What if our Moon had a twin?
Seeing not just one, but two of these satellites in the night sky
might be spectacular.
But how would a second moon affect the ocean tides?
This is WHAT IF,
and here's what would happen
if the Earth had two moons.
Despite what you think, the Earth isn't really the monogamous type.
Along with the Moon, Earth has another moonlike companion -
a small asteroid wandering around it.
But it's so far and so small,
that it can only be considered a quasi-satellite to our planet.
In our scenario, we're talking two real moons.
Just like the Earth had during its formative period.
Yep, we likely had two satellites once.
Both of them formed when a Mars-sized protoplanet
slammed into Earth and shattered into small pieces.
So what exactly would happen
if the Earth had another moon parked in orbit around it?
Let's assume our second moon would be around 1,000 km (620 miles) wide,
and about one-thirtieth the mass of our current Moon.
It would be about the same distance from Earth, too.
Just like the sister satellite our Moon had 4.5 billion years ago.
Absolutely.
The second moon would just appear about three times smaller.
Still, it would be a spectacular view.
Along with two moons would come some big tides.
The newly captured moon would have a much smaller tidal effect
than that of the Moon.
But the tidal force from both satellites combined would make waves, literally.
Although those waves would be bigger,
they wouldn't be devastatingly big.
In the end, I think surfers will be pretty happy.
The second moon might stay in Earth's orbit for tens of millions of years.
Until eventually, as the Moon retreated further from the Earth,
it would destabilize the other moon's orbit.
Then, just like they did over 4 billion years ago,
the two satellites would collide in slow motion.
Because they'd be moving slowly towards each other,
the debris from the collision wouldn't shower back on Earth.
The small moon would splatter itself across our Moon
as an extra layer of solid crust.
The new mountains of crushed rock visible from the near side of our Moon
would be the only reminders of its existence.
Now, what if the second satellite
happened to be the same size as the Moon
and orbited the Earth at half the lunar distance?
This time things wouldn't be so pretty.
The second moon alone would produce tides 8 times greater
than what we see right now.
That would force people away from the coastal areas
because the difference between high and low tides
would now reach 300 meters (1,000 feet).
Constant tidal flooding would shrink the habitable area on Earth.
But once we adapted to this new world,
we'd get to enjoy a beautiful double-moon.
This time, the second satellite would look bigger from Earth
due to its closer orbit.
The moons would also have different phases,
which means we'd have to come up with another way to measure a month.
And then there's some worse news.
The two moons would be slowly moving away from Earth,
and eventually crash into each other.
This collision would send debris back to Earth.
It would be a shower of meteorites of epic proportion.
And it could wipe us out entirely.
Whatever debris didn't fall to Earth
would form yet another new moon in Earth's orbit.
At that point, a new, post-human life form may begin to evolve
and become Earth's next civilization.
But that's a story for another WHAT IF.