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: Mercury, the Littlest Planet

Let the exploration of the Milky Way Galaxy commence! I posted about stars a few weeks ago, so now let’s talk about the planets! I heart all of the planets equally so we'll just talk about them in order, starting with Mercury...

Mercury is the small planet right next to the sun. It is the smallest planet in our solar system (about the size of Earth’s moon), but is the second (to Earth) most dense planet. Being dense basically means it is really heavy for its size (science people are cringing at this definition, but it works, so back off!). Mercury is the closest planet the sun. At its closest it is only 28,580,000 miles (46,000,000 kilometers) away from the sun’s surface. Being so close to the sun means daytime temperatures on the surface of this tiny planet reach a sweltering 430°C (800°F). Mercury does not have an atmosphere (atmospheres are like a big blanket - they can hold in warmth and keep out space trash) so a night on Mercury usually plummets to around -180°C (-290°F). Imagine dressing to go out for dinner.

Mercury is named after the Ancient Roman god, Mercury. Mercury (the god) was the FedEx god who could get places the fastest with his super-fly winged shoes. The name is fitting since the planet Mercury orbits the sun faster than any other planet. One year (a full rotation around the sun) takes Mercury 88 Earth days. A day on Mercury (one full rotation around the axis – an imaginary line running through the center of the planet) is 59 Earth days long. Since it is going around the sun so quickly, but rotating so slowly, it takes 176 Earth days to have 1 solar day (to go from sunrise to sunset). Isn’t that kind of bizarre?

Being so small and close to the sun makes seeing Mercury a little difficult. Thirteen times a century, Mercury will pass in front of the sun and people on Earth will be able to see the planet (this is called a transit). The next time we can do this is May 9, 2016.

In 1974-1975 the US space probe, Mariner 10, did flybys of Mercury and provided people on Earth with the first up close images of the planet. Basically, it looks like our moon – it’s full of craters and mountains created by comet and meteor impacts. Radar imaging done in 1991 shows that despite being so hot, the poles (which stay cold) may contain frozen water. NASA has the Messenger probe aimed at Mercury now. The probe did flyby pictures in 2008 and 2009. Messenger will settle into orbit around Mercury in 2011 and study the planet’s composition and magnetic field for a year.