Neptune's discovery came about by using mathematics to predict where this distant world--which is 30 times further from the Sun than Earth--would be and then finding it with the use of a telescope. Its gravitational effects on Uranus led to this method of discovery in 1846.
Considerations
Planets such as Jupiter, Uranus and Saturn are larger but Neptune is still so huge that it could contain as many as 60 planets the same size as Earth if it were a hollow globe.
Size
Neptune is 30,775 miles in diameter, takes only 19.1 hours to complete one rotation on its axis and requires almost 165 years to orbit once around the Sun.
Gravity
Even though Neptune has 17 times more mass than Earth, a 100-lb. individual on Neptune would weigh just 19 lbs. more.
Features
Scientists think the core of Neptune is rock that is covered by a methane-ice-ammonia combination that serves as a mantle. The atmosphere is a deadly mix of hydrogen, methane gas and helium.
Fun Fact
One of Neptune's moons, Triton, is the single coldest object measured by man in the solar system, with a temperature of minus 391 degrees Fahrenheit.
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