When astronomers think of Trojans, they rarely think of inhabitants of ancient Troy or harmful computer programs. This refers to special celestial bodies: Trojans are asteroids that either run ahead of or behind a planet in its orbit. While the giant planet Jupiter has so far had almost 10,000 such Jupiter trojans in our solar system, only one such companion was previously known to exist on Earth. However, he now has company. A team led by Toni Santana-Ros from the University of Alicante announced the discovery of the second Earth Trojan in the journal Nature Communications.
The one named 2020 XL5 christened asteroid precedes the earth on its orbit. Just like the first earth trojan TK discovered in 20117 moves around the Lagrange point L4. Celestial bodies at this point form an equilateral triangle with the Earth and the Sun, which stabilizes the orbit of these objects.
Earth Trojans like 2020 XL5 are difficult to find
There are probably more of these celestial bodies out there. There is no reason why Earth should not be accompanied by many more Trojans. Because Trojans are not a special class of asteroids per se, but celestial bodies at the Lagrange points L4 and L5. The Lagrange points describe theoretical points in a system of two massive celestial bodies at which a third, lighter body can be located, quasi powerless. The James Webb Space Telescope, for example, recently arrived at its destination: an orbit around the Lagrange point L2.
In contrast to L2 are the Lagrange points L4 and L5 stable. This means that if a light celestial body is there, it will remain there for the foreseeable future – such as the thousands of Jupiter trojans or now the newly discovered 2020 XL5, which according to calculations will precede the earth for around 4000 years. However, Earth Trojans are very difficult to find and observe: Due to the geometry – Sun, Earth and the Lagrange point L4 form an equilateral triangle – these objects can often only be observed from our perspective close to the sun. In addition, they are usually in the shade and are therefore very faint.