Using the 4.1-meter Southern Astrophysical Research (SOAR) Telescope at Cerro Pachón in Chile, astronomers led by Toni Santana-Ros of the University of Alicante and the University of Barcelona’s Institute of Cosmos Sciences, observed the newly discovered asteroid 2020 XL5 to limit orbit and size.
Their results confirmed that asteroid 2020 XL5 is an Earth Trojan, an asteroid companion to Earth that orbits the Sun along the same path as planet Earth, and that it is the largest ever discovered.
“Trojans are objects that share an orbit with a planet, clustered around one of two special gravitationally balanced areas along the planet’s orbit known as Lagrange points,” said Cesar Briceño of NOIRLab NSF. 2/2022).
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Several planets in the Solar System are known to have Trojan asteroids, but 2020 XL5 is only the second known Trojan asteroid discovered near Earth. Observations of XL5 2020 were also made with the 4.3-meter Lowell Discovery Telescope at the Lowell Observatory in Arizona and by the European Space Agency’s 1-meter Optical Earth Station on Tenerife in the Canary Islands.
Discovered on December 12, 2020 by the survey telescope Pan-STARRS1 in Hawaii, 2020 XL5 is much larger than the first Earth Trojan discovered, called 2010 TK7. The researchers found that the 2020 XL5 is about 1.2 kilometers (0.73 mi) in diameter, about three times the width of the first (2010 TK7 is estimated to be less than 400 meters or yards).
When 2020 XL5 was discovered, its orbit around the Sun wasn’t known enough to tell if it was just a near-Earth asteroid crossing our orbit, or if it was really a Trojan. The SOAR measurements were so accurate that the Santana-Ros team was then able to go back and search for the 2020 XL5 in archival images from 2012 to 2019 taken as part of the Dark Energy Survey using the Dark Energy Camera (DECam) on the Víctor M Blanco 4-meter Telescope located at CTIO in Chile.
With nearly 10 years of data at hand, the team was able to improve our understanding of the asteroid’s orbit. While other studies have supported the identification of the Trojan asteroid, the new results make that determination much more robust and provide an estimate of the size of 2020 XL5 and what type of asteroid it is.
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