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Dwarf
Planets
In
August of 2006 the IAU ( International Astronomical
Union) redefined the term planet and created a class
called dwarf planets. According to the IAU: A dwarf
planet is a celestial body that (a) is in orbit
around the Sun, (b) has sufficient mass for its
self-gravity to overcome rigid body forces so that
it assumes a hydrostatic equilibrium (nearly round)
shape,
(c) has not cleared the neighborhood around its
orbit, and (d) is not a satellite.
In the last ten years many Pluto like objects have been
discovered out past Neptune. This created the problem of
how to include them into the family of planets and of
having to name perhaps hundreds or thousands of such
objects that might eventually be discovered. One, now
officially called Eris, is slightly larger than Pluto!
In the next lab you'll see its orbit.
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For those trans-Neptunian objects that don't meet the
dwarf planet definition they will be part of the class
of "Small Solar System Bodies". But all trans-Neptunian
objects including Pluto and Eris also form a class
called "Plutonian Objects". Getting confused? Reality is
not always neatly compartmentalized! |
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VIEW MOVIE
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Pluto
Mass = 0.0026 Earths
Diameter = 2,190 km (60% of the moon!)
Density = 2.1 g/cubic cm
Plutonian day = 6.3867 Earth days
Distance from Sun = 39.3 AU
Pluto
has a composition that is very similar
to the larger satellites of Jupiter
and Saturn. Pluto also has a moon,
Charon, that is more than half its
size. If we stood on the surface of
Pluto, Charon would be as large as
eight of our moons side by side in
the sky.
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Small Solar
System Bodies
All objects
orbiting the sun that don't meet the
definitions of planet or dwarf planet are
now called Small Solar System Bodies.
These currently include most of the Solar
System asteroids, most Trans-Neptunian
Objects (TNOs), comets, and other small
bodies. This according to the IAU.
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Pluto
was the odd-ball of the planets. If it were discovered today, we would not call it a planet. It does not have a composition
similar to any of the other planets. In fact, it has a composition that is very
similar to the larger satellites of Jupiter and Saturn. Pluto also has a moon, Charon, that is more than half its size. If we stood on the surface of Pluto, Charon would be as large as eight of our moons side by side in the sky.
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