It only takes a glimpse into the night sky to realize our closest neighbor is the Moon, our own natural satellite. Traveling a distance of roughly 240,000 miles (386,400 kilometers) it takes around 3 days to make a one way journey to the Moon. The planets of our solar system are much further away some more so than others so planets like Neptune take a while to reach.
What Is Neptune?
Once just a theoretical planet Neptune is what is known as an Ice Giant. It is the eighth and most distant planet from the center of our solar system, the Sun. Neptune is so distant from Earth, the third planet from the Sun, that it is the only planet that is not visible with the naked eye from Earth’s surface.
Its vast distance from the Sun means that from its discovery in 1846 until 2011 it had made just one full rotation of its orbit around our solar system’s only star. It takes roughly 165 years for Neptune to complete its orbit of the Sun.
How Far Is Neptune from Earth?
Neptune at its closest is 2.7 billion miles from Earth. However when they are furthest apart from each other they are 2.9 billion miles apart. This may not seem like a huge difference but it does equate to a variance of 200 million miles.
How Far Is Neptune from the Sun?
An astronomical unit (AU) is equal to the distance from the Sun to the Earth and Neptune is 30 AU from our solar system’s star. This equates on average to 2.8 billion miles (4.5 billion kilometers). Interestingly, although usually closer to the Sun than the Dwarf planet Pluto, every 248 years for a 20 year period the two switch in terms of relative distance from the Sun. The last time this happened was between 1979 -1999.
How Long Does Neptune Take to Go Around the Sun?
Neptune is the eighth and most distant known major planet from our Sun in the solar system. It is in fact so far away from the Sun that its orbital period takes 60,190 Earth days, or almost 165 Earth years.
The rotation speed of Neptune is relatively fast, taking just 16 hrs. When you couple this short day with the massive orbital period you discover that a Neptunian year has 89,666 Neptunian days. When Neptune was last in its current region in space in 2023 the following events took place:
- Minnesota becomes the 32nd US state
- Abraham Lincoln accepts the nomination of the Republican party to become a US Senator
- Future US President Theodore Roosevelt is born
What Is an Ice Giant Planet?
Ice giants are massive planets composed mainly of elements heavier than hydrogen and helium. These might include oxygen, carbon, nitrogen and sulfur. Our solar system is home to two ice giants, Uranus and of course Neptune.
Ice giants form when gravity pulls together swirling gas and dust. They may form closer to a star but migrate further away over time becoming colder as they go. They usually have a smaller rocky core with most of their mass being made up of materials such as water, methane and ammonia.
Neptune’s Structure
Over 80% of Neptune’s mass consists of a hot dense fluid which includes water, methane and ammonia. This covers a rocky core which produces a very intense gravitational pull. This is why even though Neptune is not the largest planet in the solar system it is the densest.
Scientists believe there may be a boiling ocean of super hot water below Neptune’s cold clouds. The density and gravitational pull of the planet however means it does not boil away due to incredibly high pressure. Essentially the boiling water layer is under too much pressure to actually evaporate as it would on Earth.
Surface
There is no solid surface to Neptune as the atmosphere extends to great depths in the planet. This consists of mainly hydrogen, helium and methane. As this atmosphere gets closer to the core it merges into water and other melted ices. This core is estimated to have the same mass as the entirety of the planet Earth.
Atmosphere
The atmosphere on Neptune comprises mostly hydrogen and helium with a small amount of methane as well. This combination of gases make Neptune appear a vivid blue shade which indicates there may be something else in the atmosphere we do not yet understand.
It is our solar system’s most active planet in terms of wind despite being further from the Sun than most. The winds on Neptune are three times stronger than Jupiter’s and up to nine times more intense than those on Earth.
Magnetosphere
The main axis of Neptune’s magnetic field is out of line by about 47 degrees when compared to the planet’s rotation axis. This causes wild variations with the field as the planet rotates with it at times reaching up to 27 times the strength of Earth’s.
Does Neptune Have Moons and Rings?
According to NASA Neptune has 14 known moons the largest of which is Triton which was itself discovered just over 2 weeks after Neptune was. Named for the Sea God Neptune, its moons all bear the names of other lesser known sea deities of antiquity.
Triton is unique in our solar system in that it is the only moon that circles its planet in a direction opposite to Neptune’s own. This is a strong indication that Triton may be a captured body caught in Neptune’s orbit by its intense gravitational pull.
The moons of Neptune are:
- Triton
- Thalassa
- Sao
- Psamathe
- Larissa
- Naiad
- Nereid
- Neso
- Proteus
- Despina
- Galatea
- Halimede
- Hippocamp
- Laomedeia
Neptune has at least five main rings as well as 4 prominent ring arcs which have been discovered so far. The main rings are known as:
- Galle
- Leverrier
- Lassell
- Arago
- Adams
These rings are not thought to be especially old and may not be around for long in stellar terms.
The ring arcs of Neptune Liberté (Liberty), Egalité (Equality), Fraternité (Fraternity), and Courage are interesting in that they are clumps of dust. Laws of motion suggest they should spread out evenly however it is thought that the moon Galatea may be stabilizing these arcs with its gravitational effects.
History of the Observation of Neptune
Neptune was unknown to ancient astronomers as it could not be seen with the naked eye from Earth. It would not be until telescopes were invented and they reached a certain level at development that Neptune was finally officially confirmed.
Galileo Galilei’s drawings produced on 28th December 1612 and 27th January 1613 show plotted points which match up with the positions of Neptune in the sky on those dates. Of course Galileo did not realize what he had seen so he is not considered the discoverer of Neptune.
Over two centuries later in 1821, Alexis Bouvard published astronomical tables of the orbit of Uranus. Uranus being a near neighbor of Neptune and known since antiquity it was noted that substantial deviations from the tables indicated an unknown body may be affecting its orbit. It was theorized that gravitational interactions from a potential unseen planet may be causing the deviations.
This captured the attention of several astronomers in the next few decades. It was predictions as to location by Urbain Le Verrier that led Johann Galle to finally locate Neptune through his telescope in 1846. Several astronomers had seen and noted Neptune over the years but none had realized they were seeing this elusive 8th planet of our solar system.
Space Exploration
To date the only spacecraft to travel to Neptune is Voyager 2. It passed by the planet on 25th August 1989. During the encounter, signals from the spacecraft took 246 minutes to reach Earth. This is why Voyager 2’s mission relied on preloaded commands. On its way there the spacecraft performed a close pass of the moon Nereid. On the same day as Voyager 2 passed Neptune it also passed close to Triton.
There are several current proposed missions to return to Neptune seeking to confirm and discover some aspects of its structure and the nature of its moons. Both China and the US are still considering future missions.
How Long Does It Take to Get to Neptune?
Thanks to the Voyager 2 mission we have a real world example of how long a journey to Neptune takes. This mission was a flyby so it was done in the quickest way possible but still took 12 years and 5 days to pass close to the planet.
As yet no mission has been planned to place a spacecraft in Neptune’s orbit so we don’t know how long this would take. We can be certain however that it would take far longer than a flyby because it has to travel much slower to be captured into the planet’s orbit.
Final Thoughts
Neptune is an interesting planet that we still have a lot to learn about and ideally one day a mission into the planet’s orbit may be needed. As one has never been planned it is unsure how long this might take but we do know for a much quicker flyby trip it takes just over 12 years.