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Neptune's mass of 1.0243 × 10 26 kg [8] is intermediate between Earth and the larger gas giants: it is 17 times that of Earth but just 1/19th that of Jupiter. [g] Its gravity at 1 bar is 11.15 m/s 2, 1.14 times the surface gravity of Earth, [71] and surpassed only by Jupiter. [72] Neptune's equatorial radius of 24,764 km [11] is nearly four ...
According to the IAU's explicit count, there are eight planets in the Solar System; four terrestrial planets (Mercury, Venus, Earth, and Mars) and four giant planets, which can be divided further into two gas giants (Jupiter and Saturn) and two ice giants (Uranus and Neptune). When excluding the Sun, the four giant planets account for more than ...
The term gas giant was coined in 1952 by the science fiction writer James Blish [6] and was originally used to refer to all giant planets.It is, arguably, something of a misnomer because throughout most of the volume of all giant planets, the pressure is so high that matter is not in gaseous form. [7]
The transition between Earth's atmosphere and outer space lacks a well-defined physical boundary, with the air pressure steadily decreasing with altitude until it mixes with the solar wind. Various definitions for a practical boundary have been proposed, ranging from 30 km (19 mi) out to 1,600,000 km (990,000 mi). [16]
Also, these stars have high UV radiation and winds that could photoevaporate the gas in the disk, leaving just the heavy elements. [62] For comparison, Neptune's mass equals 17 Earth masses, Jupiter has 318 Earth masses, and the 13-Jupiter-mass limit used in the IAU's working definition of an exoplanet equals approximately 4000 Earth masses. [62]
The IAU definitions of planet and dwarf planet require that a Sun-orbiting astronomical body has undergone the rounding process to reach a roughly spherical shape, an achievement known as hydrostatic equilibrium. The same spheroidal shape can be seen on smaller rocky planets like Mars to gas giants like Jupiter.
A giant planet, sometimes referred to as a jovian planet (Jove being another name for the Roman god Jupiter), is a diverse type of planet much larger than Earth. Giant planets are usually primarily composed of low-boiling point materials (), rather than rock or other solid matter, but massive solid planets can also exist.
The following outline is provided as an overview of and topical guide to Neptune: . Neptune – eighth and farthest known planet from the Sun in the Solar System.In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet.