A trip back in time with the Trojans
Project Sunride
Breaking boundaries in student-led rocketry with diverse propulsion and mission profiles.
The Trojan asteroids are a group of more than 9,800 asteroids that share the same orbit as Jupiter. They are called the Trojan asteroids because the first asteroid, found in 1906, was denoted 588 Achilles, and each asteroid since has been given a name associated with the Trojan war. There are two groups, each located at one of Jupiter's stable lagrangian points, a point between Jupiter and the Sun where small bodies can remain stationary in relation to both the sun and Jupiter. These groups are L4, 60 degrees ahead of the planet's orbit, and L5, 60 degrees behind. About 65% of the asteroids are located in the L4 group, with the rest being located in the L5 group. The leading L4 orbit group, or the ‘Greek’ group, are named after members of the Greek camp, and the trailing L5 ‘Trojan' group are named after members of the Trojan camp. There are two exceptions, 617 Patroclus and 624 Hektor, who were named before the Greek camp - Trojan camp nomenclature was implemented, and so are in the wrong camps, Patroclus in the trailing Trojan group and Hektor in the leading Greek group.?
There are a few different theories about where the Trojan asteroids came from, one suggests that they formed in the same area of the solar system as Jupiter, and got caught in its orbit as it grew larger and its gravitational pull increased. Another theory suggests the Trojan asteroids formed further out, but were captured when the giant planets became unstable 500-600 years after the solar system was formed. As Uranus and Neptune moved outwards they displaced the Kuiper belt, and some of the objects were thrown inwards, some of which got caught in Jupiter's gravitational field and became the Jupiter Trojans.?
Regardless of the correct theory of their formation, the Trojan asteroids have been trapped within Jupiter’s orbit for billions of years. This makes them extremely interesting. To look into the Trojan asteroids is to look back into the past, to the formation of the solar system. The Trojan asteroids are thought to be the remnants of the material that formed the outer planets and provide a unique insight into the primordial solar system as it was beginning.?
The Lucy mission sets out to send the first spacecraft to visit the asteroids, and is aiming to visit more destinations in one mission than any other in history. Launched in October 2021 the Lucy space probe is on a 12 year mission to visit eight asteroids, a main belt asteroid as well as seven of the Trojan asteroids, with the aim of surveying the diversity of the Trojan asteroids. There are three main types of asteroids found within the Trojan asteroids, the C, P and D types. Lucy’s journey will visit all three types, visiting both clusters of Trojan asteroids and providing the first close up view of the asteroids. Although we do not know where the asteroids come from, the P and D type both have a strong resemblance to those found in the Kuiper belt, and the C type are similar to the asteroids located between Mars and Juipiter. The Trojan asteroids are thought to be carbon rich and may even hold water below the surface.?
It is not a simple journey to the Trojan asteroids. Their extreme distance from Earth means that Lucy won’t actually reach them until 2025. Before it can reach the asteroids it first has to fly past Earth twice to make use of its gravitational field. First going past the moon and then back to Earth, then going as far as Mars, before then making it to Jupiter. It will reach the main belt asteroid Donaldjohanson in 2025, before then moving on to 5 of the L4 trojans between 2027 and 2028. Lucy will return to Earth’s orbit for another gravity boost before returning, this time to the L5 group, reaching them in 2033. Although this will mark the end of the Lucy mission, the Lucy space probe will remain within a stable orbit and will continue visiting the Trojan asteroids for years to come.?
Lucy’s payload is mainly made up of scientific cameras, focused on exploring the composition of the Trojan asteroids, as well as looking for surface activity. The payload includes the Linear Etalon Imaging Spectral Array, or LEISA, an infrared spectrometer to find, among other things, organic matter that may exist on the surface of the asteroids. Another instrument is the Multispectral Visible Imaging Camera, or MVIC, which will look for surface activity, as well as taking colour images of the asteroids to help determine their composition. Other payloads are designed to measure the surface temperature of the asteroids, as well as to determine their shapes and masses. By the end of the mission it is hoped that we will have a better understanding of both the Trojan asteroids and of the early solar system.
?Article author: Anna Bennison
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Photo credits
Jupiter, taken from the Hubble Space Telescope on June 27, 2019,Credits: NASA, ESA, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley)
The Atlas V rocket with Lucy aboard, Image Credit: NASA/Bill Ingalls
Artist concept of Lucy at a Trojan Asteroid. Credit: NASA/Lockheed Martin