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Trojan Asteroid

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Last updated date: 19th Jul 2024
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What is Trojan Asteroid?

The Jupiter trojans, also known as Trojan asteroids or simply Trojans, are a large group of asteroids that orbit the Sun alongside Jupiter. The Trojan asteroids follow Jupiter's orbit, but they stay far ahead of or behind the Giant Planet and are not in danger of being engulfed.

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The Trojan asteroids follow Jupiter's orbit, but they stay far ahead of or behind the Giant Planet and are not in danger of being engulfed. Neptune has one Trojan, and Mars has many. There are no confirmed true Earth Trojans, though 3753 Cruithne has a nearly identical orbital cycle and follows a strange ‘horseshoe' path around the Earth.

There are asteroids with highly eccentric orbits, such as 944 Hidalgo and 5335 Damocles, that resemble comets. Damocles, for example, has a period of 40.9 years and crosses the orbits of Mars, Jupiter, Saturn, and Uranus, but it is not in danger of colliding due to its orbital inclination of 61 degrees. It has a diameter of no more than 15 kilometres.

Introduction to Trojan Asteroid

Any of a variety of asteroids that occupy a stable Lagrangian point in a planet's orbit around the Sun is known as a Trojan asteroid or Trojan planet.


Joseph-Louis Lagrange, a French mathematician as well as an astronomer, predicted the presence and position of two groups of small bodies near two gravitationally stable points in Jupiter's orbit in 1772. Those are the locations (now known as Lagrangian points and named L4 and L5) where a small body can be held at one vertex of an equilateral triangle whose other vertices are occupied by the large bodies of Jupiter and the Sun by gravitational forces.


Two of the five theoretical Lagrangian points in the solution to the circular restricted three-body problem of celestial mechanics are those positions that lead (L4) and trail (L5) Jupiter by 60° in the plane of its orbit. The other three stable points are on a line that runs between the Sun and Jupiter. Other planets, especially Saturn, however, disturb the Sun-Jupiter-Trojan asteroid system sufficiently to destabilise those points, and no asteroids have been discovered near them. Because of this destabilisation, most of Jupiter's Trojan asteroids orbit at an angle of up to 40 degrees from Jupiter's orbit and at a distance of up to 70 degrees from the real Lagrangian points' leading and trailing positions.


Max Wolf, a German astronomer, discovered the first of the expected objects, (588) Achilles, near L4 in 1906. Two more were discovered within a year: (617) Patroclus, near L5, and (624) Hektor, near L4. It was later agreed to keep naming asteroids after characters from Homer's epic work

The Trojan War is defined in the Iliad, and those near the leading point are named after Greek warriors, while those near the trailing point are named after Trojan warriors. With the exception of two “misplaced” names already bestowed, this tradition has continued (Hektor, the lone Trojan in the Greek camp, and Patroclus, the lone Greek in the Trojan camp).

Jupiter Trojan Asteroids

There are 7,040 Jupiter trojans in total. In 1906, German astronomer Max Wolf discovered the first Jupiter trojan, 588 Achilles. As of October 2018, a total of 7,040 Jupiter trojans had been discovered. They are all named after characters from Greek mythology who played a role in the Trojan War, hence the name "Trojan."

Earth Trojan Asteroid

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Max Wolf, a German astronomer, discovered the first of the expected objects, (588) Achilles, near L4 in 1906. An Earth trojan is an asteroid with an orbit identical to Earth's that orbits the Sun near the Earth–Sun Lagrangian points L4 (leading 60°) or L5 (trailing 60°). There have only been two Earth trojans found so far.

Significance of Earth Trojan

Even though they would be hundreds of times farther away, the orbits of any Earth trojans may make them less energetically expensive to reach than the Moon. Asteroids like these could one day be useful as sources of elements that are scarce near Earth's surface. Iridium and other siderophiles are hard to come by on Earth, having sunk to the planet's centre shortly after its creation. Even if its overall composition is identical to Earth's, a small asteroid may be a rich source of such elements; due to their small size, such bodies would lose heat much more quickly than a planet once formed, and thus would not have melted, a requirement for distinction (even if they differentiated, the core would still be within reach). 

Their weak gravitational fields would also have prevented substantial separation of denser and lighter material; an asteroid the size of 2010 TK7 would have a surface gravitational force of less than 0.00005 times that of Earth (though the asteroid's rotation could cause separation).

Mars Trojans

According to a new investigation, the Trojan asteroids that orbit Mars may have originated from the planet itself, blown off in an ancient impact rather than being late arrivals.

Trojan Asteroids — bodies that move ahead of or behind the planet — are found on most planets in the solar system. Jupiter, for example, has tens of thousands of planets. 

At least one has been found on Earth, and it was discovered in 2010. They are also found on Uranus, Neptune, and Venus. Trojan asteroids got their name from the fact that the first ones found were named after characters from the Trojan War, such as Achilles and Agamemnon. In 2021, NASA plans to launch Lucy, a mission to research six of Jupiter's Trojan asteroids.

FAQs on Trojan Asteroid

Question 1) What is the Trojan Solar System?

Answer) The Main Belt asteroids, which are found between the orbits of Mars and Jupiter, make up the majority of asteroids in our Solar System. However, asteroids can also be found in several less-populated areas. The Trojan asteroids are one such example, which are unique in that they share the orbit of a planet around the Sun.

Question 2) What is Trojan Orbit?

Answer) Jupiter trojans have orbits with radii ranging from 5.05 to 5.35 AU (the mean semi-major axis is 5.2 0.15 AU) and are found in elongated, curved regions around the two Lagrangian points; each swarm extends for around 26° along Jupiter's orbit, covering about 2.5 AU in total.