Recently discovered astronauts could share the Earth’s orbital orbit around the Sun.
If confirmed, it is only the second of its kind identified so far, suggesting that more of these hidden asteroids may be lying in the Earth’s gravity pockets.
Trojan asteroids are space rocks that share the orbital path of larger planetary bodies in the Solar System, hanging out in graphically stable regions called Lagrangian points.
These are pockets where the gravitational movements of the planet and the Sun balance perfectly with the centrifugal force of any small group in that region to hold it in place.
Each two-body system has five Lagrange points, as shown in the image below. There are five between the Earth and the Moon; and five more between Earth and the Sun.
These are really useful – we can put spaceships in them and be reasonably confident that they will last. The James Webb Space Telescope, for example, goes into the Earth-Sun L.2 Lagrangian.
(NASA / WMAP Science Team)
Lagrangians, however, can capture space rocks, and the phenomenon is well-known in the Solar System.
Jupiter has the largest number of trojans, with over 9,000 registered, but the other planets do not go without it. Neptune has 28, Mars has 9, and Uranus and Earth have one confirmed apiece.
Earth-certified Trojan, named 2010 TK7, a piece of rock about 300 meters (984 feet) across hangs around L in front of the Earth4 Lagrangian in an oscillating tadpole-shaped orbit called libration.
The new item, called 2020 XL5, which was first seen in November and December last year, apparently.
According to amateur astronomer Tony Dunn, who described the orbit of the object using NASA’s JPL-Horizons software, it is also orbiting the Earth’s Solar L4 Lagrangian, orbiting near the orbit of Mars, and crossing the orbit of Venus.
In the gif below, the orbit of the asteroid is in teal, with Earth in blue and Mars in orange. Venus and Mercury are both white.
(Tony Dunn / Twitter)
There is one Trojan asteroid on Earth, 2010 TK7. But the recently discovered 2020 XL5 is a good candidate as it orbits the Earth’s L4 point, and will continue to do so for thousands of years. pic.twitter.com/mXUyFIIOSw
– Tony Dunn (@ tony873004) January 28, 2021
Because it draws so close to Venus, if 2020 XL5 as a trojan, it may not be stable over long timeframes. According to symbols run by Dunn, for a few thousand years, the asteroid will pass above and below the orbital plane of Venus as it intersects, keeping the planet from disturbing its orbit.
Eventually, however, a gravity interaction should move away from the L.4 point. This is supported by simulations run by amateur astronaut Aldo Vitagliano, creator of orbital proof software Solex and Exorb.
“I can confirm that 2020 XL5 right now Trojan Earth is moderately stable (I mean stable on a time scale of 2-4 thousand years), ”he wrote on the Minor Planets Mailing List.
“I have downloaded the named elements and their covariance matrix from the Neodys site, thus generating 200 clones of the body. The 200 clones, are connected up to AD 4500, although they are spread over on an orbital arc of more than 120 degrees, keeping librating around the L.4 point. The first clone jumps over the L3 point around year 4500, and by year 6000 many have made the jump and a few go around the L3.5 point. “
2010 TK7 is not stable in its current state in the long run, either. A study in 2012 found that it only became a trojan around 1,800 years ago, and appears to have moved away from the L.4 point in about 15,000 years, into orbit in the shape of a horseshoe, or into L.5.
Although there is only one additional data point, 2020 XL5 it could help us find out how to find other potential Earth trojans. We’ve done that – both the OSIRIS-REx and Hayabusa2 spacecraft scanned the L.4 and L.5 individual points in 2017 while on their way to their individual targets, but found nothing. Searches from Earth have been almost fruitless.
That is not surprising. Any objects that lingered on the Lagganians would move around a lot, leaving a huge patch of scrubbed sky looking for relatively small materials. From Earth, too, the position towards the sun makes a challenging discovery.
Scientists have eradicated a stable population of primordial trojans hiding since the beginning of the Solar System.
Nevertheless, even with the current observational limitations, scientists have estimated that we could find hundreds of Earth trojans that were similar in size to 2010 TK7. Gaining a better idea of how they move around the Lagrangians could help us narrow down where the skies are facing.
What we find – whether it’s a whole bunch of trojans, or a handful of anything – certainly tells us more about the dynamics of our Solar System.
H / T: Sky & Telescope