10th Planet? I don't think so...

They are calling it Xenia and now they find it has a moon as well. Still if you ask most astronomers, this is not a planet. For that matter, neither is Pluto. Even the discoverers of Xenia agree there are doubts.

Funny thing is, there is no actual definition of what a planet is. Pluto was called a planet after its discovery but in the years afterward, most astronomers realized it was probably a mistake. The problem is, you have several generations of school kids who were taught it was a planet and countless text books with the same claim.

So, why is it not a planet?

The answer has to do with the way we think the solar system was formed 5 Billion years ago. The gas and dust cloud that eventually came to be our home in the cosmos formed into a spinning disk that flattened out. Eventually the planets all formed in basically the same plane. In other words, you could set the sun at the middle of the table and all the other planets would be on the same flat table. None would be much above or well below it. The inner planets lost their original atmospheres of hydrogen and Helium and Methane because the molecules were moving too fast in the sun's heat to stay attracted in the relatively weak gravity.

The planets farther out beyond Mars however, were much farther from the sun and all the gas congealed into the gas giant planets of Jupiter, Saturn Uranus and Neptune. There was almost another planet between Mars and Jupiter but because of Jupiter's HUGE size and powerful gravity this planet could not come together and all the rocks are still out there spinning around the sun. This is the asteroid belt.

Beyond Neptune there is the Kuiper Belt. Another ring of rocky objects.. many well over 100km across. It is also in the plane of the ecliptic... or, on the flat table with the other planets. Although it is not as flat as the 8 planets.

Most of the planets around the sun also orbit in basically a circle. The earth's orbit around the sun is a slight ellipse. We are closer to the Sun in January and farther away in July.(This will change in 25,800 years or so.) Mercury has one of the more eccentric orbits coming closer to the sun and then moving quite a bit away as it goes around. Still it is close to a circular orbit.

None of the planets are as strange as Pluto though. It's orbit is far from circular. At times it is closer to the sun than Neptune. It is also "not on the table". It's plane of orbit is off the ecliptic. It is a rocky body, not a gas giant as the current theory of our solar system proposes.

The new planet Xenia, which is even bigger than Pluto, it also not orbiting in the plane of the ecliptic. Nor is it a gas giant. It is a rocky world.

Pluto and Xenia are large kuiper belt objects. Not planets.

The solar system has 8 planets. Not 9, and not 10. Most astronomers agree with this. Some do not. Then again, there are some who feel that landing a man on the moon was faked and pro wrestling is real. Go figure!

Later,
Dan