The Aditya-L1 probe will reach its final destination in just a few days in the space between Earth and the Sun, approximately a million miles away.
A Special and Interesting Place
There are already four active spacecraft in orbit near the first Lagrange point, also known as L1 in the Earth-Sun system, with other spacecraft stationed nearby.
It is a special place where the gravitational pull of our planet, the gravitational pull of the Sun, and the centrifugal force of the spacecraft’s orbit nearly cancel each other out, creating a “island” of relative stability in the constantly changing gravitational field of the solar system, where gravitational fields continuously change with the motion of the planets. The result is that spacecraft orbiting the Sun near L1 – a region that actually extends for hundreds of thousands of miles – remain stable with respect to Earth without needing to consume large amounts of fuel.
Sun Monitoring
Astronomer Neil Cornish from Montana State University, who has worked in this field and contributed to NASA’s final explanation of the Lagrange points, says: “The first Lagrange point is a wonderful place if you want to observe the Sun. There is no obstruction from Earth at any point in the orbit – you can just sit there and gaze at the Sun.”
Aditya-L1 Mission
The arrival time of the Aditya-L1 probe at its final destination has not been determined until the first week of January, but the probe has already started its observations of our parent star with its first images of the solar disk. It will soon enter a “halo” orbit around L1, allowing the probe to orbit the Sun stably, through small pulses from its thrusters every few weeks. Cornish points out that this stable area is so wide that the numerous spacecraft near L1 do not see each other and do not come into collision with one another. He says: “There is no danger at all of collision with anything there.”
Lagrange Region
L1 is not the only island of relative stability in space. Each planet around the Sun has its own Lagrange points. They also have moons and planets that share their orbit around the Sun – including our Moon and Earth – which also have Lagrange points.
Scientists have known about these points for decades, since the Swiss mathematician Leonhard Euler introduced three of them as solutions to the “three-body problem” that arose from Isaac Newton’s laws of gravity. The Italian-French astronomer Joseph-Louis Lagrange expanded on Euler’s work and discovered five such points that arise from the gravity between the Sun and Earth. They are now known as Lagrange points in his honor.
The Third, Fourth, and Fifth Points
The third point, or L3, is located directly on the far side of the Sun and is a bit further out than Earth’s orbit. Earth’s viewpoint of this point is always blocked by the Sun, preventing direct communications to and from our planet, so no spacecraft are stationed there.
The fourth and fifth points, or L4 and L5, share Earth’s orbit around the Sun but are located 60 degrees directly in front of and behind Earth, respectively. Observations show that both L4 and L5 are occupied by temporary clusters of asteroids that take advantage of Earth’s gravity. These space rocks are known as “Trojan asteroids,” and similar Trojan asteroids exist at the fourth and fifth points of other planets like Jupiter.
L2 Point
The true essence of all the Lagrange points between Earth and the Sun is L2, which is located about a million miles from Earth but outside our planet’s orbit, in the opposite direction of L1. When viewed from L2 towards the Sun, Earth, the Moon, and the Sun always appear clustered together in the sky, allowing spacecraft to block out any stray light that might emanate from any of the three. Consequently, L2 has become a favored destination for numerous space probes, including the James Webb Space Telescope. The latest inhabitant of this point is the European Space Telescope Euclid, which reached L2 last year to measure the effects of dark energy and dark matter in the universe.
The Road
The Interplanetary Gateway
For Martin Lo, an expert in spacecraft trajectories at NASA’s Jet Propulsion Laboratory, the Lagrange points serve as gateways to a “space highway” that stretches throughout the entire solar system.
There are seven key Lagrange points within 1.2 million miles of Earth, according to his observations, with points L1 and L2 in the Earth-Sun system and five “lesser” points for the Earth-Moon system. Because all of these nearby regions share similar orbital energies, a spacecraft needs only a small “boost” to move from one point to another – much like a person swinging from bar to bar on a playground swing set.
Planetary Exploration and the Search for Extraterrestrial Life
The potential of these Lagrange points to allow for efficient orbital transport shapes Lo’s work in NASA’s Artemis mission, which aims to return astronauts to the Moon and establish a crewed space station orbiting near the first Lagrange point between Earth and the Moon. He is currently studying the complex trajectories that exist between the Lagrange points found between Saturn and its many moons. One of these moons, Enceladus, may be the best place in the solar system to search for extraterrestrial life.
“Enceladus emits icy plumes near the south pole, and we are using these trajectories to determine how to enter orbit around it and capture materials from it” – a matter of using the smallest possible boosts to get to the right location, speed, and timing.
Tom Metcalfe is a freelance journalist based in London. He writes most of his articles about science, space, archaeology, Earth, and the oceans. He has also written for Live Science, BBC, NBC News, National Geographic, Air & Space, and many others.
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