it's proven to be one of the most
divisive issues in modern science in one
stroke
thousands of textbooks were after date
in my role as public astronomer here in
Greenwich I'm always being asked about
Pluto why was it reclassified and if
it's not a planet anymore then what an
earth can it be right from its discovery
Pluto seemed different from the other
planets here at the Royal Observatory we
have records going back for hundreds of
years and some where we should have a
record of the discovery of Pluto 1917
that's too early 1987 much too late
Clyde Tombaugh had been set the specific
task of finding a planet so when he saw
his moving point of light in 1930 what
else was he going to think he'd found
here we have the president council and
Fellows of the Royal Astronomical
Society sending the Lowell Observatory
their heartiest congratulations on the
great discovery of the trans-neptunian
planet but trouble is brewing from the
word go
within weeks Pluto's status has been
called into question its eccentric orbit
and small mass set it apart from the
other planets more importantly some
scientists argue that Pluto might not be
alone over the decades
our ideas about the formation of the
solar system developed it was suggested
that the edge of the dust and gas cloud
from which our planets formed would have
been too spread out to condense into
planets instead there could be something
very different
scientists reasoned that there could be
hundreds of thousands of icy objects on
the edge of the solar system that had
failed to be incorporated into one of
the major planets they called this
region the Kuiper belt and Pluto status
as a planet started to be called into
question on the 5th of January 2005 came
the fatal blow scientists in California
discovered another small moving point of
light
this was Eris a world they believed was
bigger than Pluto this was huge news the
likelihood was there could be many more
large objects out there scientists were
faced with a choice either opened the
doors to potentially hundreds of new
planets or Pluto is for the chop
in 2006 the International Astronomical
Union put it to the vote and it wasn't
good news for Pluto the IAU decided that
a planet had to be an object in orbit
around the Sun that was massive enough
for gravity to squeeze it into a
spherical shape but also it had to be
gravitationally dominant and that meant
it must have cleared its surrounding
region of other similarly sized objects
but with everything else out there in
the Kuiper belt
this was Pluto's downfall so where did
this leave Pluto the IAU decided to
classify it as a dwarf planet too many
this was seen as a demotion but I'm not
so sure as a planet it was the last gasp
on the edge of the solar system but now
it's an exciting example of a brand-new
class of objects whatever we learned
from it will change the way we think
about our corner of the galaxy