Is Pluto a Planet Once Again?

A recent debate by Harvard scholars has many astronomers and space science enthusiasts asking, is Pluto a planet once again?

After being sent into planetary limbo for years, Pluto may reclaim its status as a planet once again. The Harvard-Smithsonian Center for Astrophysics recently hosted a public debate between three experts on the issue. The panel consisted of Dr. Owen Gingerich, chair the IAU planet definition committee (the body that originally declassified Pluto’s planetary status), Dr. Dimitar Sasselov, who serves as the director of the Harvard Origins of Life Initiative, and the associate director of the Minor Planet Center, Dr. Gareth Williams. Each of the three held a specific definition on what constitutes a planet, and whether Pluto should be a planet once again.

Dr. Gingerich maintained that the word “planet” itself held some sort of a cultural connotation and, therefore, Pluto should be a planet again if the general population deemed it to be. Dr. Sasselov took a much more scientific stand, arguing that the most accurate definition of a planet would be any major mass that orbited or formed around a star; since Pluto is a mass that orbits the sun, it should be classified as a planet once again. Lastly, Dr. Gingerich maintained the IAU’s original definition of a planet should prevail which would, in his opinion, mean that Pluto should not be a planet once again.

After the panel discussion, those in attendance were asked to vote on which definition that they felt was the most accurate and to determine Pluto’s status. The overwhelming majority agreed that Dr. Sasselov’s position was the most accurate and, to the delight of Pluto enthusiasts everywhere, believe that the tiny little mass should indeed be declared a planet once again.

But how did Pluto lose its planetary status to begin with? In 2006, the IAU (International Astronomical Union) chose a set of criteria to define what they believe constitutes a planet. They came up with a set of three standards.

  1. It must orbit a star (and can not be a star itself)
  2. It must have a spherical shape, being round or nearly round
  3. It must have claimed the space in it’s own orbit (that is to be the largest object in it’s own orbital neighborhood).

The problem for Pluto is that although it clearly met the first two criteria, Pluto may not the largest object in its own neighborhood. Questions on that last criteria may be what leads Pluto to being declared a planet once again. In 2005, the discovery of Eris, which was considered a possible tenth planet, brought Pluto’s status into question. Eris was believed by some to be about 27 percent more massive than Pluto. This prompted the IAU to chose a standard definition for the word “planet,” and Pluto lost its status. But there is some doubt to whether the assumed measurements for Pluto and Eris are correct, and with the large consensus preferring a different definition, Pluto may indeed reclaim its status as a planet once again. Eris could also be declared as the tenth planet once again as well.

In July of 2015, the spacecraft New Horizons will visit Pluto, giving us the first glimpse in known history of this far away celestial body. This will bring new information to light that is likely to end the debate and finally, officially, declare Pluto a planet once again. Head researcher for the New Horizons mission, Alan Stern, stands firmly behinds Pluto’s planetary status, and felt that IAU were out of line in attempting to create the definition in the first place, telling CNN, “It’s a matter for planetary scientists, not astronomers.”

Public opinion seems to agree with Stern. Do you think that Pluto should be a planet once again?

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