What Are Lagrange Points?

If you’re learning about the locations of spacecraft or asteroids, you’ve probably come across Lagrange points that are sweet spots for small objects. Let’s find out what they are and how they work in this article.

What Are Lagrange Points?

Lagrange points are places where the gravity of two bodies is in balance. There are five of them: L1, L2, L3, L4, and L5. L1, L2, and L3 are unstable, whereas the other two points are stable. These five locations exist between any two objects where the second object orbits the first object, such as Jupiter and the Sun, Earth and the Sun, and Earth and the Moon.

The L4 and L5 points are stable, so they can hold natural objects with ease. These asteroids caught in those points are called Trojans, with the most prominent group being the Jupiter trojans, with members existing near both the L4 and L5 points. There are trojans of other planets, including Earth. The first Earth trojan is 2010 TK7, found by the WISE space telescope.

Positions of Lagrange Points

Let’s talk about the positions of the 5 Lagrange points in this section. Note that we will use the Sun and the Earth as an example, and these properties apply to any pair of objects where one object orbits the another.

L1, L2, and L3 are in the imaginary line connecting Earth and the Sun. L1 and L2 mark the boundaries of the Hill sphere of Earth. The Hill sphere is where an object can retain a satellite because its gravity is dominant in this place. L3 is 180 degrees behind Earth in orbit around the Sun. If a spacecraft enters any of these Lagrange points, they tend to stay in a halo orbit, which revolves around the exact point of balance. Without regular rocket firings, these space probes will eventually drift away because of other forces.

The L1 point is closer to the Sun than the Earth. Therefore, an asteroid should orbit faster than Earth. However, Earth’s gravity pulls the asteroid toward itself, meaning the asteroid and Earth will orbit in sync. The L2 point works the same way. The asteroid should orbit slower than Earth, but Earth’s gravitational pull speeds the asteroid up to just the right velocity so that it goes around the Sun once a year.

Meanwhile, the L4 and L5 points are located 60 degrees ahead of and behind Earth in Earth’s orbit, respectively. However, fuel is not required to stay around these points. If any outside forces are acting on the asteroid, the asteroid will still maintain its position thanks to the stability of the L4 and L5 points. That’s why so many asteroids are trapped in the L4 and L5 points of Jupiter without getting ejected. For these Lagrange points to hold objects with stability, Earth must be more than 24.96 times as massive as the asteroid.

How Do We Use Lagrange Points?

Lagrange points are handy for space exploration as space probes can use them for convenience. The L1 point can give us a constant view of the Sun while maintaining stable communications with Earth. This eliminates the possibility of solar conjunctions, which can corrupt commands sent from Earth. Some solar explorers, such as SOHO, ACE, and Wind, resides in this spot over the years.

The L2 point is an ideal home for space telescopes. Other than preventing solar conjunctions, it can provide a clear view of the Universe. The Sun and Earth essentially only occupy a relatively small amount of space from the telescope’s view, allowing large observation areas with minimal obstructions.

Conclusion

In this article, we’ve discussed Langrage points and their purpose. They can be really useful for space exploration, and you should know these sweet spots that facilitates communications and observations. If you want to know more, you can search online or visit the sites in the references below.

References and Credits

1. ESA – Operations. (n.d.). What are Lagrange points? Retrieved May 21, 2021, from http://www.esa.int/Enabling_Support/Operations/What_are_Lagrange_points
2. Elizabeth Howell. (2017, August 22). Lagrange Points: Parking Places in Space. Retrieved May 21, 2021, from https://www.space.com/30302-lagrange-points.html
3. NASA/WMAP Science Team. (2018, March 27). What is a Lagrange Point? Retrieved May 21, 2021, from https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/
4. NASA Jet Propulsion Laboratory. (2011, July 27). NASA’s WISE Finds Earth’s First Trojan Asteroid. Retrieved May 22, 2021, from https://www.jpl.nasa.gov/news/nasas-wise-finds-earths-first-trojan-asteroid
5. Fraser Cain. (2016, August 26). What Are The Lagrange Points? Retrieved May 22, 2021, from https://www.universetoday.com/102785/what-are-lagrange-points/