It's pretty reasonable to assume that Earth is the ultimate Eden in the universe,

a paradise planet that's just perfect for life.

After all, not only is it our home, but it's also the only place we know life has evolved.

But, as it turns out, there might be even better places to live,

planets even more suitable for life.

Scientists call them superhabitable planets.

They're worlds that could sustain life more than five times longer than Earth, and while

we haven't found one for sure yet, there might be billions of them lurking in our galaxy alone.

The idea of superhabitable planets was introduced in 2014 by two North American researchers:

René Heller and John Armstrong.

And while each planet could look a little different, they would have two main features

that would make them better than Earth.

First, these planets would be able to maintain liquid water much longer than ours.

Earth's cozy, life-sustaining environment is largely thanks to its position relative

to the Sun, along with other factors like the atmosphere.

We exist in what's called the habitable zone,

or the area around a star where liquid water can exist on a planet's surface.

But that won't last forever.

In five billion years or so, toward the end of its lifetime,

our Sun will have expanded into a larger red giant.

And it will actually go through some pretty major changes even before that point.

Over time, as the Sun burns through the fuel in its core, it will gradually become hotter and brighter.

That means it will let out more energy, so the habitable zone will migrate outward.

For us, that means that it will eventually become so hot that the water on Earth will be vaporized.

Which isn't exactly great for anything that wants to live here.

The Sun's habitable zone is currently pushing outwards at about a meter a year.

And it's predicted that we'll fall off the zone's inner edge in some 1.75 billion years.

Two billion years is a really long time,

but it turns out that other planets will stay in their stars' habitable zones for much longer,

because they'll orbit stars better than our Sun.

The Sun is a G-class yellow star, or one of the mid-sized, longer-lived stars in the universe.

But smaller stars actually live even longer.

That's because there's less gravity to power the fusion reactions in the core,

so they burn slower, and their fuel lasts longer.

That means their habitable zones will migrate outwards more slowly, too.

So a planet will be able to maintain the right temperatures for liquid water for many more years.

The smallest stars are M-class red dwarfs, which live for trillions of years.

But they come with their own problems, like explosive solar flares.

So instead, scientists think the ideal stars for habitable planets are the intermediate

K-class orange stars.

They're about 50 to 80% the mass of our Sun and can live more than 30 or 40 billion years.

But superhabitability doesn't just come down to the star.

The second trick to being better than Earth involves tweaking the planet itself;

its atmosphere, geology, and geography.

Earth is pretty good, but we still have deserts, ice caps,

and big chunks of deep ocean without as much complex life.

A superhabitable planet would do away with these barren landscapes to support more species

and more diversity.

And one of the ways of doing that is to be more massive than Earth.

According to researchers, an Earth-like planet maybe twice as massive as ours

would have a bunch of great things for life.

For one, it would have more gravity, which would help to hold on to more atmospheric gases.

That would give the planet more greenhouse-style warming, so it could orbit a little

farther from its star and still stay warm enough to have liquid water.

That would buy it even more time before it fell off the inner edge of the habitable zone.

Stronger gravity would probably also help heat the center of the planet,

which might cause more active plate tectonics.

That would likely be a good thing for life.

A geologically active planet would keep renewing elements like

phosphorus and calcium, which life needs to thrive.

All the shifting plates would keep bringing the elements to the surface,

stopping them from getting trapped in the planet's crust for too long.

And, if that wasn't enough,

higher gravity would also cause the iron core of a planet like this to be hotter.

That would likely result in a stronger magnetic field,

which would protect the planet's atmosphere from particles and flares flying off its star.

So, in around two billion years, when it's time for humans to find a new home,

we have our checklist of requirements.

And the good news is, there might be a pretty good chance of us finding one of these superhabitable worlds.

When scientists peer into the night sky,

K-class stars are actually about twice as common as Sun-like stars.

And since research suggests there are planets around most of the stars in the universe,

there's potential for more than 10 billion superhabitable planets in the Milky Way alone.

Using new space telescopes like TESS, scientists soon hope to study the characteristics and

atmospheres of promising candidates, like one 1200 light-years away called Kepler-62f.

Then, they can see if their hypotheses about superhabitability hold up.

So, while it might come as a bit of an unwelcome surprise that Earth probably isn't the best

place in the universe, there's no need to be too bummed out.

We're well on our way to finding a new Eden out there among the stars.

Then all we have to do is figure out how to get there.

Thanks for watching this episode of SciShow Space!

Whether we're talking about planets, galaxies, or missions,

we love learning about the universe and exploring our place within it.

If you'd like to help us keep making videos like this one, you can go to patreon.com/scishow.

And to all of our patrons, thank you! We couldn't do this without you.

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