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How Large Is the Planet Neptune?

By Edited Feb 24, 2016 5 3
Planet Neptune
Credit: Public domain photo, by NASA.

Incredible image of Neptune showing darker spots, which are storms. Photo taken by NASA's Voyager 2 spacecraft in 2001.

The most distant of the eight major planets

Neptune was not discovered until 1846.  When the planet Uranus was being observed in the years prior to this, there were unexpected changes in its orbit that caused French astronomer Alexis Bouvard to conclude that there must be another large planet further away. Neptune was thus known to exist before anyone ever saw it in a telescope.[1]

The planets in our solar system are eight, and there are thought to be hundreds or possibly thousands of dwarf planets also. Neptune is the furthest from the sun of the eight major planets, located approximately 30 times further than Earth.[2]

By comparison, the next-closest planet, Uranus, ranges from about 18 to 20 times the distance from the sun as Earth.[2] This means Neptune is located at a distance of about 50% further from the sun.

Neptune is the third-largest planet by mass. The two that have more mass are Jupiter and Saturn. Uranus is actually larger by diameter and circumference, although it is less dense than Neptune, which is why Uranus has less mass overall.[1]

The mass of Neptune compared with other solar system bodies

The planets and the sun can be measured in comparison with the Earth. If Earth's mass receives a value of 1, then the other largest objects in our solar system are as follows:[3]

Sun: Mass of 333,000 times that of Earth.

Jupiter: 318

Saturn: 95

Neptune: 17

Uranus: 15

Venus: 0.9

Mars: 0.1

Mercury: 0.06

Ganymede (moon of Jupiter): 0.02

Titan (moon of Saturn): 0.02

Earth and Neptune comparison

Proportions with one another shown accurately

Neptune and Earth Comparison
Credit: NASA public domain image.

The diameter of Neptune compared with other solar system bodies

If measuring the objects of our solar system by their diameters, and Earth has a value of 1, we would get:[3]

Sun: Diameter 109 times that of Earth.

Jupiter: 11

Saturn: 9

Uranus: 4

Neptune: 3.9

Venus: 0.95

Mars: 0.5

Ganymede: 0.41

Titan: 0.4

Mercury: 0.38 

Gravity on Neptune

The gravity of Neptune, at its gaseous surface (it would be impossible to stand on a planet composed of gas) is greater than that of Earth, and second in the solar system behind only Jupiter of the major planets.[3] To find your weight on this planet, multiply your weight by 1.125.  If you weight 150 lbs for example, then on the gaseous surface of Neptune you would weigh 168.8 lbs.[4]

The Gas Giants

Top to bottom: Neptune, Uranus, Saturn, Jupiter

The Gas Giants
Credit: NASA public domain image.

This image, created by NASA, shows these planets' relative sizes and approximate true coloration.



Dec 27, 2014 2:34pm
It's really incredible (to me) that a planet can even be deemed a planet when it has a gaseous surface. Fascinating read, as always.
Dec 27, 2014 2:37pm
It's a different type of planet, that's for sure. Thanks for reading and commenting!
Jan 6, 2015 8:17am
The sizes and scale of the solar system is amazing. That photo of Neptune is fantastic!
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  1. "Neptune." Wikipedia. 27/12/2014 <Web >
  2. "Solar System." Wikipedia. 27/12/2014 <Web >
  3. "List of Solar System objects by size." Wikipedia. 27/12/2014 <Web >
  4. "Your Weight on Other Worlds." Exploratorium. 27/12/2014 <Web >

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