November 27, 2021

Lucy, a space mission to discover the Trojan asteroids

Her name is Lucy. In reference to the famous Australopithecus more than 3 million years old, whose skeleton was discovered in Ethiopia in 1974 and which provided a wealth of information on the hominids that preceded the birth of the genus Homo. By taking the name of Lucy for its new mission, NASA hopes that the probe which is to take off Saturday, October 16 from the Kennedy Space Center (Florida) will also bring a plethora of new knowledge on other origins, more distant, those of the Solar System. .

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They are called Hector, Achille, Priam, Patroclus… Named after the characters of The Iliad, these are the so-called “Trojan” asteroids. Numbered in the thousands, they are divided into two groups located in two very specific places in the orbit of Jupiter, the Lagrange points L4 and L5. The laws of gravitation mean that in these zones, which represent the vertices of the two equilateral triangles whose base would be the Sun-Jupiter segment, the respective attractions of our star and the giant planet are balanced. They are therefore havens of stability – or traps if one sees things more bleakly. L4 precedes Jupiter by 60 ° in its revolution around the Sun while L5 follows it by 60 °.

Real odyssey

Several space missions have already targeted asteroids but none has ever visited the Trojans and Lucy will therefore be a great first. After take off, this 1.5 ton machine (including 771 kg of fuel) will begin a veritable odyssey in the Solar System. First of all, and twice – in 2022 and 2024 -, it will have an appointment with the Earth to benefit from a gravitational boost from our planet, which will send it to L4. During this trip, on April 20, 2025, she will meet a representative of the main asteroid belt located between Mars and Jupiter, a large pebble named Donaldjohanson… in homage to the American paleoanthropologist who co-directed the mission that discovered Australopithecus Lucy. The meeting with this asteroid will be the opportunity to perform a dress rehearsal for the probe, which carries three instruments: a very high resolution camera and two spectrometers to determine the chemical composition of crossed stars.

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Lucy will arrive at L4 in 2027 and, on August 12 of that year, will fly over her first Trojan, Eurybate, an asteroid about sixty kilometers in diameter that has two peculiarities: the first is to belong to a family of Trojans resulting from a cataclysmic collision, the second to be equipped with a small satellite named Queta. From September 2027 to November 2028, Lucy will visit three other asteroids, Polymele, Leucos and Oros. Then, the probe, with its two huge solar panels more than 7 meters in diameter, will go to L5.

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