In ancient times, people didn’t even know the planet Neptune existed. Astronomers, scientists who study space, didn’t discover the big blue planet until the 1840s.

Neptune is usually the eighth planet from the Sun. So far as astronomers know, only the planet Pluto is farther from the Sun. However, Pluto’s orbit sometimes brings it closer to the Sun than Neptune is, making Neptune the planet farthest from the Sun. This happens every 248 years.

HOW DID WE FIND NEPTUNE?

Astronomers found Neptune by watching the planet Uranus. Uranus wobbles as it orbits the Sun. A British astronomer and a French astronomer used math to figure out that the gravity of another planet was making Uranus wobble. A German astronomer finally saw Neptune through a telescope in 1846. Astronomers named the newly found planet Neptune after the ancient Roman god of the sea.

STUDYING NEPTUNE

It took astronomers a long time to learn anything about Neptune because the planet is so far away. Neptune is about 2.8 billion miles (about 4.5 billion kilometers) from the Sun. That’s 30 times as far as Earth is from the Sun! It takes Neptune almost 165 years to go around the Sun once.

Looking through telescopes, astronomers can tell that Neptune is a big planet. It is about four times larger than Earth. They call Neptune a giant planet. It is the smallest of four huge planets made mostly of gas. Jupiter, Saturn, and Uranus are the other gas giants.

Astronomers learned most of what they know about Neptune from a spacecraft named Voyager 2. Voyager 2 is the only spacecraft that has visited Neptune. It flew past in 1989. It took pictures and made measurements of Neptune.

Astronomers also study pictures of Neptune made by the Hubble Space Telescope. Hubble orbits high above Earth.

WHAT IS IT LIKE ON NEPTUNE?

You could not breathe on Neptune, and the fierce winds would blow you away. Even without the winds, you could not walk on Neptune because the planet has no solid surface.

A thick layer of clouds surrounds Neptune. The clouds are part of the planet’s atmosphere. An atmosphere is made of gases. Neptune’s atmosphere is made mostly of hydrogen and helium gases. Some methane gas high in the atmosphere gives Neptune its bluish color. You could not breathe the gases in Neptune’s atmosphere. You need to breathe oxygen in order to live. There is no oxygen in Neptune’s atmosphere.

Blowing clouds make striped patterns around Neptune. Sometimes there are spots in the clouds. The spots are storms. Neptune has the fastest winds in the solar system. The winds on Neptune can blow at 1,200 miles per hour (2,000 kilometers per hour).

Scientists have made guesses about what the inside of Neptune is like. Scientists think the planet’s thick atmosphere blends into an ocean of water. The core (center) of Neptune may be made of ice and rock.

DOES NEPTUNE HAVE MOONS?

Astronomers have found 11 moons around Neptune. The biggest moon is Triton. Triton is mostly made of ice. There may be some rock in its core. Triton is one of the coldest spots in the solar system. The temperature there can drop to -390° Fahrenheit (–235° Celsius).

Triton once had volcanoes. Its volcanoes did not shoot out melted rock as volcanoes on Earth do. Triton’s volcanoes shot out slushy, half-melted ice.

Astronomers also have found four rings around Neptune. The rings are dark and hard to see, even in pictures from Voyager 2. They may be made of dust and rocks.

HOW DID NEPTUNE FORM?

Astronomers think the Sun and all the planets formed from a disk of gas and tiny particles of rock, metal, and ice. The rocky planets closest to the Sun formed mainly from rock and metal. The planets farthest from the Sun formed mostly from gas and chunks of ice.

Source: Microsoft ® Encarta

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