Earth has a second partner in its orbit. Trojans are asteroids that share the orbit of a planet or moon, moving along the same path just in front of the larger body or behind it, in locations called Lagrange points. Until now, we only knew of one Earth trojan 鈥� most of those in our solar system belong instead to Jupiter 鈥� but a team of researchers has found a second one called 2020 XL5.
The new trojan asteroid was first discovered by astronomers in 2015 using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) in Hawaii. At the time, we didn鈥檛 have enough data to know whether it was a trojan, so at the University of Western Ontario in Canada and his colleagues used the University of Hawaii 2.2-Meter Telescope at Mauna Kea to take more observations.
They found that it is a trojan, although its orbit around the sun isn鈥檛 exactly the same as Earth鈥檚 鈥� it is slightly oval-shaped and tilted, with a small wobble. 鈥淚f you imagine it鈥檚 a racetrack, Earth is like a car that鈥檚 going smoothly around the track, and this object is driving more erratically,鈥� says Wiegert. 鈥淭hey鈥檙e on the same track, but not always in the same lane.鈥�
Advertisement
The orbit of 2020 XL5 brings it within 15 million kilometres of Venus 鈥� around 10 per cent of the distance between Earth and the sun 鈥� every 30 years or so. This means it is likely to be pushed out of its stable orbit in around 6000 years, after which point it will probably become 鈥渁 garden-variety near-Earth asteroid鈥�, says Wiegert. The researchers calculated that it has probably been in its current orbit since 1444.
Because objects like this remain close to Earth for extended periods of time, they make particularly intriguing topics for missions to visit asteroids. They also help us understand the dynamical history of our solar system.
鈥淭here are different dynamical niches where asteroids could exist, for example this Trojan state, and whether there are asteroids in those states or not gives us clues as to how the solar system formed,鈥� says Wiegert. 鈥淲e鈥檙e taking a sort of inventory of the objects in our solar system and which niches they can occupy for how long.鈥�
Reference:
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
