Astronomers Identify Second Earth Trojan Asteroid: 2020 XL5

by johnsmith

2020 XL5 will be an Earth Trojan asteroid for at least 4,000 years, according to a paper published in the journal Nature Communications.

This composite image, taken by the Lowell Discovery Telescope on February 22, 2021, shows 2020 XL5. Image credit: Santana-Ros et al., doi: 10.1038/s41467-022-27988-4.

This composite image, taken by the Lowell Discovery Telescope on February 22, 2021, shows 2020 XL5. Image credit: Santana-Ros et al., doi: 10.1038/s41467-022-27988-4.

The classical work of J.L. Lagrange published in 1772 on the three-body problem had to wait until 1906 to find an empirical verification with the discovery of the asteroid (588) Achilles.

This asteroid is orbiting around a theoretical point located 60° ahead of Jupiter along its orbit.

After discovering Achilles, many other objects were found orbiting around nearly the same point or its mirroring position 60° behind Jupiter.

Both points are the so-called triangular Lagrange points and are commonly known as L4 (for the former) and L5 (for the latter).

Asteroids orbiting around these points of a planet-Sun system are known as Trojan asteroids.

Although Trojan asteroids have been known for decades in other Solar System planets such as Venus, Mars, Jupiter, Uranus, and Neptune, it wasn’t until 2011 that the asteroid 2010 TK7 was found to be the first Earth Trojan asteroid.

“Trojans are objects sharing an orbit with a planet, clustered around one of two special gravitationally balanced areas along the orbit of the planet known as Lagrange points,” said Dr. Cesar Briceño, an astronomer with NSF’s NOIRLab.

“There have been many previous attempts to find Earth Trojans, including in situ surveys such as the search within the L4 region, carried out by NASA’s OSIRIS-Rex spacecraft, or the search within the L5 region, conducted by JAXA’s Hayabusa-2 mission,” said Dr. Toni Santana-Ros, an astronomer in the Departamento de Fisica, Ingeniería de Sistemas y Teoría de la Señal at the Universidad de Alicante and the Institut de Ciències del Cosmos at the Universitat de Barcelona.

“All the dedicated efforts had so far failed to discover any new member of this population.”

The 2020 XL5 asteroid was discovered by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS 1) telescope at Haleakala Observatory on December 12, 2020.

Early observations suggested that it could be an Earth Trojan asteroid, but due to low observational coverage, orbital uncertainties were too large for confirmation.

Dr. Briceño, Dr. Santana-Ros and their colleagues finally confirmed that 2020 XL5 is an Earth Trojan asteroid.

To study its orbit, they used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories.

The analysis of its orbital stability shows that 2020 XL5 will remain in L4 for at least 4,000 years.

The researchers propose it is a C-complex type asteroid, which is predominately composed of carbon.

It has a diameter of 1.18 km — larger than 2010 TK7, the first known Earth Trojan asteroid.

“2020 XL5 could have been ejected from the main asteroid belt, following an interaction with Jupiter, however further research would be needed to confirm its origins,” the authors said.


T. Santana-Ros et al. 2022. Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5. Nat Commun 13, 447; doi: 10.1038/s41467-022-27988-4

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