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Posted by Henry Spencer on November 1, 2005, 12:35 am
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>It does show that Pluto should have a different orbit than when
>considering the first moon alone.
Not very different, given that the new ones are much smaller and much
farther out.
>I've seen an speckle interferometry plot from the Charon discovery
>and it does indicate as many as 6 moons when this new data is taken into
>account.
Note that these two were discovered by a thorough search of the full
volume of space in which moons could be gravitationally bound to Pluto.
If there are any more, they're much smaller yet.
>These are tiny moons as pluto is pretty small, but together they explain
>why Pluto was thought by early observations to be a much bigger planet.
Not really. These two new ones are so faint that they simply weren't
detectable by early observations; they wouldn't have influenced estimates
of the system's size. And in any case, those estimates were based on
indirect evidence, not on imaging of what people thought was a disk; it
simple wasn't possible to resolve the system then.
The main reason why Pluto was long thought to be much bigger was simply
that people thought there were unexplained anomalies in the orbits of
Uranus and Neptune, and one of the attempts to analyze those predicted a
planet in roughly the place where Pluto was found. To have any effect on
Uranus and Neptune, Pluto had to be much more massive, and thus larger.
(Although the matter is not quite fully settled, the current best estimate
is that when you correct for a long-standing small error in the mass of
Neptune -- rectified when Voyager 2 measured it directly -- there *are*
no unexplained perturbations of the outer planets.)
>The finding of asteroids with multi-moon systems seems to show that
>in this kind of belt or near it there are a lot of smaller objects
>that the larger objects can capture ( these are the special ones that
>haven't crashed into the surface.)
The problem is that there's no obvious mechanism by which such captures
might take place. Last I heard, there's still a lot of debate about the
origin of such moons, especially the ones in nice circular equatorial
orbits like these; it is not clear that they're captured.
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spsystems.net is temporarily off the air; | Henry Spencer
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