A Limited Number of Parking Spaces...

Since the first artificial satellite was launched in 1957, governments, corporations, and scientific institutions have planted flags among the stars. While there may appear to be plenty of space in this vast expanse, some pieces of heavenly real estate are more valuable than others.

Each of these dots is a Lagrange point, and they may be the most critical locations in our solar system for human space exploration.

Lagrange points, named for the 18th century mathematician who discovered them, are rare regions of equilibrium in our continually shifting universe. All celestial bodies have gravitational forces that draw neighboring objects into and out of orbits. Gravity, along with various other apparent forces, determines the shape of such orbits. Lagrange points, on the other hand, are locations where all of these forces balance out.

If we position a low-mass object here, it will keep a constant distance from the enormous things pulling on it.

Lagrange points are essentially cosmic parking lots—once an item is there, it requires little to no energy to stay put. Whenever humans wish to hold an object in one position for an extended period of time without burning a lot of fuel, it must orbit a Lagrange point.

However, there are only so many parking spaces available In our solar system, pairs of heavy bodies form sets of five Lagrange points.

This means that our Sun has five points with each of our planets, and each of our planets has five points with each of their moons.

There are about 1,000 Lagrange points in our solar system, but only a few of them are relevant for human uses. Many are in locations that are either inaccessible or ineffective.

Many others are unstable for reasons we'll discuss later. Only two of these points are currently heavily used by humans. However, we will most certainly employ many more in the future, making these few points exclusive real estate. That begs the question, what should we park in them? The answer is determined by the location of each point.

Take a look at the five Lagrange points produced by the Sun and the Earth.

L1 is located 1.5 million kilometers distant from Earth in Earth's orbit.

L1 is an ideal location for solar-observing satellites due to its unimpeded panoramic view of the Sun.

L2 is the same distance from Earth as Earth but beyond its orbit and sheltered from the Sun, giving it an ideal location for observing deep space.The James Webb Space Telescope will be operational here in 2022.

L3 is in a particularly enigmatic place that can never be seen directly from Earth's surface.

This has made L3 a common setting in science fiction, albeit it has yet to be of much service to scientists.L4 and L5 are, nevertheless, distinct from their siblings. The first three Lagrange points in each set of five are mildly unstable.

This means that items will gradually drift away from them, while maintaining what we've parked there in place is still cheap in terms of energy. However, the stability of L4 and L5 varies from set to set. If the heavier of the two bodies generating the points has a mass that is less than 25 times that of the lighter body, the points are too unstable to park in. However, if the heavier body is large enough, as in the Sun-Earth pairing,

The relevant forces will always bring items back to these equilibrium positions, making them our most stable parking sites.As a result, sites like this naturally accumulate space objects, such as the Sun-Jupiter set's L4 and L5, which are home to thousands of asteroids.

Each Lagrange point in our solar system has its own peculiarities. Some may be ideal for scavenging building materials from drifting asteroids.Others could serve as great fuel depots for ships heading into far space, or perhaps as home to entire human colonies.These points now house significant technical achievements, but they may soon become our stepping stones to the stars.