Neptune
The furthest planet in the Solar System, and the second of the ice giants. Learn more about the big blue planet here!
Formation
The formation of the ice giants is controversial and shrouded in mystery. Models suggest that Neptune was able to form by gathering a core of about a few solar masses. Unlike the gas giants, the ice giants never reached the critical mass required to gather large amounts of gas and stopped becoming larger. Another model suggests that Neptune formed close to the Sun and migrated out towards the present-day position.
Composition
The composition of Neptune is not similar to the composition of the young Solar nebula. Around 80% of the atmosphere is composed of hydrogen, 19% helium, and 1% other elements, mostly dominated by methane. Not much is known about the interior composition of Neptune, though the mass of the planet suggests that the composition is similar to the atmosphere with certain elements and compounds, besides hydrogen and helium, more unknown.
Structure
An ice giant such as Neptune has structural layers different from the ice giants. Suspected to have a rocky core surrounded by a mantle of ices, not much is known about this part of the planet. The icy mantle is surrounded by the lower atmosphere, which has a large composition of methane, ammonia, and water ice. Finally, the upper atmosphere of Neptune completes the structure.
Atmosphere
The atmosphere of Neptune is made up of mostly hydrogen, with methane clouds dominating. Unlike the gas giants, Neptune does not have prominent bands of weather across the whole planet. Thanks to the internal heating mechanism of Neptune, even though the planet is further from the Sun than Uranus, there is weather in the upper atmosphere. Neptune has a great dark spot and a small dark spot, named after the great red spot on Jupiter.
Magnetic Field
The magnetic field of Neptune is peculiar. Unlike the other planets, the field does not originate from the planet’s core. Instead, the magnetic field is offset from the center by about one-half of the planet’s radius. This causes a highly unsymmetrical magnetic field. The cause of this peculiar magnetic field is thought to be electrodynamics within the mantle producing a strange magnetic field.
Planetary Rings
Neptune has five main rings that are narrow and dusty. Named after prominent astronomers who worked on the planet, these rings are dark and hard to detect. The main ring, Adams, has five arcs which are separate portions of the ring itself with gaps in between each arc. At the present time it is not known why these arcs exist, as most models suggest that the arcs should merge back into a solid ring on short timescales. A suggestion is that the moon Galatea keeps the arcs separated from one another and not forming a solid ring.
Satellites
Voyager 2 is the only satellite to visit Neptune. Discovering four new rings and six new moons, the Voyager 2 flyby was able to image the system in detail. Voyager 2 also was able to study the magnetic field, discovering the strange configuration that the magnetic field exhibits. While Voyager 2 was able to glean information from the flyby, a dedicated orbiter is required to learn more about Neptune.