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Neptune is the eighth and farthest known planet from the Sun. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth. Compared to its fellow ice giant Uranus, Neptune is slightly more massive, but
In the 1990s, it was determined that Uranus and Neptune were a distinct class of giant planet, separate from the other giant planets, Jupiter and Saturn, which are gas giants predominantly composed of hydrogen and helium. [1] Neptune and Uranus are now referred to as ice giants. Lacking well-defined solid surfaces, they are primarily composed ...
The temperature of Triton's upper atmosphere, at 95 ± 5 K, is higher than that at its surface, due to heat absorbed from solar radiation and Neptune's magnetosphere. [ 48 ] [ 53 ] A haze permeates most of Triton's troposphere, thought to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane.
Conversely, freshly-deposited nitrogen ice may be translucent, before later shattering as seasonal swings in temperature induce repeated phase changes between solid nitrogen's α- and β-phases, brightening older ice. [19] At the time of Voyager 2 ' s arrival, Triton was experiencing an unusually intense southern hemisphere summer.
The volatile ice sheet basal heating model is proposed to account for both the significant eruption flux and localization to the ice cap, with the caveat that this layer must be at least 100 metres (330 ft) thick. Internal heat from Triton drives melting and convection and possibly localized melting within the nitrogen ice at the pole.
Ice giants have distinctly different interior compositions from gas giants. The Solar System's ice giants, Uranus and Neptune, have a hydrogen-rich atmosphere that extends from the cloud tops down to about 80% (Uranus) or 85% (Neptune) of their radius. Below this, they are predominantly "icy", i.e. consisting mostly of water, methane, and ammonia.
Ice I h that has been transformed to ice XI and then back to ice I h, on raising the temperature, retains some hydrogen-ordered domains and more easily transforms back to ice XI again. [105] A neutron powder diffraction study found that small hydrogen-ordered domains can exist up to 111 K. [106]
The Great Dark Spot (also known as GDS-89, for Great Dark Spot, 1989) was one of a series of dark spots on Neptune similar in appearance to Jupiter's Great Red Spot. In 1989, GDS-89 was the first Great Dark Spot on Neptune to be observed by NASA's Voyager 2 space probe. Like Jupiter's spot, the Great Dark Spots are anticyclonic storms.