Earth also seemed to lack a Trojan asteroid until astronomers found one in 2010 at the Lagrange point L4, 60 degrees ahead of Earth. Subsequent searches were fruitless until Pan-Starrs, an automated sky survey in Hawaii, discovered a gravitational object, 2020 XL5, which appeared likely to be pulsating as well. around L4.
But the initial observations were not enough to determine the object’s orbit unambiguously. In 2021, an international team of astronomers including Dr Santana-Ros made further XL5 2020 sightings using three ground-based telescopes. The team was then able to search through images dating back to 2012 where the asteroid actually appeared, although no one recognized it as one.
A decade of data is finally enough to chart the elliptical orbit of the XL5 2020. Dr Santana-Ros said: “We are 100% sure this is the Earth Trojan.
Although 2020 XL5 is trapped in orbit around the stable Lagrange point, it is not particularly close to L4. Its elliptical orbit, tilted nearly 14 degrees to the orbits of the planets, sweeps it closer to the sun than Venus and almost farther than Mars.
This makes it vulnerable to the gravitational pull of other planets, especially Venus.
The researchers ran computer simulations of 2020 XL5’s orbit, tuning it 800 times. Sometimes asteroids escape the Lagrange point within 3,500 years; sometimes it lasts for 5,000 years or more. But the orbit doesn’t seem to be able to stay stable much longer than that
Visually, XL5 2020 is a dark, carbon-rich object, perhaps an interloper from the main asteroid belt between Mars and Jupiter. The researchers estimate its diameter at about three-quarters of a mile, much larger than the Earth Trojan discovered in 2010, which is estimated to be about a quarter of a mile in diameter and is also located at the L4 Lagrange point. .
While the two known Earth Trojans appear to be only temporary additions to our orbital neighborhood, other celestial bodies hovering near stable Lagrange points can stay in place indefinitely, raises the possibility that some of Earth’s primitive building blocks could still be found there.
https://www.nytimes.com/2022/02/02/science/astronomy-asteroid-trojan.html Astronomers find new Trojan asteroid that shares Earth’s orbit