off on it
to end Cassini's life.
The scenario is 42 short orbits
from November 16
to September 17.
And then 20 orbits of that 42
were what we call F ring orbits
just outside the F ring.
And then 22 grand finale
orbits which are inside;
so the F ring orbits are here.
The yellow and the
blue are the last set
of the 22 grand finale orbits.
All right, so how are we going
to do this and do it safely?
This area is full of
ring material, okay?
And ring material that you run
into can affect the spacecraft,
can affect it to the point
of even knocking it out.
So we had to be really careful.
So the start of figuring
out how to get in there,
that was the dynamists
that we're using Titan
to allow us to do that.
But now we had to
be very creative
to say well exactly where,
okay, can we go where we have -
where we can minimize
the ring particles
and then minimize
the opportunity
to damage the spacecraft
such that it would survive
because we wanted to be in
complete control to be able
to ditch it, all right?
It starts with shadows.
The sun in this picture is
behind the planet Saturn, okay?
This image is about an
eight or nine hour exposure
of the faintest light
that's in the Saturn system.
And its light from the sun
that shines on the rings
that reflect back onto the
planet, that then reflect back
out and that's what
you're seeing.
Now what's really spectacular is
you see all sorts of new things.
Here is the orbit
of Enceladus, okay?
The material that is coming from
the plumes, the walls of water
that actually escape
that moon end
up orbiting the planet,
all right?
So that's not very comforting.
That's just full of material.
Here's the F rings, so the
first set of orbits would be
in this area right here.
The next set of orbits
would be right below here.
So, the first thing we're going
to do is figure out how to close
to the F ring we can get.
We're going to take
a really good look
at this particular area
that's shown in red.
Here that area is
blown up and surprise,
we found a couple new rings.
The eclipse technique is the
only way to be able to do this.
So this is Janice
and Epimetheus,
this is a brand new
ring right here we saw.
Pallene ring, this
is the Enceladus ring
and there's the G ring.
And so we want - we
want to get in here.
So this looks like the
best place right here,
all right based on
scattered light, okay?
This is all scattered
light, the ring material
and this looks like the darkest.
That must have the lowest
number of particles.
Now those particles may be the
size of baseballs or bigger,
and very few of them which would
still give you that dark area.
But we're taking a
chance on that, okay?
So if we laid out the
rings and distance
from the cloud tops we
decided then here's the set
of the first orbits
we want to go to.
This is the clear area.
And then from these images
we also decided okay,
we got to hug the planet
cloud tops, all right?
So this ring material actually
is falling into the planet.
We're really very lucky
to be living in a time
where these rings exist.
Because in reality the
ring material is falling
into Saturn, okay?
It's dissipating over time.
And so this particular area
we decided it was the darkest
in our images, we could
probably get away with flying
through here, being hit by
a number of ring particles.
But perhaps the flux
of material raining
down from the rings
is low enough
that we could survive that.
So that's the - that's
the process.
And of course we executed
that in a spectacular way.
Now what we found when we did
this is from that vantage point
over the pole some spectacular
images of these smaller moons
that we could only see from
afar, here's what they look
like from a Ravioli
looking moon,
which this actually
is ring material.
So the orientation of this
image is a little awkward,
but you know the camera takes
it, you use it but the -
this belly band actually
is in the ring plain.
So as ring materials moving
from one part of the ring
into a different ring, it's
crossing this area in pan.
This moon picks it up, okay?
It will pick it up and
accrete it, all right?
And so here's another one Atlas,
this also is embedded
in the rings.
And this is a set
of ring material.
Atlas has an orbit that's not
quite completely co-plainer
with the rings, it's
at a slight angle
and so the ring material has an
opportunity to be sloshed all
over it as you can see here.
And then several
of these objects,
like this on in particular
Helena I believe is the name
of it - can't quite
see it from here.
That looks like a comet.
This looks like what we've seen
before when we fly by comets.
So these big objects
Saturn, Jupiter, Uranus,
Neptune they must also
be capturing comets
as they have gone
along and orbited.
So those are just
some of the surprises.
And of course, we
flew over the pole.
Here's the north pole of Saturn
and we see this spectacular
hexagon pattern, okay?
This is absolutely spectacular.
Now this is the size
of a couple earth's.
So one earth could be like here
and another earth and size here.
So this is just an
enormous region.
We really don't' understand
this hexagon very well.
How come it's set up
in the atmosphere?
It's a jet stream, okay?
And in fact, we've
recognized now
that this is probably
a little higher
than the surrounding
clouds, okay?
Down here at lower latitudes.
This is of course, what
we would call hurricane.
The one that's coming this way
would be itty bitty compared
to the size of this one, okay?
Yeah that's comforting.
And then this particular feature
which is another spectacular
feature we've taken a really
good look at and you can
see based on the shadows
that these are beautiful
cloud structures swirling
around the pole.
This is exactly the
pole of Saturn.
And indeed these cloud
structures like cumulus clouds,
just reach way up into the sky.
And so this is the cloud
dynamists were just really
enjoying the observations that
were made in these dynamics
that they're seeing now.
Now this is an artist conception
of what happened in pretty much
in the final orbit and indeed
because we had on the order
of 22 orbits that we did,
the last orbit was the
last little kiss by Titan
and it enabled it then to
shorten the orbit well enough
to begin to enter
the atmosphere.
This is indeed what happens,
the spacecraft would
burn up on its way in.
But we put in the process,
executed the antenna
hold process such that
as the spacecraft was going
in it was communicating back the
data - back the data to earth,
and going through the
atmosphere and being moved
around in the atmosphere and
would constantly fire it's jet
and reacquire the earth,
make sure we got -
we got the data back.
We got some unbelievable
spectacular upper atmospheric,
ionospheric profiles and data
that were really astounding
and - and some of the
chemistry is quite different
that we ever expected.
I don't know why we didn't
think of this but indeed
as the ring materials flowing
into the planet it's
creating a rain
of organic material that's
falling onto this body.
And so the chemistry
is really exotic, okay?
That we found and so this
is actually a mosaic made
up of quite a few images,
but the last orbit just
before it went around and then
into the planet on
the other side.
And as you can see the sun,
the sun is on that far side.
And the earth is
not in view here,
but is definitely would be able
to see the spacecraft
in that final orbit.
That's how we organized it.
And it was just a
spectacular event.
That whole event was
a broadcasted live.
And the Cassini outreach
team won an Emmy this weekend
for that live broadcast.
It was done so well.
It was sprinkled in with
a variety of interviews
and some emerging science that
was coming out, we were talking
about that and in and
out of the control room,
and it was quite an
emotional event for many of us
because this spacecraft had
done so much for us to learn
about these gas giants.
So I'm just thinking
back of course.
New horizons, now here's
another planetary mission,
flew by Pluto.
Let me go back here.
What you may not know is this
mission was launched 2006,
January of 2006, encountered
Pluto July 14, 2015, all right?
When it was launched
we didn't really know
where Pluto was, all right?
Now that sounds pretty strange;
what do you mean we didn't
know where it was, okay?
We used Kepler's Laws.
Kepler's Law tell us
where planets are.
And for Kepler's
Laws to work we have
to watch the body make a
complete orbit, all right?
So one orbit of Pluto is on
the order of you know 248 years
and we just discovered it
85 years ago, all right?
So we had a piece of the orbit
and we can draw 1,000 orbits
between those observations,
all right?
Now when we flew by
Pluto because it was four
and a half hours light travel
time from the spacecraft
to us we had to have
everything on automatic pilot.
So, when we said okay point
your camera and take a picture
of Pluto and we pointed
it, Pluto better be there.
Okay? And if it's off by 1,000
kilometers we'd be looking
at sky, all right?
So how were we going
to solve that?
How are we going to solve that?
We're going to start solving
these things by looking
at precise measurements
of where it's at, okay?
And it starts with occultations.
An occultation are when as
we see the body you know move
in the solar system and there
are stars in the background
that are much further away,
they pass in front of that star,
that star light goes away.
And by timing it we can
get idea of all kinds
of things whether the body has
an atmosphere, its distances,
its size, whether there's
moons, whether there's debris,
understanding if there's
debris in the way.
We could be flying by Pluto
and get smacked by all sorts
of smaller debris that you
just can't possibly see.
We can hardly see Pluto itself,
you know which is on the order
of 2,000 kilometers in size, you
know like the state of Texas.
It's a country of its own right.
So, we had an opportunity
using Sophia
to take an occultation
measurement.
And so what you do in these
measurements is you sit there
and look at Pluto, study
it, watch it move, okay.
And then have it pass
in front of a star.
And so here's the star light
that we're steadily measuring
and all of a sudden
Pluto starts to pass
in front of it, down it goes.
And then it comes back.
Now this is what we saw.
If Pluto did not have
an atmosphere at all,
this would be what we
call a square wave.
It would follow that black line,
go right down, go right back up,
that's what - that's
what we should see.
If it didn't' have
an atmosphere.
But it does.
And so that atmosphere starts
to attenuate what we call reduce
the light from the star, okay?
As we see it, and in this
configuration so down it goes.
And then when that star is
directly behind the planet it
illuminates the atmosphere,
so the light comes -
bends around the
atmosphere and we get
to see this little flash, okay?
So this flash right
here tells us also a lot
about the atmosphere too,
and then we get the
compliment on the other side.
These were critically
important observations,
that plus many other
observations including Hubble,
including New Horizons which
would take navigation images
as it's moving towards
the target and allowing us
to triangulate it, gave
us a really good idea
as to where Pluto was.
And of course, this is
the spectacular body.
It surprised me and I'm
not easy to surprise
but this is an active body.
Its atmosphere is
modifying its surface.
This heart region that we see,
actually this is an impact
for which the atmosphere's
collapsed into it.
Pluto's atmosphere
is largely nitrogen
and so this is nitrogen snow,
ices that end up in this area.
That actually move on the
surface like toothpaste.
You know it's not as solid.
And then - and then there's
all sorts of these dark regions
that we then had an opportunity
to really get a good idea
as to what the chemistry
of those areas are.
But one of the things that
we absolutely plan to do
when we flew by Pluto and
got on the other side is
to take this image, okay, this
is Pluto in our rearview mirror
and the sun is directly
behind it.
And it is illuminating
the atmosphere just
like the occultation
image from Sophia.
And this enabled us then to
then take a really good look
and high resolution of what
this atmosphere looked like
and it's banded, and then
we could get composition
and all kinds of
information about it.
Now as Evista, when you look at
this you know this is glacial.
These are high mountains.
I don't see any craters
in any of this, all right?
You couldn't go any
place on the moon,
certainly over the scale
length and much smaller even
without finding craters.
Now that doesn't mean
this body hasn't been hit.
It's been hit plenty of times.
It should look more
moon like than it does.
And this is why we know this
body is very active still today.
And the atmosphere and land
interactions are quite strong
and it's modifying the
surface of the planet.
One of the exciting things was
we could look at the atmosphere
and what we found out is
the methane that Pluto has
from sunlight and
also from hitting -
being hit by solar wind
creates new molecules, ethaline,
acetylene and these are chains.
And these chains
can come together
and when they get heavy enough
as they - as they continue
to combine they will drop
to the surface of the planet
and that means it will
snow these compounds.
And we call these complex
carbon compounds tholins.
And we can actually go in
laboratory and make them, okay?
We know - we know
what they consist of.
And in fact, when
- when you look
at Pluto here is the regions
where tholins continually
snow out.
This turns out to be close to
the equatorial band of Pluto.
The pinkish colors now
we're coloring Pluto based
on composition.
The pinkish colors actually
are water, there's a lot
of water on its surface.
It's frozen.
It's frozen so solid it's
harder than granite, okay?
Harder than granite
here on earth.
We see all kinds
of ammonia snows,
and then we can see
the carbon monoxide
and the nitrogen snows too.
So really spectacular and it's
because of the occultation
technique
that helped us find it, and
the occultation technique
that helped us even
do more research
on the atmosphere of Pluto.
Now we're moving on to another
object, New Horizons is going
to fly by a smaller building
block, a Pluto like objects;
it's called - when it was
found in 2014 by Hubble,
no ground based telescope
can see it.
Only Hubble has been able
to see this object, okay?
And so this is the nomenclature
of anything you find starts
with the date, the letters
and numbers are all
about calendar time.
And so this was seen in October
of 2014, it's called MU69
and we had a contest
as to what to name it
at least provisionally and
it's provisional name is called
ultima thule, okay?
So what we found is that MU69
is it's moving in its orbit
because we don't really
know where it is either.
You know this is going to be,
you know 380-400 year orbit
and we just found it in 2014,
just four years ago, okay?
So we're going to have to
use every trick in the book
if we're going to repay figure
out where this object is
so we can fly by
it and not miss it.
Okay? So we found out that there
are with the star back ground,
opportunities to
do occultation's.
What we know about this region
of space called Kuiper Bet
for which - for which
Pluto is a member
of the Kuiper Belt is there's
tens of thousands of objects,
Pluto-like objects and objects
like this building blocks
of Pluto's and many of them are
binary, are multiple objects.
30% of these are viewed
as multiple objects.
And so if this then works out
we can watch an occultation.
Even though we can't see the
object, if we can just look
at the star and watch the
light go away, that object had
to be moving in front of it
blocking that light, okay?
Even though we can't
see the object.
Last year 2017 we had
three occultation's.
Here they are as they
are over the globe, okay?
As you can see, we don't have a
lot of land to go to, all right.
So Sophia actually we used
Sophia to go out in the ocean
and get this one and then we set
up observations in South America
and South Africa and then
South America for each
of these occultation's.
And this was really hard to do.
Now how you do this
is you calculate
where you think this shadow
is going to be as it races
across the country at
53,000 miles an hour, okay?
And you create a picket
fence of telescopes, okay?
So here's the telescopes
and they're -
each of these are
looking at the star, okay?
And you're hoping that that
shadow that you're only backing
out and guessing where
it's going to be based
on your best calculations
and the knowledge of position
of that star, casting
that shadow
so you want this picket
fence to be long enough
so that you actually catch
the winking of the star.
Now here's the telescopes.
The stars are bright
enough that the telescope
like this works great.
And it's all about timing.
It's all about taking
measurements of star image,
you know what's it's intensity
over and over and over again,
many, many, many, many times
per second in the hopes that -
that it will wink,
it will wink at you.
It will come and go.
And then you get that timing.
So here's from one
of the telescopes
looking at the star field.
So has everyone seen
where MU69 is?
Right here in the center
and it passes right in front
of that star, and
the star winks.
Okay? That's it.
Now we know where it's at.
And the picket fence you know
many of these telescopes saw it.
When we put the observations
together from these telescopes
so - so here's the set of
observations where it winked,
so that's one telescope.
Another one, another
one, another one,
if we had a telescope here
sometimes we have operational
problems, sometimes
they're cloudy,
sometimes it just
doesn't work for us.
And then we got another one.
So here's the original
data, all right?
Now you're going to try to
figure out what this object is.
Is it - does it look like
this or does it look -
is it actually two objects.
Is it actually like the rest
of the Kuiper Belt objects
where they're binaries?
There's several of them.
Now that's important because
that means this stuff is
still accreting.
They're still trying
to come together
and there's probably
debris all over the place.
So that's kind of a
tough thing to swallow.
So here's an artist conception
of what they might look like,
but we're flying by Ultima thule
on January 1, 2019, all right?
And when we observe it, it
will be the first time we will
observe a building
block of Pluto.
This is a very different
building block,
than a building block
of the earth, all right?
These will be made
mostly of ices, all right.
And this particular object we
believe, if its two as we see,
we don't quite know the size,
but if it's one object it's
on the order of 30
kilometers in size, all right?
Okay which is much smaller
than even Enceladus
at 300 kilometers.
All done by occultation's.
All right.
Other ways we use shadows, we'll
talk about eclipses, all right?
So we have a telescope
called Kepler.
It looks at star light
and it makes a measurement
of the brightness of that light.
And when it drops like this,
then an object is
past in front of it.
And the bigger the object,
the bigger the drop, okay?
And it's that technique that
tells us about exoplanets.
Tells us about planets
orbiting other stars, all right.
And Kepler does that by
looking at 120,000 stars all
at once, all the time.
And it did it for nearly
two years, all right?
From that data we then started
to call out of that what kind
of planets are they,
how big are they?
Now as you can see the depth
of that curve tells
us about the size.
The orbit can be calculated
based on how long -
how long that reduced
intensity was, all right?
So the further the planet
is away, the slower it moves
and therefore the longer
it takes for it to come
across the disc of the planet.
And so the light will be
low for longer periods
of time the further
the orbit is away.
So we can get size and
we can get orbit, okay?
And of course we
can also get number.
So if we plot the
number of planets
that Kepler has been observing
during this time period
and their size, here's
the distribution.
To me this is shocking,
all right?
It's shocking because I felt
that what we would see would
be planets that are dominated
by Jupiter size objects, okay?
Here's Jupiter, all right?
Now here are earth size objects.
So at any - any solar system
that you go exo solar system
you know, we are equally likely
to find Jupiter as we are an
earth sized terrestrial planet.
But the surprise was this set
of planets right here, okay?
Huge number of planets that are
terrestrial planets that are
about one to two times the
size of the earth, okay,
and that was a shocker.
We don't have - we don't
have a planet like that.
There's no planet like
that in our solar system.
These are called super earths.
Now we can see Neptune's -
Neptune make it a little bigger,
now Neptune is - as you can see
three to five times the radius
of the earth, all right?
You can create these gas planets
that are further away from the -
further away from Jupiter.
We had no problem with that.
We did - suspected there'd
be a range of gas planets.
But super earths are
completely different objects.
So we now know that they're
terrestrial planets and the -
when we follow up with
other observations
and can find the density
of these planets then
our models tell us some
of these planets
are water worlds.
That there's huge oceans on
many of these bodies, okay?
So an earth has a core,
mantle and a crust.
In a similar way we expect super
earth's that are made close
to the parent start be
primarily earth-like all rocky,
and of course even though there
are one to two times the size
of the earth, the density
might be as much as 10 times
that of the earth, okay?
So talk about heavy, all right?
You know bodies are very heavy -
gravity on the surface is
very much higher than ours.
And then there are those
for which the density
tells us there has
to be an extended envelope.
This is an artist conception, so
the ocean isn't really that big
but it's an ocean atmosphere
because it will be evaporation
going on and an extended region
but covering the planet.
So these super earth's are
generated further from the star
where water could actually exist
without being boiled
off or frozen out.
So pretty - pretty
spectacular planet.
So why won't we have
a super-earth?
Well we don't know.
We don't' know but it's probably
because of Jupiter, all right?
Jupiter has robbed us of
another planet that was forming
that would have been
in the asteroid belt.
The asteroids that we have that
exist in the region between Mars
and Jupiter are trying
to become a planet.
But Jupiter robs them
of that opportunity
because as they crash and then
reform into a bigger body,
they crash disperse,
but Jupiter's gravity
pulls these parts away
and makes them more
difficult to get together.
And that's why they haven't come
together because of Jupiter.
It's also because - Mars is
a rut because of Jupiter too.
Mars is a terrestrial planet
much smaller than the earth.
Now if we didn't have Jupiter,
we may have had a
super-earth there, okay?
And if it's a super-earth there
trying to create a space program
to go to a super-earth
land, rove, look at it
and for human exploration
to get off of it,
that would be really difficult.
So in a way thank
goodness for Jupiter
because it's made Mars a runt
and made it accessible to us.
We can land on it, we can walk
around and we can leave it.
We can actually blast
off from that planet
without having the
infrastructure we have
at Cape Canaveral.
So other - in the future for
eclipses are really shown here.
This is an eclipse in
our own solar system.
This is Venus.
This is our sun.
An indeed you can see the
sunlight illuminating the
atmosphere as it is
bent around the planet.
And it's during these times
we want to take a spectra.
It's during these times we want
to tease out what it looks like,
would it look like Mars,
would it look like Earth,
would it look like Venus.
So our future missions to
really look for exoplanets
with atmospheres and then
what those atmospheres are
and whether they
could be habitable
with life is indeed
going to be done
in these eclipses,
just like this.
And so here would be a
detailed spectra of earth
in that same position where we
can tease out of it all sorts
of variations in that
spectra attributed to life.
So our future missions are
really going to be moving
in that particular area.
So finally, let me end with
a shameless plug, okay?
This is my podcast, it's
called Gravity Assist,
in its second season
it's pretty popular.
We have an enormous
number of downloads.
It's about 20 minutes long
and I talk to the scientists
of the day that are deep
into these discoveries.
They really understand
what's going on
and can explain it really well.
Things that we talk about
won't be in textbooks
for perhaps a half a
decade or even a decade.
And it just gives
you a great feeling
for how fast a whole field
is - whole field is moving.
Get it on iTunes.
You can also go to
NASA and pull it down.
All right, well thank
you very much
and I hope you've enjoyed
how we use eclipses
to do some pretty
spectacular science.
[ Applause ]
>> Stephanie Marcus:
I'm going to blame all
of my problems on Jupiter.
We'll have time for some
questions, those of you
that have to leave, leave.
But a few questions
for the speaker
and he will repeat the question.
>> Dr. James Green: Yes sir?
>> Dr. Green, just curious,
we've seen photographs
of the earth and [Inaudible]
we've got [Inaudible] liquid
lava and [Inaudible].
For the sun, if we live the
science fiction we're going
to be able to go straight
toward the center of the sun.
Is there a solid
aspect to the center
or will you pass all the way
through some plasma
radiating out?
>> Dr. James Green:
It's all plasma,
all the way through the center.
Yep. Now it's under
enormous pressure,
and so the density
increases radically.
So repeating the question,
is the sun have any
soli aspects of it?
And the answer is no.
It's all plasma, its all gasses.
It's just under different
pressure scenarios.
Yes sir.
[ Inaudible ]
>> Dr. James Green: We know
the ice on Pluto is harder
than granite by going
into the laboratory,
reproducing the conditions.
And freezing it.
In fact, we know
water, H2O as we take it
down in temperature
it's not like -
like the ice cube you
put in your drink.
The whole matrix of water
can get closer together
and making it harder.
It readjusts itself and so we -
we have actually
several divisions
of that lattice structure.
We call it ice one, ice two,
ice three, ice four, okay?
And then so when you find the
temperatures and pressures
and look at the conditions,
the only way water can
exist is in the structures.
And then reproducing
in laboratory tells us
how strong they are.
Yeah. Yes sir?
[ Inaudible ]
>> Dr. James Green:
The question is how -
how did we get all the nitrogen?
Why is that so abundant?
It's got to be a major part
of our collapsing cloud.
Nitrogen is what we
call an inert gas.
It doesn't react.
It doesn't create whole
slew of stuff, it compounds.
And so it's - it's
very important gas.
We have a significant
amount of it here.
Venus has virtually
none, all right?
Mars has a little but not
a lot and as you go further
out in the solar
system we see a lot of -
a lot of these places are
dominated by nitrogen.
We've been able to hang onto our
nitrogen and perhaps that's one
of the reasons why
we have life here.
So it's actually
kind of connected
to our - to the life question.
But it came from the
original collapsing cloud.
Yes sir?
>> Kind of a culture question.
What are your thoughts on the
big Pluto, no planet, planet?
>> Dr. James Green:
so what do I think
about Pluto being a planet.
So I can - I can tell you
as a NASA employee
that we don't care.
We don't care if the -
I'm a planetary scientist,
so I don't care if astronomers
run around calling it you know,
itty bitty dwarf planet or
whatever they want to call it.
Because this object is well
worth studying in its own right.
But when we flew by
it and you look at it,
I am absolutely shocked
by what I saw.
It has an atmosphere.
It is an active body.
It is modifying its surface.
I can list a gazillion
things about it
that happen just
like a planet, okay?
And so I think, now I'm going
to give you my personal
perspective.
That whole definition needs
to be revised, relooked at.
Now that we've flown by
Pluto and taken a good look
at what these objects are like.
Just because it's small
doesn't mean it's -
it doesn't have planet
like features.
And it's got a bunch of them.
>> As Chief Scientist, perhaps
you can make that your mission.
>> Dr. James Green: There's
only so much I can do.
Yes sir?
>> Activity implies energy.
If there's activity on Pluto is
most of it coming from gravity,
interactions with its moons?
>> Dr. James Green: So
activity implies energy;
so where is the energy on Pluto?
Really great question.
We've been after that.
So part of that is sunlight.
Another part is that it must
be coming from the interior.
This is brought up the idea
that Pluto actually has an
under crust, deep in its
interior a layer of water.
And that water is starting
to go from liquid to solid.
That liberates heat and that
creates heat that's moving
through the body, okay?
So that whole concept is
how we get to the place
where we believe Pluto
is a water world, okay?
It's got - it's got a layer
of water underneath it.
Now we also believe
that that's the case
because that heart region
where the nitrogen ices are
is very depressed, okay?
It's where the least gravity is.
And it is exactly
opposite Sharon, okay?
And so wherever that
impact occurred,
that whole planet
shell shifted such that
that least gravity was
exactly opposite Sharon, okay?
That fits perfectly
well with that idea too.
And those are exactly
the questions we answer
and these are the things that
we come up with to great effect,
that give us great confidence
that Pluto is indeed
a water world.
Yes?
[ Inaudible ]
>> Dr. James Green: Yeah, so
what kind of tools are we using,
like on the exoplanets when
we look at an atmosphere.
How are we going to do that?
We know what to do.
Most of the instruments
that will make those kind
of measurements haven't
been developed.
We have thoughts on
what they need to do
and what they need to be.
And we're investing in some
of the instrumentation
in those areas.
It's going to take several you
know, many years to be able
to develop and perfect them
and then figure out a way
to test them, you know
perhaps with other eclipses.
We'll find a way to do that and
then - and then launch a mission
that has those kind
of instruments on it
that will really tease it out.
Now we're sort of getting
close with the web telescope.
Web telescope can look
at the atmospheres
of bigger planets, okay?
Because typically the bigger
planets are further away
from the suns.
And the - the light that -
those planets receive are coming
from the suns, absorbed
in the atmosphere
and then that's a
perfect wave length regime
for web to tease out.
So we'll make a huge stride
with web, particularly
on the larger planets,
but we can't quite get
down to an earth
size atmosphere yet.
That's going to require
some technology development.
>> One more, just one more.
>> Dr. James Green: Yes sir.
[ Inaudible ]
>> Dr. James Green: So
the question is I did talk
about some pretty spectacular
discoveries, but I didn't talk
about or dwell on the discovery
of water everywhere, okay?
That's my other lecture
called the search
for life beyond earth.
So perhaps next year I'll
be invited back and we'll -
then that story is
all about the water.
>> Stephanie Marcus:
Okay start working on it.
Maybe we'll get one
on weird life too.
>> Dr. James Green: Well
that would be part of it.
I'll talk about what we
know about weird life.
Yeah. Yeah that will
draw in an audience.
>> Stephanie Marcus:
Thank you again.
>> Dr. James Green:
Thank you very much.
[ Applause ]