Trojan Asteroids
Trojan asteroids are a unique class of space rocks that share an orbital period with a planet, allowing them to maintain a stable distance from that planet. They are located at specific points known as Lagrange points—specifically L4 and L5—where the gravitational forces of the sun and the planet create a balance that allows these asteroids to orbit alongside, ahead of, or behind the planet without the risk of collision. Most known Trojan asteroids are associated with Jupiter, with a significant number also identified near Mars and Neptune. The first Trojan asteroid, 588 Achilles, was discovered in 1906, and these asteroids are often named after figures from the Trojan War, with Greek names assigned to those in the L4 position and Trojan names for those in L5.
In recent years, scientists have discovered Trojan asteroids near Earth, such as 2010 TK7, which is situated about 20 million kilometers ahead of our planet. Due to their stable orbits and unchanged nature over billions of years, Trojan asteroids are of significant interest for potential mining and scientific exploration. NASA's Lucy mission, launched in 2021, aims to explore these asteroids to gather insights into the early solar system, highlighting their importance for future space research and observation opportunities.
Trojan Asteroids
FIELDS OF STUDY: Astronomy; Observational Astronomy
ABSTRACT: Trojan asteroids are small, rocky objects that share an orbital period with a planet and maintain a consistent distance from the planet. This makes collision between the planet and a Trojan asteroid unlikely. Trojan asteroids’ stable paths make them good candidates for future space study missions, and their composition could tell scientists much about the early solar system.
Orbital Paths of Trojans
Some asteroids cross paths with planets and could collide with them. Trojan asteroids share an orbital period with a planet and orbit at a consistent distance from that planet. This reduces the potential for collisions. This stable path is possible because the asteroids are located at the libration points. Libration points are places where the gravitational forces of the sun and a planet are such that a third, small body is able to remain steady. Trojan asteroids hold a consistent orbit alongside, ahead of, or behind a planet as it orbits the sun.
These libration points are also called Lagrange points after Joseph-Louis Lagrange (1736–1813). Lagrange was a mathematician who tried to calculate a solution to the "three-body problem." Scientists and mathematicians had long tried to figure out the relative motion of three space bodies based on their mass, velocity, and position. Lagrange determined that if one body is much smaller than the other two, it is possible to identify five points in relation to the two larger objects where the smaller object could maintain a consistent distance from the others. At the Lagrange points, the gravitational force of the planet is equal to that of the sun. Although the sun is much more massive than the planet, the sun is so far from the Trojan asteroid that it exerts a gravitational pull equal to the planet’s. These points of equilibrium became known as the Lagrange points, or L-points, and are labeled L1 through L5. Asteroids located in the more stable L4 or L5 positions form one point of an equilateral or equal-sided triangle. The sun and the planet make up the other two points.
Where Trojans Are Found
Most of the known Trojan asteroids share an orbital period with Jupiter. The first Trojan asteroid to be discovered, 588 Achilles, was first identified in orbit around Jupiter by astronomer Max Wolf (1863–1932) in 1906. About 65 percent of Jupiter’s Trojans are in orbit ahead of the planet in the L4 position, and the rest trail behind the planet in the L5 spot. The gravitational forces of other planets—most notably Saturn—cause slight oscillations in the orbit of those asteroids. However, Jupiter’s gravitational force is sufficient to keep them within a small range of variation. These asteroids are named after warriors from the Trojan War. L4 asteroids have Greek names, and L5 asteroids have Trojan names. There are two exceptions to this rule. One of Jupiter’s L4 asteroids was named after Hektor, a Trojan who spied on the Greeks, and an L5 asteroid was named Patroclus, after a Greek warrior who tricked the Trojans.
While most of the known Trojan asteroids are near Jupiter, they have been found orbiting several other planets as well, including Mars and Neptune. In 2011, scientists using the National Aeronautic and Space Administration’s Wide-Field Infrared Survey Explorer (WISE) space telescope discovered a Trojan asteroid orbiting with Earth. Scientists had long theorized that a Trojan asteroid would be found near Earth. However, the asteroid’s small size and tendency to be obscured by the sun’s brightness made finding it difficult. Earth’s Trojan asteroid is about 300 meters (1,000 feet) across and 20 million kilometers (12.4 million miles) ahead of Earth in its orbital path. Its name is 2010 TK7.
Future Trojan Space Bases
Asteroids are valuable to scientists because they are made up of materials left over from the formation of the solar system about 4.6 billion years ago. Because of their stable paths, Trojan asteroids are less likely than other asteroids to have collided with other objects. Trojan asteroids are of interest to astronomers because they have likely gone unchanged for billions of years.
Their consistent presence near other planets gives Trojan asteroids further potential for mining sites and as space bases and observation posts. The possibility of traveling to a Trojan asteroid could provide valuable data about the origins of the solar system. It could also provide a base for observation of other parts of the galaxy.
In 2021, the National Aeronautics and Space Administration (NASA) launched the first mission to explore the Trojan asteroids near Jupiter. The mission, dubbed Lucy after the nickname given to the fossilized remains of an ancient human ancestor, launched on October 16, 2021. Lucy is slated to fly by one larger non-Trojan asteroid and seven Trojans during its twelve-year mission.
Principal Terms
- asteroid: a small, rocky space object that orbits the sun and is categorized by its composition.
- Lagrange points: a set of five points found in relation to two large objects, such as a planet and the sun, where gravitational forces allow a third, smaller object to maintain a consistent distance from the other two; also known as libration points or L-points.
- libration points: another name for Lagrangian points, or the five points shared by two large objects where gravitational forces allow a third object to maintain a consistent distance from the other two.
- Trojan asteroid: an asteroid that shares an orbital period with a planet and maintains a consistent distance from it at the Lagrangian points.
Bibliography
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