There are hundreds of billions
of alien worlds in the Milky Way galaxy.
And scientists have already discovered
and confirmed over 5,000 of them.
They call these worlds exoplanets.
Some of them are really small,
like Kepler-37 b.
This tiny planet
is even smaller than Mercury,
the smallest plant in our Solar System.
Kepler-37 b is just slightly larger
than our own Moon.
It could easily replace
our cosmic companion in the night sky.
Only it's pretty far from us.
This tiny space rock is located
208 light-years from Earth,
where it orbits a star
that's a bit smaller
and cooler than our Sun.
Small rocky worlds like Kepler-37 b
are a pretty rare find.
Because they're so tiny,
they're more difficult to spot.
But scientists have still managed
to confirm about 200 of these worlds.
Most of them are many, many times
closer to their stars
than our planet is to the Sun.
And Kepler-62 c is no exception.
This Mars-sized exoplanet orbits its star
roughly four times
closer than Mercury orbits our Sun.
It only takes a little over 12 Earth days
to make a full orbit.
Kepler-62 c must be scorching hot
and extremely volcanic.
It's definitely not
the kind of place you'd want to visit.
And neither is this exoplanet.
KOI-55 b.
Scientists think this planet
used to be the size of Jupiter,
but then its sun exploded into a red
giant and swallowed the planet whole.
And no surprise there.
KOI-55 b is incredibly close to its star.
So close that it takes this hellish world
less than five hours to make one orbit.
And KOI-55 b is evaporating
so much that it will soon
disappear from its planetary system.
It's not alone.
Many of these planets
have their atmospheres
torn away by their host stars.
Some 41 light-years from Earth,
there's a super-Earth
that used to be a mini-Neptune.
GJ 1132 b might have had a thick
hydrogen atmosphere in the past,
but its young hot star stripped it away,
leaving only a rocky core behind.
When its star stripped away its original atmosphere,
some of the gasses were
absorbed into the planet's mantle.
And now, through this planet's volcanism,
they're released back.
GJ 1132 b could have become
a potentially habitable world,
but it's 26 times closer to its star
than Mercury is to the Sun.
No chances for life on this super-Earth.
But life might be possible
on these slightly larger super-Earths.
Scientists have found
many of these worlds orbiting
in their Sun-like star's habitable zones,
and that's good news.
Now, we'd have to go and explore
more of these planets up close
to find out
what their atmospheres are like.
This one seems intriguing.
Kepler-452 b is 1.6 times
the size of Earth,
and it's about six billion years old.
Earth is a youngster
compared to this world.
Our planet is only four
and a half billion years old.
Okay, now I know this is
your favorite exoplanet,
Kepler-22 b.
And I like it too.
This super-Earth might be covered
in a super-ocean.
It sits comfortably in its star's
habitable zone
and has a huge potential for life.
The only problem is that it's big.
Kepler-22 b is 2.4 times larger than Earth
and about nine times more massive.
If Kepler-22 b was the size of Earth,
it would have an average surface
temperature of about 16 °C (60 °F).
But because it's a lot bigger than Earth,
it could be a rocky planet,
a waterworld, or even
a gaseous planet like Neptune.
And speaking of gaseous planets,
at this size, exoplanets stop being
super-Earths and become gas giants.
More than half of all exoplanets
we've discovered
are either Neptune-like
ice giants or gas giants like Jupiter.
And many of them orbit
a little too close to their host stars
and they pay a high price
for that proximity.
For one, they're incredibly hot,
and sometimes their host star
rips their atmosphere away.
Kind of like what
GJ 1132 b went through.
But among them,
there are some cold planets, too.
This is Kepler-16 b.
It's not quite as large as Jupiter,
but the cool thing about it
is that it orbits
not one but two stars.
Only you wouldn't
be able to see those stars
because you wouldn't be able
to stand on its surface.
You see, Kepler-16 b is
a Saturn-sized gas giant.
It might have
some rocky elements inside it,
but its two host
stars are much cooler
than our Sun, making Kepler-16 b
a frigid, lifeless world.
Speaking of lifeless worlds, well,
that might be what Earth becomes
if we don't work to stop
climate change.
You've seen
the hundreds of wildfires
spreading across Canada.
Well,
this is due to climate change,
making the world hotter and drier.
This toxic air
made its way to New York,
Toronto, Detroit and Chicago,
resulting in
some of the worst
air quality in the world.
California is trying
to prevent wildfires
by purposefully
burning thousands of acres a year.
This is in order to
reduce vegetation
that could fuel
a catastrophic wildfire.
And this is just one example
of what we need to do
to help with climate change.
Check to see what your local
and federal governments
are doing to help,
because we only have one Earth
and we don't want it
to turn into one of these
uninhabitable exoplanets.
OK, now on to the worlds
that are bigger than Jupiter.
This delicious exoplanet
has the density of a marshmallow.
TOI-3757 b is slightly larger than Jupiter,
but it's not nearly as massive.
But there are always bigger
and badder planets out there.
Like Kepler-7 b.
This one is interesting.
Kepler-7 b is larger than Jupiter,
but it has half of Jupiter's mass.
This means
the planet is like a superlight cloud.
A scorching hot superlight cloud.
Kepler-7 b is a hot Jupiter planet.
It's 12 times hotter
than the king of the Solar System.
Still, Kepler-7 b is not the hottest
or the weirdest of the exoplanets.
Some of these gas giants
are so unimaginably hot that
they tear molecules apart.
And some planets are just doomed.
1,400 light years away from Earth,
a star slightly bigger
and hotter than our Sun
is devouring its planet.
This planet is called
WASP-12 b.
It's almost double the size of Jupiter,
but it's not going to last very long
as far as planetary lives go.
WASP-12 b is so close to its star
that it takes just over one
Earth day to complete its orbit.
Its own star
is actually eating
the planet's atmosphere,
making it stretch
into the shape of this egg.
10 million years from now,
WASP-12 b will be gone.
And some exoplanets
are unimaginably huge.
The biggest one of them
is almost seven times
larger than Jupiter.
HD 100546 b isn't just seven times
larger than Jupiter,
it's also 750 times more massive.
HD orbits its star ten times further away
than Jupiter orbits the Sun.
That's pretty far.
And it makes scientists
wonder how this gigantic exoplanet formed
so far away from its star.
There's no doubt that some exoplanets out there
look promising for finding life.
We've found quite a lot of them
orbiting in the habitable
zone of their stars.
In fact, some of these worlds
might even be better for life than Earth.
But that's a story
for another WHAT IF.