Looking for Planet Nine

November 19, 2018
What is Planet Nine?

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What is Planet Nine? Find out more about a possible new planet in our solar system.

Everyone likes planets.  They’re familiar.  We live on one.  Ask your Aunt Lucie to name a few of the solar system’s Moons or to recite five stars, and you’ll probably get a blank stare.  But ask her to name all the planets, and no problem.

It’s been a while since anyone found a new planet in our solar system.  The world was amazed at the discovery of Uranus in 1781 and Neptune in 1846. 

Pluto’s discovery in 1930 also generated global excitement. It didn’t hurt when Walt Disney named his only nonspeaking character after it a year later. (The dog had been “Rover” in an earlier cartoon). 

But as we all know, Pluto was demoted in 2006—officially designated a “dwarf” like so many other Disney characters. See definition of a dwarf planet.

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Image: NASA. Dwarf planets Pluto and Eris orbiting through the Kuiper Belt, beyond Neptune.

We’re ready for a new one.  And we may get it.  Researchers recently discovered that the weird orbits of six very distant icy objects can be explained if they’re being tugged by a huge unseen world far away.

IF a planet is discovered, it would have to be several times larger than Earth.  And achingly distant.

If Earth’s distance from the Sun is 1 astronomical unit or AU, and Pluto averages 40 AUs from the Sun, a new planet would have to have a highly eccentric non-round orbit that comes as close as 200 and goes as far away as at least 500 AUs. That’s way out there.

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Image: NASA. If Planet X exists its orbit might exist in the frozen Kuiper Belt region of our outer solar system, counterbalancing the orbits of the other Kuiper objects with its gravitational pull.

Hypothetically, it would be at its farthest away right now. That would make it incredibly dim, something like magnitude 22, or a thousand times fainter than Pluto. Tough to find.  So far, it’s being called Planet Nine.  No doubt, if it exists, it will be named after some Roman god, to match the other planets.

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Image: The imaginary Planet Nine.

At a time when all the naked-eye planets are visible at the same time, it’s exciting to think that our solar system might have a large, mysterious new member.  Aren’t we all kind of rooting for Planet Nine?

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s hub for everything stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe