One of my lifelong goals
is to find an Earth sized planet in an Earth like orbit about a sun like star.
One that has a thin atmosphere, and that has water oceans.
One where we can we can point to a specific star
and say that star has a planet like Earth.
What I love to dream about is maybe there's some life on that planet
you know, looking back at our Earth and our star and saying the same thing.
Like how amazing would that be?
It would be amazing.
Now, this idea - that the stars have planets of their own
and that those planets might have aliens living on them
has been around for centuries.
At first it had some pretty harsh critics.
But by 20th century, it was mainstream.
Alien worlds showed up in books and then movies and TV.
"In this galaxy, there's a mathematical probability of three million Earth-type planets."
But here’s the thing - even after all that,
even when this episode of Star Trek: The Next Generation aired in 1987
scientists still hadn’t confirmed the existence of a single planet outside our solar system.
For all we knew, these so-called “exoplanets” could only be found in fiction.
But the next generation of astronomers,
armed with new telescopes and more powerful computers,
set out to change that.
This is Sara Seager.
She’s a professor of astrophysics at MIT.
It's the spirit of us being the first explorers, you know.
We get to see what's out there for the very first time.
We get to know if there are other planets like ours.
Here’s a map of what they’ve found so far:
It's our night sky, which is a sphere projected onto this square map.
It's sort of one of the maps of the world, it's like, well,
obviously we're on a globe, but this is all stretched out.
Exactly, it’s all stretched out
The black dots are visible stars with the North Star, Polaris
up here at the top of the map.
And this band is the densest part of our own Milky Way Galaxy.
The lines trace out constellations.
So we can look for a familiar constellation like the Big Dipper.
Up here.
And here's Orion, actually.
And these colorful dots mark the position of stars with known “exoplanets”.
The very first exoplanet around a sun-like star
wasn’t discovered until 1995.
It was called 51 Pegasi b.
And this was an incredible planet.
It's astonishing.
It's about a Jupiter mass.
But the time that it takes to go round it star
remember Jupiter takes 12 years, 51 peg takes four days.
So it's year is four days long.
Yeah, I don't think you could celebrate New Year's.
But on 51 Peg b you’d have other things to worry about.
The planets in our solar system that are about its size
aren’t great places to live.
They’re mainly just hydrogen and helium.
There’s no surface.
It just gets hotter and hotter and higher and higher pressure
and eventually we would melt and we would be crushed.
Plus it’s really close to its star
much, much closer than even Mercury is to our sun.
So it’s likely as hot as molten lava.
Great, what else we got?
After all this dreaming for millennia, it turns out
our very nearest star to our sun has a planet.
And that is Proxima Centauri.
About an earth mass planet, we don't know the mass exactly
and it's in the habitable zone of that star.
The Goldilocks zone or the habitable zone
has the right temperature for liquid water.
It's not too hot.
Not too cold.
But just right for life.
The hotter the star the further away you've got to be.
Proxima Centauri is a red dwarf much cooler than our sun
so you've gotta be really close to stay warm.
When a planet is that close to its star, its rotation becomes locked.
Meaning that one side of the planet always faces toward the star
one always faces away.
That’s what happened to our moon.
That’s why we see only one side of it.
If could visit that planet, the sun or the star
would be in the same place in the sky at all times.
So basically, yeah, there'd be a line on the world
-where it would always be sunset or sunrise, essentially. -Exactly.
-What's going on with this giant blob over here? -It's amazing.
This blob is where NASA's Kepler space telescope
stared at for about four whole years.
“Two, engine Start, one, zero! And liftoff of the Delta 2 rocket with Kepler.”
The Kepler Space Telescope found thousands of exoplanets
by focusing on one patch of sky.
Here’s all the discoveries made by other telescopes.
And here’s Kepler’s contribution.
So back here in the Kepler field
there's a really interesting planet called Kepler 16 B.
It was the first one where one planet is orbiting two stars.
Sometimes science fiction is right - Tatooine.
But in this case, it's a giant exoplanet.
So once again, probably not one where we'd be walking around
and talking to Obi Wan Kenobi or anything.
No, but still, it is supposedly in or near the habitable zone of Kepler 16.
So people like to see if it has a moon.
That moon actually could be habitable.
Imagine the sky there, lit by two suns...
...Two shadows, two sunsets...
...and dominated by a massive planet.
Okay, let's look for pretty much the favorite exoplanet system right now.
-Great. -It's called TRAPPIST-1.
It has seven planets around it.
And they're all around about Earth mass.
So you were talking about Mercury before as sort of a reference point
for the distance to the star: do you know how far...
Yeah, all these planets would be interior to what would be Mercury's orbit.
-It’s a very cute sort of planetary system. -Cute and they’re all lined up in a plane.
Y'know if we were on one of these planets
we could see the other planet in the sky would be
like bigger than our moon or something.
And probably moving then.
You would look up and see a moon shooting across your sky.
Scientists think that planets E and F fall in that sweet, sweet Goldilocks zone.
But even if that’s off, some of these planets must be the right temperature for life.
The James Webb Space Telescope...
Which launched on Christmas morning 2021.
...it has targeted every planet in the Trappist system.
So we’ll be learning a lot more about it.
And what’s going to be different about that versus what we’ve seen before?
The James Webb will be much more powerful, it has a bigger collection area.
And it'll be orbiting very far from Earth where the environment is just quieter and darker.
Plus the telescope can see infrared light
which will make it easier to study exoplanet atmospheres.
This is where the science seems to be headed:
fewer surveys of broad swaths of sky, more targeted investigations
of nearby stars and the atmospheres of planets we’ve already found
to see if any of our neighbors might support life.
You know, there's sort of a habitable zone for marshmallows.
Actually there really is and it’s down here right by the coals.
Okay, here we go.
Oh yeah.
So we’ve found like 4,000?
Yeah, thousands.
Thousands of planets.
What has been most exciting to you?
It's everything!
I mean, it's the sheer surprise, like we'll find planets we had no idea existed.
In our nice familiar system, we’ve got a handful of petite rocky planets.
And a handful of massive fluffy giants.
And nothing in between.
But out in the rest of the galaxy
the most common planets we’ve found are big, dense, rocks nicknamed Super Earths.
And big, less dense “Sub-Neptunes.”
To me what's the most mysterious is our solar system is not incredibly common.
The surveys have been going on for long enough
that they should have seen lots and lots ofJupiters
but they’ve maybe only found one or two that resemble ours.
And still no sign of a true Earth twin.
Do you think that’s out there?
It's definitely out there somewhere!
The question is:
is one around a near enough star that the telescopes we're trying to build
can actually find?
Even if we do find that though,
it won’t be for a long time that we're ever able to visit or communicate.
And maybe never.
So what’s the point?
People always ask me, why are we doing this?
Why are we searching for other planets?
Why do we want to find another Earth?
It's human nature to explore.
We want to know what's out there.
We've surveyed all the land on Earth, most of the oceans.
And what's out there now it's outer space.
We want to try to understand, why are we here?
How did our Earth come to be?
And finding other worlds like our own is a step in that direction.