Neptune

The Distant Ice Giant

Neptune, the icy giant of our solar system, exists in a realm of darkness, coldness, and relentless supersonic winds. Being the eighth and most remote planet from the Sun, it’s the only planet within our solar system that is not visible to the naked eye.

Picture of Neptune, taken by Voyager 2. Credits: NASA/JPL-Caltech.

Picture of Neptune, taken by Voyager 2. Credits: NASA/JPL-Caltech.

In the early days of astronomy, Galileo Galilei was among the first to identify Neptune as a celestial body. However, due to its gradual motion, he mistakenly categorized it as a star. In 1846, the ice giant made history as the first planet to be pinpointed through mathematical calculations, with Johann Galle’s remarkable discovery confirming the predictions of Urbain Le Verrier. Due to its distinctive blue hue, it was named after the Roman god of the sea, as suggested by Le Verrier.

Neptune, along with Uranus, is an ice giant in the outer region of our solar system. Its radius measures 15,299.4 miles (24,622 kilometers), making it roughly four times wider than Earth.

A size comparison of Neptune and Earth

A size comparison of Neptune and Earth

More than 80% of Neptune’s mass is composed of a dense and hot fluid consisting of “icy” substances such as water, methane, and ammonia. This fluid envelops a small rocky core. Despite such frigid conditions with an average temperature of -331°F (-201°C), scientists speculate the presence of a hot ocean of water beneath Neptune’s icy clouds. The water does not evaporate due to the immense pressure that keeps it trapped.

Neptune, unlike terrestrial planets, lacks a solid surface. Its atmosphere primarily consists of hydrogen and helium, with a small presence of methane. While the atmospheric methane gives Uranus, Neptune’s neighboring planet, a blue-green color, Neptune itself appears as a more vibrant and brighter shade of blue. This suggests the existence of an unknown component responsible for such intensified color.

A comparison of Uranus (left) and Neptune (right). Credit: NASA/JPL-Caltech.

A comparison of Uranus (left) and Neptune (right). Credit: NASA/JPL-Caltech.

Neptune holds the title of the windiest world in our solar system. The powerful winds whip across the planet, propelling frozen clouds at astonishing speeds of over 1,200 miles per hour (2,000 kilometers per hour). In comparison, even the strongest winds on Earth reach speeds of only around 250 miles per hour (400 kilometers per hour).

Cloud streaks over Neptune’s surface, taken by Voyager 2. Credit: NASA/JPL.

Cloud streaks over Neptune’s surface, taken by Voyager 2. Credit: NASA/JPL.

Neptune maintains an average distance of 2.8 billion miles (4.5 billion kilometers) from the Sun, positioning it approximately 30 times farther away than Earth. The planet completes a full rotation, known as a Neptunian day, in about 16 Earth hours, and it takes roughly 165 Earth years to complete an orbit (Neptunian year).

This global color mosaic shows Neptune’s largest moon, Triton. Credits: NASA/JPL-Caltech.

This global color mosaic shows Neptune’s largest moon, Triton. Credits: NASA/JPL-Caltech.

Among Neptune’s celestial companions are 14 known moons, with the largest one named Triton. What sets Triton apart is its unique behavior of orbiting Neptune in the opposite direction to the planet’s rotation. This characteristic suggests that Triton may have been an independent object that Neptune captured in its gravitational pull.

The only spacecraft to have embarked on a close encounter with Neptune is NASA’s Voyager 2. This historic mission took place in 1989 as Voyager 2 was on its trajectory out of the solar system.

Editors’ finds

Words of wisdom

“I'm sure the universe is full of intelligent life. It's just been too intelligent to come here.” ―Arthur C. Clarke

“Nothing happens until something moves.” ―Albert Einstein

“We are an impossibility in an impossible universe.” ―Ray Bradbury

“In three words I can sum up everything I’ve learned about life: it goes on.” ―Robert Frost

Bibliography

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