Space · Moons
Helene
A moon of Saturn — A Trojan moon of Dione — orbits at Dione's leading L4 Lagrange point.
Quick facts
Parent planet
Diameter (mean)
36 km
Mass
7.1 × 10¹⁵ kg
9.7e-08 Moon masses
Mean orbital radius
377,420 km
Orbital period
2.737 Earth days
Discovery year
1980
Discoverer
Pierre Laques & Jean Lecacheux
Naming origin
Helen of Troy
Surface conditions
Helene is a 'Trojan' moon of Dione, orbiting Saturn at the same distance as Dione but 60° ahead of it (the leading Lagrange point L4). The trojan-moon configuration is rare in the solar system; Helene was the first such body discovered around a non-Jupiter planet.
Missions and observations
Every Saturn-system mission has had an opportunity to image or characterize Helene. The list below is the Saturn-system mission catalog; specific Helene encounters are documented in mission archives.
| Mission | Year at Saturn | Status |
|---|---|---|
|
Pioneer 11 NASA |
1979 | Completed |
|
Voyager 1 NASA |
1980 | Completed |
|
Voyager 2 NASA |
1981 | Completed |
|
Cassini-Huygens NASA/ESA/ASI |
2004 | Completed |
|
Dragonfly NASA |
2034 | On the way |
Naming etymology
Helene is the Greek name of Helen of Troy. The IAU adopted the name in 1988.
Methodology & sources
Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.