Solar System Exploration – Neptune


Neptune was discovered in 1846, the credit of discovery is split between Urbain Le Verrier and John Couch Adams. Both these astronomers used permutations in the orbit of Uranus to locate Neptune before observing it.  Neptune is the only planet to have been discovered from mathematical computation rather than direct observation. Although Galileo had observed Neptune in 1613 and had mistaken it for a star, so he is not credited for it’s discovery. Neptune is named after the Roman God of the sea and is also known as Poseidon as the Greek god of the sea.

Neptune is composed of an icy / metallic core and a helium / hydrogen atmosphere, the core making up  90% – 95% of it’s mass. The remaining 5% = 10% is it’s helium / hydrogen atmosphere. By comparison the core’s  is  between 10 x and 15 x Earth’s mass.


Facts about Neptune




Moons and rings

Many of Neptune’s moons have not been discovered until recent times, some not until the 1980’s from Earth and then in 1989 with the Voyager 2 flyby and still subsequently with Hubble.

Neptune has some amazing names attached to it’s Moons like Triton, Larissa, Thalassa, Despina and Galatea. Here a few that we know something about.



Triton is named for the son of Poseidon in Greek mythology, it was discovered in 1846 by William Lassell.

Triton has a retrograde orbit, this means it orbit Neptune the opposite way to the other moons, because of this and it’s similar composition to Pluto it’s been suggested that Triton is a captured dwarf planet.

Made up of a surface of frozen nitrogen and 30-40% water ice. Triton is a very cold place to be with temperatures of -38K (-235C). Despite these frozen conditions Triton is one of the few moons in the solar system that’s know to be volcanic.


The volcanism doesn’t involve hot lava as on Earth, rather this is cryo volcanism. The sub surface Nitrogen vapourises under the surface until the pressure build enough to erupt to the surface. When Voyager 2 passed by in 1989 it captured images of geyser like eruptions coming from the surface.













Names after the shape changing God of the sea Proteus is 420km across and is the second largest of Neptune’s moons. It was discovered by Voyager 2 while on approach to Neptune. It wasn’t discovered from Earth because it is so close to Neptune.




Larissa was discovered from Earth by a star occultation in 1981. It’s the fourth largest of Neptune’s moons and is made up of debris from other moons smashed up by Triton.



During the Voyager 2 flyby’s it discovered and photographed the rings of Neptune, faint and thin but several sets of rings were discovered. This settled a long standing discussion about discoveries of ring from Earth that couldn’t be substantiated. As usual these rings are likely to be made up of rock and ice.




This is the final piece in Holst’s The Planets suite. With Neptune being 30x further from the sun than the Earth it’s a mysterious place and this is beautifully captured in his piece in Neptune.



Recent Events

The first and only spacecraft to have visited Neptune is Voyager 2 back in 1989. It carried out a flyby mission, taking photographs taking measurements of Neptune and it’s moons, finding out anything it could about this mysterious world.


What was immediately obvious is that Neptune is a world that’s very different from it’s neighbour Uranus. Neptune is a world that is visibly active with storms that have wind speeds over the speed of sound, clouds and spots.


Voyager 2 picked up the great dark spot on it’s approach, with smaller storms in in the lower bands of the planet. As Neptune is so far from the Sun, the most likely cause of these storms is the internal heating effect of the planet itself. Voyager found so much when it visited this distant and mysterious world, things that from Earth would be so difficult to observe. Storms, rings, volcanoes on Triton. There was far more than anyone expected or could have hoped for.

Artist’s impression of how Triton, Neptune’s largest moon, might look from high above its surface. The distant Sun appears at the upper-left and the blue crescent of Neptune right of centre. Using the CRIRES instrument on ESO’s Very Large Telescope, a team of astronomers has been able to see that the summer is in full swing in Triton’s southern hemisphere.

There are no plans to go back and visit Neptune in the near future. The legacy that Voyager left behind as it left our solar system lives on though. With so much to go back for it’s only a matter of time before blue gem has to give up it’s secrets for us.

Planet Simon



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13 thoughts on “Solar System Exploration – Neptune

      1. Those pictures from Voyager 2! They were in pretty much all the books I read about space as a kid, because they were still quite new back then (erk, showing my age here!). And the fact that it’s so far away… I think it’s safe to say I’ll never get to visit it myself!

        Liked by 1 person

      2. I think that’s a safe bet. I remember voyager 2 visiting Neptune too. I was nearly at school leaving age and I thought it was amazing. Now that’s showing my age lol

        Liked by 1 person

  1. Simon, I find this piece so interesting. You certainly fulfill the definition of writer. You’ve covered everything in a clear and concise manner. Well actually, I love this!

    Liked by 2 people

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