Planets beyond Neptune

Planets beyond Neptune

Planets beyond Neptune are mysterious worlds that might exist far out in our Solar System. After Neptune was discovered in 1846, many people wondered if there could be another planet even farther away. A man named Percival Lowell spent years looking for a planet he called Planet X. He thought it might explain small changes in the orbits of Uranus and Neptune.

In 1930, astronomer Clyde Tombaugh discovered Pluto. It was excited as the ninth planet. But later studies showed Pluto was too small to affect the orbits of the bigger planets. This led some to wonder if there might be a tenth planet instead. As we learned more about space, we found many small icy objects beyond Neptune. Because of this, scientists changed how they decide what counts as a planet. In 2006, Pluto was reclassified as a dwarf planet. Now Neptune is the farthest known planet from the Sun.

Even though the old idea of Planet X didn’t work out, some astronomers still believe there might be a big, unseen planet out there. They call it Planet Nine. This possible planet could be between 2 and 15 times the size of Earth. It might travel on a strange, tilted path around the Sun, far beyond where we’ve seen anything else. While we haven’t found it yet, this idea helps explain why some distant objects in space move the way they do.

Early speculation

See also: Discovery of Neptune

In the 1840s, scientists wondered if there might be a planet beyond Neptune. They saw odd movements in the orbits of Uranus and Neptune and thought the gravity of an unknown planet might be causing this.

Many astronomers, including Urbain Le Verrier and Alexis Bouvard, suggested that one or more planets could be far from the Sun. Some even guessed where these planets might be, but no one found them then. Years later, in 1930, the planet Pluto was discovered, which made some think they had found the missing planet astronomers were looking for.

Planet X

Main article: Pluto

In 1894, Percival Lowell began searching for a planet beyond Neptune. He believed this planet, called Planet X, might explain why Uranus moved differently than scientists expected. Lowell took many pictures of the sky hoping to find this hidden planet.

In 1930, Clyde Tombaugh discovered Pluto. At first, many people thought Pluto might be the Planet X Lowell had predicted. But later studies showed that Pluto was too small to change the orbits of other planets. Scientists now think that the idea of a large Planet X affecting Uranus's orbit is not correct. Today, most experts believe that Planet X, as Lowell imagined it, does not exist.

Discovery of further trans-Neptunian objects

See also: History of the Kuiper belt

After Pluto was found, no more objects beyond Neptune were seen until 1992. That year, 15760 Albion was spotted. Since then, thousands of these objects, called trans-Neptunian objects, have been discovered. Most are part of the Kuiper belt, a group of icy bodies that orbit the Sun just beyond Neptune.

In 2005, astronomers found an object named 2003 UB₃₁₃, later called Eris. At first, some thought it might be a planet because it was a little bigger than Pluto. In 2006, a new way to decide what is a planet was made. Pluto and Eris were called dwarf planets instead. Some scientists still think these objects should be called planets.

Subsequently proposed trans-Neptunian planets

Although most astronomers think Lowell's Planet X does not exist, some believe a large unseen planet might affect the outer Solar System. These objects are often called "Planet X," though they may be different from Lowell's idea.

The discovery of Sedna raised questions about its orbit. Sedna's path is unusual, and scientists wonder what could have caused it. Some ideas include a passing star, capture from another planetary system, or the pull of an unseen planet beyond Neptune.

In recent years, astronomers have studied the orbits of distant objects beyond Neptune. They noticed that some objects have orbits that seem to be grouped together. This led to the idea of a planet called Planet Nine, which could be about ten times the size of Earth and located far beyond Neptune.

Constraints on additional planets

Observations from space telescopes like the WISE telescope show that there are no big planets, such as ones the size of Saturn or Jupiter, hiding far from the Sun. These telescopes help scientists look for heat signals that large planets would give off.

Studies of how planets like Saturn, Earth, and Mars move in their orbits suggest that any unknown planet would have to be very far away from the Sun. For example, a planet even a little bigger than Earth would need to be hundreds of times farther from the Sun than Earth is.

Scientists also study the paths of objects that orbit far beyond Neptune. Some of these objects seem to be grouped in ways that suggest the pull of a hidden planet, possibly hundreds of times farther from the Sun than Earth is.