Sucks to be Pluto

The moment I finished the space odyssey, I began getting grief about not including Pluto. Sorry friends, but Pluto is not a planet. Sure it used to be, but it was downgraded. Like most other scientists I have to agree that it doesn’t deserve to be in the same class as bodies like Jupiter and Saturn.

The International Astronomical Union (IAU) is who started the drama around Pluto. They are the big shot organization that controls how we think about space. They are also the ones with the authority to name heavenly objects.

The drama started in January 2005 when Eris (official name: Eris 136199) was discovered. Eris was found orbiting out past Pluto in the Kuiper Belt. It was determined to be 27% more massive than Pluto. NASA started calling Eris the tenth planet and got excited about the high probability of finding more planets, but the IAU had something to say about that.

In August 2006, the IAU held a meeting in Prague and passed Resolution 5A. This resolution established guidelines to determine if something is a planet or a dwarf planet.

To be a planet, an object must:
1. Orbit the sun
2. Be large enough to produce enough gravity to make itself (mostly) round
3. Clear the neighborhood around its orbit

To be a dwarf planet, an object must:
1. Orbit the sun
2. Be large enough to produce enough gravity to make itself (mostly) round
3. Not have cleared the neighborhood of its orbit
4. Not be a satellite (moon)

All other objects (i.e. comets, asteroids, etc) are classified collectively as “Small Solar System Bodies”.

Pluto is tiny (only about 70% the size of our moon), but it is able to meet requirements one and two of being a planet. The problem lies in requirement three. Pluto orbits in the Kuiper Belt (basically the same thing as the asteroid belt, just a little larger. It starts right outside the orbit of Neptune). A true planet would have cleared the belt out of its orbit, but Pluto did not.

Picture from http://www.mathiaspedersen.com/

Just like that, Pluto got its planet card revoked. Our solar system only contains 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune). In Resolution 6A, Pluto was officially named a dwarf planet as well as the prototype for a new variety of trans-Neptunian objects, which (according to Resolution 6B) will be called “Plutonian Objects”.

Now Pluto gets to hang out with the other dwarfs, like Ceres and Eris.

Whatever, I would rather hang out with them anyway!

Robert’s Out of This World Space Odyssey: Neptune, The Final Planet

Neptune is the 8th and outermost planet in our solar system (Pluto is no longer a planet and we will talk about that another time), orbiting 2.8 billion miles (4.5 billion kilometers) away from the sun. That makes Neptune far enough away for people on Earth not to be able to see it without a telescope. Even then it just looks like a fixed star. If you remember an older post, you will know that since Neptune is hard to see from Earth (impossible without a telescope), it is actually the first planet discovered using math. Two astronomers working in the mid-nineteenth century, John Couch Adams and Urbain Le Verrie, both realized that the orbit of Uranus was not as predicted – something with a large gravitational force must be altering it. It must be another planet. On September 23, 1846, Neptune was discovered and named after the Roman god of the sea (the international community of astronomers didn’t like naming the planet after Le Verrie).

Neptune is roughly 4 times bigger than Earth and is comprised mostly of hydrogen, helium, water and silicates (the stuff you make rocks out of). Like its sister ice giant, Uranus, Neptune has an inner rocky core (about the size of Earth), surrounded by a liquid layer that blends into layers of thick clouds. These clouds whip around the planet, sometimes at speeds greater than the winds on Jupiter. The clouds contain methane, which provides the planet’s brilliant blue color.

Being the farthest from the sun also means taking the most time to complete an orbit. One full year (a complete orbit around the sun) on Neptune takes 165 Earth years. One day on Neptune (full rotation around its axis) lasts 16 hours 7 minutes.

Neptune has 6 thin, hard to notice and non-uniform rings. It also has 13 identified moons. Triton is the largest moon and is the only major moon in the universe to orbit a planet in the opposite direction the planet rotates. It is believed that Triton started life as a comet orbiting the sun. One day it got a little too close to Neptune and before it realized what was happening; it got sucked into orbit by Neptune’s gravity and became a moon. The surface of Triton is the coldest known place in our solar system, coming in at a bone chilling -390°F (-235°C).

And that’s it. You have now learned a little something about all of the planets in our solar system. I hope you enjoyed our lovely little space odyssey!