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Triton is unique among all large moons in the solar system for its [retrograde orbit]? around the planet (i.e., it orbits in a direction opposite to the planet's rotation). Jupiter's moons Ananke, Carme, Pasiphae and Sinope and Saturn's moon Phoebe also orbit retrograde, but all of them are less than 1/10 the diameter of Triton. Moons in retrograde orbit cannot form out of the same [solar nebula]? as the planets they orbit, they must be captured from elsewhere; it is thought that Triton may be a captured Kuiper belt object. The capture of Triton may also explain the extremely eccentric orbit of Neptune's outermost moon Nereid, as well as having provided the heat necessary to melt and differentiate Triton's interior. Its similarity in size and composition to Pluto, as well as to Pluto's eccentric Neptune-crossing orbit, provides further tantalizing hints to Triton's possible origin as a Pluto-like planetary body. |
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Triton is unique among all large moons in the solar system for its [retrograde orbit]? around the planet (i.e., it orbits in a direction opposite to the planet's rotation). Jupiter's moons Ananke, Carme, Pasiphae and Sinope and Saturn's moon Phoebe also orbit retrograde, but all of them are less than 1/10 the diameter of Triton. Moons in retrograde orbit cannot form out of the same [solar nebula]? as the planets they orbit, they must be captured from elsewhere; it is thought that Triton may be a captured Kuiper belt object. The capture of Triton may also explain the extremely eccentric orbit of Neptune's outermost moon Nereid, as well as having provided the heat necessary to melt and differentiate Triton's interior (tidal heating resulting from an eccentric post-capture orbit being circularized could have kept Triton liquid for a billion years). Its similarity in size and composition to Pluto, as well as to Pluto's eccentric Neptune-crossing orbit, provides further tantalizing hints to Triton's possible origin as a Pluto-like planetary body. |
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Triton has a density of 2.0, and is probably about 25% water ice with the remainder being rocky material. It has a tenuous nitrogen atmosphere with small amounts of methane. Its atmospheric pressure is only about 0.01 millibar. Triton's surface temperature is only 34.5 Kelvin, as cold as Pluto's. Surprisingly, however, Triton is geologically active; its surface is fresh and sparsely cratered, and the Voyager 2 probe observed numerous volcanoes erupting liquid nitrogen, dust, or methane compounds from beneath the surface in plumes up to 8 km high. This volcanic activity is thought to be driven by seasonal heating from the Sun, or perhaps by tidal heating of the moon's core by Neptune. |
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Triton has a density of 2.0, and is probably about 25% water ice with the remainder being rocky material. It has a tenuous nitrogen atmosphere with small amounts of methane. Its atmospheric pressure is only about 0.01 millibar. Triton's surface temperature is only 34.5 Kelvin, as cold as Pluto's. Surprisingly, however, Triton is geologically active; its surface is fresh and sparsely cratered, and the Voyager 2 probe observed numerous volcanoes erupting liquid nitrogen, dust, or methane compounds from beneath the surface in plumes up to 8 km high. This volcanic activity is thought to be driven by seasonal heating from the Sun, unlike the tidal heating responsible for the volcanoes of Io. There are extensive ridges and valleys in complex patterns all over Triton's surface. These are probably the result of freezing/thawing cycles. |
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*Orbital radius: 354,800 km *Diameter: 2,700 km *Mass: 2.14×1022 *Density: 2.07 g/cm3 *Orbital period: 5.87685 days retrograde *Orbital inclination: 157.35° |
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