- [Narrator] We inhabit a little blue planet called Earth.
Earth is habitable because it had the right conditions
and ingredients to enable life as we know it
to evolve and flourish.
And one of the most important factors
in making our blue planet habitable
is the wet stuff itself, water.
It's kind of extremely important for life.
When it comes to the search for habitable exoplanets,
planets outside our solar system,
we think the ability to have liquid water
on a planet's surface is just as important for those worlds.
There's a handy concept astronomers use
to help them figure out where to look around any given star
for exoplanets that just might have the right stuff light.
It's called the habitable zone.
It's the distance from a star where a rocky planet
with an atmosphere could have liquid water on its surface.
In our solar system, the habitable zone extends
from around the orbit of Venus to around the orbit of Mars.
Earth happens to be nice and comfy in the middle.
But it takes more than just a good location.
Orbiting in the habitable zone does not guarantee a planet
will be habitable.
After all, the Moon is right here with us,
but it's certainly not habitable.
Sorry, Moon.
The location of the habitable zone depends
on how big and bright a star is.
The nearest star to our sun, Proxima Centauri,
has at least one planet in the habitable zone.
But because Proxima is much smaller and dimmer than our sun,
its habitable zone is way smaller and closer to the star.
So every star has a habitable zone,
but that doesn't mean there will be planets there.
For example, the star known as Kepler-90 is similar
to our sun and it too has eight planets,
but they're all huddled super close to the star,
well inside of the habitable zone.
But the longer we look,
the more likely it becomes that one day,
we'll find another little blue water-covered planet
right in its own comfy habitable zone.
And that would be a planet worth a closer look, indeed.
(playful music)