Everyone’s aware of gravitational force. It’s the force which has kept our solar system intact in a nutshell till today. This force is applicable to every body in this universe. Right from gravitational force of attraction between two people standing on the surface of our planet to the gravitational force that holds our Earth in it’s orbit around the Sun. This all physics is just a play of centripetal force of attraction between different bodies which holds this galactic system.
For instance, the centripetal force between the Earth and Sun holds our planet in it’s desired orbit around the Sun. In between these centripetal lines of force there exist some unique equilibrium points. These points are called as Lagrange Points. A Lagrange point is a location in space where the combined gravitational forces of two large bodies, such as Earth and the sun or Earth and the moon, equal the centrifugal force felt by a much smaller third body. These points are named after Joseph-Louis Lagrange, an 18th-century mathematician who wrote about them in a 1772 paper concerning what he called the "three-body problem."
Structure of Lagrange points:-
There are five Lagrange points around major bodies such as a planet or a star. Three of them lie along the line connecting the two large bodies. In the Earth-sun system, for example, the first point, L1, lies between Earth and the sun at about 1 million miles from Earth. L1 gets an uninterrupted view of the sun, and is currently occupied by the Solar and Heliospheric Observatory(SOHO) and the Deep Space Climate Observatory.
L2 also lies a million miles from Earth, but in the opposite direction of the sun. At this point, with the Earth, moon and sun behind it, a spacecraft can get a clear view of deep space.
The third Lagrange point, L3, lies behind the sun, opposite Earth's orbit. For now, science has not found a use for this spot.
Points L4 and L5, however, are stable, "like a ball in a large bowl," according to the European Space Agency. These points lie along Earth's orbit at 60 degrees ahead of and behind Earth.
Benefits of Lagrange points:-
If a spacecraft uses a Lagrange point close to Earth, there are many benefits to the location.
The Jet Propulsion Laboratory is carrying a mission headed by Amy Mainzer. Mainzer is the principal investigator of NEOWISE, a mission that searches for near-Earth asteroids using the Wide-Field Infrared Survey Explorer (WISE) spacecraft that orbits close to our planet. Mainzer proposed that, a spacecraft placed at a Lagrange point would be able to do more.
Far from the interfering heat and light of the sun, an asteroid-hunting spacecraft at a Lagrange point would be more sensitive to the tiny infrared signals from asteroids. It could point over a wide range of directions, except very close to the sun. And it wouldn't need coolant to stay cool, as WISE required for the first phase of its mission between 2009 and 2011 — the location itself would allow for natural cooling.
Lagrange point science:-
After knowing the definition and the benefits of the Lagrange point, it is essential to know how it all works.
Lagrange points being stationary points in free space, achieve an equilibrium state. Therefore, the space debris such as dust particles, dust clouds as well as asteroids tends to accumulate at such points. Such positions where accumulation of these space debris is quite high at the Lagrange points can act as natural satellites in free space. However, these predictions are not yet proved.
Lagrange Points in Action:-
In 2016, NASA released a video of the Earth spinning through an entire year. The time-lapse was based on 3,000 pictures taken every two hours by the EPIC camera on the Deep Space Climate Observatory (DSCOVR) satellite, which was at L1. Besides showing pretty views, EPIC provides scientists with metrics on climate such as cloud height, ultraviolet reflectivity, or ozone and aerosol levels.
In February 2017, the OSIRIS-REX mission — then on its way to asteroid Bennu — spent about 10 days looking for additional Trojan asteroids in Lagrange points near Earth. "That would be the most fascinating thing we could discover," mission lead scientist Dante Lauretta, a planetary scientist with the University of Arizona's Lunar and Planetary Laboratory, told a NASA science advisory group in January. The search revealed no new Trojans, but perhaps other spacecraft will look again in the future.
· Neil DeGrasse Tyson: The Five Points of Lagrange (Natural History magazine)