Since people first realized that Earth is a part of a larger group of planetary bodies, the solar system has been growing. Not actually growing, as in it’s somehow picking up more stuff, but growing in that we’ve been finding more things that are part of it. First there was the Sun. Certainly, it was seen long before any planet. It was first proposed that the Sun was a star in 450 BC, but it wasn’t conclusively proven until the 1800s. The Babylonians discovered Mercury, Venus, Mars, Jupiter and Saturn in the 1000s BC. In 1781, Uranus was discovered, and Neptune followed sixty five years later. Then came Pluto, the little planet found in 1930. But then our solar system stopped. While people postulated that a 1oth planet may exist, nothing materialized, and everyone settled in to the thinking that our system was made up of nine planets – and that’s that!

But then some malcontents started making noise that Pluto wasn’t really a planet. It is too small, it’s orbit is all messed up. Others fought the notion, not wanting to give up any of all that hard-won solar real estate. But alas, in 2006 Pluto was relegated from planet to dwarf planet. Our solar system shrunk, and shrinking is not usually good. Today, like the stock market on a rally, it got massively larger again.

Konstantin Batygin and Mike Brown, two astronomers out of Caltech in Pasadena, found some odd movements in the orbits of the six known objects in the Kuiper Belt, or the region of space beyond the orbit of Neptune. After a lot of hard work and investigation, they came to the conclusion that the only thing that could cause what they were seeing was a planet – a really big planet.

This planet is soooo big…

How Big is it?

Currently the two astronomers estimate it being the mass of about ten Earths. So, it’s not as big as the smallest known gas giant (Neptune), but would be the largest terrestrial planet in the system by a long shot if its solid.

How Far Out is it?

Well, it’s way out there. An astronomical unit (AU) is defined as roughly the distance from the Earth to the Sun. Since this distance constantly changes, the exact definition is 93 million miles. So the Earth is one AU from the Sun. Mars is about 1.5 AUs out. Jupiter gets a little farther out there at 5.2 AUs. Saturn is 9.5, Uranus 19.2, and Neptune 30.1. Pluto – I know, it’s not a planet any more – is 39 AUs out. The most distant object discovered so far is Sedna, a likely dwarf planet that has an elliptical orbit ranging between 76 AUs at perihelion (its closest to the sun) and a whopping 940 AUs at its farthest – its aphelion. This new planet is estimated to be 200 AUs at is closest, and may venture out as far as 1200! It is so far out there that the last time it was in its current relative position in its orbit, humans were only beginning to migrate to the Americas – or about 15,000 years ago.

How Did it Get There?

This is an interesting one. It doesn’t seem likely that something the size of ten Earths could coalesce in an orbit so far out. The theory is that this big planet was somehow blown out of the “traditional” solar system to its current far-flung orbit sometime around 4.5 billion years ago.

What Does it Look Like?

Unfortunately, this newly discovered planet will remain a visual mystery for some time. Other astronomers must be convinced of its existence, then resources – primarily in the form of telescope time – must be spent to find it.

What’s its Name?

Right now, this new planet has no official name. Hopefully once more astronomers get on board, it will get one. Until then, it carries an ominous moniker: Planet Nine


Photo credit: JPL


Posted by Darren Beyer

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