An illustration of the Lucy spacecraft passing one of the Trojan asteroids near Jupiter Southwest Research Institute/NASA
NASA’s latest mission to study the Trojan asteroids is set to launch on 16 October from Cape Canaveral, Florida, aboard an Atlas V rocket. The Lucy spacecraft will be the first to study these asteroids up close, giving us a window into the formation of our solar system.
The Trojan asteroids circle the sun in two swarms that share Jupiter’s orbit like a police escort for the planet, one moving ahead of Jupiter and the other just behind it. They are some of the most pristine relics from the early solar system, thought to be leftovers from the process that formed the outer planets.
“They’re held there by the gravitational effect of Jupiter and the sun, so if you put an object there early in the solar system history, it [will be] stable forever,” said mission leader Hal Levison at Southwest Research Institute in Texas, during a press conference on 13 October. “These things really are the fossils of what planets form from.”
Despite their importance, the asteroids’ strange orbits mean that we have never studied them up close. To get there, Lucy will have to follow a complex trajectory over the course of 12 years. First, it will make two fly-bys of Earth to build up momentum, which will toss it towards the leading swarm of asteroids. On its way there, in 2025, it will fly past a non-Trojan asteroid named (52246) Donaldjohanson after the discoverer of Lucy, a famous fossilised skeleton of a human ancestor for which the mission is named.
Once the spacecraft reaches the leading swarm, it will examine four Trojan asteroids, one of which has its own moon. Finally, Lucy will swoop past Earth again and visit a pair of asteroids in the trailing swarm in 2033. After that, if all goes well, it will keep flying back and forth between the two clouds of Trojans every six years until the solar-powered spacecraft deteriorates.
Lucy carries three main scientific instruments. One will measure the heat coming off the asteroids in an effort to figure out their surface properties, while another will examine the light bouncing off them to learn what they are made of. The third instrument is a camera that will take detailed colour images.
Over the course of its journey, Lucy will visit all three main types of Trojans, which are defined by the colour and reflectivity of their surfaces. The three different types may indicate different compositions or birthplaces of these asteroids, which could help us understand where in the solar system they formed and how they were tossed around as the giant planets migrated to their current locations.
“One of the really surprising things about the Trojans when we started to study them from the ground was how different they are from each other,” said Levison. “If you want to understand what this population is telling us about how the planets formed, you need to understand that diversity, and that is what Lucy is intended to do.”
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