Experts meet to decide Pluto fate, Finally we'll know what a 'planet' is... |
Experts meet to decide Pluto fate, Finally we'll know what a 'planet' is... |
Aug 14 2006, 06:06 AM
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Member Group: Members Posts: 295 Joined: 2-March 04 From: Central California Member No.: 45 |
-------------------- Eric P / MizarKey
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Aug 15 2006, 01:47 PM
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
It's also worth mentioning that Ceres used to be called a planet, but once it became clear how many other bodies were in the asteroid belt, it lost that status. (Be interesting to learn exactly how that happened; I suspect there wasn't any kind of formal vote.)
Besides, there's a nice symmetry in having eight planets and two asteroid belts. The four terrestrial planets are inside the original asteroid belt and the four jovian planets are between that asteroid belt and the Kuiper belt. Just tell the public they're not losing a planet -- they're gaining a new asteroid belt. I think most people aren't even aware there's a Kuiper belt at all. |
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Aug 15 2006, 04:56 PM
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Member Group: Members Posts: 809 Joined: 11-March 04 Member No.: 56 |
It's also worth mentioning that Ceres used to be called a planet, but once it became clear how many other bodies were in the asteroid belt, it lost that status. (Be interesting to learn exactly how that happened; I suspect there wasn't any kind of formal vote.) You're right, there wasn't. The following historical summary discusses how it happened: When Did the Asteroids Become Minor Planets? The decision was in the hands of the compilers of astronomical almanacs. For the first 50 years after the discovery of Ceres, asteroids were listed together with the planets, between Mars and Jupiter, in order by length of their semi-major axes. In 1841 the British Nautical Almanac and Astronomical Ephemeris began to collectively name the four then-discovered asteroids as "Minor Planets". In 1851 asteroids 5-15 and Neptune were moved "to the back of the book" of the Berliner Astronomisches Jahrbuch. At the same time, numbers were substituted for the astronomical symbols that had been invented for them. In 1867, Ceres, Pallas, Juno and Vesta went "to the back of the book" as well. Likewise, in 1868, the Paris Observatory began to classify these four asteroids as "petites plančtes". So for a few decades, at least, there were three categories of planet: major (Mercury-Neptune), minor (asteroids 5+) and a nameless middle group consisting of asteroids 1-4. In the '50s and '60s other almanacs also stopped printing the ephemerides of the asteroids in the same section with the planets or abandoned them altogether. The distinct treatment of Ceres, Pallas, Juno and Vesta depended not so much on their size (though Ceres, Pallas, and Juno were drastically overestimated) but, I think, on the fact that they had been treated as planets for forty or fifty years -- in a situation comparable to that of Pluto today. They were, you might say, "grandfathered in". Astraea and the others were (c. 1850) newcomers, only discovered in the past decade, and so not worthy of the same degree of reverence! If Pluto, 2003UB313 and some others are granted a middling status like "mesoplanet", perhaps we can expect them also to drift into being merely "minor planets" some decades from now. |
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