Thronium family

Lore & Background

The Thronium family is a collisional asteroid family, meaning its members are fragments from a collision with an original larger asteroid, 9799 Thronium. This distinguishes it from a dynamical group, where asteroids share similar orbits due to gravitational interactions with planets rather than a common physical origin. The family is considered non-catastrophic because 9799 Thronium makes up nearly all of the family's total mass, rather than being simply the largest among many fragments each comprising a small fraction of the original body.

All known members of the Thronium family are dark, with albedos around 0.06, and are assumed to be C-type asteroids. The family is part of the broader Jupiter Trojan dynamical group, which consists of asteroids in a 1:1 orbital resonance with Jupiter, staying about 60 degrees ahead of or behind the planet at the Lagrange points L4 and L5. The Thronium family specifically resides in the L4 cloud, known as the Greek camp.

Reader's Guide

The Thronium family is significant as a rare example of a non-catastrophic collisional family within the Jupiter Trojan population. Unlike typical asteroid families where the largest member is merely the biggest fragment of a shattered parent body, here 9799 Thronium retains nearly all the original mass, indicating a relatively gentle disruption event. This provides insight into the collisional history and internal structure of Trojan asteroids, which are thought to be primitive bodies from the early Solar System. The family's location in the L4 Greek camp also helps refine models of Trojan orbital dynamics and the long-term evolution of asteroid groups under Jupiter's gravitational influence. Its dark, C-type composition suggests primitive, carbonaceous material, linking it to other dark asteroids in the outer main belt and Trojan swarms. The existence of at least 15 confirmed members demonstrates that even small families can persist over billions of years, offering a window into the collisional processes that have shaped the asteroid belt and Trojan populations.

Did You Know?

• The Thronium family is named for its largest member, 9799 Thronium, which is 68 kilometres across.
• It is a non-catastrophic asteroid family, meaning 9799 Thronium makes up nearly all of the family's total mass.
• All members are dark, assumed to be C-type asteroids with albedos of around 0.06.
• The family lies in the L4 Lagrange point cloud of Jupiter trojans, known as the Greek camp.