Sunday, January 13, 2013

Why Pluto isn't a planet?

Pluto was originally discovered in February of 1930 by Tombaugh and publicly announced in March of 1930. However, after the International Astronomical Union (IAU) formally defined a planet, it was demoted from its planet status in 2006.

The IAU defines a planet as,
1. Should orbit around the sun
2. Should have sufficient mass to attain round shape (hydrostatic equilibrium)
3. Should clear the neighborhood of its orbit

Pluto failed the third criteria, since it has other objects in its orbital neighborhood such as Charon, Orcus and Ixion. Any object that clears the first two criteria and fails to clear the third criteria is called as a "dwarf planet". Pluto is now redefined as a dwarf planet.
The objects in Pluto's orbit, also called as Plutinos
Some people argue that Pluto should be called as a planet and called for the IAU to redefine the Planet criteria again. Lets see some comparisons that gives validity to Pluto's new status of "dwarf planet".

Pluto isn't even the largest dwarf planet

Dwarf Planets to scale, size wise, left to right - bigger to smaller
Below table shows the numerical data used in above diagram. Notice that there are larger dwarf planets than Pluto. Pluto isn't even the biggest dwarf planet. If Pluto is to be accepted as a planet, then Eris needs to be accepted as a planet before Pluto.

Dwarf Planet
Diameter (in KM)
Eris
2326
Pluto
2306
Makemake
1420
Haumea
1300
Ceres
974 

Pluto scores lesser than Earth's Moon

Pluto scores even lesser than Earth's Moon in terms of mass, radius and gravity (g).
Acceleration due to gravity (g) of solar system objects and planets compared visually in a graph

Mass of solar system objects and planets compared visually in a graph


Radius of solar system objects and planets compared visually in a graph

That settles it. Pluto is disqualified!

 

 The planets to scale. The infographic that inspired this post.


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