ever since is discovering 1930 Pluto has
always considered something of an
oddball planet compared to the others
for one its orbit is inclined by about
17 degrees compared to the other planets
in our solar system not only is Pluto's
orbit inclined but its orbit intersects
Neptune's in fact from 1979 to 1999
Pluto was closer to the Sun than Neptune
was when its moon Charon was discovered
in 1978 it became clear that Pluto had
another unique characteristic rather
than remaining relatively stationary
while Charon orbits Pluto and Charon
orbit a common center of gravity called
a bury center located outside of Pluto
surface in recent years new observations
show that Pluto was simply one of over
70,000 large objects each more than 100
kilometers across scattered in a vast
outer region known as the Kuiper belt as
telescopes grew larger and more powerful
astronomers began discovering larger and
larger bodies in the Kuiper belt
in 2003 Jaleo was discovered measuring
only a little smaller than Pluto it even
had two moons of its own in 2005 another
object designated Makemake was
discovered to be only a little smaller
than Pluto
astronomers realized that it was only a
matter of time before an object larger
than Pluto would be discovered in the
Kuiper belt
sure enough in 2005 astronomer Mike
Brown dropped the bombshell Braun and
his team announced the discovery of Eris
an object that orbited farther and was a
little bit larger and more massive than
Pluto itself meanwhile Pluto is
continuing to turn up surprises of its
own in 2005 two new moons Nix and Hydra
were discovered Pluto was seeming less
like a traditional planet and more like
a collection of objects all orbiting the
same center of gravity all of these
discoveries led astronomers to question
the very definition of a planet and so
in 2006 at the 26th General Assembly of
the International Astronomical Union a
vote was taken to officially define a
planet as an object that meets the
following criteria
first it needs to be in orbit around the
Sun obviously Pluto meets this criteria
second it needs to have enough
gravitational pull to bring itself into
a spherical shape granted no planet is
perfectly spherical compared to say a
lumpy asteroid Pluto fits that criteria
as well third it needs to have cleared
the neighborhood of its orbit and this
is where Pluto has a problem you see as
the planets formed they became the
dominant object in their orbit around
the Sun over billions of years any other
objects in the same orbit either
collided with and became part of the
planet or were simply ejected out of the
planet's orbit entirely for example
earth is 1.7 million times the mass of
any other object in its orbit but Pluto
is hardly alone in its orbit around the
Sun it's only just one of 70,000 large
objects in the Kuiper belt and accounts
for less than 1% of the total mass of
the debris in its orbit and so Pluto
Eris Makemake and habeo along with Ceres
in the asteroid belt were redesignated
as dwarf planets since they meet the
first two criteria fortunately Pluto is
hardly forgotten the New Horizons
spacecraft launched in 2006 will fly
past Pluto in 2015 giving humanity its
first ever direct limps at this distant
world following its flyby
New Horizons will press on to explore
the outer Kuiper belt it help us better
understand this unexplored region of our
solar system though it is no longer
considered a traditional planet Pluto
has opened a new chapter in our
understanding of our solar system and
now seventy years after its discovery we
are just beginning to understand it
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