Our Solar System is a very busy place. There are millions of objects moving around, from planets and moons to comets and asteroids. And every year we discover more and more objects (usually small asteroids or fast comets) that call the Solar System home.

Astronomers had found eight major planets by 1846. But that didn't stop us from looking for more. Over the past 100 years, we have found smaller distant bodies that we call dwarf planets, which we now classify as Pluto.

The discovery of some of these dwarf planets gave us reason to believe that something else might be lurking on the outskirts of the Solar System.

Could there be a ninth planet?

There is a good reason why astronomers have spent hundreds of hours searching for the ninth planet, also known as "Planet Nine" or "Planet X". Because the Solar System as we know it makes no sense without it.

Every object in our Solar System revolves around the Sun. Some move fast, some move slow, but all move in obedience to the laws of gravity. Everything with mass has gravity, including you and me. The heavier something is, the more gravity it has.

A planet has so much gravity that it affects how things move around it. We call this "gravity". Earth's gravity is what keeps everything in place.

Our Sun also has the greatest gravitational pull of any object in the Solar System, and this is the main reason why the planets revolve around it.

It is by understanding the force of gravity that we can get the biggest clue to the existence of the Ninth Planet.

When we look at really distant objects, such as the dwarf planets beyond Pluto, we find that their orbits are somewhat unexpected. They move on very large elliptical (oval-shaped) orbits, grouped together and on an inclination compared to the rest of the Solar System.

When astronomers used a computer to model the gravitational forces required for these bodies to move in this way, they found that a planet at least ten times the mass of the Earth was needed to cause this.

That's super exciting! But then the question is: where is this planet?

The problem we're having right now is trying to confirm whether these predictions and models are correct. The only way to do that is to find Planet Nine, which is certainly easier said than done.

 

Source: https://www.sciencealert.com/