A Trojan asteroid travels either before or behind a planet in its orbit of the Sun, in an area of the orbit known as the Lagrange point.
Each planets' orbit has five Lagrange points, but only in points L4 and L5 are space objects able to be drawn in and kept there for a while.
These spots remain relatively stable as the gravity from the Sun and the planet cancel each other out.
This second Trojan asteroid in Earth's orbit was first detected in December 2020.
Named 2020 XL5, Dr Toni Santana-Ros from the University of Barcelona said it was not known at the time if it was an asteroid.
A team of international astronomers used three different telescopes between February and March last year to try and find the object to confirm if it was an asteroid.
The team also looked through 10 years worth of data, finding a speck in sky surveys dating to 2012.
"When you look at [a single image], you can have some doubts that this is really an object; it could be some kind of dust in your camera," Dr Santana-Ros said.
"But when you link all the images from different years, you realise they are following an orbit."
Through this information, they could work out the rock's size and path.
"There is no doubt that this is our object and that it can not just be some blurry thing."
The team believe the Trojan asteroid will remain by the Earth's side for the next 4,000 years or so.