Now, the furthest planet from the sun in our solar system (after Pluto was downgraded to a dwarf planet), this blue giant was named after Poseidon, the god of the sea. This eighth planet belongs to the gas giant family along with Jupiter, Saturn, and Uranus.
The four gas giants are massive, as they consist of a thick atmosphere and a dense molten core. Neptune’s atmosphere is primarily composed of helium and hydrogen. There are theories it also contains nitrogen. Both Neptune and Uranus are sometimes grouped as “ice giants” because unlike Jupiter and Saturn, these two contain higher proportions of water, ammonia, and methane, which are referred by planetary scientists as “ices”. Even though Neptune is further from the sun than Jupiter or Saturn, it has an internal heat source that radiates two times as much energy as it gets from the Sun.
Most of what we know about Neptune we learned from the Voyager 2 spacecraft. It visited Neptune in 1989 and has been the only spacecraft to do so. Recent ground based observations from the Hubble Space Telescope have given us more information on Neptune. Voyager 2 encountered Neptune’s Great Dark Spot, half the size of Jupiter’s Great Red Spot. Years later, Hubble found that the Great Dark Spot disappeared which also indicated that this blue planet has an ever-changing atmosphere. Voyager 2 also discovered the existence of Neptune’s rings, which from Earth appeared as faint arcs and not complete full rings. Their composition is still unknown.
Neptune is also known to have a large number of moons, 14 to be exact, with the most famous being Triton. Triton was discovered in 1846, a few weeks after the discovery of Neptune by Johann Galle. Neptune’s existence was actually predicted and not truly discovered. Urbain Le Verrier detected irregularities in Uranus’s orbit and based on Newton’s Law of Gravity, he knew there must be another planet between Saturn and Uranus disturbing the path of the two. The night of September 23rd into the 24th, Johann Gottfried Galle discovered Neptune using Le Verrier’s calculations. There is still much to find out about this planet and unfortunately it won’t be anytime soon. The most recent proposal is for the NASA spacecraft Argo, which will launch in 2019 and will be sent to study Neptune and Triton. It will reach them in 2029. Let’s hope this proposal will come into fruition.