by Our solar system is a pretty busy place. Millions of objects move – from planets to moons to comets and asteroids. And every year we discover more and more objects (usually small asteroids or fast-moving comets) that make up the solar system.
By 1846, astronomers had found all eight major planets. But that doesn’t stop us from looking for more. In the last 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 has given us reason to believe that something else might be lurking on the edge of the solar system.
Could there be a ninth planet?
There’s a good reason astronomers spend hundreds of hours trying to locate a ninth planet, also known as “Planet Nine” or “Planet X.” And that’s because the solar system as we know it doesn’t really make sense without it.
Every object in our solar system orbits the sun. Some move fast and some move slowly, but all move according 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’s gravity is so great that it affects how things move around it. This is what we call its “gravity”. The gravity of the earth keeps everything on the ground.
Also, our sun has the greatest gravitational pull of any object in the solar system, and that’s basically why the planets orbit around it.
Our understanding of the gravitational force gives us our biggest clue to a possible Planet Nine.
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Unexpected Behavior
When we look at really distant objects like dwarf planets beyond Pluto, we find that their orbits are somewhat unexpected. They move in very large elliptical (oval-shaped) orbits, are clustered and tilted compared to the rest of the solar system.
When astronomers use a computer to model the gravitational forces required for these objects to move in this way, they find that it would have taken a planet at least ten times Earth’s mass to cause it.
It’s super exciting stuff! But then the question is: Where is this planet?
The problem we have now is trying to confirm if these predictions and models are correct. The only way to do this is by finding Planet Nine, which is definitely easier said than done.
The hunt continues
Scientists around the world have been searching for visible evidence of Planet Nine for many years.
Based on the computer models, we believe that Planet Nine is at least 20 times farther from the Sun than Neptune. We try to spot it by looking for sunlight that can reflect it—just like the moon shines from reflected sunlight at night.
However, because Planet Nine is so far from the Sun, we expect it to be very faint and difficult to see for even the best telescopes on Earth. Also, we can’t just look for it every season.
We only have small nighttime windows where conditions need to be just right. In particular, we must wait for a moonless night when the spot we are observing from faces the right part of the sky.
But don’t give up hope just yet. Over the next decade, new telescopes will be built and new sky surveys will begin. They might just give us the opportunity to prove or disprove whether Planet Nine exists.
Sarah WebbPostdoctoral Research Fellow, Center for Astrophysics and Supercomputing, Swinburne University of Technology
This article was republished by The Conversation under a Creative Commons license. Read the original article.
