How the Universe Works

All across our solar system,

scientists are discovering thrilling new worlds,

dwarf planets.

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

oceans of subterranean water,

ice volcanoes, and vanishing mountains.

The whole idea that dwarf planets are small

and insignificant and boring

has just been shattered in the last few years.

Dwarf planets defy many of the rules

we thought governed our solar system.

Dwarf planets are very interesting bodies

scientifically,

but beyond that, they tell us something

about the origin of our own world.

Believe it or not, they may harbor life.

Dwarf planets are rattling the cages of scientists

and shaking up our understanding of how the universe works.

They may have fed the early planets

and even seeded them with the precursors of life.

Dwarf planets just may be the most important objects

in the solar system.

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Our solar system has eight confirmed major planets,

but we're discovering many other small worlds

called dwarf planets.

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

but the more we study them,

the more shocking and intriguing they become.

Naively, I would expect these objects

to not be terribly dynamic.

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

and they're just sitting there,

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

There is all kinds of stuff going on.

They're full worlds with really interesting geology

and interesting histories

that can tell us a lot about the solar system.

Scientists believe there may be

hundreds of dwarf planets in our solar system.

So far, we've only identified six.

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

red-colored Sedna;

bright, distant Eris;

makemake, and bean-shaped Haumea...

All live billions of miles from the Sun,

out beyond Neptune in the Kuiper belt.

They're just the tip of the iceberg.

There are probably many, many more dwarf worlds

that are out there waiting to be discovered.

The sixth dwarf planet, Ceres,

lives in the inner solar system.

It orbits around 260 million miles from earth

in the asteroid belt.

The asteroid belt is a region of the solar system

between Mars and Jupiter,

and this is where most of the asteroids are.

This is rubble

left over from the formation of the solar system.

In early years of the solar system,

small rocks collided with one another, stuck together,

and built the rocky inner planets.

Dwarf planets grew in the same way.

Ceres was actually starting to get pretty big.

It was on its way to becoming a planet

before it stopped growing, and that makes it

stand head and shoulders above everything else there.

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

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

First, it needs to be a sphere.

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

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

Ceres ticks just two of the boxes.

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

Only 600 miles across.

That's the size of Texas.

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

It's surrounded by asteroids,

so it misses out on being a planet.

Even though we call these objects dwarf planets,

small and dwarf does not equal insignificant.

But being small does have its problems.

When the molten core of a young dwarf planet cools,

so does the heat engine that drives geologic activity.

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

It's a small body.

It should have cooled off long ago.

Nothing very interesting is going on,

and when we actually got out to Ceres,

nothing could have been further from the truth.

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

As the dawn spacecraft pulled up to Ceres,

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

and then all of a sudden,

something totally mysterious rotated into view.

One of the craters had two bright spots,

almost like two eyes staring right back at us.

It was such a puzzle to the science community

because what are these doing here?

Are they ice? It looks very fresh.

What on earth could it be?

Scientists find over 100

of these mysterious white spots.

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

They are, unexpectedly,

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

Sodium carbonate, a kind of salt.

We believe the salts on Ceres

as actually very young.

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

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

And that is super weird, right?

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

It's happening now, today.

What could cause patches of salt

on a world long-presumed dead?

Planetary geologist Jani Radebaugh believes a clue

might be found at mono lake in California.

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

off in the distance

and standing on massive white deposits.

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

at one point.

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

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

as it evaporated away,

and these things are, you know, salts.

They're kind of granular in texture,

and just to make sure, we taste it

and yeah, sure enough, it's salty.

The salt at lake mono

crystallizes as the water evaporates,

the only way it can form.

The researchers believe the same process

is taking place on Ceres.

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

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

These bright spots are located in the centers of craters.

They're located around cracks in the surface,

and that is telling us that this material

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

Absolutely nobody expected there to be liquid water

beneath the surface of Ceres.

We cannot explain what is keeping that water warm.

On some moons,

gravitational tugging keeps the interiors warm,

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

So the amazing thing is that we may not even understand

how rocky planets work.

There may be another source of energy,

another mechanism for heating the interior

that we haven't even discovered yet.

To find out how Ceres has liquid water,

we have to rewind the clock 4.6 billion years.

Debris left over from the formation of the Sun

slams together to form the dwarf planets.

As they take shape, the heavier, rocky material

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

Slushy water-ice floats to the top.

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

it freezes and forms the solid mantel and crust.

That surface should still be solid,

so the salt patches remain a perplexing mystery.

We still haven't answered the question,

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

That's still a hard question to answer.

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

if you've mixed it with something else.

Some scientists have proposed

that a salty ocean lies beneath the surface.

The high concentration of salt

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

When asteroid impacts fracture the crust,

this salty water oozes up from below.

The liquid swiftly evaporates, but the salt remains,

leaving a brilliant white spot on the surface.

In fact, I'm willing to bet

there could be water coming up now,

bringing salts up to the surface,

evaporating away into space,

and that means liquid water is very close

to the surface of Ceres right now.

Ceres has an even more startling card up its sleeve.

Recent research suggests that it's an immigrant.

It didn't form anywhere near the asteroid belt.

Ceres may have been born

alongside hundreds of other dwarf planets,

many billions of miles away from the Sun.

So how did it get here?

Most of the dwarf planets we've discovered

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

but Ceres orbits between Mars and Jupiter

in the asteroid belt.

But its location isn't the only hint

Ceres might be an interloper.

Normally, celestial objects are made of the same materials

as the other bodies in their neighborhoods,

but that's not the case with Ceres.

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

composed of the same heavy elements