The Earth has a second companion for at least the next 4,000 years. It is a Trojan asteroid nicknamed 2020 XL5 , approximately 1 kilometer wide and located at the Lagrange point L4, according to the scientists of the study that has just been published in the journal Nature Communications.
What is a Trojan asteroid?
These are space rocks that orbit in the same plane as a planet , but do not collide with it because they move in “dead zones” where gravitational forces allow the rock to circulate in a “sweet spot” at precisely the same speed as the planet, becoming a companion of it. It will share our orbit around the Sun for a few thousand years. After that time, gravitational interactions will pull it out of its current orbit.
This is the second Earth Trojan (the first was discovered in 2010, called 2919 TK7 ) and the fifth Trojan of the Earth-Sun system, since we had already detected this type of asteroid before. The most famous are the Jupiter Trojans (which has more than 5,000), the first to be discovered.
“There is no doubt that it is a terrestrial Trojan” , commented the astronomer Toni Santana-Ros from the University of Alicante and the Institute of Cosmos Sciences of the University of Barcelona and leader of the work.
The second terrestrial Trojan asteroid is three times larger than the first ; the first, less than 400 meters wide; this has a diameter of about 1.18 km, according to the researchers, who also propose that it is a type C Trojan, the most common in the solar system, very rich in carbon and generally dark.
The fact that it shares the same stable orbit as Earth makes it a good candidate for future flyby missions and we won’t have to worry about when, given the predicted number of years experts believe it will stay in that position.
His discovery
The asteroid was discovered by the Pan-STARRS1 Survey Telescope in Hawaii in December 2020. Astronomers had data suggesting this could be a second Trojan asteroid, and follow-up observations were vital in confirming this theory. The 4.3-meter Lowell Discovery Telescope, the 4.1-meter SOAR (Investigación Astrofísica del Sur) Telescope on Cerro Pachón in Chile, and the European Space Agency’s 1-meter Optical Ground Station on Tenerife in the Canary Islands noted also its instruments to observe this celestial body. Finally, the combination of all the data resulted in the confirmation they expected.
“The SOAR data allowed us to make a first photometric analysis of the object, revealing that 2020 XL5 is probably a C-type asteroid, larger than a kilometer in size,” said Santana-Ros.
The fact that astronomers have discovered a second object like this not far from Earth means that 2010 TK7 is not a rarity and that we could find many more Trojans like it. And asteroids are important because their peculiar orbits can help us better understand what the early solar system was like and how it evolved.
Referencia: Santana-Ros, T., Micheli, M., Faggioli, L. et al. Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5. Nature Communications 13, 447 (2022). https://doi.org/10.1038/s41467-022-27988-4
