Neptune has a core of molten rock. Around the core, there is very cold water layer.The top layer is made of hydrogen, helium and small amount of methane. Methane gives it blue color.
Neptune is the eighth planet from the sun. It was the first planet to get its existence predicted by mathematical calculations before it was actually seen through a telescope on Sept. 23, 1846. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest that the gravitational pull from another celestial body might be responsible. German astronomer Johann Galle then relied on subsequent calculations to help spot Neptune via telescope. Previously, astronomer Galileo Galilei sketched the planet, but he mistook it for a star due to its slow motion. In accordance with all the other planets seen in the sky, this new world was given a name from Greek and Roman mythology — Neptune, the Roman god of the sea.
Only one mission has flown by Neptune – Voyager 2 in 1989 – meaning that astronomers have done most studies using ground-based telescopes. Today, there are still many mysteries about the cool, blue planet, such as why its winds are so speedy and why its magnetic field is offset.
While Neptune is of interest because it is in our own solar system, astronomers are also interested in learning more about the planet to assist with exoplanet studies. Specifically, some astronomers are interested in learning about the habitability of worlds that are somewhat bigger than Earth.
Those that are closer to Earth's size are called "super-Earths", while those that are closer to Neptune's size are "mini-Neptunes." However, there is some debate about those terms given that today's telescope technology does not make it possible to view how much atmosphere is on those planet types, making it difficult to make a distinction.
Like Earth, Neptune has a rocky core, but it has a much thicker atmosphere that prohibits the existence of life as we know it. Astronomers are still trying to figure out at what point a planet is so large that it may pick up a lot of gas in the area, making it difficult or impossible for life to exist.