science for all newsletter What are Trojan asteroids?

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

Scientists have finally discovered a Trojan asteroid for Saturn, thereby establishing the presence of these celestial bodies alongside all giant planets in our solar system. For a very long time, Saturn remained the only giant planet in our solar system with no Trojan asteroid.

What are Trojan asteroids?

Trojan asteroids are a class of asteroids that occupy a stable Lagrange Point in a planet’s orbit around the sun. According to NASA, a Lagrange Point is essentially a position in space where objects can “stay put”. At these positions, the gravitational forces of two larger objects balance out with the motion of the smaller object. This balancing of forces allows the smaller object to stay in a relatively stable position without drifting away.

For all celestial bodies in orbit, five Lagrange Points exist. L1, L2, and L3 are unstable, and L4 and L5 are stable.

Trojan asteroids are usually found around L4 or L5 points, which makes them gravitationally stable. Their orbit around the sun is similar to the orbit of the planet they are associated with.

Trojan asteroids were discovered by German astrophotographer Max Wolf in 1906, but they were named so later.

Since Trojan asteroids have unusual orbits, the Austrian astronomer Johann Palisa suggested naming them after Achilles, Patroclus, and Hektor, characters in the Greek epic poem Iliad. As astronomers continued to find more of these celestial bodies, they continued to name them after heroes of the Trojan War, with which the Iliad is concerned. This tradition led to the whole class being called Trojan asteroids, although names of Trojan War characters are reserved for Jupiter’s trojans.

Trojan asteroids remain gravitationally stable for long periods of time and studying them can provide useful insights into the evolution of the solar system.

What are the findings of the new research?

According to the new study, Saturn’s Trojan asteroids may have gone unseen because of the movement or migration of planets, destruction due to collisions, smaller stable regions around L4 and L5 compared to those of other planets like Jupiter, and/or long-term gravitational interactions.

The object in question – 2019 UO14 – was first discovered in 2019. The new research used previously collected data and refined the calculated orbit to reach the conclusion that 2019 UO14 is a Trojan asteroid associated with Saturn. It probably became trapped at Saturn’s L4 position around 2,000 years ago and is likely to maintain its orbit for another thousand years.

The researchers uploaded a preprint paper describing their findings to the arXiv repository on September 29, 2024.