Hyrrokkin.space

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

Hyrrokkin

Saturn XLIV · S/2004 S 19

An eight-kilometre moon with a lopsided light curve, named for the giantess who launched Baldr’s funeral ship.

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Hyrrokkin at a glance
Object typeIrregular, retrograde moon of Saturn[1]
GroupNorse group[2]
DiscoveredDec. 12, 2004, Subaru Telescope, Mauna Kea[2]
NamedApril 2007 (spelling corrected from “Hyrokkin”)[1]
Diameter≈ 8 km[1]
Rotation period≈ 12.76 hours[1]
Mean distance≈ 18.3 million km from Saturn[3]
Orbital period≈ 928 days[3]
Inclination≈ 150° (retrograde)[3]
Eccentricity≈ 0.34[3]

A 12¾-hour day

Cassini measured Hyrrokkin’s rotation in March 2013 at about 12 hours 45 minutes, later refined to 12.76 hours.[1]

A lopsided light curve

Its light curve shows three minima, like Ymir and Siarnaq, but one minimum is much shallower than the others.[1]

A twin of Greip?

Hyrrokkin’s rotation period and orbit are similar to Greip’s, with only the inclination appreciably different — but it isn’t known whether they are closely related.[1] NASA places it in a subgroup that includes Skathi, Skoll, Bergelmir, Farbauti and Kari.[2]

The giantess and the ship

Named in April 2007, Hyrrokkin honours a giantess who launched Hringhorni, Baldr’s funeral ship.[1] The gods could not move the ship, so they sent for her; she arrived riding a wolf and pushed it so hard that fire flashed from the rollers.[4]

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Orbit

Hyrrokkin orbits backwards between about 12.2 and 24.5 million km from Saturn, taking about 928 days.[3]

Saturn Titan (1.22 million km)Phoebe (12.93 million km) farthest ≈ 24.5 million km closest ≈ 12.2 million km
Top-down orbit of Hyrrokkin to scale, computed from JPL orbital elements (a ≈ 18.34 million km, e ≈ 0.336).[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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Hyrrokkin and Baldr’s funeral ship

The Norse myth behind the name.

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Moons with three dips

What Hyrrokkin’s odd light curve suggests.

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Hyrrokkin’s relatives

Subgroups among Saturn’s Norse moons.

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Sources

  1. Hyrrokkin (moon) — Wikipedia
  2. Hyrrokkin — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Baldr — Wikipedia
  5. Light curve — Wikipedia

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