Jupiter Trojans

Region · Trojan swarms · orbits Sun

Sharing Jupiter’s orbit, two swarms of asteroids ride the gravitationally stable Lagrange points 60° ahead of and behind the planet. Over 12,000 are known, and models suggest the swarms rival the main belt in number. They are thought to be planetesimals captured during the giant planets’ early migration - which makes them time capsules from the Solar System’s first few million years.

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Quick facts

The two swarms are named the “Greek camp” (leading) and “Trojan camp” (trailing).
The first Trojan, 588 Achilles, was found in 1906.
Lucy will fly past eight Trojans between 2027 and 2033.

Lagrange points

At two special points along a planet’s orbit, the pull of the Sun and the planet balance in a way that lets small bodies circle stably for billions of years. NASA’s Lucy mission is the first to visit these clouds.

Physical characteristics

Diameter	0 km
Dimensions	two swarms near 5.2 AU, 60° ahead of and behind Jupiter km

Atmosphere and composition

Composition

Dark, reddish primitive bodies - likely captured planetesimals rich in organics and ice.

Missions

Lucy NASA · Flyby probe · 2021 · en route

Lucy is on a 12-year tour of the Jupiter Trojan asteroids - primitive leftovers trapped in Jupiter’s orbit - with its main tour beginning in 2027. Practice flybys of the main-belt asteroids Dinkinesh and Donaldjohanson have already delivered surprises.

What is still uncertain

Rendered as a selectable region, not individual bodies; listed extent is the swarm geometry.