Pluto is a frigid world located billions of miles from Earth and is 30 times less massive than Mercury. According to the International Astronomical Union (IAU), Pluto has five satellites whose largest moon, called Charon, measures half its size. The view of the Solar System changed since the discovery of Pluto in what was called the transneptunian region, an area beyond Neptune.
But with so many Trans-Neptunian Objects (TNOs) in that region, astronomers also found some more massive objects than Pluto. With that being said, members of the IAU begin to ask themselves what could constitute a "planet"?
Pluto Demoted 15 Years Ago
The IAU is responsible for naming planetary bodies and their moons since the early 20th century. IAU President Ron Ekers explains that the union establishes conventions intended to help understand astronomical objects and their processes.
They created committees that gather information from a broad scientific interest with insights from astronomers, planetary scientists, science publishers, and historians. The union's Planet Definition Committee was formed and prepared a draft resolution that explains the true definition of a planet.
By 2006, in the IAU General Assembly in Prague, the new definition of a planet slowly took shape. Then on August 14, 2006, the new definition was voted at the Closing Ceremony wherein its members voted that the resolution on the definition of a planet in the Solar System will be changed, leaving Pluto out.
According to Space.com, researcher Mike Brown from the California Institute of Technology (Caltech) remarked that the decision had rendered Pluto dead. Finally, there are only eight official planets in the Solar System.
The decision was made after 424 astronomers voted in favor of the resolution. Alan Stern, leader of NASA's New Horizon's mission to Pluto, said that he is embarrassed for astronomy with only less than 5% of the world's astronomers voted. Stern told Space.com that the definition stinks for technical reasons.
Other astronomers have criticized the decision as well. However, science is not sentimental. It does not care whether many people are fond of it or whatever mnemonics children have learned in school. The revision has enabled many scientists to learn more about the Solar System and the universe.
What is a Planet?
It was 15 years ago when Pluto was demoted when the IAU released a new definition of what constitutes a planet. As Science News reported, the IAU's definition of a planet required that an astronomical body to (1) orbit the sun, (2) have enough mass to be spherical or close to that, and (3) have a clear neighborhood in its orbit.
Astronomical objects that meet the first and second criteria but not the third criterion will not pass as a planet. This is the case with Pluto, which is now designated as one of the "dwarf planets" in the Solar System.
Astronomer Catherine Cesarsky of CEA Saclay in France, whos IAU president in 2006, said that she believes the decision was the correct one, noting the oddness of Pluto from the eight planets would make it difficult to keep up with the changing number of solar system planets where more massive objects than Neptune were being discovered.
She clarified that the definition was not intended to demote Pluto but rather to promote a prototype of new astronomical objects in the Solar System that have great importance and interest.
Check out more news and information on Pluto in Science Times.
