But as its core shrinks,

the Sun itself grows larger.

And it will continue to grow,

until one day,

it engulfs the Earth.

Every one billion years,

the Sun becomes 10% hotter.

But here on What IF,

we're going to take billions of years

and condense the action into one month.

Get ready,

because we're going to be moving

really fast this time.

Instead of one billion years,

it would only take four days

for the Sun to become 10% hotter.

This means you'll see the Earth

engulfed by the Sun in just one month.

That is,

if you're still around to witness

the final event.

On day one,

you'd be blissfully unaware

of the tragedy about to befall Earth.

Maybe it's a little hotter,

but that's just weather.

It happens.

But by day four,

space agencies across the globe

would be sounding the alarm bells.

By this time,

the Sun would be about

10% brighter and hotter.

And while 10% doesn't sound like a lot,

it will be the beginning of the end for us.

As the Sun heat up,

more and more water from Earth's surface

will evaporate into the atmosphere.

This will increase the

greenhouse gas effect,

causing global temperatures to skyrocket.

All of a sudden,

it will become very humid,

and very hot.

But the Sun's high-energy light would

bombard the atmosphere,

splitting those water molecules

into hydrogen and oxygen.

Earth will begin to lose its water.

And you won't be able to escape

the lethal radiation on Earth's surface.

If you want to survive,

you'll have to go deep underground.

But even under a protective layer

of Earth's soil,

you won't be safe for long.

By day 16,

the Sun would be almost 40% brighter.

Our planet's oceans will boil,

and there won't be any moisture left

in the atmosphere.

The beautiful,

lush Earth that you grew up on

will become a hot,

dry,

barren rock.

Around day 20,

the Sun would run out of hydrogen.

So instead,

it will start to burn helium in its core.

The Sun is now a red giant star,

and would expand rapidly

while losing its mass.

The Sun's gravitational pull on Earth

would be weakened,

and our planet would begin to drift away

from the expanding Sun.

But not far enough.

According to researchers Klaus-Peter Schroder and Robert C. Smith,

the Earth would only have moved about 0.0002 astronomical units.

An astronomical unit

is the distance between Earth and Sun.

While Earth is moving away

from the encroaching Sun,

the red giant would grow up to 1.2 AU in radius.

The Sun would be larger than Earth's orbit.

It would swallow the planet whole.

Once it's inside the Sun's atmosphere,

Earth would collide with particles

of gas and spiral inward.

And Earth wouldn't be the only casualty

of the expanding Sun.

Mercury and Venus would be vaporized.

The rings of Saturn would melt.

Pluto would become much warmer.

And if there is a liquid surface,

and a thick atmosphere

on this distant dwarf planet,

it even might become inhabitable.

Unfortunately,

30 days doesn't give the human race

enough time to prepare for such

a catastrophic event.

But if we had more time,

like billions of year's worth,

we could come up with an evacuation plan.

But that's a story for another What IF.