New research: Pluto should be reclassified as a planet

Back in 2006, the International Astronomical Union determined that the definition of a planet is one where a body must “clear” its orbit. This means to be classed as a planet the object must be the largest gravitational force in its orbit. The International Astronomical Union acts as the internationally recognized authority for assigning designations and names to celestial bodies (like stars, planets, asteroids) and any surface features on them.

This new definition has consequences for Pluto. This is because Neptune’s gravity influences Pluto, and Pluto shares its orbit with frozen gases and objects located within the Kuiper belt. Pluto’s current designation is as a dwarf planet, which is defined as a planetary-mass object that is neither a true planet nor a natural satellite and which has not cleared the neighborhood of other material around its orbit. The 2006 decision relating to Pluto has proved controversial ever since.

The Pluto system as we know it today. Four small moons–Styx, Nix, Kerberos and Hydra, orbit the central “binary planet” comprising Pluto and its large, nearby moon Charon.

NASA/STScI/Showalter

In a new study University of Central Florida researchers state that the definition adopted for classifying planets is unsuitable and consequently Pluto should be reclassified as a planet. According to Dr. Philip Metzger, from the university: “We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it’s functionally useful.”

As a new way forwards, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape. Metzger presents the case for Pluto’s complexity, stating that the planet has many features of interest, including an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons.

Pluto By Moonlight: On July 14, New Horizons mission scientists will soon obtain the first images of the night region of Pluto, using only the light from Charon, itself softly illuminated by a Sun 1,000 times dimmer than it is at Earth.

JHUAPL / SwRI

This position is, however, challenged by planetary scientist Mike Brown, who was involved with the original decision to declassify Pluto. Dr. Brown, according to Space.com, is not impressed arguing that “those who want Pluto to be considered a planet are simply searching for whatever rationales they can get their hands on.”

The research has been published in the journal Icarus. The research paper is titled “The Reclassification of Asteroids from Planets to Non-Planets.”