Arkesilaos family
A collisional family of dark asteroids in Jupiter's L4 cloud.
The Arkesilaos family is a collisional asteroid family, a group of at least 37 asteroids that are fragments from a single larger body. It takes its name from its largest member, 20961 Arkesilaos, which measures about 22 kilometers (14 miles) across. This family belongs to the larger dynamical group known as the Jupiter trojans—asteroids that share Jupiter’s orbit, staying roughly 60 degrees ahead of or behind the planet at the Lagrange points L4 and L5. Specifically, the Arkesilaos family is part of the leading cloud at L4, often called the Greek camp. All members of the family are dark, assumed to be C-type asteroids, with albedos around 0.06. The family is classified as catastrophic because its largest member, 20961 Arkesilaos, accounts for only about one-fifth of the family’s total mass.
- Designation
- 008
- Number of members
- at least 37
- Largest member
- 20961 Arkesilaos
- Largest member diameter
- 22 km (14 mi)
- Albedo
- around 0.06
- Spectral type
- assumed to be C-type (dark)
- Location
- Jupiter trojans, L4 (Greek camp)
Lore & Background
The Arkesilaos family is a catastrophic asteroid family, meaning it was created by a collision with an original larger asteroid, and the fragments continue on similar orbits to the original. The family's largest member, 20961 Arkesilaos, accounts for only a fifth of the family's total mass, indicating a highly disruptive event. All members of the family are dark, with albedos of around 0.06, and are assumed to be C-type asteroids.
The family is part of the larger dynamical group of Jupiter trojans, which are 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 Arkesilaos family belongs to the L4 cloud, known as the Greek camp. It is distinct from a purely dynamical group because its members are physically related fragments of 20961 Arkesilaos, not merely asteroids concentrated by gravitational interactions.
Reader's Guide
The Arkesilaos family is significant as an example of a collisional asteroid family within the Jupiter trojan population, demonstrating that catastrophic disruptions have occurred among these distant bodies. Its classification as a catastrophic family, where the largest remnant holds only a fifth of the total mass, suggests a high-energy impact event that shattered the original parent body. The family's location in the L4 Greek camp of Jupiter trojans places it among a large dynamical group, but its members are genetically linked through the collision, providing a case study for understanding the collisional history of the outer Solar System. The dark, C-type composition of its members, inferred from low albedos, aligns with the typical spectral properties of many trojans. With at least 37 known members, the Arkesilaos family is relatively small, but its study helps refine models of asteroid family formation and evolution in the Trojan swarms, where gravitational dynamics and collisional processes interact.
Did You Know?
- The Arkesilaos family is named after its largest member, 20961 Arkesilaos, which is 22 km across.
- The family is part of the Greek camp, the leading cloud of Jupiter trojans at the L4 Lagrange point.
- The family is considered catastrophic because its largest member makes up only a fifth of the family's mass.
Frequently Asked Questions
What is the Arkesilaos family?
It is a collisional family of at least 37 asteroids that all broke off from a single, once-larger parent body. The group orbits in Jupiter's L4 Lagrange region, the so-called Greek camp, and takes its name from its biggest member, 20961 Arkesilaos.
How large are the members of the Arkesilaos family?
The family's biggest asteroid, 20961 Arkesilaos, spans roughly 22 kilometers (about 14 miles) in diameter. The remaining 36-plus fragments are smaller, but together they make up a compact cluster of dark objects sharing similar orbital paths.
Where exactly does the Arkesilaos family orbit?
All members sit in the L4 cloud of Jupiter trojans, trailing about 60 degrees ahead of Jupiter in its path around the Sun. This places them in the region fans commonly call the Greek camp, as opposed to the L5 Trojan (or "Lagard") camp behind the planet.
What do Arkesilaos family asteroids look like?
They are uniformly dark, with a low geometric albedo of roughly 0.06, meaning they reflect only a small fraction of the sunlight that hits them. Their spectral characteristics lead researchers to classify them as C-type (carbonaceous) bodies, the most common type among main-belt and Trojan asteroids.
How did the Arkesilaos family come to exist?
The family is the debris field left behind when a single larger asteroid was shattered by a high-energy impact. Over time, the fragments drifted into a tight cluster of similar semi-major axes and inclinations, which is how astronomers identify them as one collisional family rather than unrelated objects.
More in Notable Asteroids, Part 4 1-24
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