Lagrange points: Park your spacecraft here - Fabio Pacucci
Since the launch of the first
artificial satellite in 1957,
governments, companies,
and research institutions
have been planting flags among the stars.
But while it might seem like there's
plenty of room in this vast expanse,
some pieces of celestial real estate
are more valuable than others.
Each of these dots is a Lagrange point,
and as far as human space exploration
is concerned,
they may be the most important places
in our solar system.
Named after the 18th century mathematician
who deduced their positions,
Lagrange points are rare places
of equilibrium
in our constantly shifting universe.
All celestial bodies exert
a gravitational force on nearby objects,
pulling them in and out of orbits.
And gravity acts alongside several
apparent forces
to determine what those orbits look like.
However, Lagrange points are places
where all these forces balance out.
So if we place a relatively
low mass object here,
it will maintain a constant distance
from the massive bodies pulling on it.
Essentially, Lagrange points are
celestial parking spaces—
once an object is there, it requires
little to no energy to stay put.
So whenever humans want to keep
an object in one place for a long time
without using tons of fuel,
it needs to be orbiting a Lagrange point.
However, there are only so many
of these parking spots.
Pairs of massive bodies
in our solar system
generate sets of five Lagrange points.
This means our Sun has
five points with every planet,
and our planets have five points
with each of their moons.
Adding these up, there are over 1,000
Lagrange points in our solar system—
but only a few are useful
for human purposes.
Many are in locations that are
too difficult to reach
or simply not very useful.
And for reasons we'll explain in a bit,
many others are unstable.
Currently, only two of these points
are heavily used by humans.
But we’ll likely use many
more in the future—
making these limited points
exclusive real estate.
Which begs the question:
what exactly should we park in them?
That answer depends
on where each point is.
Consider the five Lagrange points
generated by the Sun and the Earth.
L1 is located inside Earth's orbit,
about 1.5 million kilometers
away from the planet.
With this panoramic view of the Sun,
unobstructed by Earth’s shadow,
L1 is the perfect place
for solar-observing satellites.
L2 is at the same distance from Earth
but outside its orbit
and shielded from the Sun,
making it the perfect spot
to observe outer space.
In 2022, the James Webb Space Telescope
went online here,
in a spot where the Sun and Earth
only occupy a tiny fraction of the sky.
L3 is in a particularly
mysterious location
that can never be directly observed
from Earth’s surface.
This has made L3 a frequent locale
in science fiction,
though it hasn’t offered much use
to scientists yet.
L4 and L5, however, are a bit different
from their siblings.
In every set of five, the first three
Lagrange points are slightly unstable.
This means objects will slowly drift
away from them,
though keeping what we’ve parked there
in place is still energetically cheap.
The stability of L4 and L5, however,
varies from set to set.
If the heavier of the two bodies
generating the points
has less than 25 times the mass
of the lighter body,
these points are too unstable
to park things in.
However, if the heavier body is massive
enough— like it is in Sun-Earth set—
then the relevant forces will always
return objects
to these equilibrium points,
making them our most stable parking spots.
That’s why points like these
naturally accumulate space objects,
such as the Sun-Jupiter set’s L4 and L5,
which host thousands of asteroids.
Every Lagrange point in our solar system
has its quirks.
Some might be perfect for scavenging
construction materials
from drifting asteroids.
Others might make ideal gas stations
for ships headed to deep space,
or even host entire human colonies.
These points are already home
to advanced technological achievements,
but soon, they could become
our stepping stones to the stars.
