The Hunt for Planet Nine

Back in 2006, our solar system lost a planet. It didn’t go missing. Astronomers decided that Pluto should be reclassified as a dwarf planet—a space object that’s smaller than a planet but that also moves around the sun. Since then, our solar system has been a party of eight.

But that number may change again soon. Astronomers at the California Institute of Technology recently found evidence of a ninth planet. If it exists, the planet—temporarily called Planet Nine—is a big one.

Today, there are eight planets in our solar system. There used to be nine. But in 2006, astronomers decided that Pluto was too small to be a planet. They named it a dwarf planet instead. It’s smaller than a planet but still moves around the sun. 

The number of planets in the solar system may change again soon. Scientists recently found signs of a ninth planet. For now, they’re calling it Planet Nine. 

Mike Brown and Konstantin Batygin made the discovery while studying the Kuiper (KYE-pehr) belt, a vast region of icy asteroids and comets at the edge of the solar system. Most objects orbit the sun in predictable patterns. But scientists noticed that some objects in the Kuiper belt had strangely tilted orbits, and no one could figure out why.

In 2014, Batygin and Brown started using computer models to study why the objects moved the way they did. They tested many possibilities before finding one that seemed likely. They believe that gravity from a planet far beyond Neptune is pulling the objects into odd orbits. 

Mike Brown and Konstantin Batygin work at the California Institute of Technology. They made the discovery while studying the Kuiper (KYE-pehr) belt. This is a large region of space rocks and icy comets at the edge of the solar system. 

The scientists noticed some odd objects in the Kuiper belt. Most objects orbit, or circle, the sun in a similar way. But the objects the scientists saw had strangely tilted orbits. 

In 2014, Batygin and Brown created computer models. They used them to study why the objects moved the way they did. They tested many possibilities. Then they found a likely answer. 

They believe a planet exists far beyond Neptune. And it’s a big one. That means its gravity, or pulling force, is big too. It could be tugging nearby objects into unusual orbits. 

If the scientists’ calculations are correct, Planet Nine is about 10 times as large as Earth. And it has a huge orbit around the sun. One year on Planet Nine would last 20,000 Earth years! 

Since no one has seen Planet Nine, some scientists aren’t convinced it exists. But that could soon change. Astronomers are racing to observe it through a telescope—now that they know where to look. They’re scanning parts of the sky where the planet might be and hope to catch a glimpse within five years. “We’re going to find it,” says Batygin. 

Scientists think Planet Nine is about 10 times larger than Earth. And it has a huge orbit. It would take 20,000 Earth years to circle the sun. 

No one has actually seen Planet Nine. Some scientists aren’t convinced it exists. But that could soon change. Astronomers now know where to look for the planet. They’re racing to spot it through a telescope. They hope to catch a glimpse within five years. “We’re going to find it,” says Batygin.