Original subtitles

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- [Narrator] Space is vast, yet, collisions are commonplace.

Gas and dust electrostatically flock together.

Gravity takes over coalescing grains into rocks,

rocks into boulders; then, asteroids

colliding again and again,

striking planets and each other.

Stars collide creating monsters of light and energy.

Even galaxies collide over millions of years.

Space is a rough place to be.

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That peaceful night's sky cloaks a hidden danger.

It might appear bejeweled, docile, and permanent,

but if you look closely, you can see things happening;

violent things.

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Stars engulfing planets and each other,

protoplanets colliding,

explosions rippling through gas clouds,

triggering the birth of young stars,

black holes devouring everything in their path.

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Closer to home, a more immediate danger

is the debris from the creation of our solar system,

spinning about in a heliocentric orbit

just waiting to bang into something,

something like Earth.

Collision avoidance is the name of the game,

and we now have the technology to do something about it.

- Catalina Sky Survey and other survey programs

are really sort of the start

of the whole planetary protection ecosystem.

If it starts with discovery,

goes onto follow-up and characterization,

impact risk analysis, mitigation studies,

but you can't follow-up and you can't characterize

and you can't calculate the impact risk

of something you don't discover.

In order to find a near-Earth asteroid,

we take four images of a patch of sky

separated by about five minutes.

- And we take those four images

and we blink them really fast,

and it creates this little animation

so we can see that the stars in the background

are a astatic, as they should be,

and if there's anything that's moving, it'll pop out.

- [Martin] Then, our software compares those images

and identifies things that are not moving,

which are stars, and removes those,

identifies things that are transient from frame to frame

and tries to link those up.

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- We've probably seen about a million asteroids

in the last seven years that

the Pan-STARRS has been operating.

It's like picking a needle out of a haystack.

We're looking for distinctive motion,

and when we see distinctive motion in asteroids,

we report them to the Minor Planet Center.

The Minor Planet Center is the sort of

world clearing house for near-Earth asteroids.

- The Center for NEO Studies takes the observations

from the Minor Planet Center

and computes the high-precision orbits

that we use to make predictions.

CNEOS is also kind of an early warning system

for newly discovered asteroids.

We take the early data and we compute

whether or not that asteroid could hit the Earth.

If there's a chance, we'll send out an early warning

and alert for follow-up observation,

so that we can get more data and then,

we would know perhaps whether it can hit the Earth or not.

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- Asteroid impacts are a fact of life.

The Earth has been impacted by asteroids

continually through its history.

- We saw in 2013 in Russia a fairly small,

by the standards of what we're finding,

asteroid did hit the Earth.

I feel little bit like a guardian of the planet.

I'm doing my bit to try to protect people.

It is a long-term process.

It's gonna take many, many years to find

all of the dangerous asteroids.

- [Martin] The goal is to

find near-Earth asteroids before they find us.

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- [Narrator] Having the right tools

helps us look further away in greater detail.

The Hubble Space Telescope was one such tool

that was able to capture the first spectacular impact

seen in our solar system;

the Shoemaker-Levy 9 cometary fragments,

which struck Jupiter, leaving a surprising impression.

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Even more remarkable was the recent arrival

of an interstellar object.

- It was a special day when this object

was first discovered.

We have been waiting for the discovery

of an interstellar object for decades, basically.

- [Kelly] Well, when I first heard about

this interstellar object it was very exciting,

just from a scientific point of view,

that, finally, there's been an actual observation

of such an object.

- This object is simply a piece of another solar system

that was expelled and it has been

traveling through interstellar space for

hundreds of millions of years,

billions of years, we don't know.

- A number of our survey projects

and other observatories immediately

turned their telescopes to take observations of this object.

From the observations we have so far,

it looks like it's a very elongated object,

maybe about a quarter mile in length.

- We think this object, 2017 U1, is very long.

Perhaps 400 meters or so long, and very narrow, skinny,

perhaps maybe 40 meters or so in the other dimensions.

That's a very unusual shape.

We don't see that in our solar system.

None of the asteroids in our solar system look like that,

so it's very puzzling how it could have obtained this shape.

- We also see that it's very reddish in color,

which indicates that it's been

possibly in space a long time

and irradiated by, not only the light from our sun,

but other suns, as well.

- Well, there's still quite a bit to learn

about this interstellar object and limited time because

it's on its way out of the solar system.

- It's fading very fast.

It's a relatively small object so it's very dim,

but we are continuing to try to use NASA assets,

like the Hubble Space Telescope and Spitzer,

to take observations to determine more

about its size and composition.

- NASA's Planetary Defense Coordination Office

has a Near-Earth Object Observations Program,

which funds efforts that survey the skies

to look for near-Earth asteroids

and to calculate their orbits and their trajectories

and to determine if any of them

might pose a hazard to Earth, and as part of doing that,

some amazing discoveries can happen,

and the discovery of this interstellar object

was one of them.

- As our observational capabilities improve,

Pan-STARRS has been getting better,

other surveys have been getting better.

There are new generation surveys that will come online.

We will be detecting more of these in the future.

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- [Narrator] New observatories are being constructed.

To be launched in the coming year,

the James Webb Telescope will orbit

at Earth's L2 Lagrange Point;

1.5 million miles from Earth, away from the sun.

It's low temperature sensors will be shielded from

the sun, Earth, and moon.

There're also three new ground-based observatories underway.

A multi-national project being built in Hawaii,

the Thirty Meter Telescope, or TMT,

will use 492 hexagonal elements, each about 1.44 meters,

to construct the single primary mirror

of 30 meters diameter.

The secondary mirror will be 3.1 meters in diameter.

The largest of all will be Europe's

Extremely Large Telescope, or ELT.

The primary mirror consists of 798 segments,

each 1.4 meters wide but only 50 millimeters thick,

with a light-collecting area of 978 square meters.

The optical design calls for an immense secondary mirror,

four meters in diameter,

bigger than the primary mirrors of any of

ESO's telescopes at La Silla.

Then, there is the Giant Magellan Telescope

currently under construction in the Chilean Andes,

which will be ready by 2022.

It consists of seven 8.4 meter diameter mirrors,

making a total effective aperture of 24.5 meters.

Housed in a rotating 22-story high building,

it will produce images 10 times sharper than Hubble

with a total collection area of 368 square meters.

- This is a project that we began in 2003.

It was a small group of U.S. institutions

and has now grown to an international project

that includes Australia, Korea, Chile,

and, most recently, Brazil.

The next steps, as we launch construction of this telescope,

are to build the mount, the steel mount,

that will hold the mirrors for the telescope,

to build the enclosure, which is a 22-story building,

that has to rotate to allow you

to move to different parts of the sky

as you're looking out with the telescope.

- [Edward] It's a new epic in the field of astronomy.

It's a new epic for cosmology, astrophysics,

and the history of the universe.

And so we'll be able to see things further and fainter

than anyone has ever seen before.

- [Patrick] It just takes us to that next level of

technical capability and these technical leaps

are what enable new discoveries.

- [Narrator] The first four giant mirrors for Magellan

have been manufactured, number five is underway,

as is construction at the site in the Chilean Andes.

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- GMT is really an exciting thing

because we know that over the last 400 years

that telescopes have gotten bigger

and that has allowed us to see things

with better detail and to see fainter things

and to figure out what the history of the universe has been.

Our technology for doing this is getting better and better.

We're able to build big mirrors and we know how to do this;

we know how to build GMT.

We know to build its individual mirrors

and put them together.

We know that when you build a telescope view,

and the GMT will have a view

that is 10 times sharper than the Hubble Space Telescope,

and when you build a telescope that collects more light,

and the GMT will collect 100 times as much light

as the Hubble Space Telescope does,

that you are going to be able to do things that

we can imagine and set out as our goals

to look at the history of the universe,

how things have changed,

find out more about the dark energy and the dark matter.

Those are things that we know you can do,

but I think the really exciting things

will be things that we haven't yet thought of,

that the new questions that will come.

The other part that's really interesting

about a big telescope on the ground

is that you can change it;

that is you can change the instrument,

so I think that even when we build the telescope,

that won't be its final form.

Those instruments will eventually be replaced

by better ones that use the technology

that's developed over the period from now to then.

We know that the universe has changed

from a very homogeneous, kind of,

goo, at the time of the big bang,

into a highly differentiated world

where there are planets, stars,

galaxies, clusters of galaxies.

The universe has gotten kind of interesting and complicated

through the action of gravity over time.

We'd like to see how that works

and by looking at what happened long ago,

which means looking at very distant, very faint galaxies,

and looking in detail, which means having the resolution

to kind of really see what's going on.

- [Narrator] No doubt revealing

cosmic collisions far back in time and space.

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Not as close as the asteroid field,

but still in our neighborhood,

are other phenomena colliding in space.

Out beyond the edge of our galaxy,

the Milky Way is a cloud of hydrogen gas

called Smith's Cloud after its 1963 discoverer, Gail Smith.

It is traveling at 312 kilometers per second

and is about to collide into the Perseus Arm of our galaxy;

well, in 27 million years or so.

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It was believed to have been ejected

from the Milky Way some 70 million years ago.

Why, is still not known but,

when it collides with the galactic arm,

it will trigger a brilliant burst of star formation

with enough gas to produce over two million stars.

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Another major event to occur soon

is in the heart of our galaxy,

where a super-massive black hole resides.

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This black hole's mass is a hefty

four million times that of the sun.

ESO telescopes have been tracking the motion of stars

around the giant black hole for 20 years.

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Although huge, it is currently supplied

with little material and is not shining brightly,

but that is about to change.

Recently, they have discovered a cloud of gas

traveling towards the gravity sync hole

on a collision course.

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- The cloud consists mainly of hydrogen gas,

gas which we see anyhow in the galactic center

all over the place.

This particular cloud weighs more or less

three times the mass of Earth,

so it's a rather small and tiny blob only,

but it glows very brightly in the light of the stars

which are surrounding the cloud.

- We really don't know where the cloud came from,

but we do know that most of the material,

which is currently flowing into

the galactic center black hole, comes from stellar winds,

material which ejected by nearby stars

and it could be that this particular cloud

also was coming from a star ejecting material

but happened to produce a very compact

and directed it right at the black hole.

Well, the next few years will be really fantastic

and exciting because we are probing the territory.

Here, this cloud comes in, gets disrupted,

but now it will begin to interact with the hot gas

right around the black hole.

We have never seen this before.

We expect it gets hotter.

It may even start emitting x-rays, very hot radiation,

and then it gets disrupted, and then, in the end,

we expect it to fall into the black hole,

once it's sort of going through all of this churning.

- [Narrator] As the astronomers watched,

the cloud has been picking up pace

as it gets closer to the giant black hole.

It's speed has doubled in the last seven years

and it is now speeding towards the black hole

at more than eight million kilometers an hour.

The astronomers have already seen

the cloud's outer layers becoming more and more disrupted

over the last few years as it approaches the black hole.

- The black hole, imagine it sitting here,

has a tremendous gravitational force.

And the cloud, as it comes in,

it will be elongated and stretched.

It will become, essentially, like spaghetti.

It will be elongated and falling into the black hole.

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- [Narrator] Observations of other massive black holes

at the center of galaxies have revealed

many varied phenomena.

One galaxy's super-massive black hole

is emitting a powerful outflow of material.

And, to the surprise of astronomers, is forming stars.

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Results from ESO's very large telescope

are the first confirmed observations

of stars forming in this kind of extreme environment.

The discovery has many consequences

for understanding galaxy properties and evolution.

Black holes at the centers of galaxies

still hold many secrets.

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Galaxies are the building blocks of the universe.

The giant galaxies we see today, even our own,

were built-up from many smaller galaxies

and construction isn't over.

Today, full-grown galaxies approach

and interact with each other.

They may collide and eventually merge,

growing larger and more influential.

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As the galaxies approach each other,

the tug of gravity creates tides that distort their shapes,

stars and gas stream into new orbits.

Sometimes they're completely ejected,

trailing into the depths of intergalactic space.

Clouds of gas are compressed in the chaos

and ignite with intense runs of new star formation.

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Computer simulations have been conducted

and compared to actual images of galactic collisions,

an uncanny resemblance.

Because stars create most of the chemical elements,

each galaxy has a particular chemical makeup.

This makes identifying groups of stars

from different galaxies easier.

This infrared image of our sky

shows our point of view of the Milky Way,

half a billion stars.

Most are in our galaxy,

some belong to companion galaxies that orbit our Milky Way,

and some are in between.

Astronomers have discovered that some groups of stars

belong to a different galaxy,

called the Sagittarius Dwarf Elliptical,

and the Milky Way is cannibalizing it.

As the dwarf galaxy passes through the Milky Way's disk,

gravitational tides stretch the dwarf stars

into long streams that wrap around the galaxy's orbit.

For the dwarf, it's a fatal attraction.

For the Milky Way, just another one of several

similar events in its history.

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But something much bigger is headed our way;

M31, the Andromeda Galaxy.

This is the Milky Way's biggest neighbor

of roughly the same size mass and type,

and it is speeding towards us.

Astronomers say the crash will begin

in about two billion years.

Super computer simulation shows how the event

may unfold over billions of years.

The first pass distorts the two great spirals,

stars are tossed into the intergalactic

night-like sparks thrown from a campfire,

and our sun, complete with planets in tow,

could be similarly ejected.

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Gravity will eventually merge Andromeda and the Milky Way

into a bigger single entity.

With a new generation of telescopes looking skyward,

we are sure to discover more dangers lurking in the heavens,

though fortunately for us,

we are millions or billions of years

in time and distance away.

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