Is Pluto A Planet Once Again?

Social media has lit up this week with rumors that Pluto has been restored to its status as a planet. Is this true or false?

It’s not true.

Pluto’s status was recently debated in Cambridge Massachusetts, and the consensus upon the conclusion of that debate is that Pluto should be classified as a planet. That consensus, however, was not reached by an entity in charge of such a classification.

In other words, it wasn’t an official decision.

Harvard Debate

The rumor started from a debate on the topic reported on September 22, 2014 by Harvard-Smithsonian Center for Astrophysics. The debate occurred on September 18 among three planetary science experts who presented their thoughts on the question: “What is a planet?”

Harvard astronomer Owen Gingerich asserted that Pluto is a planet, and that “a planet is a culturally defined word that changes over time.” Dr. Dimitar Sasselov of the Harvard Origins of Life Initiative argued that a planet is “the smallest spherical lump of matter that formed around stars or stellar remnant,” meaning that Pluto should be called a planet. Gareth Willliams of the IAU’s Minor Planet Center argued against Pluto’s planetary status, stating, “Jupiter has cleared its neighborhood. Earth has cleared its neighborhood. Ceres, which is in the main asteroid belt, hasn’t. Pluto hasn’t. In my world, Pluto is not a planet.”

At the conclusion of the debate, the audience voted on the definition of a planet and whether or not Pluto should qualify for this classification.

The result of this unofficial vote: Pluto is a planet.

Pluto as a Planet

The solar system’s 9th planet was discovered in 1930 and retained that classification until 2006 when the International Astronomical Union (IAU) redefined Pluto as a “dwarf planet.” The resolution which “demoted” Pluto held that planets must meet the following criteria:

• The object must orbit the Sun.
• The object must be large enough to be a sphere by its own gravitational force.
• The object must have cleared the neighborhood around its orbit.

Although Pluto meets the first two criteria, it does not meet the third. For this reason, Pluto was reclassified as a dwarf planet.

2015 Encounter

One possible reason for renewed interest in the classification of Pluto is the planned 2015 approach by the New Horizons spacecraft. That flyby will mark the first time that Pluto has been visited by a man-made craft, and will deliver scientists their first-ever closeup look at the dwarf planet.

New Horizons was launched in January 2006 – eight months before Pluto’s demotion. Representatives from that project derided the decision to reclassify Pluto.

2008 Debate

The 2014 Harvard debate is not the first on the matter. A high-profile debate also occurred back in 2008 at Johns Hopkins University. Dubbed “The Great Planet Debate,” the two-day conference included a moderated debate among Neil deGrasse Tyson and Mark Sykes.

The conclusion of that debate, according to a press release, was that, “No consensus was reached.”

Bottom Line

A recent debate highlighted the belief by some that Pluto should regain its status as a planet. The conclusion was not a binding decision by any official entity, and at this time Pluto remains a dwarf planet.