Pluto May Become a Planet Once Again With a New Proposal

Wednesday, 22 February 2017 - 7:29PM
NASA
Solar System
Wednesday, 22 February 2017 - 7:29PM
Pluto May Become a Planet Once Again With a New Proposal
NASA
We're all familiar with the "Pluto is a planet" controversy - classified as a planet in the 1930s, sadly demoted to a "dwarf planet" in 2006, still the subject of heated debates amongst astronomers and laypeople alike. Now Alan Stern, head of NASA's New Horizons mission to Pluto, is out to change what it means to be a planet.

Stern and his team submitted a proposal to the International Astronomical Union (IAU) that could potentially add over 100 new planets to the solar system, including Pluto. Science Alert reports that the most important change in this new definition is how cosmic bodies in our solar system no longer need to orbit the sun to be classified as a planet; a potential planet's physical properties should be more important than its behavior around stars. Until this point, the IAU defined "planet" as follows:
Opening quote
A celestial body that (a) is in orbit around the sun (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit.
Closing quote


Under this definition, Pluto is not a planet because it has not "cleared the neighborhood around its orbit," being surrounded by icy space debris. But Stern is unsatisfied with this explanation - calling it, in no uncertain terms, "bullshit" in a 2015 interview with Tech InsiderStern and his team, in their proposal, outlined all the problems with the current definition (emphasis ours): 

Opening quote
"First, it recognizes as planets, only those objects orbiting the sun, not those orbiting other stars or orbiting freely in the galaxy as 'rogue planets.' Second, it requires zone clearing, which no planet in our solar system can satisfy since new small bodies are constantly injected into planet-crossing orbits... Finally, and most severely, by requiring zone clearing, the mathematics of the definition are distance-dependent, requiring progressively larger objects in each successive zone."
Closing quote


Stern also points out that the other official planets all have adjectives like "terrestrial," "giant" and "ice giant," and no experts would claim a giant planet isn't a planet. So making an exception for dwarf planets like Pluto feels like a discrepancy.

The definition that the team alternatively proposes is simple: "a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters." Put in less complex terms, "round objects in space smaller than stars" would all be considered planets. Yes, that means even our Moon would be promoted, along with Pluto and 110 other "round objects." 

Hopefully the IAU takes pity on poor Pluto and accepts Stern's new definition. We can't wait to welcome all the new planets in our solar system. 

Science
Space
NASA
Solar System