HOMER'S TALE OF THE TROUBLE of the Trojan War is a tale of intrigue, heroes, and loss. Many of the names of those involved were attached to objects in space, just as it is with characters from Greek mythology.
When astronomical photography began to improve, it was clear that Jupiter, the largest planet in the solar system, was being accompanied by not only its own system, but also two other groups of acolytes. These were clusters made up of asteroids, which followed the orbits of giant planets precisely but either led or trailed Jupiter by approximately 60 degrees.
These clusters are located at places called Lagrange points (L4 and L5), named after the mathematician who predicted them. L4 and L5 represent traps in space created by the interaction between the gravitational fields from Jupiter and the sun. Asteroids are usually stuck in these traps once they have been caught inside one. It was amusing for their early discovery to divide these captured asteroids into two groups, so they called bodies at L4, Jupiter, after the Greek heroes of war, and L5, after the Trojans. Each camp has a spy from another.
The Siege of Troy
The belt that links the orbits of Jupiter and Mars is home to most known asteroids. The spectroscopic analysis of the sunlight reflected from these and comparisons to chunks of space rocks that fell to Earth as meteorites suggests that they are fragments from dwarf planets that subsequently collided with one another (though some, like Ceres), while the rest of the material is conglomerations from the early solar nubula, which often include pebbles made from once-molten rock called "chondrules". Conglomerate-based asteroids tend to be darkened and slightly reddish due to their high carbon content. Their spectra are similar to those of carbonaceous chondrites, which are chondrule-bearing meteorites.
However, certain asteroids located in the outer portion of the main belt have redder carbonaceous chondrites, which are essentially steroids. These types are also found in the Kuiper Belt, a distant group of asteroids, dwarf planets and chondrites. It is located beyond Neptune's orbit. Pluto is the most well-known. These types of objects are common in the nuclei of active comests. They also make up the majority of members of the Greek and Trojan camp.
These asteroids are far away from Earth and do not appear to be part of the meteorites that hit Earth. There is no way to directly compare them to other meteorites. However, their colour is believed to be due to complex organic molecules similar to terrestrial Kerogen that have collected on their surfaces. The exact chemistry of these materials will reveal where they formed in the solar system and provide insight into how objects moved in the early days. This makes the Trojans of particular interest to researchers who study the formation and evolution of planetary systems. If all goes well, NASA (America's space agency) will launch a probe on October 16th to take a look at them.
Lucy, as this planetary-ancestor-investigating mission is dubbed, after a well-known specimen of Australopithecus, an early hominid, will blast off from Cape Canaveral, in Florida, and will then follow one of the most complex paths around the solar system yet devised by NASAs orbital navigators. The diagram below shows Lucy's orbit using Jupiter's orbit as a reference. It also shows how it will accelerate first using two speed-boosting fly-bys. The craft will then travel to L4 in Greece, passing by Donaldjohanson (in honour of Lucy the Australopithecine's discoverer). It will encounter five bodies when it arrives at L4 2027: Eurybates, its small satellite Queta and Polymele as well as Leucus and Leucus.
After having examined all of them, it will depart the Greek camp in 2028 to cross the other velocity-bosting flyby of Earth to reach the Trojan camp at L5. When it reaches L5 (in 2033), its last planned encounter is with Menoetius and Patroclus.
They were initially thought to be one object until 2001 when a Gemini North telescope in Hawaii revealed that they were actually two rocks measuring approximately 100 km across and orbiting around each other. The name Patroclus was used to identify the Greek spy in Trojan camp, and is well-known by classicists. The larger of the two is now called it. Menoetius was Patroclus' father and was hurriedly put into service to identify the smaller. (For those who are curious, Hektor is the Trojan spy in the Greek Camp. Hektor is not on Lucys agenda.
David Tholen, University of Hawaii's most popular asteroids classification, has now created 14 types of spectral types. Each type is called by a letter of alphabet. The main-belt asteroids consist mainly of types C (carbon rich, as with carbonaceous and chondrites), and M (believed be metallic and derived from cores of dwarf worlds), and S (silicaceous or stony and any other types of conglomerate fragments or other types of conglomerate. Type C Trojans can also be found. However, the rarer D and P types are more common. The difference is in the shapes of their spectra.
Lucy has three instruments to help it examine its targets (Polymele and Menoetius, Orus and Leucus being type P, Orus and Leucus being type D, and Eurybates, Donaldjohanson being type C). Lucy also comes with a high-resolution camera and an optical and near infrared spectrometer. These instruments will allow the probe to map various asteroids and analyze the chemical compositions.
This will allow Harold Levison to test his ideas as the principal scientific investigator for the mission. Dr. Levison is a scientist at the Southwest Research Institute, Boulder, Colorado. He was one of the original creators of the Nice model. This hypothesis suggests that the four largest planets of the solar system, Jupiter, Saturn and Uranus, have moved significantly since their formation.
A celestial Odyssey
All of this gravitational movement would have scattered asteroids in gales, scattering them like leaves in the wind, ejecting some from the solar system and moving others away from their origins. Dr Levison believes the Trojan D and P asteroids are such travelers. Their surface chemistry will reveal that they were formed far more from the sun than Jupiter's current orbit. According to the Nice model, such distant asteroids would have been scattered by Neptune's movement. Neptune began life closer than Uranus, but now lies farther away. Some would then have been captured by Lagranges gravitational traps. The Nice model would be heavier if the D and P types Lucy meets did indeed originate far from the sun.
After Lucy has visited Menoetius and Patroclus, the formal mission will end. Space probes can sometimes live beyond their intended lifetime. For example, the New Horizons mission has observed Arrokoth, a second Kuiper belt object. Opportunity, an American Mars rover, had a design lifetime of 90 Martian day, but actually ran for 57 times that amount. Lucy's case, the craft's final orbit will send it on an interminable loop from L5 through L4 and back. Each loop will take six year. If the hardware is stable, the fuel is still available for maneuvering, and someone is willing pay to keep the mission team together financially, Trojans may be able to receive a visit.
Source: NASA
