Perfect placement: L2 provides a unique perspective on the Sun
Aditya-L1 will join four spacecraft at the first Lagrange point. This point represents an almost stable region in the gravitational field between the Earth and the Sun. The spacecraft will reach this point in the coming days, being at a distance of about 1,600,000 kilometers from our planet.
At this point, the Earth's gravity, the Sun's gravity, and the centrifugal force of the orbit work together to cancel each other out, creating an «island» relative stability in the changing gravitational field of the solar system. As a result, spacecraft orbiting the Sun near L1 — an area of about 800,000 kilometers — remain motionless relative to the Earth, while saving a significant amount of fuel.
Although Aditya-L1 has not yet reached its final position, the coronagraph has already begun making observations of the Sun, creating the first images of the solar disk. In the coming days it will enter the «halo» orbit around L1, which will allow the probe to gradually fly around the Sun, controlling its trajectory, conducting small additional tests of the propulsion system over several weeks. This nearly stable region is vast in size, allowing spacecraft to remain there without the threat of collision.
Currently, the SOHO Solar Heliospheric Observatory, a joint project between NASA and the European Space Agency (ESA), — the longest-staying device at the L1 position. It was launched in 1996 and is equipped with various instruments to study the Sun. Aditya-L1 will also provide images of the Sun in various ranges of visible, ultraviolet and X-ray radiation to further study the dynamics of the solar atmosphere.
The probe will also study «solar weather», determined by solar storms, using four scientific instruments aimed directly at the Sun, as well as three other instruments designed to observe and monitor the solar wind and on the solar magnetic field.
While the Aditya-L1 mission is initially planned for five years, the L1 location will allow the spacecraft to be used for a much longer period. For example, SOHO has already been in operation for more than 25 years, although the solar observatory was originally intended to serve only two years. The SOHO mission was recently extended until the end of 2025.
L1 — not the only point of relative stability in space. Each planet, including the Earth, has its own system of Lagrange points. These points have been known to astronomers since the 1760s, when Swiss mathematician Leonhard Euler proposed three solutions to the “three-body problem” based on Isaac Newton's laws of gravity. Joseph-Louis Lagrange, a French-Italian astrophysicist, developed Euler's ideas, and in 1772 five Lagrange points were discovered, formed by the gravitational interaction between the Sun and the Earth.
The third Lagrange point is located on the side farthest from the Sun and slightly further from the Earth's orbit. It is impossible to observe the Earth from L3, since it is always obscured by the Sun, which makes communication with our planet impossible and it is impractical for spacecraft to be there. The fourth and fifth Lagrange points are located in the Earth's orbit in front and behind it. These points are «populated» groups of Trojan asteroids that move in Earth's orbit.
Lagrange points are key locations for efficient orbital transfers, providing access to the “interplanetary high-speed highway” stretching throughout the solar system. There are seven major Lagrange points located within 1,930,000 kilometers from Earth: L1 and L2, oriented towards the Earth-Sun system, and five minor ones. points related to the Earth-Moon system. Due to the similarity of their orbital energy, the spacecraft requires only a small force to move from one region to another.
L2 — the most valuable of all Lagrange points between the Earth and the Sun. Located approximately 1,600,000 kilometers from Earth in the opposite direction from L1, it provides a unique solar viewing perspective in which the Earth, Moon and Sun always appear clustered in the same position relative to the spacecraft, making it easy to block out stray light coming from any from these three bodies. L2 has been selected as the preferred location for many missions, including projects such as the James Webb Space Telescope. L2 is also home to ESA's Euclid space telescope, which arrived there last year to study dark energy and dark matter. The L2 orbit provides a stable radiation and thermal environment, as well as a full, glare-free view of the sky.
Work on the trajectories of the Artemis missions aimed at delivering astronauts to the Moon and establishing a space station in the vicinity of the first Earth-Moon Lagrange point identified Lagrange points as effective for orbital missions. Scientists are now also studying trajectories between the Lagrange points of Saturn and its moons. Of particular interest is Enceladus, which may be an ideal place in the solar system to search for signs of extraterrestrial life. Its south pole spews ice fountains and scientists are exploring trajectories to fly around the moon and collect material from these fountains.