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Neptune's Moon Triton: The Icy Giant's Second World

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Published on June 1st, 2012 | by Yellow Magpie


Neptune’s Moon Triton: The Icy Giant’s Second World

Neptune’s Moon Triton

It is one of the largest world’s in the Solar System. Larger than Mercury, Neptune’s moon Triton is a unique place. The satellite is one of the few in the Solar System to have a retrograde orbit.

A Cold Harsh World

Triton is an extremely cold place, one of the coldest in the Solar System with an average temperature of just minus 235 degrees Celsius (minus 391 degrees Fahrenheit).

Neptune And Triton

It takes Neptune’s moon Triton just under six days to complete one orbit of Neptune doing so at a distance of 350,000 kilometres (219,000 miles) out from the Icy Giant. Triton’s 2,700 km width (1,700 miles) makes it the seventh-largest satellite in the Solar System.

Neptune’s moon Triton always keeps one side facing the planet as it orbits the Icy Giant. Although it does so in retrograde orbit – meaning it rotates in the opposite direction of Neptune. It is only large moon in the Solar System to have a retrograde orbit.

An Unusual Orbit

Perhaps most unusual of all is the almost perfect cycle orbit of Triton as it makes its way around Neptune.

Neptune's Moon Triton Showing Terrain Details

This almost perfect circular orbit is thought to have arisen due to drag from debris surrounding Neptune. Furthermore, it is believed that tidal forces may have also had a part to play in such a unique orbit.

Unlike our own Moon, which is moving farther away from the Earth each year, Neptune’s moon Triton is being drawn ever closer to the Icy Giant. Over three billion years from now the moon of Triton will reach its demise.

The Origins Of Neptune’s Moon Triton

The retrograde orbit of Neptune’s moon Triton tells us that the satellite did not come from  the same region of the Solar System as where Neptune originated.

The fact that Triton is almost identical in size and make-up as the dwarf planet Pluto suggests that Triton must also be from the Kuiper belt. Triton was therefore probably captured by Neptune as it came too close.

Showing The Surface Of Neptune's Moon Triton

If Neptune’s Triton is a captured Kuiper Belt object then this may explain why such a large planet like Neptune has so few moons.

Another interesting suggestion for Triton’s origins maintains that the satellite was part of a binary set of moons. When the binary came into contact with Neptune’s gravitational field Triton remained while the other companion was ejected. This hypothesis has been warmly greeted as many binary sets exist in the Kuiper belt.

Differentiation And Composition

Neptune’s moon Triton is comprised of nearly 55 per cent nitrogen, up to one-third water and the rest carbon dioxide. Needless to say, all of these substances are completely frozen due to Triton sub-zero temperatures.

Neptune’s moon Triton has a differentiated core which is thought to have been caused by tidal heating warming the moon. When Triton’s orbit became circular its internal warmth would have cooled as the effects of tidal heating dissipated.

Neptune's Moon Triton And Its Volcanic Plains

Radioactivity And Life?

It is believed that Neptune’s moon Triton has a rocky core that may be radioactive. Surrounding this core is thought to be a mantle of water and a crust of nitrogen.

If Triton’s core is radioactive the possibility exists that radioactive decay may have warmed the mantle sufficently enough to produce a liquid subterranean ocean.Therefore, the possibility also exists that Triton like many other moons in the Solar System, harbours life.

The Atmosphere Of Neptune’s Moon Triton

Neptune’s moon Triton possesses what is known as a tenuous atmosphere. This atmosphere consists almost exclusively of nitrogen with traces of methane and carbon monoxide.

Triton’s atmosphere was originally documented by Voyager 2 as it undertook its long journey out of the Solar System. Intriguingly, Earth-based observations have concluded that the atmosphere is much denser than what Voyager 2 originally measured. The reason for this is thought to be a extraordinarily warm summer season that occurs once every couple of hundred years.

Two Different Surfaces On Neptune's Moon Triton

A Young Thing

Neptune’s moon Triton has one of the youngest surfaces in the Solar System. Ranging from six to 50 million years old it is a world full of cryovolcanoes, ridges and valleys.

Cryovolcanoes spewing nitrogen gas into Triton’s atmosphere have been caught by Voyager 2. It is thought that the Sun plays a role in these eruptions.

The future for both Triton and mankind is unknown. So far no concrete plans have been put into place for another spacecraft to visit. Triton may well be worth another examination to see if it does indeed have a subterranean ocean. Time should tell.

Highly Recommended Reading

Check out Yellow Magpie’s Planet Neptune: The Mysterious Azure-Blue for more insight into the largest planet in the Solar System.

You may also wish to take a gander at The Solar System And Beyond: A Guide To The Cosmos.

Cosmos is a highly recommended book. It contains large, full-page pictures of the asteroids and writing on the subject by the highly competent author, Giles Sparrow.


For people living in Ireland or the United Kingdom, you can access: Cosmos from here.


For those who live in Canada, you can obtain: Cosmos here.


For Germany: Cosmos.


For France: Cosmos.

About the Author

2 Responses to Neptune’s Moon Triton: The Icy Giant’s Second World

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