The Idiot’s Guide to Everything: Neptune

Posted on December 14, 2011




The final planetary stop in our solar system, Neptune is the eighth and farthest planet from our sun. It is twinned with Uranus and is the 2nd ice giant, or the 4th gas giant, depending on where you stand. Either way, Neptune is the fourth largest planet by diameter, and the third largest by mass. It has a mass that is 17 times that of the Earth, so it is considerably more massive than Earth, but it is still dwarfed by Jupiter, being only 1/19th its mass. This shows just how massive Jupiter is in comparison to the rest of the solar system.

The composition of Neptune is very similar to that of Uranus. It also has large amounts of hydrogen and helium in its atmosphere, as well as traces of ices such as water, ammonia, methane and hydrocarbons. At the high altitudes, the atmosphere can be as much as 80% hydrogen and 19% helium with mere traces of the ices. It has a rocky interior that is mostly composed of ice, and again the traces of methane in its atmosphere give it is distinctive blue appearance. There are huge differences between the core and surface temperatures, which create the huge wind storms that are found on Neptune. The average temperature at the top clouds is minus 220 degrees Celsius, where as the core has a temperature of 7000 degrees Celsius, which is comparable with the sun. The core of Neptune contains more rock and metal than any other gas giant. In fact, it is this huge generation of heat from within that sets Neptune apart from Uranus, as the heat differences give Neptune active and visible weather patterns, unlike Uranus. Despite being half again the distance from the sun as Uranus, the surface temperatures are very similar. Neptune has the strongest sustained winds of any planet in the solar system, with recorded wind speeds of up to 2,100km/h. Most of the winds on Neptune rage in a retrograde with the planets rotation, which means they move in the opposite direction. In 1989, when Voyager 2 made the only recorded fly by of the planet, Neptune’s southern hemisphere had a massive storm comparable to the Great Red Spot of Jupiter, which was named the Great Dark Spot. This storm has since vanished. Neptune still has some visible storms on its appearance however, unlike the bland featureless façade of Uranus. Most of these clouds are made of methane crystals however.

Neptune’s furthest distance from the sun is 2825 million miles, and its closest position is 2769 million miles. This immense distance is the reason that Neptune is not visible to the naked eye. Neptune takes a total of 164.8 Earth years to orbit the sun, and a day on the planet lasts 18hurs at the equator and 12 hours at the poles, because of the differing speeds of cloud rotation. It has a very similar axial tilt to Mars and indeed Earth, which leads to it having similar seasons, all be it ones that last around 40 years. As mentioned previously, Neptune has only ever been visited once, by the Voyager 2 spacecraft, which flew by in 1989. As with all of the other gas giants, Neptune has a ring system. These rings were first discovered in 1968, but it wasn’t until the Voyager 2 fly by that they were confirmed. Neptune has five rings, all of which are named after the astronomers who worked towards its discovery. It has a system of 13 known moons, but only one of these is large enough to be spheroidal. This is called Triton, and it accounts for 99% of the mass around Neptune. It is the only major satellite in the solar system that orbits its parent planet in a retrograde manner, which indicates that it could have been a dwarf planet that Neptune captured. Triton is also very close to Neptune, and there are theories that it is getting closer, which would lead it to be torn apart. In about 3.6 billion years however. As Neptune is named after the Roman god of the sea, all of the moons are named after other lesser known sea gods.

As with Uranus however, the main area of fascination and interest with Neptune centres around its discovery. Like Uranus, Neptune had been observed long before it was unearthed as a planet. Indeed, our old friend Galileo observed it in 1612, but he mistook it for a star. When Uranus was discovered in 1781, it became clear that the strange orbit of the new planet was being influenced by something out in the distance, possibly another planet. Urbain Le Verrier, a French mathematician, developed calculations that estimated the position of this planet, but the hope for a search was met with little enthusiasm. Le Verrier took to Berlin to urge Johann Galle, a German astronomer, to search. Sure enough, on September 23rd 1846, Neptune was discovered within a single degree of Le Verrier’s predictions. Therefore, Neptune became the first planet discovered by mathematical prediction. It’s major satellite, Triton, was discovered soon after. At first, it was known as ‘Le Verrier’s Planet’, after the man who had predicted its position. The first real suggestion put forward for the planet was ‘Janus’, and shortly after this England proposed that it be called ‘Oceanus’. After attempting to push the planet to being named after himself officially, Le Verrier relented and proposed the name ‘Neptune’, which stuck and soon became the internationally recognised name for the 8th planet. It was a return to using Roman gods as the basis for planetary names after the Greek excursion of Uranus.

Neptune is so far from the sun and has such intense weather patterns that there is absolutely no point entertaining the thought of it harbouring life. Indeed, if you were floating stationary in the upper atmosphere, any single movement of your body would smash the sound barrier. However, this doesn’t make the farthest planet from the sun in our solar system any less interesting, and it provides a beautiful end to any journey through the planets, including this one.