Imagine looking up into the night sky
and seeing not one
but 79 different moons
beaming back at you.
Jupiter is the biggest planet
in our Solar System.
With 79 moons,
it falls just behind
Saturn’s moon count of 82.
And these moons come in different sizes.
The teeny-tiny S/2010 J2
is 2 km (1.2 mi) wide,
while the massive Ganymede is
one and a half times the size of our Moon.
Jupiter’s enormous gravitational pull
is to blame for keeping
so many moons in its orbit.
At 778 million km (484 million mi) from the Sun,
it’s not losing any moons
in a gravitational tug of war.
Now, imagine all those moons moved to Earth.
With so many cluttered objects in our orbit, would they all collide
and rain debris down on Earth?
With 79 more moons,
the night sky would look busier.
But since most of the new moons in our orbit would be
less than 10 km (6 mi) wide,
they’d appear more like
bright stars at first glance.
But you’d also have the awesome view of
four giant moons
beaming right back at you.
Those would be IO, Europa,
Ganymede and Callisto.
Of these, Europa would be the moon that looks the most familiar.
It’s about 90% the size of our Moon.
But there would be at least one big difference.
Europa is covered in ice.
That means it would reflect
about five and a half times more sunlight than our Moon.
You’d be wise to wear sunglasses
if you wanted to admire it,
even at night.
The most dramatic effects of having Jupiter’s moons
would come from Ganymede.
While it may be only one and a half times the size of our Moon,
it has double its mass.
With more of its own gravitational pull,
it would have a significant impact on our tides.
Yeah, get ready for massive tsunamis,
extreme earthquakes
and more volcanic activity.
Earth’s tides would be higher too.
Coastal cities would be flooded and abandoned.
In the U.S., where 40% of the population lives near the coast,
127 million people would be displaced.
And so would billions more around the world.
Ganymede’s gravitational pull
could even be strong enough
that the Earth would become tidally locked to it.
This would mean that
one side of the planet
would always be facing this moon.
Now, this would be good news
if you were on that side of the planet.
Hopefully, you made some investments
in hotel property
with a good view of Ganymede.
Moon tourism would be about to boom.
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You’d also notice that Earth’s climate
was more stable if Ganymede began orbiting us.
That’s because a larger moon
would stabilize the angle of Earth's rotation on its axis.
Usually Earth's axis goes back and forth
between an angle of 22.1 to 24.5 degrees
every 41,000 years.
A more stable axis would mean
fewer seasonal changes
and no more pesky ice ages in the future.
But if Ganymede and all these other moons invaded our night sky,
you wouldn’t be able to enjoy the view for very long.
You should expect plenty of havoc.
For starters, our traditional concept of a month
would become obsolete.
Months are based around the natural orbital period of our Moon.
Maybe you’d have 80 months in the year,
one for every moon in the sky.
And not only months,
but your entire concept of a day would likely change.
With the gravitational pull of all these moons,
the Earth’s rotation would change.
With the gravitational pull of our current Moon,
the Earth’s rotation
is expected to slow down to a 30-hour day
billions of years from now.
And with all that light from the Sun
reflecting off each moon,
you’d have to get used to a very bright night.
Yeah, I hope you're not a light sleeper.
But the most chaotic aspect of having so many new moons
would be their overlapping orbital patterns.
Many of the satellites currently in orbit
would be at risk of destruction if they collided with a moon.
And it could jeopardize future space missions too.
Earth's orbit would be
dangerously clustered.
That could mean that the Earth
might end up with rings, similar to what Saturn has.
But it could be that the Earth
doesn't have a strong enough gravitational pull to
hold all 80 moons in place.
Those moons would be so close to the Sun
that the Sun's gravity could win them over.
That could put a few moons on a collision course with the Earth.
With all that potential chaos orbiting Earth,
you'd probably wish that there weren’t any moons at all.
But that’s a story for another WHAT IF.