Neptune is the eighth planet from the Sun, and one of four gas giants in our solar system. It’s also the farthest known solar planet. In terms of size, Neptune is slightly smaller than Uranus but more massive, making it the third-most-massive planet in our solar system. And because of its high density, it’s also considered to be one of the two ice giant planets (the other being Uranus).
Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 AU (4.5 billion km). Its atmosphere is made up mostly of hydrogen and helium, with some methane and water vapor thrown in for good measure. The temperature on Neptune can range from -214°C (-353°F) near its poles to about 7°C (45°F) at its equator—making it a pretty chilly place overall!
Despite being so far away from Earth, we actually know quite a bit about Neptune thanks to some recent space missions like NASA’s Voyager 2 probe which flew by in 1989 and gave us our first close-up look at this distant world.
It’s Discovery
In the 1830s, John Couch Adams and Urbain Le Verrier both independently predicted Neptune’s existence on the basis of mathematical irregularities in Uranus’s orbit. Neptune was subsequently observed on 23 September 1846 by Johann Galle within a degree of Le Verrier’s predicted position. Its largest moon, Triton, was discovered shortly thereafter, though none of its remaining smaller moons were located telescopically until well into the 20th century. Neptunian observational astronomy began in earnest only after Voyager 2 visited it in 1989..
The discovery of Neptune followed a long chain of discoveries made during what has come to be known as The Golden Age of Planetary Exploration. Starting with William Herschel’s 1781 discovery of Uranus–the first new planet found since antiquity–and continuing with Johann Galle’s 1846 discoveryof Neptune, astronomers were uncovering new worlds at an astonishing rate..
In retrospect, it seems almost inevitable that someone would have eventually stumbled upon Neptune. But at the time, its existence was far from certain–even among astronomers..
As early as 1781, British astronomer William Herschel suspected that there might be another planet beyond Saturn based on his observations of irregularities in Uranus’ orbit..
German mathematician and astronomer Carl Friedrich Gauss also independently calculated Neptune positions for several years starting around 1800; however, he did not publish his results and they remained unknown to other scientists.
Fun Facts
- Neptune is one of the three planets that were not visible to the human eye; the other two planets are Uranus and Pluto.
- Neptune took shape when the rest of the solar system formed about 4.5 billion years ago when gravity pulled swirling gas and dust in to become this ice giant.
- More than 200 years later, the ice giant Neptune became the first planet located through mathematical predictions rather than through regular observations of the sky.
THE CHRONICLES UNKNOWN 