A recent discovery left astronomers pretty excited: using the SOAR Telescope in Chile, a team spotted the largest Earth trojan asteroid ever found. This type of asteroid is made of material dating back to the birth of our Solar System – and could give us clues about the building blocks of our planet. 

You might be wondering what exactly are trojan asteroids. These types of asteroids are companions, or ‘neighbours’, to a planet, sharing the same orbit of this planet around the Sun. They can be ‘parked’ in a place where the force of gravity pulling them towards the planet and pushing them away are in balance – the so-called Lagrange points.

In the case of this specific asteroid, 2020 XL₅, we’re talking about an Earth trojan asteroid, as it is a companion to our Earth. 

It is the second Earth trojan asteroid found until now, and also the largest we’ve ever seen. 2020 XL₅ is about 1.2 kilometres (0.73 miles) in diameter, or about three times as wide as 2010 TK₇, the first asteroid of this kind found a decade ago. 2010 TK₇ is less than 400 metres (or yards) across, so you can imagine how big 2020 XL₅ is!

And how did astronomers find out that 2020 XL₅ is actually an Earth trojan asteroid and not a simple near-Earth object? The team used previous data from the Dark Energy Survey to understand the asteroid’s orbit. Images from 2012 and 2019 gave a better idea of 2020 XL₅’s path.

Astronomers believe the asteroid will not be a Trojan forever: it will remain stable where it is for another 4,000 years, and eventually it will wander through space because of a perturbation in its gravity. 
 

Image credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine. Acknowledgment: M. Zamani (NSF’s NOIRLab)