Astronomers have discovered that a recently discovered object that divides the Earth’s orbital path around the Sun could actually be a Trojan asteroid.
If confirmed, it will be only the second object of its kind identified so far, suggesting that there may be more of these hidden asteroids hiding in Earth’s gravitational pockets.
Trojan asteroids are space rocks that share the orbital path of the largest planetary bodies in the solar system, which are in gravitationally stable regions, known as Lagrangian points.
These are pockets in which the gravitational attractions of the planet and the Sun balance perfectly with the centripetal force of any small body in that region to keep it practically 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.
These are really quite useful, in fact – we can put spaceships in them and we can be quite confident that they will stay put. The James Webb Space Telescope, for example, will go into Earth-Sun2 Lagrangian.
(NASA / WMAP Scientific Team)
However, Lagrangians can also capture space rocks, and the phenomenon is well known in the solar system.
Jupiter has most of the Trojans, with over 9,000 documented documents, but the other planets are not without them. Neptune has 28, Mars has 9 and both Uranus and Earth have one confirmed.
The confirmed Trojan of the Earth, named 2010 TK7, is a piece of stone about 300 meters (984 feet) wide, hanging from the L that leads the Earth4 Lagrangian in a tadpole-shaped oscillating orbit known as the 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 object’s trajectory using NASA’s JPL-Horizons software, he and he are librarying around Earth-Sun L4 Lagrangian, which approaches the orbit of Mars and intersects the orbit of Venus.
In the gif below, the asteroid’s orbit is green, with Earth in blue and Mars in orange. Venus and Mercury are both white.
(Tony Dunn / Twitter)
Earth has a well-known Trojan asteroid, 2010 TK7. But the recently discovered 2020 XL5 is a good candidate because it libraries 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 2020 XL5 is a Trojan, may not be stable for long periods of time. According to Dunn’s simulations, for several thousand years, the asteroid will pass above and below the orbital plane of Venus when it intersects, preventing the planet from disrupting its orbit.
Eventually, however, gravitational interactions should move it away from L.4 point. This is supported by simulations led by amateur astronomer Aldo Vitagliano, creator of the orbital determination software Solex and Exorb.
“I can confirm that 2020 XL5 he is currently a moderately stable Trojan on Earth (I mean stable on a time scale of 2-4 millennia), “he wrote on the distribution list of the minor planets.
“I downloaded the nominal elements and their covariance matrix from the Neodys site, thus generating 200 body clones. All 200 clones, integrated up to 4500 AD, although spread over an orbital arc of over 120 degrees, continue to library around L4 point. The first clone jumps over point L3 around 4500, and by 6000 many of them made the leap and some of them library around L5 point.”
The 2010 TK7 is not necessarily stable in its current long-term position either. A 2012 analysis found that he became a Trojan just 1,800 years ago and is likely to move away from L4 point in about 15,000 years, in a horseshoe-shaped orbit or in L5.
Although one more data point, 2020 XL5 it could help us figure out how to look for other potential Trojans on Earth. We did this – both OSIRIS-REx and Hayabusa2 spacecraft scanned L4 and I5 points, respectively in 2017, while heading towards those targets, but found nothing. Searches on Earth have been almost as fruitless.
This is not necessarily surprising. Any objects that live in Lagrangians would move a lot, leaving a very large patch of sky to look for relatively small objects. Also, from Earth, placement relative to the Sun makes detection difficult.
Scientists have ruled out a stable population of primordial Trojans hiding from the beginning of the solar system.
However, even with current observational limitations, scientists have estimated that we may be able to detect hundreds of Trojans on Earth comparable in size to TK in 2010.7. Having a better idea of how the Lagrangians move around could help us narrow our view of the sky.
What we find – whether it’s a bunch of Trojans or a bunch of nothing – is bound to tell us more about the dynamics of our solar system.
H / T: Sky & Telescope