Helike’s unusually round orbit

How Helike compares with other Ananke-group moons.

Published 2026-10-23

Irregular moons usually have eccentric orbits. Helike’s is noticeably rounder.^[3]

The numbers

• Helike: e ≈ 0.155, i ≈ 154°.^[3]
• Harpalyke: e ≈ 0.239, i ≈ 148°.^[3]
• Iocaste: e ≈ 0.223, i ≈ 149°.^[3]
• Ananke: e ≈ 0.238, i ≈ 148°.^[3]

Still a family member

The Ananke group spans inclinations of 144.3°–155.5°, and Helike falls inside that range.^[4]

Speed

Helike moves at an average 2.48 km/s around Jupiter.^[1]

Numbered citations link to the sources list on the Helike overview page.