Post by Tim Bruening Post by email@example.com Post by George Avalos
"The Impossible Planet"
11-17-06 Dr. Who
5 stars (Clyde Tombaugh)
0-1 stars (International Astronomical Union)
Should be the other way round - Pluto's original designation was
responsible for messing up a previously fairly clean definition of a
planet at a time when it was already suspected there could be
planetismals beyond Neptune. It should never have been described as a
planet, and there wouldn't have been any fuss 70 years later.
I have read that Pluto was demoted on the technicallity that it had failed
to sweep Neptune out of its orbit. Since Neptune failed to sweep Pluto out
of its orbit, should we demote Neptune too?
It wouldn't be the reason; the reason was that, with the discovery of a
Kuiper Belt Object (KBOs) larger than Pluto, now named Eris, a new,
consistent definition of a planet was needed that would either
encompass many more than the 9-10 recognised candidates or which would
have to exclude Pluto and leave the traditional eight. The solution was
to plump for the latter, which ultimately makes things less of a
headache. The result is that Pluto, Eris and Ceres (which was, for a
very brief period after its discovery in the 17th Century, a planet -
Pluto isn't the first time an object has been incorrectly designated a
planet and then demoted, it's just the most persistent and the only one
to have entered popular consciousness as a planet) are now consigned to
a new category of dwarf planets nicknamed 'plutons'.
However, the point you mentioned may have been an argument against
designating Pluto a planet on historical grounds, as it alludes to the
reason Pluto was adopted as a planet in the first place. Since it was
discovered, Neptune's erratic orbit was unexplained in the absence of a
modern understanding of gravitation and solar system formation, and so
at the time it was thought that the only way to explain its orbit was
the invoke a mystery 'Planet X' (yes, it should have been Planet IX,
but the X stands for a mystery rather than 'Planet 10'). Pluto was
ultimately the result of this search, but it was known as soon as it
was found that it couldn't be the hoped-for Planet X because it
couldn't have affected Neptune's orbit. Therefore, there are no valid
historical grounds for designating Pluto a planet.
Undeterred, for no very good reason people decided to call it a planet
anyway and, although new models of gravitation had made an extra planet
unnecessary to explain Neptune's orbit (and Mercury's - for a while
before Einstein, oddities in that planet's orbit had led to a search
for a mythical 'first planet' nicknamed Vulcan), the idea of a 'real'
Planet X (which this time actually would be the tenth planet) did the
rounds in science fiction for a while. It's come back recently among
serious astronomers, but not as a large object affecting Neptune's
orbit, and number 10 (well, 9 again) won't be anything special if it's
found. There was a New Scientist article recently suggesting that there
could well be Mars-sized KBOs, and possibly planet-sized objects
outside the Kuiper Belt, too far for us to detect at present but still
within the solar system, that a back-of-the-envelope calculation (or at
least a guess) suggests may number a dozen or more.
Anyway, with Bellerophon, Methuselah and the legion of so-far-unnamed
planets outside our solar system, there are more than enough planets to
go around without adding any more in our system. At this rate we'll be
in danger of running out of Greek and Roman deities - there are only a
couple left, with a lot of the asteroids named after them (the most
being Quirinus, the patron god of the city of Rome, the only major
Roman deity not represented by a planet, satellite or asteroid).