Free Astronomy Magazine May-June 2022

28 MAY-JUNE 2022 ASTRO PUBLISHING Discovered on 12 Decem- ber 2020 by the Pan- STARRS1 survey telescope in Hawai’i, 2020 XL 5 is much larger than the first Earth Trojan discovered, called 2010 TK 7 . The re- searchers found that 2020 XL 5 is about 1.2 kilome- ters (0.73 miles) in diame- ter, about three times as wide as the first (2010 TK 7 is estimated to be less than 400 meters or yards across). When 2020 XL 5 was discovered, its orbit around the Sun was not known well enough to say whether it was merely a near-Earth asteroid cross- ing our orbit, or whether it was a true Trojan. SOAR’s measurements L agrange points are places in space where the gravitational forces of two massive bodies, such as the Sun and a planet, bal- ance out, making it easier for a low-mass object (such as a spacecraft or an asteroid) to orbit there. This diagram shows the five Lagrange points for the Earth-Sun system. (The size of Earth and the distances in the illustration are not to scale.) [NOIR- Lab/NSF/AURA/J. da Silva. Ack.: M. Zamani (NSF’s NOIRLab)] A stronomers have con- firmed the existence of the second known Earth Tro- jan asteroid and found that it is much bigger than the first. This video summarizes the discovery. [Images and Videos: CTIO/NOIRLab/NSF/ AURA/J. da Silva/Spaceengine, ESO/M. Kornmesser, SOAR/ J. P. Burgos. Image Process- ing: M. Zamani (NSF’s NOIR- Lab). Music: Stellardrone - A Moment of Stillness] were so accurate that Santana-Ros’s team was then able to go back and search for 2020 XL 5 in archival im- ages 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 Tele- scope located at CTIO in Chile. With almost 10 years of data on hand, the team was able to vastly improve our understanding of the asteroid’s orbit. Although other studies have