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beccastareyes) wrote2006-08-24 07:42 pm
beccastareyes) wrote2006-08-24 07:42 pm
Pluto -- the Epic Drama of Love and Betryal in the Outer Solar System
So, since a lot of people are now even more confused about things, I thought I'd made another Pluto post. Especially since it came up in class today and Dr. Margot gave me some inside information.
Wow... apparently Pluto's Wikipedia article has been locked down for vandalism. I am impressed.
Pluto
The Epic Drama of Love and Betryal in the Outer Solar System
By Becca Stareyes, Planetary Science Grad Student Extraordinaire
Chapter 1: A Man and His Planet
Once upon a time, back in the dark ages of the early Twentieth Century, there lived a young man in Kansas named Clyde Tombaugh. Like many young people in Kansas, he wanted to see things that were not Kansas. Unlike many young people in Kansas, the non-Kansas things he saw were Mars and Jupiter through a small telescope he built himself. He sent a few sketches off to the Lowell Observatory.
As it happened, Lowell Observatory was looking for someone. It had been founded by Percival Lowell, who was most famous for seeing canals on Mars, but who also made predictions about a mysterious ninth planet -- Planet X. Lowell-the-person was dead, but there was still interest to see if he was right.
Tombaugh spent a good year scanning the sky for Planet X. How he'd do it was by taking pictures of the sky several nights apart, then comparing them -- anything in the solar system would move between the two nights. Unfortunately, things other than Planet X also moved in the sky -- Tombaugh discovered 14 asteroids and took pictures of a lot more. As it happened, he found a faint speck in the January sky. It was moving too slowly to be an asteroid -- it had to be far out. After several nights, people at Lowell were certain -- they had something out beyond Neptune. It had to be Planet X.
Chapter 2: Doubts on Pluto's Parentage
The first thing astronomers noticed about Pluto was that it didn't orbit like the other planets. Most planets went in near-circular paths around the Sun, all in roughly the same direction. Pluto traveled in a tilted oval-shape. Sometimes it even came in closer than Neptune. Moreover, it had an odd relationship with Neptune -- two Pluto years were nearly exactly the same as three Neptune years.
Tombaugh wasn't able to get a picture of Pluto -- it was a speck of light. This limited its size somewhat, but it was also far away and difficult to see anyway. The problems began to arise when better telescopes couldn't get looks at a disk -- Pluto continued to be a speck in pictures. Estimates of its size dropped -- and astronomers got worried. Pluto was weird.
Someone came up with the idea that maybe Pluto was an escaped moon of Neptune. After all, it had a funny orbit, as did both of Neptune's moons. And it could have been at the right place at the wrong time several billion years ago. That was not a reassuring theory -- moons should not be planets.
Another astronomer -- by the name of Gerard Kuiper -- popularized the idea of a belt of icy objects which was where comets came from: the Kuiper (or sometimes Kuiper-Edgeworth) Belt. Pluto would be at just the right place to be a Kuiper Belt member. Either way, Pluto wasn't looking very planetary as the years went on.
Then, in 1978, James Christy noticed that Pluto had grown a bump in his pictures. The bump also seemed to be moving around the planet. It turned out that the bump was a moon -- just barely visible to the telescope. That was excellent news -- a moon meant that astronomers could find out how big Pluto actually was. The could measure its mass by watching how its moon orbited and measure its radius by watching the moon eclipse the planet.
The answers weren't good. Pluto was small. Smaller than Mercury. Smaller than a lot of the larger moons in the Solar System -- it would take five Plutos to make one Moon. However, it was still bigger than Ceres, the biggest asteroid. Pluto was a freaky little thing.
Chapter 3: The Solidarity of Kuiper Belt Objects
Flash forward to 1992. David Jewitt and Jane Luu were observing in Hawaii -- looking for interesting things outside Neptune's orbit -- and they found something. 1992 QB1 was a small, faint starlike object orbiting out around 40 AU -- about where Pluto was. More searching revealed more objects -- hundreds of them. Some of them even had orbits like Pluto's -- sharing that odd three-two pattern with Neptune. Pluto was no longer alone in the icebox of the Solar System.
Measuring sizes of these things were tricky -- Pluto was lucky because of Charon. However, estimates could be made, based on assumptions about how bright a KBO was. When large objects were discovered, that made Pluto look even less planetary -- after all, the asteroid belt had several large asteroids, surrounded by many small ones. Planets generally didn't.
Astronomers started suggesting that maybe Pluto shouldn't be considered a planet. There was precedent -- the first four asteroids had been considered planet-like in the early 1800s until the fifth asteroid was discovered and unleashed a floodgate of rocks orbiting with Ceres, Pallas, Vesta and Juno. And the KBOs weren't looking that different than Pluto -- they were made of the same stuff, some had moons, they orbited in the same funny way.
This didn't go over well. Pluto had an emotional tie to people -- they grew up with Pluto as a planet. Heck, Pluto had an emotional tie to astronomers (who are people too) -- no one would even consider demoting Pluto until Clyde Tombaugh passed away in 1997, because no one wanted to be the guy who took Clyde's planet from him.
Chapter 4: Enter the IAU
However the issue wasn't going away, and was becoming more problematic every time some astronomer found 'the largest KBO that wasn't Pluto'. Quaoar, Sedna, 2005 FY9 and 2003 EL61 were all the same size (or larger) as Pluto's moon. 2003 UB313 was supposed to be bigger than Pluto. The press was starting to call things 'tenth planets'. Clearly Something Had to Be Done.
Enter the International Astronomical Union, the one body that had enough authority to set down 'what is a planet, anyway?'. The IAU decided to draft 19 astronomers who studied such things to answer the question. These fine individuals spent two years arguing over email, eventually coming to no real consensus.
Undaunted, the IAU tried again. Realizing that 19 people couldn't even meet in person, they chose a 7 person committee to succeed where the first committee failed. These individuals -- experts on Pluto and KBOs -- met in Paris for a lovely weekend and hammered out the first definition of a planet that the lay community saw; one that was both self-consistant and was sure to keep Pluto as a planet. Basically, it defined a planet as anything massive enough to be pulled into a spheroid and that orbited the Sun.
The voting members of the IAU took one look at it and wondered what the hell drugs the committee was on.
Astronomers weren't happy. People pointed out there were 12 planets in our solar system and rising -- we didn't really know the shapes of many large asteroids and KBOs. People pointed out that the Moon wasn't a planet, but that it would be in billions of years, thanks to it moving slowly away from the earth. People pointed out how silly it was to have a planet that didn't even have a name yet (these people have never seen the exciting field of extrasolar planets). And the public was confused -- most people hadn't even heard of Ceres or UB313.
So, someone tacked on an additional definition -- planets must have kicked out anything near their size orbiting near them -- small things, like the crowd of asteroids that preceded and followed Jupiter around were allowed, but nothing that was anywhere near the size of the planet. Things that hadn't, but were still round, were dubbed 'dwarf planets'. Things that weren't round were Small Solar System Bodies. Most (but not all) astronomers in the IAU approved this definition. It helped that NASA had already agreed to launch a spacecraft to Pluto -- 'planets' got better funding than 'dwarf planets' or 'KBOs'.
Now we just have to explain it to the public without looking like a bunch of dolts. And I hope I just did.
The End.
Wow... apparently Pluto's Wikipedia article has been locked down for vandalism. I am impressed.
The Epic Drama of Love and Betryal in the Outer Solar System
By Becca Stareyes, Planetary Science Grad Student Extraordinaire
Chapter 1: A Man and His Planet
Once upon a time, back in the dark ages of the early Twentieth Century, there lived a young man in Kansas named Clyde Tombaugh. Like many young people in Kansas, he wanted to see things that were not Kansas. Unlike many young people in Kansas, the non-Kansas things he saw were Mars and Jupiter through a small telescope he built himself. He sent a few sketches off to the Lowell Observatory.
As it happened, Lowell Observatory was looking for someone. It had been founded by Percival Lowell, who was most famous for seeing canals on Mars, but who also made predictions about a mysterious ninth planet -- Planet X. Lowell-the-person was dead, but there was still interest to see if he was right.
Tombaugh spent a good year scanning the sky for Planet X. How he'd do it was by taking pictures of the sky several nights apart, then comparing them -- anything in the solar system would move between the two nights. Unfortunately, things other than Planet X also moved in the sky -- Tombaugh discovered 14 asteroids and took pictures of a lot more. As it happened, he found a faint speck in the January sky. It was moving too slowly to be an asteroid -- it had to be far out. After several nights, people at Lowell were certain -- they had something out beyond Neptune. It had to be Planet X.
Chapter 2: Doubts on Pluto's Parentage
The first thing astronomers noticed about Pluto was that it didn't orbit like the other planets. Most planets went in near-circular paths around the Sun, all in roughly the same direction. Pluto traveled in a tilted oval-shape. Sometimes it even came in closer than Neptune. Moreover, it had an odd relationship with Neptune -- two Pluto years were nearly exactly the same as three Neptune years.
Tombaugh wasn't able to get a picture of Pluto -- it was a speck of light. This limited its size somewhat, but it was also far away and difficult to see anyway. The problems began to arise when better telescopes couldn't get looks at a disk -- Pluto continued to be a speck in pictures. Estimates of its size dropped -- and astronomers got worried. Pluto was weird.
Someone came up with the idea that maybe Pluto was an escaped moon of Neptune. After all, it had a funny orbit, as did both of Neptune's moons. And it could have been at the right place at the wrong time several billion years ago. That was not a reassuring theory -- moons should not be planets.
Another astronomer -- by the name of Gerard Kuiper -- popularized the idea of a belt of icy objects which was where comets came from: the Kuiper (or sometimes Kuiper-Edgeworth) Belt. Pluto would be at just the right place to be a Kuiper Belt member. Either way, Pluto wasn't looking very planetary as the years went on.
Then, in 1978, James Christy noticed that Pluto had grown a bump in his pictures. The bump also seemed to be moving around the planet. It turned out that the bump was a moon -- just barely visible to the telescope. That was excellent news -- a moon meant that astronomers could find out how big Pluto actually was. The could measure its mass by watching how its moon orbited and measure its radius by watching the moon eclipse the planet.
The answers weren't good. Pluto was small. Smaller than Mercury. Smaller than a lot of the larger moons in the Solar System -- it would take five Plutos to make one Moon. However, it was still bigger than Ceres, the biggest asteroid. Pluto was a freaky little thing.
Chapter 3: The Solidarity of Kuiper Belt Objects
Flash forward to 1992. David Jewitt and Jane Luu were observing in Hawaii -- looking for interesting things outside Neptune's orbit -- and they found something. 1992 QB1 was a small, faint starlike object orbiting out around 40 AU -- about where Pluto was. More searching revealed more objects -- hundreds of them. Some of them even had orbits like Pluto's -- sharing that odd three-two pattern with Neptune. Pluto was no longer alone in the icebox of the Solar System.
Measuring sizes of these things were tricky -- Pluto was lucky because of Charon. However, estimates could be made, based on assumptions about how bright a KBO was. When large objects were discovered, that made Pluto look even less planetary -- after all, the asteroid belt had several large asteroids, surrounded by many small ones. Planets generally didn't.
Astronomers started suggesting that maybe Pluto shouldn't be considered a planet. There was precedent -- the first four asteroids had been considered planet-like in the early 1800s until the fifth asteroid was discovered and unleashed a floodgate of rocks orbiting with Ceres, Pallas, Vesta and Juno. And the KBOs weren't looking that different than Pluto -- they were made of the same stuff, some had moons, they orbited in the same funny way.
This didn't go over well. Pluto had an emotional tie to people -- they grew up with Pluto as a planet. Heck, Pluto had an emotional tie to astronomers (who are people too) -- no one would even consider demoting Pluto until Clyde Tombaugh passed away in 1997, because no one wanted to be the guy who took Clyde's planet from him.
Chapter 4: Enter the IAU
However the issue wasn't going away, and was becoming more problematic every time some astronomer found 'the largest KBO that wasn't Pluto'. Quaoar, Sedna, 2005 FY9 and 2003 EL61 were all the same size (or larger) as Pluto's moon. 2003 UB313 was supposed to be bigger than Pluto. The press was starting to call things 'tenth planets'. Clearly Something Had to Be Done.
Enter the International Astronomical Union, the one body that had enough authority to set down 'what is a planet, anyway?'. The IAU decided to draft 19 astronomers who studied such things to answer the question. These fine individuals spent two years arguing over email, eventually coming to no real consensus.
Undaunted, the IAU tried again. Realizing that 19 people couldn't even meet in person, they chose a 7 person committee to succeed where the first committee failed. These individuals -- experts on Pluto and KBOs -- met in Paris for a lovely weekend and hammered out the first definition of a planet that the lay community saw; one that was both self-consistant and was sure to keep Pluto as a planet. Basically, it defined a planet as anything massive enough to be pulled into a spheroid and that orbited the Sun.
The voting members of the IAU took one look at it and wondered what the hell drugs the committee was on.
Astronomers weren't happy. People pointed out there were 12 planets in our solar system and rising -- we didn't really know the shapes of many large asteroids and KBOs. People pointed out that the Moon wasn't a planet, but that it would be in billions of years, thanks to it moving slowly away from the earth. People pointed out how silly it was to have a planet that didn't even have a name yet (these people have never seen the exciting field of extrasolar planets). And the public was confused -- most people hadn't even heard of Ceres or UB313.
So, someone tacked on an additional definition -- planets must have kicked out anything near their size orbiting near them -- small things, like the crowd of asteroids that preceded and followed Jupiter around were allowed, but nothing that was anywhere near the size of the planet. Things that hadn't, but were still round, were dubbed 'dwarf planets'. Things that weren't round were Small Solar System Bodies. Most (but not all) astronomers in the IAU approved this definition. It helped that NASA had already agreed to launch a spacecraft to Pluto -- 'planets' got better funding than 'dwarf planets' or 'KBOs'.
Now we just have to explain it to the public without looking like a bunch of dolts. And I hope I just did.
The End.