New Study Could Provide The Strongest Argument As To Why Pluto Should Still Be Considered A Planet

Pluto lost its planet status in August 2006 after the International Astronomical Union (IAU) decided it did not meet three major criteria for being a full size planet. The criteria are:

  • It must be an object which independently orbits the Sun (this means moons can’t be considered planets, since they orbit planets)
  • It must have enough mass that its own gravity pulls it into a roughly spheroidal shape
  • It must be large enough to “dominate” its orbit (i.e. its mass must be much larger than anything else which crosses its orbit)

Pluto, being so small, was not able to dominate its own orbit.  

A new study by University of Central Florida alumnus Philip Metzger, however, is calling the IAU’s assessment of Pluto into question.

According to Metzger, the IAU’s reasoning is not supported in research literature.

Metzger says of the IAU’s definition of a planet:

It’s a sloppy definition. They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.

Oh, snap. So Pluto was disqualified for the same reason EARTH could be disqualified. But…Earth is a planet, right? I mean, how do we know?

Metzger addresses that too.  What should define a planet?

According to UCF, Metzger believes that “the definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet’s orbit.”

“Dynamics are not constant, they are constantly changing,” Metzger says. “So, they are not the fundamental description of a body, they are just the occupation of a body at a current era.”

Do any of the current criteria fit his idea?  Well, yes: one.  

“It must have enough mass that its own gravity pulls it into a roughly spheroidal shape.”

“And that’s not just an arbitrary definition,” Metzger says. “It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body.”

Metzger also has a fondness for Pluto as a planet, because Pluto is “more dynamic and alive than Mars.  The only planet that has more complex geology is the Earth.”

The IAU has yet to comment on the challenge to their 12-year-old decision. Is it possible we will see Pluto demoted and promoted in its planetary journey twice in one lifetime?

Let’s see if we will. How exciting!

H/T: UCF, Library Of Congress