In December 2020, astronomers came across an object that appeared to be traveling a bit ahead of us in our orbit around the Sun, but they weren’t quite sure. New observations now confirm that suspicion, revealing that the asteroid is only the second known land-based Trojan.

In addition to confirming that asteroid 2020 XL5 is a transient Earth Trojan, the new Nature Communications to study provides up-to-date estimates of the object’s orbit, size, and physical characteristics. The asteroid is three times larger than 2010 TK7, the only other known terrestrial Trojan, and it will remain a Trojan for the next 4,000 years. The new paper, co-authored by astronomer Toni Santana-Ros of the University of Barcelona in Spain, also shows that our largest ground-based telescopes can aim low on the horizon to spot things that hadn’t been seen. seen before.

Trojan horses are small celestial bodies that share a planet’s orbit around the Sun, and they do so by parking themselves in gravitationally stable places called Lagrange points (or, more precisely, they perform small orbits around the Lagrange points). In this case, 2020 XL5 has settled at the fourth Lagrange point, where it sits 60 degrees in front of Earth. Trojan asteroids are common in the solar system, including a large number locked in Jupiter’s orbit.

2020 XL5 was discovered on December 12, 2020, by the Pan-STARRS1 telescope in Hawaii. Preliminary observations suggested its Trojan nature, but insufficient observational evidence and uncertainties about the object’s orbit made confirmation difficult.

“In order to improve the knowledge of its orbit, we carried out follow-up observations in February and March 2021, which allowed us to calculate with great precision the orbit of the object”, explained to me Santana- Ros in an email. “In turn, this allowed us to find auxiliary data of the object in the data archives.”

These follow-up observations were made by three ground-based observatories: the 13.5-foot (4.1-meter) Southern Astrophysical Research Telescope (SOAR) on Cerro Pachón in Chile, the 14.1-foot Lowell Discovery Telescope ( 4.3 meters) in Arizona and the European Space Agency’s 3.2-foot (1 meter) optical ground station in the Canary Islands. This was combined with archival data collected between 2012 and 2019 as part of the Dark Energy Survey.

“These are very difficult observations, requiring the [SOAR] telescope to track properly at its lowest altitude limit, as the object was very low on the western horizon at dawn,” Cesar Briceño, study co-author and researcher at NOIRLab, said in a Press release.

A photometric analysis of 2020 XL5 revealed it to be a C-complex type asteroid – dark, carbon-rich objects that represent the most common type of asteroid in the solar system. The object is 0.73 miles (1.18 km) wide, making it themore powerful than the first known terrestrial Trojan, 2010 TK7. 2020 XL5 will remain as an Earth Trojan horse for another 4,000 years, after which it will become free and venture into space on a new trajectory.

2020 XL5 is not a primordial Trojan, meaning it has not been parked at L4 since our planet was born. It is sad because primordial Trojans “may provide us with information about the formation of its host planet” and, in turn, keys to a better understanding of the evolution of the solar system, Santana-Ros said. Interestingly, 2020 XL5 only became a Trojan about 600 years ago.

The discovery of this terrestrial Trojan “confirms that 2010 TK7 is not a rare exception and that there are likely more bodies populating L4 and probably L5 of the Earth-Sun system,” Santana-Ros explained, adding that it will “encourage us to continue”. improve our investigative strategies to find, if it exists, the first primordial terrestrial Trojan horse.

The new object is also interesting in that it could be the target of a future flyby mission, or even a cool place to set up a space station or a resource mine. In the meantime, there is Mission Lucia to look forward to. Launched late last year, the NASA probe is currently on the way to Jupiter, where he will explore the Jovian Trojans for a period of 12 years.