On Pluto
Yesterday, I wrote about our new Solar System family member, Makemake. Then it got me thinking about how vociferously the general public opposed the demotion of Pluto in 2006. So here are some thoughts and facts about Pluto, and the history of our classification that you might like to know:
Pluto was discovered in 1930. Big deal, we all knew that. We probably all had a generation of teachers who said "when I was a kid, Pluto was a big question mark. We didn't know exactly WHAT it was". Well, now we know a LOT about what it is, and a planet, it ain't.
Firstly, it's small. Less than 1500 kms in diameter, roughly half the size of Mercury. That's a little frakkin small for a planet, and it's certainly too small to hold an atmosphere (in the interests of full disclosure, the ability to hold an atmophere is not a requisite of what it means to be a planet).
Secondly, from what we can tell, it is REALLY icy. So icy, in fact, that if it were closer to the sun, say around the orbits of Mercury or Venus, it would have a huge ice-tail, like a comet. After a few thousand years, the ice will have been blown off, and Pluto would be even smaller!
Thirdly, its orbit is really freaky-deaky. It's on a tilt against the plane of the rest of the system (which is consistant with comets and the kuiper belt objects), and it even interesects with Neptune's orbit. Planets don't have orbits like that. Freaks like comets do. I'm certainly not suggesting Pluto is a comet, merely that its as much a comet as it is a planet. So the definition of both are too vague.
Fourthly, one of the requisites of the planet designation is that a planet has a certain leve of gravitational impact on the surrounding space. Pluto's mass is so rinky-dink, that it's larget moon, Charon doesn't orbit it the way other moons orbit their host planets. Since Charon is roughly half the size and mass of Pluto, the two bodies almost orbit each other, constantly dancing around each other in their unsual orbit around the sun. So much do they dance around each other that for a while, astronomers considered that Pluto was a binary planet system. Freaky.
One more point on this issue of school children now having to learn something wholly different from what we were taught. It's a bit of a silly issue, and I don't think that its a serious argument, but the next time someone says that to you, tell that this very process has happened before. In 1801, Ceres was discovered. It was thought to be a new, tiny planet between Mars and Jupiter. Then, they found another one, Pallas. Then another one, Juno. And again, Vesta. Astronomers realized they weren't looking at new planets, but a peculiar system that is chocked-full of rocky bodies. After nearly a half-century of teaching that Ceres et. all were planets, they were demoted, and the classification of the Asteroid Belt was born. Today, our situation is VERY similar: We find Pluto, and we think is a planet. We keep looking around in the area, and we find similar bodies: Eris, Makemake, Sedna, Orcus, Varuna....and eventually, we realized that we had something very different going on. We effectively had another asteroid belt in our system. Like the belt in between Mars and Jupiter, the Kuiper Belt contains huge amounts of bodies, some as large as Pluto, most as small as a pea.
H'okai, so, there were two options: 1) expand the definition of a planet to include Pluto, but would aslo force us to include Ceres, Iris and Makemake (then-named 2005Fy9), or 2) limit the defintion of a planet that would cut Pluto out, and effectively make a new designation for Pluto-like objects; after all, under the old way, calling Ceres an asteroid was also a bit ridiculous because of its spherical shape and its sheer size and mass.
They went with option 2, and we're all the better for it. As astronomers learned more about how the solar system works, they learned that our older ways of defining and classification were outdated and simplistic.
So Pluto gets demoted slightly, while Eris, Ceres and Makemake get a boost. If space had an ego, this would be a net-gain for our solar system. And now, our system seems richer to the average person: we now have THREE types of planetary bodies now: rocky planets, gas giants, and dwarf planets. Personally, I think Pluto can take one for the team. It's been coasting for too long on its affectionate position.
Pluto was discovered in 1930. Big deal, we all knew that. We probably all had a generation of teachers who said "when I was a kid, Pluto was a big question mark. We didn't know exactly WHAT it was". Well, now we know a LOT about what it is, and a planet, it ain't.
Firstly, it's small. Less than 1500 kms in diameter, roughly half the size of Mercury. That's a little frakkin small for a planet, and it's certainly too small to hold an atmosphere (in the interests of full disclosure, the ability to hold an atmophere is not a requisite of what it means to be a planet).
Secondly, from what we can tell, it is REALLY icy. So icy, in fact, that if it were closer to the sun, say around the orbits of Mercury or Venus, it would have a huge ice-tail, like a comet. After a few thousand years, the ice will have been blown off, and Pluto would be even smaller!
Thirdly, its orbit is really freaky-deaky. It's on a tilt against the plane of the rest of the system (which is consistant with comets and the kuiper belt objects), and it even interesects with Neptune's orbit. Planets don't have orbits like that. Freaks like comets do. I'm certainly not suggesting Pluto is a comet, merely that its as much a comet as it is a planet. So the definition of both are too vague.
Fourthly, one of the requisites of the planet designation is that a planet has a certain leve of gravitational impact on the surrounding space. Pluto's mass is so rinky-dink, that it's larget moon, Charon doesn't orbit it the way other moons orbit their host planets. Since Charon is roughly half the size and mass of Pluto, the two bodies almost orbit each other, constantly dancing around each other in their unsual orbit around the sun. So much do they dance around each other that for a while, astronomers considered that Pluto was a binary planet system. Freaky.
One more point on this issue of school children now having to learn something wholly different from what we were taught. It's a bit of a silly issue, and I don't think that its a serious argument, but the next time someone says that to you, tell that this very process has happened before. In 1801, Ceres was discovered. It was thought to be a new, tiny planet between Mars and Jupiter. Then, they found another one, Pallas. Then another one, Juno. And again, Vesta. Astronomers realized they weren't looking at new planets, but a peculiar system that is chocked-full of rocky bodies. After nearly a half-century of teaching that Ceres et. all were planets, they were demoted, and the classification of the Asteroid Belt was born. Today, our situation is VERY similar: We find Pluto, and we think is a planet. We keep looking around in the area, and we find similar bodies: Eris, Makemake, Sedna, Orcus, Varuna....and eventually, we realized that we had something very different going on. We effectively had another asteroid belt in our system. Like the belt in between Mars and Jupiter, the Kuiper Belt contains huge amounts of bodies, some as large as Pluto, most as small as a pea.
H'okai, so, there were two options: 1) expand the definition of a planet to include Pluto, but would aslo force us to include Ceres, Iris and Makemake (then-named 2005Fy9), or 2) limit the defintion of a planet that would cut Pluto out, and effectively make a new designation for Pluto-like objects; after all, under the old way, calling Ceres an asteroid was also a bit ridiculous because of its spherical shape and its sheer size and mass.
They went with option 2, and we're all the better for it. As astronomers learned more about how the solar system works, they learned that our older ways of defining and classification were outdated and simplistic.
So Pluto gets demoted slightly, while Eris, Ceres and Makemake get a boost. If space had an ego, this would be a net-gain for our solar system. And now, our system seems richer to the average person: we now have THREE types of planetary bodies now: rocky planets, gas giants, and dwarf planets. Personally, I think Pluto can take one for the team. It's been coasting for too long on its affectionate position.