The Debate Over Pluto’s Planetary Status: Scientists Weigh In
In 2006, the world bid farewell to many notable figures, including actress Shelley Winters, soul icon James Brown, and naturalist Steve Irwin. However, it also lost a planet—Pluto. Discovered in 1930 by American astronomer Clyde Tombaugh, Pluto quickly captured the public’s imagination and became beloved for its association with Mickey Mouse’s pet dog. But in 2006, CalTech professor Mike Brown controversially stripped Pluto of its planetary classification, sparking a heated debate that continues to this day.
To commemorate the 94th anniversary of Pluto’s discovery, a discussion was held with Mike Brown and Philip Metzger, a retired planetary physicist at NASA’s Kennedy Space Center. They represent opposing sides of the Pluto/No-Pluto argument. Brown, known for his book “How I Killed Pluto and Why it Had it Coming,” argues for reducing Pluto’s significance and focusing on new discoveries like the yet-unconfirmed “Planet Nine.” Metzger, on the other hand, believes Pluto should be reinstated as a planet, claiming that the International Astronomical Union (IAU) violated its own bylaws when downgrading Pluto’s status.
The debate centers around the criteria for planet status. According to the IAU’s 2006 decision, a planet must orbit a star directly, be large enough to pull itself into a round shape through gravitational rounding, and gravitationally dominate its orbit by clearing the neighborhood of other bodies. While Brown argues that Pluto doesn’t fit these criteria and astronomers were forced to acknowledge this reality, Metzger contends that the IAU’s definition is flawed and that scientists should use a taxonomy that aligns with theories rather than relying on astrological-based classifications.
The debate also delves into the question of whether our attachment to Pluto is rooted in a desire for symmetry. Brown dismisses this notion, stating that astronomers were willing to add new planets if necessary, but the pro-Pluto faction’s attempt to change the definition of a planet was misguided. Metzger adds that the fixation on a specific number of planets is cultural rather than scientific, and it contradicts the dynamic nature of the cosmos.
The discussion also touches on the search for “Planet Nine,” a hypothetical planet that could explain certain phenomena observed in the outer solar system. Brown acknowledges that while it remains a hypothesis until directly observed, it offers the best explanation for these phenomena. However, he emphasizes that it is not intended as a replacement for Pluto.
Ultimately, the attachment to Pluto stems from its unique characteristics and the awe-inspiring images captured by the New Horizons spacecraft during its flyby. Metzger describes Pluto as geologically diverse, with mountains, glaciers, a layered atmosphere, and possibly an underground ocean. He argues that Pluto is not only a planet but also the most planet-like planet, resembling Earth more closely than any other celestial body. Brown admits to having an attachment to Pluto, acknowledging its mysterious allure and cool aesthetic.
The debate over Pluto’s planetary status continues to captivate both the scientific community and the public. While scientists like Mike Brown argue for redefining our understanding of planets based on new discoveries, Philip Metzger advocates for a broader perspective that embraces the dynamic nature of the cosmos. As our understanding of the universe evolves, so too does the debate over what constitutes a planet.
