Fornjot.space

Irregular moon of Saturn (retrograde) · Outer Saturnian system · Norse group

Fornjot

Saturn XLII · S/2004 S 8

Saturn’s outermost named moon: round, faint, and named for the father of giants.

Key factsTelescope picker
Fornjot at a glance
Object typeIrregular, retrograde moon of Saturn[1]
GroupNorse group[2]
DistinctionOutermost named moon of Saturn[1]
DiscoveredDec. 12, 2004, Subaru Telescope, Mauna Kea[2]
Diameter≈ 6 km[1]
Rotation period6.9 or 9.5 hours (ambiguous)[1]
ShapeProbably very round — little brightness variation[1]
Mean distance≈ 24.9 million km from Saturn[3]
Orbital period≈ 1,470 days[3]
Inclination≈ 170° (retrograde)[3]
Eccentricity≈ 0.21[3]

Saturn’s outermost named moon

Fornjot is the outermost named moon of Saturn. It had the largest semi-major axis of all Saturn’s known moons until Saturn LVIII was recovered in 2019.[1]

Probably round

Fornjot shows very little variation in brightness, so it is probably very round. Its rotation period is ambiguous — either 6.9 or 9.5 hours. It was the faintest moon measured by Cassini.[1]

Found in 2004

It was one of 12 Saturnian moons found on 12 December 2004 by Sheppard, Jewitt and Kleyna with the Subaru telescope.[2]

Father of giants

NASA describes Fornjot’s namesake as the giant in Norse myth who was father to the giants and commanded the wind, the sea and fire.[2]

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Orbit

Fornjot orbits backwards between about 19.6 and 30.2 million km from Saturn, taking about 1,470 days — about four years.[3]

Saturn Titan (1.22 million km)Phoebe (12.93 million km) farthest ≈ 30.2 million km closest ≈ 19.6 million km
Top-down orbit of Fornjot to scale, computed from JPL orbital elements (a ≈ 24.94 million km, e ≈ 0.213).[3] Titan and Phoebe orbits shown for comparison.[3] Mean orbital elements; the real orbit is tilted steeply and shifts over time, so this top-down view flattens it onto one plane.

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At the edge of Saturn’s family

How far out Fornjot orbits compared with Titan and Phoebe.

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The faintest moon Cassini measured

What a nearly flat light curve tells us about Fornjot.

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Why Saturn’s backwards moons have Norse names

The IAU’s naming scheme for the Norse group.

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Sources

  1. Fornjot (moon) — Wikipedia
  2. Fornjot — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Norse group — Wikipedia

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.