For many years, scientists have believed that a big, mysterious planet might be hiding in the dark parts of our solar system. This possible planet is called Planet Nine. Some astronomers think the strange paths of icy rocks beyond Neptune suggest something large is pulling on them. But even after many searches, this hidden planet has never been found.

Now, a team of three scientists in the United States, who were looking for Planet Nine, have instead found something else. They discovered what seems to be a new dwarf planet. This discovery may change how scientists think about Planet Nine.

The new object is named 2017 OF201. According to a study published online last week (not yet reviewed by other scientists), it is about 700 kilometres (430 miles) wide. That makes it three times smaller than Pluto. However, it is still big enough to be called a dwarf planet, said the study's lead author, Sihao Cheng, from the Institute for Advanced Study in New Jersey.

An object from the deep space

The newly found object is very far away from Earth—three times farther than Neptune. It also has an extremely long and stretched-out orbit. During its orbit, 2017 OF201 travels more than 1,600 times the distance between Earth and the Sun. It even moves into an area called the Oort Cloud, where icy rocks surround the solar system.

Cheng said that during its 25,000-year orbit, the object can only be seen from Earth for about 100 years. That is just 0.5% of its full orbit. "It's already getting fainter and fainter," Cheng added. He also said the discovery suggests "there are many hundreds of similar things on similar orbits" in the area beyond Neptune known as the Kuiper Belt.

Cheng said he took a big risk by spending more than half a year looking through a difficult set of data while searching for Planet Nine. But he was happy to find something at all.

Now, the team wants to use powerful telescopes like the James Webb Space Telescope, the Hubble Space Telescope, and the ALMA telescope to learn more about this object. Meanwhile, a 23-year-old amateur astronomer from California named Sam Deen has already tracked 2017 OF201 using old space data. "OF201 is, in my opinion, probably one of the most interesting discoveries in the outer solar system in the last decade," Deen said.

What does this mean for Planet Nine?

For years, scientists noticed that many icy objects beyond Neptune have orbits that seem to be grouped in one direction. This led them to believe there might be a large planet—possibly ten times bigger than Earth—pulling on them. They called it Planet Nine or Planet X.

In fact, back in 1930, when astronomers were looking for Planet X, they discovered Pluto. But Pluto was later found to be too small and was reclassified as a dwarf planet in 2006. There are now five official dwarf planets, and Cheng believes that 2017 OF201 could become the sixth.

However, when researchers studied the orbit of 2017 OF201, they found that it does not match the same pattern as other similar objects. This could make the Planet Nine idea weaker. Cheng said more information is needed to be sure.

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