A scorching hot never-ending day
on one side
and a permanent frozen night on the other.
This is what our planet would be like,
if it was tidally locked to the Sun.
Earth makes one full rotation on its axis
every 24 hours.
And every 365 days,
we complete our orbit around the Sun.
This is what gives us our sunrises,
sunsets and changes of season.
If the speed of this rotation
and revolution were the same,
then Earth would be tidally locked.
This means that one side of the planet
would always be facing the Sun.
And the other would face away,
shrouded in perpetual darkness.
This is why you can only see one side of the Moon.
It’s tidally locked to the Earth.
You should enjoy that nighttime view while you still have it.
Depending on what side of the planet you’re on,
you may never see the Moon or stars ever again.
With one side of the planet facing the wrath of the Sun
and the other facing the darkness of space,
your best odds for survival would be
to live somewhere between the two.
Welcome to the twilight zone.
This thin strip of land that borders both day and night
is also called the terminator line.
It would possibly be the only area
on a tidally locked Earth
where things are not too hot and not too cold.
Just like our Solar System’s Goldilocks zone.
The width of the terminator line
would likely be exactly the same as it is today,
about 60 km (37 mi).
The only difference is that
instead of moving across the planet every day as it rotates,
this strip would be permanent.
If this area of never-ending dusk
and dawn were the only place for humans to live,
things would be quite crowded.
It would mean everyone would squeeze
into a space as large as Argentina
or 25% of the United States.
That is, if you got lucky and the entire strip was made of land
and not water.
Whether anywhere outside of this zone is habitable
would depend on how well heat
could be transported around the planet.
If there are strong enough jet winds on each hemisphere,
they could move hot air from one side and cold air to the other.
With an atmosphere as thick as ours,
these winds could take the scorching daytime side
down a few notches.
And you’d be thankful for every cloud
providing some temporary shade from the Sun.
This hemisphere could end up resembling
the temperatures of Earth’s current tropical regions.
Life would be challenging on our planet.
You know even with a temperature difference as small as 10 °C (50°F)
between each side,
there would be a big pressure difference.
That could turn these once helpful jet winds
into super powerful destructive ones
One of the things you’d find hardest to get your hands on
would be liquid water.
For this to be the case,
areas of the daytime side
would need to have a milder climate.
Even with this,
it may not be enough to sustain everyone.
And on the darkside,
the water would likely freeze to ice.
With such an extreme temperature variation,
you could see water molecules going through a vicious cycle.
On the daytime side,
the intense heat could lead to evaporation.
Then, they could drift over to the dark side,
form back into clouds
and return to the daytime side
where the process would be repeated all over again.
So you’d have to get creative.
You could develop some kind of mining
and transport operation
to take ice from the cold side and melt it.
Or you could convert water vapor
from the day side into liquid water.
One thing you'd have enough of is
solar power.
On the sunny side of the planet,
your supply would be endless.
You'd just have to make sure your solar panels
could withstand the intense heat.
Solar panels already don’t work properly
in some of the hotter places in the world.
Temperatures as high as 50 °C (122 °F),
plus a large build-up of dust
could make these panels 50% less effective.
But you could use the blazing temperatures themselves
as a way to generate electricity.
You'd need what's called thermoelectric technology.
By placing one end of the device on the hot side of the planet
and the other on the cold side,
you could get free electricity
simply from the temperature difference.
There’s a chance this wouldn’t give you much to work with though.
That's because these thermoelectric devices
are usually only used for things
that don’t demand a ton of power.
So you could back up your batteries
or keep your minifridge cool.
Trying to figure out how
and where you could live outside the twilight zone
would be tough.
On the hot side,
you could be dealing with rocks melting around you.
You wouldn't be able to build a house
on a permanent magma ocean.
And the cold side
would make surface living nearly impossible.
Instead you could live deep underground.
There, you'd enjoy the warmth of geothermal heating.
Closer to the twilight zone,
you could get by
in heavily insulated houses.
You'd just need to crank up the air conditioner,
electric radiator
or geothermal furnace.
If you wanted to take more drastic measures
to cool down the hot side of the planet,
you could try to block out the Sun.
And no, I don’t mean with a giant shade.
You could borrow a trick from the 1991
volcanic eruption of Mount Pinatubo in the Philippines.
This released so much sulfur dioxide into the stratosphere
that it cooled the entire planet down by 0.5 °C (0.9 °F).
For global warming,
this could be a helpful solution.
But it wouldn't be quite enough
to cool down the entire hot side of the planet.
You’d also need to come up
with some new ways to support plant life.
If they didn't freeze first,
plants wouldn’t be able to perform
photosynthesis on Earth's dark side.
On the light side,
most plants would be cooked within hours.
You’d need to supply them with artificial sunlight.
Along the terminator line,
you’d be able to harvest a few plants
that don’t need much light
like wheatgrass
and white asparagus.
Or you could go the fungus route
with different varieties of mushrooms.
And if all this weren't enough already,
the sky would never change.
You'd need to find a new way to measure hours, days and months.
And if you didn't settle on the dark side of the Earth,
you'd never see much of the night sky ever again.
No Moon,
no stars
and no planets to dream about.
A few generations down the line
and you could find that humans have forgotten
about the rest of the Solar System
or Universe entirely.
But hey, things could be worse.
Instead of spinning very slowly,
Earth could be spinning at the speed of light.
But that’s a story for another WHAT IF.