The Beatles sang “Lucy in the Sky with Diamonds”. Lucy in the sky with asteroids, NASA answers. This Saturday, October 16, at 11:34 am (Paris time), the US Space Agency will launch Lucy, so the probe that will for the first time will closely monitor asteroids, known as “Trojans”, which are objects that share the same orbit. Like Jupiter. The goal: to go back in time, to understand the composition of our solar system. Hence the name of the expedition, borrowed from one of our ancestors, the most famous of which is Australopithecines (which, for the record, was named in reference to the Fab Four song). The journey will last 12 years.
The Trojans of Jupiter, of which about 7,000 are known, develop around the sun in two groups, one preceding the giant planet (“Greeks”), and the other following (“Trojans”), according to the gravitational phenomenon that continues to fascinate today. After the first of these bodies, Achilles, was discovered by astronomer Max Wolf in 1906, it was agreed to give each one the name of a hero of Greek mythology.
Trojans represent the curiosity of scientists. Although they are located in a very narrow space, they are very different from each other. Some, for example, are gray, others are red. “If we look at it from Earth, the Trojans are very far away and very dark. To study them, there is no other choice but to go and see them,” explains Patrick Michel, director of research at CNRS.
No meteor to inform us
Unlike the Osirix-Rex and Hayabusa 2 probes, which went to meet asteroids to “sniff out,” Lucy will only fly over them, requiring budget and fuel constraints. Because its journey has nothing to envy Ulysses: it will go first in 2025 near the body of the main asteroid belt located between Mars and Jupiter, before visiting six Trojans. Including two asteroids, their final destination, in 2033.
Although from a distance, Lucy can help answer important questions: What are these asteroids made of? Where did they come from? “These bodies, which have changed a little, will tell us part of the history of the early solar system, because they represent an intermediate stage between the disk of the protoplanets. [NDLR: antérieur à l’apparition des planètes] and the last planets,” continues Patrick Michel.
In recent years, NASA, like the Japanese space agency Jaxa, has increased the number of flights to these small celestial bodies. “All missions that see small bodies are very interesting, because we have very little information about them from Earth. Going to see these new regions, which have appeared in conditions different from those on Earth, we have, so far, surprises every time. There is no doubt In that that will be the case again this time: unlike some asteroids in the main belt, the Trojans never cross the course of the Earth. Also, it is certain that none of these objects meteorite fell on our planet. That is why their formation, At the moment, it is still unknown.
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