Trojans are asteroids gravitationally locked to stable Lagrange points either 60° ahead (L4) or behind (L5) the planets in their orbits around the Sun. 2020 XL5 was found around the L4 point.
Massive Jupiter has more than 9,000 Trojans.
In theory, Trojan orbits would be stable around every planet except Saturn, where Jupiter’s gravity pulls them away.
So far, Trojans have been found sharing orbits — at least temporarily — with Neptune, Uranus, Mars, Venus, and Earth.
Earth Trojans are hard to find because during most of their orbits, they appear close to the Sun in the sky.
Not only that, but the gravitational resonance does not hold them in lockstep at 60° ahead and behind of the Earth, explains Dunn.
Instead, the objects trace paths around the L4 and L5 points, which are themselves moving as Earth orbits the Sun.
NASA’s Wide-field Infrared Survey Explorer spacecraft spotted the first Earth Trojan, 2010 TK7, also locked to the L4 point, in October 2010 when it scanned the infrared sky 90° from the Sun. Two other observers recovered it a few months later with the Canada-France-Hawaii Telescope. It’s slightly smaller than 2020 XL5.
The orbits of our two Trojans are best visualized along with that of Earth’s and, in the case of 2020 XL5, the orbits of all the inner planets.
When viewed relative to Earth, 2010 TK7 drifts between a spot close to Earth to the L3 point on the other side of the Sun from Earth, but it doesn’t pass through the L4 point.
The orbit of 2020 XL5 ranges more widely, drifting inward to inside Venus’s orbit and outward almost to Mars [as shown here].
Full article here.
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Animation showing the Lagrange points (the triangles are equilateral).
via Tallbloke’s Talkshop
February 5, 2021 at 11:07AM