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.

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 could 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 recognised six.

Five of them, Pluto with its moon Charon, red-coloured Sedna, bright, distant Eris,

Makemake, and the bean-shaped Haumea, live billions of kilometres 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 about 410 million kilometres 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 out there are.

This is rubble left over from the formation of the solar system.

During the 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

fulfill three cosmic criteria 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 fulfills just two of these requirements it is a sphere It's

clear, although a small one, only 914 kilometers across.

And it does orbit the Sun.

However, it hasn't cleared its path of debris, and it's surrounded by asteroids,

so therefore cannot be classed 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 its 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.

In March 2015, NASA's Dawn Probe arrived 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 discover over a hundred of these mysterious white spots.

The largest is in a 90-kilometer-wide crater called Ocotor.

Sodium carbonate, a type of salt.

We believe the salts on Ceres are actually very young.

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

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

I know that is super weird, right?

That's happening not on sort of 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 can liquid water exist 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 understand how Ceres has liquid water, we have to travel back 4.6 billion years.

To when debris left over from the formation of our sun slammed together to form the dwarf star system.

Dwarf planets as they took shape, the heavier rocky material sunk to the center and formed a hot molten core.

Slushy water ice floated to the top, and for a while it stayed as a liquid.

But once the core cooled, it froze, forming the solid mantle and crust.

However, 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 secret.

Recent research suggests that it's not from our solar system, and didn't form anywhere near the asteroid belt.

Ceres may have been born alongside hundreds of other dwarf planets many billions of kilometers away from the Sun.

So how did it get here?

Most of the dwarf planets discovered lie far out in the solar system, beyond the orbit of Neptune.

However, 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 that form the rocky inner planets.

Ceres is very different.

Ceres is essentially an icy world, right?

It's made out of ices instead of rocks.

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

The ice on Ceres also contains chemical compounds that in the early years of the

solar system didn't exist in the asteroid belt.

The more we learned about Ceres, the more mysterious it became.

One of the things is that Ceres has quite a lot of ammonia on it.

And we don't find ammonia anywhere near the inner part of the solar system.

But it is found on Pluto, its moon Charon, and out in the frozen Kuiper Belt,

where we find the other dwarf planets.

We think that the origin of that ammonia would have had to be in a very cold part of the solar system.

Colder than where we find Ceres today.

But how an icy dwarf planet with ammonia came to inhabit a place where ammonia can't form is a huge puzzle.

I'm up here in the mountains where it's rather snowy at the moment.

Down a few thousand feet below us, it's rather warm and summery.

And that's actually a pretty good analogy for our solar system.

In the earliest days of the solar system, when the sun was just forming,

of course, as it was turning on, it was quite warm in the inner solar system.

When the sun burst into life 4.6 billion years ago, it was more energetic than it is today.

It blasted all the lighter elements, such as ammonia and helium, out past a point called the snow line.

That's why the rocky planets, like the one we live on, here in the inner solar system, are made of rock and metal.

It just wasn't the ability for some of the lighter molecules in the solar system to exist.

But out beyond the snow line, um, beyond where we find Jupiter today,

the temperatures were much colder.

This suggests to us that Ceres perhaps formed in the outer solar system and then

migrated inwards to its present location in the asteroid belt.

We used to think that planetary orbits were completely immutable.

That they simply ran like clockwork and they didn't move around.

Now we know that that's not the case.

In the early stages of planet formation, planets move around through the gaseous

disk that encircles the young sun, much like rafts that are pushed around by ocean currents.

Ceres' ammonia suggests that dwarf planets moved around on the gaseous disk,

along with the young planets.

Ceres is sort of a smoking gun, that solar systems are much more dynamic,

much more dramatic than we know.

There's mounting evidence that Ceres formed far throughout in the solar system,

and something brought this little world in.

What could possibly have done that?

The answer is the planet Jupiter.

After it first formed, the giant planet migrated in towards the Sun.

Its massive gravity disrupted the orbits of other bodies in the solar system,

including that of Ceres.

The solar system formed out of a disk of gas and dust.

And as Jupiter formed, it would have been plowing through this material.

And if it plows through that material, it's experiencing drag.

As it was losing energy, it would start to move in toward the Sun relatively slowly.

Ceres formed in the outer edges of the solar system.

It was dislodged from the Kuiper Belt and pulled inwards by the migration of Jupiter.

And when Jupiter stopped migrating, so did Ceres.

It then settled into a new, stable orbit in the asteroid belt.

Once you realize that something that strange and dramatic can happen,

that a dwarf planet can form far out in the solar system and be brought in,

it makes you wonder how many times that happened before.

Could there have been other generations of dwarf planets that got thrown in towards the Sun?

Or maybe were thrown out of the solar system entirely?

Scientists believe that rocks and icy dwarf planets may have hurtled into the inner solar system.

Hundreds began the journey.

Only one survived.