: SECOND EARTH TROJAN ASTEROID DISCOVERED Imagine being an amateur astronomer and discovering
an object that turns out to be gravitationally connected with our planet Earth.
Well, this is pretty much what happened in 2020 to Tony Dunn.
Amateur astronomer Tony Dunn has reported there is a second Trojan asteroid sharing
the Earth's orbit.
The asteroid, which was dubbed 2020 XL5, is a few hundred meters across and its orbit
is tied to a gravitationally stable region ahead of Earth in its orbit, and orbits around
the L4 point, one of the “parking places” of our solar system.
What's a Trojan?
But what type of object is it?
Does every planet have its own Trojans?
Follow us in this video to know the answer to all of these questions!
First of all.
What's a Trojan?
In astronomy, a rojan is a small celestial body, most of the times it is an asteroid,
that shares the orbit of a larger one, remaining in a stable orbit approximately 60° ahead
or behind the main body near one of the so-called “Lagrange points”.
Trojans can share the orbits of planets or of large moons.
The term "trojan" originally referred to the "trojan asteroids" (Jovian trojans) that orbit
close to the Lagrangian points of Jupiter.
These have long been named for figures from the Trojan War of Greek mythology.
By convention, the asteroids orbiting near the L4 point of Jupiter are named for the
characters from the Greek side of the war, whereas those orbiting near the L5 of Jupiter
are from the Trojan side.
(we find, for example, 588 Achilles and 1172 Äneas!)
How big is a Trojan, and what it's made of?
Like other asteroids, Trojan are space rocks.
We know some asteroids are as small as boulders.
Others are as big as football fields.
Some asteroids are almost as large as planets, and astronomers sometimes argue about whether
really big asteroids ought to be called planets or not.
Asteroids are made of rock, metals and other elements.
Some even contain water, astronomers say.
Asteroids that are mostly stone sometimes are more like loose piles of rubble.
Asteroids that are mostly iron are more, well, rock-solid.
Meteorites found on Earth often come from asteroids, and so they help astronomers figure
out what's in asteroids.
An iron meteorite can be 91 per cent iron and 8.5 per cent nickel and might also contain
cobalt.
A stony meteorite can contain oxygen, silicon, magnesium, calcium and other elements.
Most Jupiter Trojans are D-class asteroids, which predominate in the outer regions of
the asteroid belt.
Very few have been classified as P or C-type asteroids.
Water hasn’t yet been detected on any of them; however, there is a possibility that
some of them might contain it.
Recent studies suggest that the Jupiter Trojans resemble comets or Kuiper Belt objects when
it comes to their composition, mainly water-ice with a layer of dust; however, observations
continue.
So, what was Tony Dunn discovery?
And why it was so important?
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.
2020 XL5 is almost certainly a garden-variety bit of rock that went close to Venus and got
perturbed into an orbit with a period very close to one year, says Bill Gray of Project
Pluto.
Aldo Vitagliano, a retired Italian chemist said that the orbit should remain stable for
2,000 to 4,000 years, but gravitational tugs would eventually move it to another orbit.
So far 2020 XL5 has only been observed for only a few weeks, and amateur astronomer Sam
Deen says we may have to wait until more observations can be made to pin down its orbit.
As you can see in this simulation it even almost reaches the orbit of Mars (the one
in Orange) and in that sense, it’s actually a really interesting object, because first
of all, all this means that eventually, Mars will destabilize this orbit and so the object
will probably move away possibly escaping somewhere else or even becoming a Trojan of
Mars!
The existence of Trojan asteroids at the Lagrange points (and some other planets) can be seen
as proof that such gravitational points exist.
The existence of these points allows humans to place satellites and telescopes at Lagrange
points, allowing them to stay in the same position relative to the Earth while not using
any fuel to hold themselves in place.
This is WONDERFUL, and that's why we called the Lagrange points “parking places” of
our Solar System.
What about the first Earth Trojan?
When was it discovered?
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The first Earth Trojan, dubbed 2010 TK7 because it was discovered in 2010, comes within 20
million kilometres (12 million miles) to Earth every few hundred years; it is currently drifting
away.
Models show its orbit is stable enough to stay in a one-to-one resonance with Earth
for about a quarter-million years!
Does every planet have its own Trojans?
The answer is, probably YES.
But, in order to say why we have to explain what a Lagrangian Point is.
In fact, as we said, Trojans are asteroids gravitationally locked to stable Lagrange
points L4 or L5.
Lagrange Points are positions in space where the gravitational forces of a GENERICAL two
body system like the Sun and the Earth (but they could be The Sun and Jupiter or the Sun
and Mercury) produce enhanced regions of attraction and repulsion.
These can also be used by spacecraft to reduce fuel consumption needed to remain in position.
Lagrange points are named in honour of Italian-French mathematician Josephy-Louis Lagrange.
There are five special points where a small mass can orbit in a constant pattern with
two larger masses.
The Lagrange Points are positions where the gravitational pull of two large masses precisely
equals the centripetal force required for a small object to move with them.
This mathematical problem, known as the "General Three-Body Problem" was considered by Lagrange
in his prize-winning paper (Essai sur le Problème des Trois Corps, 1772).
We could say that in the circular restricted three-body problem, there are a set of 5 points
that if we place our spacecraft there, it’ll never move relative to the two bodies.
These are the Lagrange points.
But whenever we find an equilibrium point in a dynamic system the first question should
always be “is it stable?
Of the five Lagrange points, three are unstable and two are stable.
The unstable Lagrange points - labelled L1, L2 and L3 - lie along the line connecting
the two large masses.
In plain English, UNSTABLE means that if we place any object close, but not perfectly
on one of these Lagrange points the object will move away from the Lagrange point.
The stable Lagrange points - labelled L4 and L5 - form the apex of two equilateral triangles
that have large masses at their vertices.
L4 leads the orbit of earth and L5 follows.
So every planet has its own L-points, which means, every planet could potentially have
its own Trojans!
And, in fact, it is so!
Currently, we know: more than 7.000 Jupiter Trojans, 9 Martian Trojans, about 22 Neptunian
Trojans, 2 Earth Trojans, 2 Uranus Trojans, and One temporary Venusian Trojans.
What about Saturn?
Well, because of the proximity of Saturn to Jupiter (essentially because of the planetary
interactions and because Jupiter is really really massive) so far we actually haven’t
discovered any trojans around Saturn.
Saturn seems to be lacking them and it’s not really because they’re just not there.
They’re probably there or might actually be really small, but no major ones have been
found and we believe this is really because of the gravitational interactions with Jupiter,
meaning that Jupiter probably just stole all of them and now they are orbiting the other
planet!
Anyway, the same arrangement can of course appear when the primary object is a planet
and the secondary is one of its moons, whereby much smaller trojan moons can share their
orbit.
All known trojan moons are part of the Saturn system.
Telesto and Calypso are trojans of Tethys and Helene and Polydeuces of Dione.
Is there any chance for us to find other Trojans of Earth?
Astronomers are stepping up their search for Earth Trojans.
The “Catalina Sky Survey” has expanded the area it covers, and a group at the Vera
C. Rubin Observatory is also planning observations once that observatory comes online in a year
or two.
A population of Earth Trojans should have survived since the planet formed if its orbit
hasn’t changed since then.
Their existence has other implications, too.
Searching for ancient Trojans could help explain why the leading hemisphere of the Moon has
about 70% more young craters than the trailing side, a difference current models can’t
explain.
Earth Trojans slowly escaping from their orbits might account for the extra young craters.
Two spacecraft were on their way to visit near-Earth objects searched Trojan regions
in 2017, but NASA's Osiris-Rex found nothing at L4 and the Japanese Hayabusa 2 found nothing
at L5.
However, the observations were not definitive, and in 2019 Renu Malhotra (University of Arizona)
wrote that the Earth could still have up to several hundred Trojans at least a few hundred
meters in diameter, amounting to several per cent of the some 10,000 near-Earth objects
of that size.
We are going to end this video, but first...here's a bunch of “Did you know that”... we collected
for you!
Did you know that...
The second-largest Jupiter Trojan is 617 Patroclus.
It has a diameter of 140 km / 86.9 mi.
The asteroid with the highest albedo of the Jupiter Trojans, and all known Trojans, is
4709 Ennomos – having an albedo of 0.18.
This high albedo may indicate the presence of water-ice.
The Jupiter Trojans 911 Agamemnon, and 617 Patroclus have very weak absorptions at 1.7
and 2.3 μm.
It might indicate the presence of organics!
Based on simulations, around 17% of Jupiter Trojans are unstable over the age of the solar
system.
“This video ends here!
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