NASA's Lucy becomes the first spacecraft to reach Jupiter's Trojan asteroids, after 2.2 billion miles

NASA's Lucy spacecraft has arrived in the region of the Trojan asteroids, a swarm of ancient rocks that shares Jupiter's orbit around the Sun, NASA said on 28 October. About five years after launch and more than 2.2 billion miles into its journey, Lucy is the first spacecraft to enter this region.

Asteroids that travel with Jupiter

The Trojans gather in two groups around Jupiter's Lagrange points: one near L4, which moves ahead of the planet, and one near L5, which trails behind. Lucy has reached the leading L4 group. The Trojans lie about 484 million miles from Jupiter, as far from Jupiter as the planet is from the Sun, and are on average more than 6 million miles apart.

Earlier spacecraft visited Jupiter and used its gravity to travel farther, but none visited the Trojans, and Lucy is the only one built to explore them. Scientists hope the Trojans, which NASA calls primitive bodies of the solar system, will help explain how the planets formed about 4.5 billion years ago and how they ended up where they are now.

Four flybys in two years, then the trailing swarm

Lucy launched on 16 October 2021. Its first asteroid encounter, with Eurybates, is set for 11 August 2027, followed by Polymele in September 2027, Leucus in April 2028 and Orus in November 2028. The spacecraft will then return to Earth in 2030 for a third and final gravity assist that sends it to the trailing swarm, where it is due to fly past the binary pair Patroclus and Menoetius in March 2033.

Engineers track Lucy's approach using its radio signals and images of the stars around it. It is now operating more than five times farther from the Sun than Earth is, and its spacecraft and instruments are working as expected, according to NASA. The update was written by Katherine Kretke of the Southwest Research Institute.

What comes next

The first close-up images of a Trojan asteroid are still about nine months away. Until then, Lucy will cruise through the L4 region toward Eurybates. More missions are collected under space exploration.