An object recently discovered that shares the Earth’s orbit around the sun could be a Trojan asteroid, astronomers have found.
If confirmed, it would be only the second object of its kind identified so far, suggesting that more of these hidden asteroids could be hiding in Earth’s gravity pockets.
Trojan asteroids are space rocks that share the orbit of larger planetary bodies in the solar system, which hang out in gravity-stable regions known as Lagrangian points.
These are bags where the gravity of the planet and the sun balance perfectly with the centripetal force of any small body in that region to keep it basically in place.
Each two-way system has five Lagrange points, as seen in the diagram below. There are five between the earth and the moon; and five more between the earth and the sun.
This is actually very useful – we can put spacecraft in it and be pretty sure they will stay. The James Webb Space Telescope, for example, will go into Earth-Sun L.2 Lagrangian.
(NASA / WMAP Science Team)
However, lagrangians can also capture space rocks, and the phenomenon is well known in the solar system.
Jupiter has the most Trojans, with more than 9,000 documented, but the other planets do not go without it. Neptune has 28, Mars has 9, and both Uranus and Earth have one confirmed piece.
Earth’s confirmed trojan, named 2010 TC7, is a piece of rock that hangs about 300 meters (984 feet) transversely, and hangs around the Earth-Leading L4 Lagrangian in an oscillating frog-shaped orbit, known as libration.
The new object, named 2020 XL5, first observed in November and December last year, look similar.
According to amateur astronomer Tony Dunn, who calculated the orbit of the object using NASA’s JPL Horizons software, it also vibrates around the Earth-Sun L4 Lagrangian, runs near the orbit of Mars and crosses the orbit of Venus.
In the poison below is the orbit of the asteroid in the winter count, with the earth in blue and Mars in orange. Venus and Mercury are both white.
(Tony Dunn / Twitter)
Earth has one known Trojan asteroid, 2010 TK7. But newly discovered 2020 XL5 is a good candidate because it libraries around the Earth’s L4 point and will do so for thousands of years. pic.twitter.com/mXUyFIIOSw
– Tony Dunn (@ tony873004) 28 January 2021
Because it comes as close to Venus as 2020 XL5 is a trojan, it may not be stable on long time scales. According to simulations performed by Dunn, the asteroid will move for several thousand years above and below the orbital plane of Venus as it crosses, so that the planet can not disrupt its orbit.
Eventually, however, gravitational interactions must move it away from the L4 point. This is supported by simulations performed by amateur astronomer Aldo Vitagliano, creator of the Solex and Exorb revolution software.
‘I can confirm it 2020 XL5 is currently a moderately stable Earth Trojan (I mean stable on a time scale of 2-4 millennia), ‘he wrote on the Mailing List of Minor Planets.
“I downloaded the nominal elements and their covariance matrix from the Neodys website, generating 200 clones of the body. All 200 clones, integrated up to 4500 AD, although distributed over an orbit of more than 120 degrees, continue to vibrate around the L4 point. The first clone jumps about 4500 over the L3 point, and by year 6000 many of them have made the leap, and some of them vibrate around the L5 point. “
2010 TK7 is also not necessarily stable in its current position in the long run. A 2012 analysis found that it only became a trojan about 1800 years ago and is likely to move away from the L4 point in about 15,000 years, in a horseshoe-shaped orbit, or in L5.
Although there is only one data point left, 2020 XL5 can help us figure out how to search for other potential Earth Trojans. We did it – both the OSIRIS-REx and the Hayabusa2 spacecraft scanned the L4 and L5 points respectively in 2017 while on their way to their respective targets but found nothing. Searches from the earth were almost as fruitless.
This is not necessarily surprising. Any objects that live in the Lagrangians will move around a lot and cause a very large sky to move in search of relatively small objects. From Earth, the placement of the sun also makes it difficult.
Scientists have ruled out a stable population of primeval Trojans hiding since the beginning of the solar system.
Nevertheless, with the current observational limitations, scientists have estimated that we could detect hundreds of Earth Trojans comparable to the size of 2010 TK7. If we get a better idea of how they move around in the Lagrangians, it may help us to look in the air.
What we find – whether it’s a whole bunch of Trojans, or a whole bunch of nothing – will probably tell us more about the dynamics of our solar system.
H / T: air and telescope