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All across our solar system,

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scientists are discovering
thrilling new worlds,

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dwarf planets.

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They may be small,
but they're full of riddles,

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oceans of subterranean water,

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ice volcanoes,
and vanishing mountains.

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The whole idea
that dwarf planets are small

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and insignificant and boring

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has just been shattered
in the last few years.

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Dwarf planets defy
many of the rules

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we thought governed
our solar system.

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Dwarf planets are
very interesting bodies

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scientifically,

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but beyond that,
they tell us something

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about the origin
of our own world.

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Believe it or not,
they may harbor life.

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Dwarf planets are
rattling the cages of scientists

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and shaking up our understanding
of how the universe works.

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They may have fed
the early planets

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and even seeded them
with the precursors of life.

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Dwarf planets just may be
the most important objects

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in the solar system.

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Our solar system has
eight confirmed major planets,

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but we're discovering
many other small worlds

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called dwarf planets.

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We used to think they were just
dull lumps of rock,

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but the more we study them,

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the more shocking
and intriguing they become.

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Naively,
I would expect these objects

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to not be terribly dynamic.

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They're probably just, you know,
airless, rocky, icy worlds,

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and they're just sitting there,

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and what we're finding out is
that that is not true at all.

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There is all kinds of stuff
going on.

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They're full worlds
with really interesting geology

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and interesting histories

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that can tell us a lot
about the solar system.

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Scientists believe there may be

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hundreds of dwarf planets
in our solar system.

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So far,
we've only identified six.

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Five of them...
Pluto, with its moon, Charon;

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red-colored Sedna;

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bright, distant Eris;

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makemake,
and bean-shaped Haumea...

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All live billions of miles
from the Sun,

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out beyond Neptune
in the Kuiper belt.

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They're just
the tip of the iceberg.

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There are probably many,
many more dwarf worlds

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that are out there
waiting to be discovered.

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The sixth dwarf planet, Ceres,

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lives in the inner solar system.

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It orbits around
260 million miles from earth

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in the asteroid belt.

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The asteroid belt
is a region of the solar system

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between Mars and Jupiter,

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and this is where
most of the asteroids are.

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This is rubble

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left over from the formation
of the solar system.

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In early years
of the solar system,

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small rocks collided with
one another, stuck together,

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and built
the rocky inner planets.

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Dwarf planets grew
in the same way.

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Ceres was actually
starting to get pretty big.

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It was on its way
to becoming a planet

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before it stopped growing,
and that makes it

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stand head and shoulders
above everything else there.

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So why is Ceres called
a dwarf planet and not a planet?

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To be a planet, it must tick off
three cosmic boxes.

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First, it needs to be a sphere.

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Second, it needs to orbit
the Sun and not another body.

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Third, it needs to clear its
orbital area of orbital debris.

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Ceres ticks
just two of the boxes.

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It is a sphere,
but a small one...

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Only 600 miles across.

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That's the size of Texas.

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It orbits the Sun, but it hasn't
cleared its path of debris.

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It's surrounded by asteroids,

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so it misses out
on being a planet.

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Even though we call
these objects dwarf planets,

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small and dwarf
does not equal insignificant.

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But being small
does have its problems.

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When the molten core
of a young dwarf planet cools,

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so does the heat engine
that drives geologic activity.

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Ceres, we thought, would
basically be a big, dead rock.

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It's a small body.

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It should have
cooled off long ago.

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Nothing very interesting
is going on,

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and when we actually
got out to Ceres,

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nothing could have been
further from the truth.

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March 2015, NASA's
dawn probe arrives at Ceres.

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As the dawn spacecraft
pulled up to Ceres,

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we saw the craters and the
surface that we expected to see,

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and then all of a sudden,

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something totally mysterious
rotated into view.

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One of the craters
had two bright spots,

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almost like two eyes
staring right back at us.

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It was such a puzzle
to the science community

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because what are these
doing here?

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Are they ice?
It looks very fresh.

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What on earth could it be?

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Scientists find over 100

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of these mysterious white spots.

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The largest is in a 50-mile-wide
crater called Occator.

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They are, unexpectedly,

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made up of a substance
we find on earth...

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Sodium carbonate,
a kind of salt.

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We believe the salts on Ceres

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as actually very young.

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We think they're as young
as 4 million years old,

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and that's basically like
yesterday in terms of geology.

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And that is super weird, right?

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That's happening not on sort of
on a geologic era.

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It's happening now, today.

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What could cause patches of salt

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on a world long-presumed dead?

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Planetary geologist
Jani Radebaugh believes a clue

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might be found at mono lake
in California.

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All right, I'm here looking at
this beautiful lake

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off in the distance

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and standing on
massive white deposits.

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These white deposits
used to be a part of this lake,

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at one point.

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The lake had dissolved
a lot of the materials in it,

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and then as it receded,
it left behind the materials,

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as it evaporated away,

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and these things are,
you know, salts.

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They're kind of granular
in texture,

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and just to make sure,
we taste it

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and yeah,
sure enough, it's salty.

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The salt at lake mono

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crystallizes
as the water evaporates,

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the only way it can form.

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The researchers believe
the same process

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is taking place on Ceres.

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This means there must be liquid
water beneath the surface...

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...but how, out in the deep
freeze of the asteroid belt?

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These bright spots are located
in the centers of craters.

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They're located around
cracks in the surface,

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and that is telling us
that this material

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is coming from under the surface
and welling up onto it.

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Absolutely nobody expected
there to be liquid water

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beneath the surface of Ceres.

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We cannot explain
what is keeping that water warm.

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On some moons,

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gravitational tugging
keeps the interiors warm,

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but Ceres is not really near
anything else that's very large.

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So the amazing thing is that
we may not even understand

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how rocky planets work.

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There may be
another source of energy,

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another mechanism
for heating the interior

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that we haven't even
discovered yet.

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To find out how Ceres
has liquid water,

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we have to rewind the clock
4.6 billion years.

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Debris left over
from the formation of the Sun

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slams together
to form the dwarf planets.

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As they take shape,
the heavier, rocky material

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sinks to the center
and forms a hot, molten core.

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Slushy water-ice
floats to the top.

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For a while, it stays liquid,
but once the core cools,

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it freezes and forms
the solid mantel and crust.

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That surface
should still be solid,

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so the salt patches
remain a perplexing mystery.

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We still haven't
answered the question,

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"how could there actually
still be liquid water on Ceres?"

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That's still
a hard question to answer.

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One way this could happen is if
it's not actually pure water,

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if you've mixed it
with something else.

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Some scientists have proposed

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that a salty ocean
lies beneath the surface.

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The high concentration of salt

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lowers the freezing point
of the water, keeping it liquid.

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When asteroid impacts
fracture the crust,

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this salty water
oozes up from below.

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The liquid swiftly evaporates,
but the salt remains,

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leaving a brilliant white spot
on the surface.

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In fact, I'm willing to bet

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there could be water
coming up now,

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bringing salts up
to the surface,

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evaporating away into space,

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and that means liquid water
is very close

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to the surface of Ceres
right now.

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Ceres has an even more
startling card up its sleeve.

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Recent research suggests
that it's an immigrant.

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It didn't form anywhere near
the asteroid belt.

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Ceres may have been born

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alongside hundreds
of other dwarf planets,

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many billions of miles
away from the Sun.

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So how did it get here?

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Most of the
dwarf planets we've discovered

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lie far out in the solar system
beyond the orbit of Neptune,

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but Ceres orbits
between Mars and Jupiter

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in the asteroid belt.

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But its location
isn't the only hint

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Ceres might be an interloper.

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Normally, celestial objects
are made of the same materials

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as the other bodies
in their neighborhoods,

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but that's not the case
with Ceres.

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The asteroid belt is mostly
made up of dry, rocky bodies

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composed of
the same heavy elements

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that form
the rocky inner planets.

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Ceres is very different.

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Ceres is essentially
an icy world, right?

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It's made out ices
instead of rocks,

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and so that's kind of weird,
considering where it is.

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The ice on Ceres
also contains chemical compounds

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that in the early years
of the solar system,

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didn't exist in
the asteroid belt.

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The more we learned about Ceres,

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the more mysterious it became.

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One of the things is that Ceres
has quite a lot

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of ammonia on it,
and we don't find ammonia

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anywhere near the inner part
of the solar system.

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But we do find it
in the outer solar system.

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We've detected ammonia on Pluto,
its moon Charon,

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and out in
the frozen Kuiper belt,

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where we find
the other dwarf planets.

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We think that the origin
of that ammonia

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would've had to be in a very
cold part of the solar system,

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colder than
where we find Ceres today.

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But how an icy
dwarf planet with ammonia

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came to inhabit a place
where ammonia can't form...

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That's a huge puzzle.

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This suggests to us that Ceres

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perhaps formed
in the outer solar system

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and then migrated inwards

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to its present location
in the asteroid belt.

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We used to think

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that planetary orbits
were completely immutable,

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that they simply
ran like clockwork

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and they didn't move around.

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Now we know that
that's not the case.

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In the early stages
of planet formation,

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planets move around
through the gaseous disc

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that encircles the young sun,

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much like rafts that are
pushed around by ocean currents.

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Ceres' ammonia
suggests that dwarf planets

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rafted around
on the cosmic ocean

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along with the young planets.

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Ceres is sort of a smoking gun
that solar systems

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are much more dynamic,
much more dramatic than we know.

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There's mounting evidence

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that Ceres formed
farther out in the solar system

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and something brought
this little world in.

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What could possibly
have done that?

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The answer
is the planet Jupiter.

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00:14:02,690 --> 00:14:04,360
After it first formed,

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00:14:04,360 --> 00:14:07,690
the giant planet migrated in
towards the Sun.

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00:14:07,700 --> 00:14:11,160
Its massive gravity disrupted
the orbits of other bodies

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in the solar system,
including that of Ceres.

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00:14:15,910 --> 00:14:20,370
The solar system formed
out of a disc of gas and dust,

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and as Jupiter formed,

252
00:14:21,980 --> 00:14:23,980
it would've been plowing through
this material.

253
00:14:23,980 --> 00:14:25,710
And if it plows through
that material,

254
00:14:25,710 --> 00:14:27,180
it's experiencing drag.

255
00:14:27,180 --> 00:14:29,850
As it was losing energy,
it would start to move in

256
00:14:29,850 --> 00:14:33,390
toward the Sun
relatively slowly.

257
00:14:33,390 --> 00:14:37,590
Ceres formed in the
outer edges of the solar system.

258
00:14:37,590 --> 00:14:39,930
It was dislodged
from the Kuiper belt

259
00:14:39,930 --> 00:14:44,330
and yanked inwards
by the migration of Jupiter,

260
00:14:44,330 --> 00:14:48,740
and when Jupiter
stopped migrating, so did Ceres.

261
00:14:48,740 --> 00:14:54,680
It settled into a new, stable
orbit in the asteroid belt.

262
00:14:54,680 --> 00:14:56,280
Once you realize

263
00:14:56,280 --> 00:14:58,550
that something that strange
and dramatic can happen,

264
00:14:58,550 --> 00:15:00,810
that a dwarf planet can form
far out in the solar system

265
00:15:00,820 --> 00:15:02,220
and be brought in,

266
00:15:02,220 --> 00:15:04,950
it makes you wonder how
many times that happened before.

267
00:15:04,950 --> 00:15:07,490
Could there have been other
generations of dwarf planets

268
00:15:07,490 --> 00:15:09,090
that got thrown in
towards the Sun

269
00:15:09,090 --> 00:15:11,490
or maybe were thrown out
of the solar system entirely?

270
00:15:17,030 --> 00:15:20,170
Scientists believe
that squadrons of rocks

271
00:15:20,170 --> 00:15:21,900
and icy dwarf planets

272
00:15:21,900 --> 00:15:24,910
may have hurdled into
the solar system.

273
00:15:24,910 --> 00:15:26,710
Hundreds set out.

274
00:15:26,710 --> 00:15:28,980
Only one survived.

275
00:15:28,980 --> 00:15:31,250
If there was a population

276
00:15:31,250 --> 00:15:32,710
of small dwarf planets

277
00:15:32,710 --> 00:15:35,320
in the outer solar system
that migrated inwards,

278
00:15:35,320 --> 00:15:39,050
Ceres might be the sole
survivor, the only one left.

279
00:15:39,060 --> 00:15:41,660
So if Ceres
settled into its new home

280
00:15:41,660 --> 00:15:43,120
in the asteroid belt,

281
00:15:43,130 --> 00:15:46,860
where are the rest of the icy
worlds and the water on them?

282
00:15:46,860 --> 00:15:49,000
The idea that Ceres
may have moved in

283
00:15:49,000 --> 00:15:50,730
from the outer solar system
is interesting,

284
00:15:50,730 --> 00:15:52,600
but why should it be important
to you?

285
00:15:52,600 --> 00:15:55,670
And incredibly, the answer
might be inside your own body

286
00:15:55,670 --> 00:15:56,870
right now.

287
00:15:56,870 --> 00:15:58,740
For the longest time,
we've wondered

288
00:15:58,740 --> 00:16:01,540
where did the majority
of earth's water come from?

289
00:16:01,540 --> 00:16:03,280
When you think about
where the earth is,

290
00:16:03,280 --> 00:16:04,810
how close it is to the Sun,

291
00:16:04,810 --> 00:16:06,480
there shouldn't have been
any water here.

292
00:16:09,820 --> 00:16:11,890
Understanding
the evolution of Ceres,

293
00:16:11,890 --> 00:16:16,020
from where it formed
to where we find it today,

294
00:16:16,030 --> 00:16:18,960
could also lead us to understand
how the earth can end up

295
00:16:18,960 --> 00:16:21,760
with more water
than we would otherwise expect.

296
00:16:21,760 --> 00:16:23,830
When the earth formed,

297
00:16:23,830 --> 00:16:26,630
it was too hot for water
to exist on the surface.

298
00:16:26,640 --> 00:16:29,840
Perhaps the squadrons
of dwarf planets

299
00:16:29,840 --> 00:16:31,510
broke up on their journey,

300
00:16:31,510 --> 00:16:35,380
showering earth with
water-rich lumps of rock,

301
00:16:35,380 --> 00:16:38,240
enough to fill earth's oceans.

302
00:16:38,250 --> 00:16:41,250
Amazingly, when we
study the chemistry of water,

303
00:16:41,250 --> 00:16:44,990
the best match is that
the water in your body right now

304
00:16:44,990 --> 00:16:46,990
came from asteroids themselves,

305
00:16:46,990 --> 00:16:49,520
asteroids and dwarf planets
that rained down

306
00:16:49,530 --> 00:16:52,730
and hit the earth
over billions of years.

307
00:16:52,730 --> 00:16:56,530
Dwarf planets
may have brought something else.

308
00:16:56,530 --> 00:17:00,670
February 2017,
scientists announce

309
00:17:00,670 --> 00:17:03,540
the discovery
of organic materials

310
00:17:03,540 --> 00:17:05,410
on the surface of Ceres.

311
00:17:05,410 --> 00:17:07,540
On earth, life uses water

312
00:17:07,540 --> 00:17:10,340
and organic chemistry,
carbon-based molecules.

313
00:17:10,350 --> 00:17:12,810
The intriguing thing
about the dwarf planets

314
00:17:12,810 --> 00:17:14,420
is that they have both of those.

315
00:17:14,420 --> 00:17:16,620
Pluto and Ceres
have organic molecules.

316
00:17:16,620 --> 00:17:18,620
There's liquid water
below the surface.

317
00:17:18,620 --> 00:17:21,290
There's a source of energy
that warms the interior.

318
00:17:21,290 --> 00:17:24,160
It is not at all impossible
that somewhere under

319
00:17:24,160 --> 00:17:27,760
these cold, icy surfaces,
there could be life.

320
00:17:27,760 --> 00:17:30,900
Could other
dwarf planets host life, too?

321
00:17:30,900 --> 00:17:36,040
Sedna and makemake
both have red-colored patches.

322
00:17:36,040 --> 00:17:38,970
The color comes from something
called tholins,

323
00:17:38,970 --> 00:17:43,440
organic molecules that could be
a precursor to life.

324
00:17:43,450 --> 00:17:46,310
Based on all the interesting
chemistry they're doing,

325
00:17:46,320 --> 00:17:48,180
these dwarf planets
could be like

326
00:17:48,180 --> 00:17:49,550
the test tubes
of the solar system.

327
00:17:53,460 --> 00:17:57,120
If there are small bodies strewn
all about the solar system

328
00:17:57,130 --> 00:17:59,990
that had liquid water or ice,

329
00:18:00,000 --> 00:18:02,460
it could possibly serve
as an Incubator for life,

330
00:18:02,460 --> 00:18:04,000
just holding on to it,

331
00:18:04,000 --> 00:18:06,470
ready to crash into
another body and seed it.

332
00:18:06,470 --> 00:18:08,670
The habitable zone now extends

333
00:18:08,670 --> 00:18:10,000
to the entire solar system.

334
00:18:10,010 --> 00:18:13,070
It really expands...
It greatly expands...

335
00:18:13,080 --> 00:18:15,940
The stage for the play of life
in the entire galaxy.

336
00:18:15,950 --> 00:18:19,350
Maybe we have
dwarf planets to thank

337
00:18:19,350 --> 00:18:20,910
for our very existence.

338
00:18:20,920 --> 00:18:24,480
All of a sudden, the smallest
bodies in our solar system

339
00:18:24,490 --> 00:18:26,820
have become some of
the most interesting things

340
00:18:26,820 --> 00:18:28,160
we've ever seen.

341
00:18:28,160 --> 00:18:32,030
The idea
of migrating dwarf planets

342
00:18:32,030 --> 00:18:35,500
opens up
some intriguing scenarios,

343
00:18:35,500 --> 00:18:39,370
including one
really out-there possibility.

344
00:18:39,370 --> 00:18:42,500
Some of that water
and organic material

345
00:18:42,510 --> 00:18:45,240
may not be
from our solar system.

346
00:19:05,330 --> 00:19:08,930
The more we learn
about dwarf planets,

347
00:19:08,930 --> 00:19:11,000
the more they surprise us.

348
00:19:20,210 --> 00:19:22,210
But there's one dwarf planet

349
00:19:22,210 --> 00:19:24,880
whose very existence
is a mystery.

350
00:19:24,880 --> 00:19:29,550
It's called Sedna,
and no one is quite sure

351
00:19:29,550 --> 00:19:32,350
what it's doing
in our solar system.

352
00:19:32,350 --> 00:19:35,960
Sedna may have my vote for
the single most peculiar object

353
00:19:35,960 --> 00:19:38,160
in the entire solar system.

354
00:19:38,160 --> 00:19:41,830
Here, we have a world which is
about 1,000 miles wide,

355
00:19:41,830 --> 00:19:47,300
<i>but it is way far out in the
solar system, way past Neptune.</i>

356
00:19:49,570 --> 00:19:51,570
Sedna is the most distant object

357
00:19:51,570 --> 00:19:54,370
we've identified
in our solar system.

358
00:19:54,380 --> 00:19:56,110
Standing on
the surface of Sedna,

359
00:19:56,110 --> 00:19:58,380
looking back
at the solar system,

360
00:19:58,380 --> 00:20:01,110
the Sun would look like
a really bright star,

361
00:20:01,120 --> 00:20:03,520
but not much more than
a really bright star.

362
00:20:06,660 --> 00:20:08,660
Just like Pluto,

363
00:20:08,660 --> 00:20:12,330
Sedna has a strange,
elliptical orbit.

364
00:20:12,330 --> 00:20:16,400
The difference is,
Sedna travels from 7 billion

365
00:20:16,400 --> 00:20:19,530
to 93 billion miles
from the Sun,

366
00:20:19,530 --> 00:20:24,000
and unlike Pluto,
its orbit can't be explained

367
00:20:24,010 --> 00:20:26,340
by its close proximity
to Neptune.

368
00:20:29,680 --> 00:20:32,350
The weird thing about Sedna
is its orbit.

369
00:20:32,350 --> 00:20:34,380
How could it have gotten
that elliptical

370
00:20:34,380 --> 00:20:37,750
when it's that far away
from any of the major planets?

371
00:20:37,750 --> 00:20:40,020
If you have an object
that's close enough to Neptune,

372
00:20:40,020 --> 00:20:42,020
Neptune's gravity
can affect its orbit

373
00:20:42,020 --> 00:20:44,020
and swing it into
an elliptical orbit.

374
00:20:44,030 --> 00:20:47,430
The problem is, Sedna never gets
that close to Neptune.

375
00:20:47,430 --> 00:20:48,830
It doesn't get anywhere
near close enough

376
00:20:48,830 --> 00:20:50,230
to be in that kind of orbit,

377
00:20:50,230 --> 00:20:53,630
and that means that something
else is going on out there.

378
00:20:58,440 --> 00:21:00,710
Sedna cannot be explained

379
00:21:00,710 --> 00:21:02,380
using objects that we know.

380
00:21:02,380 --> 00:21:04,180
Everything else,
we can understand

381
00:21:04,180 --> 00:21:06,110
why its where it is
based on, you know,

382
00:21:06,120 --> 00:21:08,720
the eight planets and many,
many other small bodies.

383
00:21:08,720 --> 00:21:10,780
Sedna cannot be explained
by that,

384
00:21:10,790 --> 00:21:13,390
and, you know, that's the sign
of a good mystery.

385
00:21:13,390 --> 00:21:15,720
Something else
must have happened.

386
00:21:18,390 --> 00:21:20,790
Looking at models
for how you can change

387
00:21:20,800 --> 00:21:22,800
the orbits of objects,
there's almost no way

388
00:21:22,800 --> 00:21:25,530
Sedna could've formed
in our solar system,

389
00:21:25,530 --> 00:21:28,670
and then had its orbit change
so that it's that elliptical

390
00:21:28,670 --> 00:21:30,600
and goes that far out
from the Sun.

391
00:21:30,610 --> 00:21:35,280
And that means maybe...
Maybe... it didn't form here.

392
00:21:35,280 --> 00:21:37,210
It may be an alien world.

393
00:21:50,020 --> 00:21:52,230
How could our solar system

394
00:21:52,230 --> 00:21:55,960
have snagged an alien world?

395
00:21:55,960 --> 00:21:58,700
Long ago, it turns out our sun

396
00:21:58,700 --> 00:22:03,370
may have rubbed cosmic shoulders
with other stars.

397
00:22:03,370 --> 00:22:07,910
It was born
in a stellar nursery...

398
00:22:07,910 --> 00:22:10,710
Close to many other
embryonic stars.

399
00:22:12,720 --> 00:22:16,320
So if the Sun was born
in a very dense neighborhood,

400
00:22:16,320 --> 00:22:18,180
whereby a lot of other stars

401
00:22:18,190 --> 00:22:20,250
were forming at the same time
in the same region,

402
00:22:20,260 --> 00:22:23,190
it is absolutely possible
that material could be exchanged

403
00:22:23,190 --> 00:22:26,130
between these stars
as they're forming planets.

404
00:22:26,130 --> 00:22:29,000
Sedna may have formed
just like any other object

405
00:22:29,000 --> 00:22:31,800
around another star...
In a nice, circular orbit

406
00:22:31,800 --> 00:22:35,070
out past the main planets
of that alien solar system,

407
00:22:35,070 --> 00:22:37,670
but if that star
got close enough to the Sun,

408
00:22:37,670 --> 00:22:42,410
our gravity may have been able
to lift Sedna out and steal it.

409
00:22:46,550 --> 00:22:49,280
It's possible
that other dwarf planets

410
00:22:49,280 --> 00:22:52,220
were abducted from other systems

411
00:22:52,220 --> 00:22:56,420
and that these alien worlds
carried alien water

412
00:22:56,430 --> 00:23:01,160
and even alien organic materials
to the inner planets.

413
00:23:03,970 --> 00:23:06,900
It's so tempting to think
that we understand something

414
00:23:06,900 --> 00:23:09,700
as basic as our own
solar system, our own home.

415
00:23:09,700 --> 00:23:11,700
When you discover something
like Sedna,

416
00:23:11,710 --> 00:23:14,640
you realize there could be a lot
out there that we haven't seen.

417
00:23:14,640 --> 00:23:16,980
There are objects
that are small like Sedna

418
00:23:16,980 --> 00:23:18,380
that are just so far away

419
00:23:18,380 --> 00:23:20,650
that they're beyond
our limit to detect them,

420
00:23:20,650 --> 00:23:24,120
so there could be hundreds,
thousands, tens of thousands

421
00:23:24,120 --> 00:23:27,050
of objects out there,
new parts of our solar system

422
00:23:27,060 --> 00:23:28,920
that are still waiting
to be discovered.

423
00:23:31,390 --> 00:23:33,990
Our understanding
of the solar system

424
00:23:34,000 --> 00:23:35,400
is changing radically.

425
00:23:35,400 --> 00:23:39,070
Newly explored dwarf planets
stun us,

426
00:23:39,070 --> 00:23:43,940
and even the most famous one,
Pluto, reveals new secrets...

427
00:23:46,340 --> 00:23:48,340
...making us ask,

428
00:23:48,340 --> 00:23:53,280
could these worlds
be as active...

429
00:23:53,280 --> 00:23:56,080
And alive as our own?

430
00:24:11,100 --> 00:24:13,770
Dwarf planets
all over the solar system

431
00:24:13,770 --> 00:24:17,100
are revealing hidden lives.

432
00:24:17,110 --> 00:24:20,770
In the asteroid belt,
salt on the surface of Ceres

433
00:24:20,780 --> 00:24:24,980
suggests liquid water
beneath the surface.

434
00:24:24,980 --> 00:24:27,710
Farther out,
the new horizons mission

435
00:24:27,720 --> 00:24:31,790
found subsurface oceans
on Pluto.

436
00:24:31,790 --> 00:24:33,790
We used to think
that water could only exist

437
00:24:33,790 --> 00:24:35,190
in this Goldilocks zone,

438
00:24:35,190 --> 00:24:37,460
where it's not so hot
that the water boils off

439
00:24:37,460 --> 00:24:39,660
and it's not so cold
that it freezes,

440
00:24:39,660 --> 00:24:41,790
but that's not the case anymore.

441
00:24:41,800 --> 00:24:43,800
We look around,
and we find water

442
00:24:43,800 --> 00:24:46,870
in the most unexpected places
in our own solar system.

443
00:24:46,870 --> 00:24:49,140
This is kind of a revelation

444
00:24:49,140 --> 00:24:50,470
of modern planetary science

445
00:24:50,470 --> 00:24:52,810
that so many of these worlds
in the outer solar system

446
00:24:52,810 --> 00:24:55,680
may have subsurface oceans
of liquid water.

447
00:24:55,680 --> 00:24:58,680
It kind of boggles the mind
to see how far we've come

448
00:24:58,680 --> 00:24:59,880
in our understanding

449
00:24:59,880 --> 00:25:03,280
of the interior structures
of these worlds.

450
00:25:03,290 --> 00:25:06,820
Finding liquid water
so far from the Sun

451
00:25:06,820 --> 00:25:08,960
left scientists stunned...

452
00:25:10,960 --> 00:25:13,760
...and the surprises
keep on coming

453
00:25:13,760 --> 00:25:17,960
as we study these distant worlds
up close.

454
00:25:17,970 --> 00:25:22,300
Makemake, 2/3 the size of Pluto.

455
00:25:22,300 --> 00:25:28,110
Its surface is covered
in ethane and methane ice.

456
00:25:28,110 --> 00:25:32,310
The methane is frozen into
1/2-inch-sized ice grains.

457
00:25:32,310 --> 00:25:37,980
It reacts with sunlight, forming
organic molecules call tholins.

458
00:25:37,990 --> 00:25:41,050
These color the planet
red-brown.

459
00:25:43,390 --> 00:25:46,130
Farther out lies Eris.

460
00:25:46,130 --> 00:25:48,530
It's 9 billion miles
from the Sun,

461
00:25:48,530 --> 00:25:50,260
and its surface temperature...

462
00:25:50,260 --> 00:25:55,330
About 400 degrees Fahrenheit
below zero.

463
00:25:55,340 --> 00:25:57,940
Eris is an absolutely
tantalizing object.

464
00:25:57,940 --> 00:25:59,940
We really don't know
much about it at all.

465
00:25:59,940 --> 00:26:02,340
It should be
very similar to Pluto,

466
00:26:02,340 --> 00:26:03,680
but one of the things we notice

467
00:26:03,680 --> 00:26:05,810
is that Pluto's surface
is kind of patchy.

468
00:26:05,810 --> 00:26:07,610
There are areas
that are very bright,

469
00:26:07,620 --> 00:26:10,080
but also areas
that are quite dark.

470
00:26:10,090 --> 00:26:13,750
Eris, on the other hand, seems
to be almost entirely bright.

471
00:26:18,030 --> 00:26:20,490
Eris is one of
the shiniest objects

472
00:26:20,500 --> 00:26:21,630
in the solar system,

473
00:26:21,630 --> 00:26:25,570
reflecting 96%
of the light that hits it.

474
00:26:25,570 --> 00:26:27,300
Scientists wondered why.

475
00:26:27,300 --> 00:26:33,310
A clue comes from
its near neighbor, Pluto.

476
00:26:33,310 --> 00:26:38,710
When new horizons flew past,
it spotted something strange.

477
00:26:38,710 --> 00:26:42,250
One of the funny little details
is that as we flew over Pluto,

478
00:26:42,250 --> 00:26:43,580
we realized
that there were things

479
00:26:43,590 --> 00:26:46,120
that looked a lot like
sand dunes down there.

480
00:26:46,120 --> 00:26:48,250
Now, that may not sound
incredibly exotic.

481
00:26:48,260 --> 00:26:51,120
You know, what's very
interesting about a sand dune?

482
00:26:51,130 --> 00:26:53,990
Sand dunes may sound dull,

483
00:26:54,000 --> 00:26:58,530
but they can reveal a lot
about the mechanics of a planet.

484
00:26:58,530 --> 00:27:01,070
Unlike the dunes
we know and love on the earth

485
00:27:01,070 --> 00:27:02,870
that are made of sand,
the dunes on Pluto

486
00:27:02,870 --> 00:27:05,140
are made entirely
of particles of ice.

487
00:27:07,940 --> 00:27:12,610
There's only one thing
that can build dunes... wind.

488
00:27:14,820 --> 00:27:17,750
Dunes are like a visual
representation of the wind

489
00:27:17,750 --> 00:27:21,020
that's moving across the valley
and carrying the sands with it

490
00:27:21,020 --> 00:27:24,490
and depositing it into these
big, beautiful dune forms.

491
00:27:26,360 --> 00:27:28,360
Our planet is large enough

492
00:27:28,360 --> 00:27:30,900
to hold on to an atmosphere.

493
00:27:30,900 --> 00:27:35,370
Air, warmed by the Sun, rises.

494
00:27:35,370 --> 00:27:39,910
Fresh air rushes in underneath,
generating winds.

495
00:27:39,910 --> 00:27:43,040
Pluto is so small
and so far from the Sun,

496
00:27:43,050 --> 00:27:47,910
it shouldn't have an atmosphere
or wind or dunes.

497
00:27:47,920 --> 00:27:49,050
The problem Pluto has,

498
00:27:49,050 --> 00:27:51,180
like other small bodies
in the solar system,

499
00:27:51,190 --> 00:27:53,590
is that it's really hard for it
to hold on to an atmosphere.

500
00:27:53,590 --> 00:27:55,120
It's just too small.

501
00:27:55,120 --> 00:27:59,530
The very thin, light atmospheric
gases basically just escape.

502
00:27:59,530 --> 00:28:02,130
Neither Haumea nor makemake

503
00:28:02,130 --> 00:28:05,330
have detectable atmospheres,

504
00:28:05,330 --> 00:28:08,540
but when new horizons
looked back at Pluto

505
00:28:08,540 --> 00:28:12,140
as the dwarf planet
passed in front of the Sun,

506
00:28:12,140 --> 00:28:17,740
scientists spotted
a thin haze of gas.

507
00:28:17,750 --> 00:28:20,950
Turns out,
Pluto has an atmosphere.

508
00:28:24,150 --> 00:28:26,750
But this atmosphere is temporary

509
00:28:26,760 --> 00:28:30,420
because Pluto's orbit
is elliptical.

510
00:28:30,420 --> 00:28:32,560
Some of the time,
it's far from the Sun.

511
00:28:32,560 --> 00:28:35,630
Other times,
it's much closer and warmer,

512
00:28:35,630 --> 00:28:38,630
creating a kind of
winter and summer.

513
00:28:40,970 --> 00:28:43,370
Pluto's atmosphere
depends on the season.

514
00:28:43,370 --> 00:28:45,570
In the summer, it's warm enough
to have an atmosphere,

515
00:28:45,570 --> 00:28:49,980
and in the winter,
that atmosphere freezes out.

516
00:28:49,980 --> 00:28:52,310
Over the course of just
a single orbit around the Sun,

517
00:28:52,310 --> 00:28:53,980
the surfaces
of these dwarf planets

518
00:28:53,980 --> 00:28:55,720
may change significantly,

519
00:28:55,720 --> 00:28:57,650
condensing and coding out
atmosphere

520
00:28:57,650 --> 00:28:59,450
when they're far from the Sun,

521
00:28:59,450 --> 00:29:01,790
having that atmosphere
revolatilize

522
00:29:01,790 --> 00:29:06,390
and redistribute the surface
when they're closer to the Sun.

523
00:29:06,390 --> 00:29:09,260
Pluto is currently
in its summer phase.

524
00:29:09,260 --> 00:29:12,200
The extra heat
during the long super summer

525
00:29:12,200 --> 00:29:16,470
evaporates some of
the nitrogen ice on the surface,

526
00:29:16,470 --> 00:29:20,410
creating a thin,
wispy atmosphere.

527
00:29:20,410 --> 00:29:22,080
It turns out that even though

528
00:29:22,080 --> 00:29:25,480
the atmosphere of Pluto
is very thin, there is wind.

529
00:29:25,480 --> 00:29:28,480
It's really light,
but there's just enough wind

530
00:29:28,480 --> 00:29:33,020
to be able to carry particles
with it once they start moving.

531
00:29:33,020 --> 00:29:35,020
The seasonal cycle

532
00:29:35,020 --> 00:29:39,230
could help explain
Eris' brightness.

533
00:29:39,230 --> 00:29:42,300
Eris is three times
further away from the Sun

534
00:29:42,300 --> 00:29:43,430
than Pluto is,

535
00:29:43,430 --> 00:29:44,960
but when you put
a nitrogen atmosphere

536
00:29:44,970 --> 00:29:46,700
three times further away,

537
00:29:46,700 --> 00:29:50,100
that nitrogen freezes solid
to the surface.

538
00:29:50,110 --> 00:29:52,040
Eris could be an indicator

539
00:29:52,040 --> 00:29:54,370
of what Pluto looks like
when it enters its winter.

540
00:29:54,380 --> 00:29:57,980
The gases will freeze, and it'll
become even more reflective.

541
00:29:59,980 --> 00:30:01,510
In winter,

542
00:30:01,520 --> 00:30:05,580
Pluto's dunes
will be locked in place...

543
00:30:05,590 --> 00:30:07,990
Frozen on the surface,

544
00:30:07,990 --> 00:30:12,990
unlike the icy features
of another dwarf planet

545
00:30:12,990 --> 00:30:16,400
and the case of
the vanishing volcanoes.

546
00:30:34,350 --> 00:30:37,280
From afar,
the dwarf planet Ceres

547
00:30:37,290 --> 00:30:39,220
looks uniform and dull...

548
00:30:41,420 --> 00:30:46,490
...but up close, one huge
feature comes into view.

549
00:30:46,490 --> 00:30:48,290
One of the strangest objects
that we saw

550
00:30:48,300 --> 00:30:50,430
when we began to map
the surface of Ceres

551
00:30:50,430 --> 00:30:54,230
was something called Ahuna Mons.

552
00:30:54,240 --> 00:30:58,300
Now, this was a strange, jutting
hill, very, very sharp sides,

553
00:30:58,310 --> 00:31:01,640
and it didn't match any of
the other terrain on Ceres.

554
00:31:01,640 --> 00:31:06,450
Ahuna Mons is a very
peculiar feature on Ceres.

555
00:31:06,450 --> 00:31:09,720
This is a mountain that is
standing three miles high,

556
00:31:09,720 --> 00:31:11,320
and there's nothing else like it

557
00:31:11,320 --> 00:31:14,720
on the entire surface of Ceres.

558
00:31:14,720 --> 00:31:18,990
Ahuna Mons dominates
the landscape of Ceres.

559
00:31:18,990 --> 00:31:21,930
With its steep sides
and enormous height,

560
00:31:21,930 --> 00:31:24,800
it looks a lot
like volcanoes on earth,

561
00:31:24,800 --> 00:31:28,330
but earth is still
geologically active.

562
00:31:28,340 --> 00:31:33,410
Ceres is so small, its molten
core should be frozen solid.

563
00:31:37,880 --> 00:31:40,010
Planetary scientist Nina Lanza

564
00:31:40,010 --> 00:31:43,150
heads to one of the most
volcanically active places

565
00:31:43,150 --> 00:31:44,950
on earth... Iceland.

566
00:31:47,290 --> 00:31:50,220
She has a drone's-eye view
of mount Helgafell,

567
00:31:50,230 --> 00:31:53,830
a volcano similar in shape
to Ahuna Mons.

568
00:31:56,160 --> 00:31:59,700
So this volcano is
what's called a rhyolitic dome,

569
00:31:59,700 --> 00:32:02,500
and so it's a type of lava

570
00:32:02,500 --> 00:32:05,770
that kind of gets squeezed out
through fissures,

571
00:32:05,770 --> 00:32:10,440
and then forms
this kind of blobby dome feature

572
00:32:10,450 --> 00:32:13,980
that gets pushed up by the magma
coming up from beneath.

573
00:32:16,320 --> 00:32:19,590
On earth,
red-hot magma bubbles slowly

574
00:32:19,590 --> 00:32:23,660
out of cracks in the surface,
building a steep-sided volcano.

575
00:32:25,860 --> 00:32:28,660
But dwarf planets like Ceres
are too small

576
00:32:28,660 --> 00:32:32,600
to have a hot core of
molten rock to power volcanism.

577
00:32:34,940 --> 00:32:37,700
There isn't molten rock
on these smaller worlds

578
00:32:37,710 --> 00:32:38,940
that have a lot of ice on them.

579
00:32:38,940 --> 00:32:42,780
Instead, what's molten
is water under the surface,

580
00:32:42,780 --> 00:32:45,210
and if the water can work
its way up through cracks

581
00:32:45,210 --> 00:32:48,350
and erupt out in the surface,
you get a volcano.

582
00:32:48,350 --> 00:32:51,880
But it's a cold-water volcano.

583
00:32:51,890 --> 00:32:55,960
We call these cryovolcanoes.

584
00:32:55,960 --> 00:32:58,160
Liquid water squeezes up

585
00:32:58,160 --> 00:33:00,630
through fissures in the surface.

586
00:33:00,630 --> 00:33:04,900
It quickly freezes,
building the mountain.

587
00:33:04,900 --> 00:33:09,170
This volcano, you can see that
it's a pretty young feature,

588
00:33:09,170 --> 00:33:11,840
and it's not very eroded.

589
00:33:11,840 --> 00:33:15,640
We expect on earth
that wind and water

590
00:33:15,640 --> 00:33:18,110
will slowly erode
this mountain away.

591
00:33:18,110 --> 00:33:20,110
With no wind or weather

592
00:33:20,110 --> 00:33:24,050
to erode Ceres' cryovolcanoes,
once created,

593
00:33:24,050 --> 00:33:26,120
they should remain
on the surface

594
00:33:26,120 --> 00:33:29,790
for billions of years.

595
00:33:29,790 --> 00:33:31,960
Ahuna Mons is very strange

596
00:33:31,960 --> 00:33:34,730
because it's the only
tall mountain on Ceres.

597
00:33:34,730 --> 00:33:35,930
Why should that be?

598
00:33:35,930 --> 00:33:38,460
You don't typically get
just one of something.

599
00:33:38,470 --> 00:33:40,930
You should have dozens of them,
and, in fact,

600
00:33:40,940 --> 00:33:44,800
Ceres may have had quite a few
cryovolcanoes in the past,

601
00:33:44,810 --> 00:33:47,340
but they're all gone today.

602
00:33:47,340 --> 00:33:48,810
Just to put that
into perspective,

603
00:33:48,810 --> 00:33:51,880
imagine if this is
the only mountain on earth.

604
00:33:51,880 --> 00:33:53,410
Why would there only be
one mountain?

605
00:33:53,420 --> 00:33:54,610
What would that mean?

606
00:33:54,620 --> 00:33:56,680
This leads us to ask
the question, you know,

607
00:33:56,680 --> 00:34:01,150
are the volcanoes on Ceres
disappearing?

608
00:34:01,160 --> 00:34:03,890
The idea that volcanoes
are vanishing...

609
00:34:03,890 --> 00:34:06,630
It just sounds
totally science fiction,

610
00:34:06,630 --> 00:34:08,560
and really,
not realistic at all.

611
00:34:08,560 --> 00:34:10,900
Of course,
volcanoes can't just vanish,

612
00:34:10,900 --> 00:34:13,500
but actually,
in the right context,

613
00:34:13,500 --> 00:34:15,970
in certain scenarios,
they actually can.

614
00:34:17,910 --> 00:34:20,910
The key to this magic trick...
Gravity.

615
00:34:20,910 --> 00:34:22,910
It can flatten solid matter.

616
00:34:22,910 --> 00:34:24,980
How quickly depends on

617
00:34:24,980 --> 00:34:28,750
the structural composition
of the material.

618
00:34:28,750 --> 00:34:30,980
If you want to build
a sand castle on the beach,

619
00:34:30,990 --> 00:34:32,250
you can't use dry sand.

620
00:34:32,250 --> 00:34:33,520
It doesn't stick together,

621
00:34:33,520 --> 00:34:35,320
so you want to mix
a little bit of water in there

622
00:34:35,320 --> 00:34:37,260
so that when you make
the structure,

623
00:34:37,260 --> 00:34:38,720
it holds together,

624
00:34:38,730 --> 00:34:41,930
but if you mix in too much
water, it just dribbles away.

625
00:34:41,930 --> 00:34:43,660
It viscously relaxes.

626
00:34:43,670 --> 00:34:45,760
It slumps.

627
00:34:45,770 --> 00:34:48,730
Even Iceland's rock volcanoes

628
00:34:48,740 --> 00:34:52,210
are slowly slumping
under their own weight.

629
00:34:52,210 --> 00:34:54,470
Strange as it is
to imagine this,

630
00:34:54,480 --> 00:34:56,210
it turns out
the mountain behind me

631
00:34:56,210 --> 00:35:00,210
is actually slowly
relaxing back down.

632
00:35:00,220 --> 00:35:01,950
It's just happening very slowly,

633
00:35:01,950 --> 00:35:05,950
not on a time scale
that we can directly observe.

634
00:35:05,950 --> 00:35:09,820
It may be that
there were many cryovolcanoes

635
00:35:09,820 --> 00:35:11,090
on the surface of Ceres.

636
00:35:11,090 --> 00:35:14,830
They no longer show
any trace of their existence...

637
00:35:14,830 --> 00:35:17,030
So if we waited around
a little bit longer

638
00:35:17,030 --> 00:35:19,230
until all of Ahuna Mons
had slowly relaxed

639
00:35:19,230 --> 00:35:23,640
back into the planet,
we'd see no trace of it, either.

640
00:35:23,640 --> 00:35:27,970
Maybe Ahuna Mons
hasn't always stood alone.

641
00:35:27,980 --> 00:35:31,580
Maybe it's just
the last of its kind.

642
00:35:31,580 --> 00:35:34,980
Ceres continues
to confound our expectations,

643
00:35:34,980 --> 00:35:37,450
and there are still
many mysteries

644
00:35:37,450 --> 00:35:39,990
with the other dwarf planets
to be solved,

645
00:35:39,990 --> 00:35:42,990
such as how they got their moons

646
00:35:42,990 --> 00:35:46,330
and why Pluto lies on its side.

647
00:36:04,580 --> 00:36:06,610
Just like their larger cousins,

648
00:36:06,610 --> 00:36:11,020
dwarf planets often
have orbiting satellites.

649
00:36:11,020 --> 00:36:16,160
We now realize that all of
the largest dwarf planets

650
00:36:16,160 --> 00:36:18,360
have moons around them,
have a moon.

651
00:36:18,360 --> 00:36:20,560
Most of them have one.
Haumea has two.

652
00:36:20,560 --> 00:36:23,900
Pluto has five.

653
00:36:23,900 --> 00:36:25,960
Four billion years ago,

654
00:36:25,970 --> 00:36:28,570
the young solar system
was chaotic,

655
00:36:28,570 --> 00:36:31,570
filled with small bodies
orbiting the Sun.

656
00:36:33,710 --> 00:36:39,310
One hit the infant earth,
forming the moon.

657
00:36:39,310 --> 00:36:44,250
Smash-ups like these happened
throughout the solar system.

658
00:36:44,250 --> 00:36:48,590
The dwarf planet Haumea formed
from an explosive collision

659
00:36:48,590 --> 00:36:52,390
between two larger objects...

660
00:36:52,390 --> 00:36:57,400
Which may account for
its unusual bean-like shape.

661
00:36:57,400 --> 00:37:01,470
All the dwarf planets
suffered huge impacts.

662
00:37:01,470 --> 00:37:03,400
Haumea had this big one
that left it spinning.

663
00:37:03,400 --> 00:37:05,970
Eris has a tiny moon,
presumably from a giant impact.

664
00:37:05,970 --> 00:37:07,470
Makemake has one.

665
00:37:07,470 --> 00:37:11,940
All these biggest objects have
these tiny fragments of moons

666
00:37:11,950 --> 00:37:14,750
showing us their history
of just getting battered

667
00:37:14,750 --> 00:37:18,620
and pieces
being knocked off everywhere.

668
00:37:18,620 --> 00:37:21,550
Most dwarf planets'
moons are tiny,

669
00:37:21,560 --> 00:37:24,760
not much bigger than asteroids,

670
00:37:24,760 --> 00:37:27,760
but one moon
is very different...

671
00:37:27,760 --> 00:37:31,230
Pluto's moon, Charon.

672
00:37:31,230 --> 00:37:36,640
Pluto's moon is, if anything,
weirder than Pluto itself.

673
00:37:36,640 --> 00:37:37,840
It's Frankenstein's moon.

674
00:37:37,840 --> 00:37:39,710
It looks like somebody
tore a moon apart

675
00:37:39,710 --> 00:37:42,240
and then just kind of
slapdashed it back together.

676
00:37:42,240 --> 00:37:43,840
One hemisphere is smooth.

677
00:37:43,840 --> 00:37:45,440
One is very rugged.

678
00:37:45,450 --> 00:37:49,050
It's got a canyon that's like a
notched carved out of the side.

679
00:37:49,050 --> 00:37:52,850
It is really bizarre.

680
00:37:52,850 --> 00:37:55,320
An impact may have formed Charon

681
00:37:55,320 --> 00:37:57,590
and left it tied to Pluto

682
00:37:57,590 --> 00:38:00,130
in an oddly
codependent relationship.

683
00:38:00,130 --> 00:38:01,930
In some ways, you can think of

684
00:38:01,930 --> 00:38:05,060
the Pluto-Charon system
as almost a binary planet.

685
00:38:05,070 --> 00:38:07,130
There is no other planet
in the solar system

686
00:38:07,130 --> 00:38:11,740
where the moon is so large in
proportion to it and so close.

687
00:38:11,740 --> 00:38:13,740
Like other binary objects,

688
00:38:13,740 --> 00:38:18,680
Pluto and Charon orbit around
a central gravitational point.

689
00:38:18,680 --> 00:38:21,280
Locked in
this gravitational dance,

690
00:38:21,280 --> 00:38:26,220
Pluto and Charon always
show each other the same face.

691
00:38:26,220 --> 00:38:28,820
One of the really interesting
things about Pluto and Charon

692
00:38:28,820 --> 00:38:30,960
is that they're
what we call tidally locked.

693
00:38:30,960 --> 00:38:32,420
When Pluto and Charon formed,

694
00:38:32,430 --> 00:38:34,830
they were probably both rotating
on their own axes,

695
00:38:34,830 --> 00:38:37,430
but the two worlds actually
slowed down their rotation

696
00:38:37,430 --> 00:38:39,030
and locked together,

697
00:38:39,030 --> 00:38:43,840
with one side constantly facing
the other as they orbit around.

698
00:38:43,840 --> 00:38:46,840
But Pluto's rotation
is tipped over

699
00:38:46,840 --> 00:38:49,180
like a top spinning on its side,

700
00:38:49,180 --> 00:38:55,310
so Charon's orbit around Pluto
is also tipped over.

701
00:38:55,320 --> 00:38:57,920
Almost every planet in the
solar system has an orbital axis

702
00:38:57,920 --> 00:39:00,120
that points in roughly
the same direction.

703
00:39:00,120 --> 00:39:03,920
Pluto's is tilted down
about 120 degrees.

704
00:39:03,930 --> 00:39:05,720
Scientists have long wondered

705
00:39:05,730 --> 00:39:07,990
what caused this disparity.

706
00:39:08,000 --> 00:39:10,200
Did Charon pull Pluto over?

707
00:39:10,200 --> 00:39:14,930
Or is the tilt a result of
the impact that formed Charon?

708
00:39:14,940 --> 00:39:17,540
A clue was revealed
when new horizons

709
00:39:17,540 --> 00:39:21,670
sent back images
of Pluto's heart.

710
00:39:21,680 --> 00:39:23,740
One of the more endearing
features of Pluto

711
00:39:23,750 --> 00:39:26,280
as the new horizon's probe
approached it

712
00:39:26,280 --> 00:39:28,850
was a gigantic
heart-shaped region

713
00:39:28,850 --> 00:39:32,950
on the side of Pluto
facing the spacecraft.

714
00:39:32,950 --> 00:39:37,090
Sputnik Planitia,
a bright, white heart

715
00:39:37,090 --> 00:39:40,960
against Pluto's dark,
pockmarked surface.

716
00:39:40,960 --> 00:39:44,960
When we got closeups of this,
it was completely fascinating.

717
00:39:47,440 --> 00:39:49,100
I gasped out loud.

718
00:39:49,100 --> 00:39:51,900
This is how shocking this was,
and I remember saying,

719
00:39:51,910 --> 00:39:54,310
"oh, my gosh.
There are no craters there!"

720
00:39:54,310 --> 00:39:57,510
It is smooth,
like it's a frozen-over lake.

721
00:39:57,510 --> 00:39:59,510
This is indicative
of something liquid,

722
00:39:59,510 --> 00:40:01,980
something flowing
under the surface of Pluto,

723
00:40:01,980 --> 00:40:06,050
and what we're seeing
is the top, frozen layer of it.

724
00:40:06,050 --> 00:40:07,990
There are even convection cells

725
00:40:07,990 --> 00:40:11,060
where the ice appears to be
warming and spreading out.

726
00:40:11,060 --> 00:40:14,330
That suggests that underneath,
there's a source of energy,

727
00:40:14,330 --> 00:40:18,200
and amazingly, there may even be
a huge basin of liquid water

728
00:40:18,200 --> 00:40:20,130
under that ice.

729
00:40:20,130 --> 00:40:23,270
Sputnik Planitia
may hide a giant,

730
00:40:23,270 --> 00:40:26,540
subterranean ocean
of liquid water.

731
00:40:26,540 --> 00:40:31,340
It's also a gigantic scar
on Pluto's surface.

732
00:40:31,350 --> 00:40:34,410
Most likely,
given the shape and size,

733
00:40:34,420 --> 00:40:37,280
Sputnik Planitia was formed
in a giant impact.

734
00:40:37,280 --> 00:40:40,020
Something smacked into Pluto.

735
00:40:40,020 --> 00:40:42,690
Could the combination
of subsurface water

736
00:40:42,690 --> 00:40:46,760
and an impact account for
Pluto's unusual tilt?

737
00:40:46,760 --> 00:40:49,160
One theory suggests
that an object

738
00:40:49,160 --> 00:40:51,760
smashed into the top of Pluto.

739
00:40:51,770 --> 00:40:54,370
The impact
shattered the surface,

740
00:40:54,370 --> 00:40:57,300
and water oozed up
to fill the crater.

741
00:40:59,710 --> 00:41:02,770
The liquid water
knocked Pluto off balance,

742
00:41:02,780 --> 00:41:05,580
and the gravitational dance
with Charon

743
00:41:05,580 --> 00:41:10,380
spun this heavy heart
out to the opposite side.

744
00:41:10,380 --> 00:41:13,390
One idea is that Sputnik
Planitia formed where it is

745
00:41:13,390 --> 00:41:15,590
because ices
can accumulate in the floor

746
00:41:15,590 --> 00:41:18,590
of a giant impact base.

747
00:41:18,590 --> 00:41:22,130
But it's not yet certain whether
that's actually the case or not.

748
00:41:25,070 --> 00:41:28,800
Dwarf planets,
once thought to be dead lumps,

749
00:41:28,800 --> 00:41:31,400
have come alive with mysteries.

750
00:41:31,410 --> 00:41:34,070
They've challenged
all our assumptions,

751
00:41:34,070 --> 00:41:37,210
and yet, we've barely
scratched the surface

752
00:41:37,210 --> 00:41:39,610
of these perplexing worlds.

753
00:41:39,610 --> 00:41:42,350
There are many more
dwarf planets to discover,

754
00:41:42,350 --> 00:41:46,890
and who knows what surprises
they may have in store?

755
00:41:46,890 --> 00:41:49,090
We don't know the final count
of dwarf planets

756
00:41:49,090 --> 00:41:50,760
because we're still
finding them,

757
00:41:50,760 --> 00:41:53,560
but I think that
there are probably somewhere

758
00:41:53,560 --> 00:41:57,900
between 100 and 200
dwarf planets out past Pluto.

759
00:41:57,900 --> 00:42:00,170
There are probably many,
many more as you go

760
00:42:00,170 --> 00:42:02,700
even further out
in the solar system.

761
00:42:02,700 --> 00:42:05,840
Dwarf planets are, perhaps,
the most interesting objects

762
00:42:05,840 --> 00:42:07,440
we've found in the solar system.

763
00:42:07,440 --> 00:42:10,040
They're diverse.
They're geologically active.

764
00:42:10,040 --> 00:42:11,840
They contain liquid water.

765
00:42:11,850 --> 00:42:13,250
Just because they're small,

766
00:42:13,250 --> 00:42:14,980
that doesn't mean
they're insignificant

767
00:42:14,980 --> 00:42:16,250
or they should be ignored.

768
00:42:16,250 --> 00:42:18,050
They are where it's at.

769
00:42:18,050 --> 00:42:20,990
For me, that is just
the best, the most exciting.

770
00:42:20,990 --> 00:42:23,320
We have all of
these new worlds to study

771
00:42:23,320 --> 00:42:27,390
that we didn't even dream
existed just a few years ago.

772
00:42:27,400 --> 00:42:28,530
That's science.