from UniverseToday Website
but we created a cool video (far below)
to go along with it yesterday
Only 22 at the time, Tombaugh was given
the laborious task of comparing photographic plates. These were two
images of a region of the sky, taken two weeks apart. Any moving
object, like an asteroid, comet or planet, would appear to jump from
one photograph to the next.
Because they had discovered it, the
Lowell team were allowed to name it. They settled on Pluto, a name
suggested by an 11-year old school girl in Oxford, England (no, it
wasn't named after the Disney character, but the Roman god of the
The most accurate measurement currently
gives the size of Pluto at 2,400 km (1,500 miles) across. Although
this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto
is tiny, but it was considered larger than anything else past the
orbit of Neptune.
Instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt.
This region extends from the orbit of Neptune out to 55 astronomical units (55 times the distance of the Earth to the Sun). Astronomers estimate that there are at least 70,000 icy objects, with the same composition as Pluto, that measure 100 km across or more in the Kuiper Belt.
And according to the new rules, Pluto
is not a planet. It's just another Kuiper Belt object.
2005 FY9, discovered by Caltech
astronomer Mike Brown and his team is only a little smaller
than Pluto. And there are several other Kuiper Belt objects in that
They had discovered an object, further out than the orbit of Pluto that was probably the same size, or even larger. Officially named 2003 UB313, the object was later designated as Eris.
Since its discovery, astronomers have determined
that Eris' size is approximately 2,600 km (1,600 miles) across. It
also has approximately 25% more mass than Pluto.
What is Eris, planet or Kuiper Belt Object?, what is Pluto, for that matter?
Astronomers decided they would make a
final 'decision' about the definition of a planet at the XXVIth
General Assembly of the International Astronomical Union, which was
held from August 14 to August 25, 2006 in Prague, Czech Republic.
One version of the definition would have actually boosted the number of planets to 12; Pluto was still a planet, and so were Eris and even Ceres, which had been thought of as the largest asteroid.
A different proposal kept the total at 9, defining the planets as just the familiar ones we know without any scientific rationale, and a third would drop the number of planets down to 8, and Pluto would be out of the planet club.
But, then… what is Pluto?
Is Pluto a planet? Does it qualify?
For an object to be a planet, it needs to meet these three requirements defined by the IAU:
What does "cleared its neighborhood" mean?
As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit.
The Earth, in comparison, has 1.7
million times the mass of the other objects in its orbit.
At least now you know why Pluto was demoted: