How Large Is Neptune? Mass, Surface Area, and Diameter

Written by Megan Martin
Published: April 15, 2023
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If you look into the sky at night, there are few planets that you won’t be able to see without the help of a telescope or similar device. Neptune just so happens to be one of these. However, despite its lack of visibility, there’s no denying it: Neptune is a rather large planet. Are you interested in learning more about Neptune’s size? Keep reading below!

Planet Profile: Neptune

Neptune is what is known as an ice giant. It is one of two ice giants in our solar system, with the other being Uranus. It is the eighth planet in the solar system and the one furthest away from Earth. Not only is Neptune far from us, however, but it is also far from the Sun. In fact, Neptune is as much as 30 times further away from the Sun than Earth is!

Life on Neptune

With a distance that far from the Sun, Neptune has longer years than we do here on Earth. Rather than 365 days (or 366 during leap years), a single year on Neptune takes 165 years. This means that, since it was first discovered in 1846, only one year has passed on Neptune. Although a year on Neptune may take much longer than a year on Earth, a single day doesn’t. Instead, a day on Neptune lasts for only 16 hours rather than 24. 

Neptune isn’t entirely different from Earth, however. One of the most interesting facts about this ice giant is the tilt of its axis. Neptune’s axis of rotation has a tilt of around 28 degrees. This is actually similar to Earth, as well as Mars. What this means is that Neptune is able to experience four different seasons. However, unlike Earth, rather than seasons lasting a few weeks or months, a single season on Neptune can last as long as 40 years on Earth. 

Neptune is named for the Roman god of the sea. Because of this, each of its 14 moons, the largest of which was discovered just after the planet itself, are named in similar themes. Triton, its largest moon, is one of the most well-known moons in the solar system aside from our own. This is because it is the only moon that rotates in the opposite direction as its planet. 

Currently, there are no signs to indicate that intelligent life is living or has lived on Neptune.

Now that you know more about Neptune, it’s time to learn just how big this interesting planet is! Keep reading below to learn more about Neptune’s mass, surface area, and diameter.  

Planet neptune

Neptune’s axis of rotation has a tilt of around 28 degrees, meaning the planet experiences four seasons.

© bhaumik

Neptune Mass

Often, mass is considered the be the same as weight. However, in physics, mass actually has its own unique definition. Rather than just being the weight of an object, mass is how much matter an object has. This means it includes factors like atoms and similar features that may not be considered when you look at weight alone.

Neptune isn’t solid like Earth is. Instead, it has a gaseous atmosphere and surface that meets water and, eventually, a frozen core. This is why it is named an iice-giant planet. However, despite being made up of mostly gas and ice, Neptune has a mass 17 times greater than Earth.

The total mass of Neptune is 2.258 × 10^26  pounds or 1.0241 × 10^26 kilograms.

Neptune Surface Area

One of the second most important aspects of Neptune’s size is surface area. To better understand the concept of surface area, imagine Neptune as an orange. If you were to peel that orange and lay out the peel flat, the surface area would be the measure of the area that the peel covers. 

Measuring Neptune’s surface area on foot would be an impossible feat. Not only because of its size but because of the fact that the surface of Neptune is almost entirely water and melted ice. However, thanks to science, we’ve been able to discover that the surface area of Neptune is 2.9 billion square miles (7.6 billion square kilometers).

Neptune Diameter

Neptune is around four times wider than Earth. If you’re having trouble visualizing just how big that is, think of a nickel (Earth) next to a baseball (Neptune) in terms of width. However, just how big is Neptune’s diameter?

First, you may wonder what diameter is if you’re unfamiliar with the term. A diameter is a straight line that passes through the middle of a circle, connecting one side to the other. The radius is half the length of the diameter, which means it’s a straight line connecting the center of the circle to the outside point. 

The radius of Neptune is 15,299.4 miles (or 24,622 kilometers). This means that it has a diameter of double this. As a result, Neptune has a total diameter of 30598.8 miles (49,244 kilometers).

The photo featured at the top of this post is ©

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About the Author

Megan is a writer at A-Z Animals where her primary focus is birds, felines, and sharks. She has been researching and writing about animals for four years, and she holds a Bachelor of Arts in English with minors in biology and professional and technical writing from Wingate University, which she earned in 2022. A resident of North Carolina, Megan is an avid birdwatcher that enjoys spending time with her cats and exploring local zoological parks with her husband.

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