| Object type | Irregular, retrograde moon of Jupiter[1] |
|---|---|
| Group | Ananke group[1] |
| Discovered | Feb. 6, 2003 by Scott S. Sheppard, Mauna Kea[2] |
| Named | March 2005, after a nymph who nursed Zeus[1] |
| Diameter | ≈ 4 km[1] |
| Orbital speed | ≈ 2.48 km/s[1] |
| Mean distance | ≈ 20.9 million km from Jupiter[3] |
| Orbital period | ≈ 618 days[3] |
| Inclination | ≈ 154° (retrograde)[3] |
| Eccentricity | ≈ 0.16[3] |
A small Ananke moon
Helike is about 4 km across, discovered by Sheppard’s team in 2003 as S/2003 J 6.[1] It belongs to the Ananke group of retrograde moons.[1]
A rounder orbit than most
JPL’s mean eccentricity of about 0.16 makes Helike’s orbit one of the least stretched among its neighbours — compare Harpalyke at 0.24 or Iocaste at 0.22.[3]
Ananke family
NASA describes the Ananke group as fragments of a captured asteroid broken up by a collision.[2] The group’s moons orbit at 19.2–21.8 million km.[4]
Named for a nurse of Zeus
In March 2005 the moon was named after Helike, one of the nymphs who nurtured Zeus in his infancy on Crete.[1]
Orbit
Helike circles Jupiter backwards between about 17.7 and 24.2 million km, once every 618 days, at an average speed of about 2.48 km/s.[3][1]
Helike in the sky
The Greek poet Aratus called the Great Bear constellation Helike (“turning”), because it turns around the celestial pole.[5] Its Big Dipper stars are a great target for binoculars.
Read more
Helike: an ancient name for the Great Bear
How a moon of Jupiter shares a name with one of the sky’s best-known constellations.
Read →Find Polaris with the Big Dipper
A simple star-hop that’s even easier with binoculars.
Read →Helike’s unusually round orbit
How Helike compares with other Ananke-group moons.
Read →Sources
- Helike (moon) — Wikipedia
- Helike — NASA Science
- Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
- Ananke group — Wikipedia
- Ursa Major — Wikipedia
Figures are rounded; where sources differ we note it. Spotted an error? Tell us.