Astronomers have discovered that a newly discovered object that shares the Earth’s orbital orbit around the Sun could be a Trojan asteroid.
If confirmed, it will be only the second object of its kind identified so far, suggesting that there would be more of these hidden asteroids hiding in Earth’s gravitational pockets.
Trojan asteroids are space rocks that share the orbital trajectory of larger planetary bodies in the solar system, located in gravitationally stable regions known as Lagrangian points.
These are pockets where the gravitational pulls of the planet and the Sun balance perfectly with the centripetal force of any small body in this region to keep it basically in place.
Each two-body system has five Lagrange points, as shown in the diagram below. There are five between the Earth and the Moon; and another five between the Earth and the Sun.
In fact, they are very useful: we can put spaceships in them and be sure that they will be maintained. The James Webb Space Telescope, for example, will go to Earth-Sun L2 Lagrangian.
(NASA / WMAP Scientific Team)
Lagrangians, however, can also capture space rocks, and the phenomenon is well known in the solar system.
Jupiter has the majority of Trojans, with more than 9,000 documented, but the rest of the planets are not lacking. Neptune has 28, Mars has 9, and both Uranus and Earth have a confirmed one.
The confirmed Trojan from Earth, called 2010 TK7, is a piece of rock about 300 meters (984 feet) in diameter, hung around the L leader on Earth4 Lagrangian in an oscillating orbit in the shape of a tadpole known as a libration.
The new object, called 2020 XL5, which was first observed in November and December last year, looks similar.
According to amateur astronomer Tony Dunn, who calculated the trajectory of the object using NASA’s JPL-Horizons software, it is also found around the Earth-Sun L4 Lagrangian, in a loop near the orbit of Mars and crossing the orbit of Venus.
In the gif below, the asteroid’s orbit is greenish green, with Earth in blue and Mars in orange. Venus and Mercury are white.
(Tony Dunn / Twitter)
Earth has a well-known Trojan asteroid, the 2010 TK7. But the newly discovered XL5 of 2020 is a good candidate, as it is located around the L4 point of the Earth and will continue to do so for thousands of years. pic.twitter.com/mXUyFIIOSw
– Tony Dunn (@ tony873004) January 28, 2021
Because it is so close to Venus, if the 2020 XL5 it is a Trojan, it may not be stable in the long run. According to Dunn’s simulations, for several thousand years, the asteroid will pass above and below the orbital plane of Venus when it crosses, preventing the planet from disrupting its orbit.
Eventually, however, gravitational interactions should move it away from the L4 point. This is supported by simulations by amateur astronomer Aldo Vitagliano, creator of the Solex and Exorb orbital determination software.
“I can confirm this XL of 20205 it is currently a moderately stable Earth Trojan (I mean stable on a time scale of 2 to 4 millennia), ”he wrote on the mailing list of the smaller planets.
“I downloaded the nominal elements and their covariance matrix from the Neodys site, thus generating 200 clones of the body. All 200 clones, integrated up to 4500 AD, although they extend over an orbital arc of more than 120 degrees , continue to hover around the L4 point. The first clone jumps above the L3 point around the year 4500 and by the year 6,000, many of them have already made the leap and some of them are hovering around the L5 point “.
TK7 2010 is not necessarily stable in its current long-term position. A 2012 analysis found that it only became a Trojan about 1,800 years ago and will probably move away from the L4 aims at about 15,000 years, in a horseshoe-shaped or L-shaped orbit5.
Although only one more data point, 2020 XL5 could help us figure out how to look for other potential Trojans on Earth. We did it: both the OSIRIS-REx spacecraft and the Hayabusa2 scanned the L4 and L5 points respectively in 2017 as they headed towards their respective goals, but found nothing. Searches from Earth have been almost as fruitless.
This is not necessarily surprising. Any object that inhabited the Lagrangians would move a lot, leaving a very large piece of sky to search for relatively small objects. From Earth, too, location relative to the Sun makes detection difficult.
Scientists have ruled out a stable population of primordial Trojans that have been hiding since the beginning of the solar system.
Nevertheless, even with current observational limitations, scientists have estimated that we may be able to detect hundreds of Earth Trojans of a size comparable to that of 2010 traditional knowledge.7. Having a better idea of how Lagrangians move around could help us reduce the location of the sky to look at.
What we find, whether it’s a bunch of Trojans, or a bunch of nothing, is sure to tell us more about the dynamics of our solar system.
H / T: Sky & Telescope