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.
— Lucy “very stable genius” Stone (@oxfordsemicolon) September 10, 2018
A new study by University of Central Florida alumnus Philip Metzger, however, is calling the IAU’s assessment of Pluto into question.
The debate is back and @DrPhiltill's new research is suggesting that Pluto is indeed a planet
Thoughts? We want to hear them https://t.co/7NbatGo8iN
— UCF (@UCF) September 6, 2018
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?
This take is interesting; it's not just being a writer being nostalgiac for Pluto. He makes a valid argument that the “planet” definition needs to be better and unanimously defined. https://t.co/HhkuMWuyba
— KROQ's Bean (@clydetombaugh) September 11, 2018
— Planet Green (@PlanetGreen) September 11, 2018
Pluto is most definitely a planet — and should never have been downgraded, say some scientists – CNN-So great to hear Pluto May come back. The only planet with a famous dog named after it! Great opportunity to involve interested kids! Use #bringbackpluto https://t.co/2t9O3oWOIS
— Stephanie Harvey (@Stephharvey49) September 11, 2018
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.”
my favorite part about this defense of pluto as a planet is when the researchers basically called mars a basic bitch pic.twitter.com/T90uvNaE5u
— emma lord (@dilemmalord) September 10, 2018
Oh Pluto. Could it be? Could we, mere humans, welcome you back as a REAL Planet to Our Little Solar System? @UCF Planetary Scientist says old data affected decision to call Pluto a 'dwarf planet' and its time Pluto came back to the Big Leagues. @WFTV pic.twitter.com/tvPRds4k14
— Jamie Holmes (@JHolmesWFTV) September 11, 2018
Pluto. A planet?
— Brad Hicks (@BradHicksFox6) September 11, 2018
— J.Clark (@BL00DYKILLS) September 11, 2018
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?
To be honest, I still consider it a Planet. Totally forgot it wasn’t one anymore
— Tyler Livesey (@Tyler_Livesey) September 11, 2018
LEAVE PLUTO ALONE pic.twitter.com/x8O8R2Xn8Q
— tommy (@Chelstastico) September 11, 2018
— Buster5ive (@Buster5ive) September 11, 2018
Of course Pluto is still a planet. And if u'r a true Chicagoan, it's still the Sears Tower. STOP PLAYIN' WITH ME, PEOPLE. pic.twitter.com/pKsgDZkHER
— Purple Rainstorm ☔ (@PrinceScrapbook) September 11, 2018
Finally some good news.
— Jake Gerber (@Gerber982) September 11, 2018
Stop sleeping on Pluto
— Izzy Icon (@IzzyStayBusy) September 11, 2018
Let’s see if we will. How exciting!