Neptune

Keywords

Giant planets

Definition

Orbiting the Sun at a mean distance of 30 AU, with a revolution period of almost 165 years, Neptune is the outmost of the giant planets, and also the smallest. Its diameter is 49,530 km, i.e., 3.9 times the terrestrial value. Still, its mass (17 terrestrial masses) is slightly greater than Uranus’ and its density (1.64 g/cm³) is thus also larger. Both Uranus and Neptune are called “icy giants” because most of their mass is contained in the icy core from which they accreted. As all other giant planets, Neptune is surrounded by a system of rings and satellites.

Overview

History of Observations

Neptune was first identified in 1846 by Johannes Galle, who followed the prediction of Urbain Le Verrier, based on celestial mechanics calculations. The quest for Neptune had started after the discovery of Uranus in 1781, as it was realized that Uranus’ orbit was perturbed by another more distant heavy body. John Couch Adam from Cambridge University and Urbain Le...