Many of the arguments I’ve read online are making a mockery of this debate, both pro and con. I have read logically fallacious appeals to tradition, arguing that Pluto should remain a planet because that’s what we were taught in school and that’s the way it has been for 76 years. On the other side of the aisle, I am reading equally spurious logic that there are enough planets and the fact that we will certainly discover more means there will eventually be too many. The media seems to simply be accepting the change as if the IAU were an authority instead of a collaboration of experts.
I’m telling you: Don’t start rewriting the textbooks yet.
The original definition was simple. In order for a celestial body to qualify as a planet, it must (1) have sufficient mass to pull it into a relatively round shape and (2) orbit the sun rather than orbit another planet.
The original draft defining planets not only included Pluto, but Ceres, UB313 (aka. “Xena”), and Pluto’s companion Charon. Charon was included because its orbital center of gravity is between it and Pluto, where Earth’s Moon would not qualify because the center of gravity is inside the Earth. The Moon orbits the Earth, Pluto and Charon orbit each other.
Pretty simple, huh?
Then, on the last day of the Prague conference, a minority of astronomers voted to add one more clarification to the definition. The new criteria requires (3) the celestial object have “cleared the neighborhood around its orbit.” According to this new definition, Pluto is not a planet because its orbit crosses Neptune’s orbit, it is instead a “Dwarf Planet” or “Pluton.”
This new criteria simply doesn’t make any sense. It is vague, inconsistent, and unscientific. The logic would work both ways. If Pluto hasn’t cleared Neptune of its orbit, then doesn’t that mean Neptune, a gas giant 17 times the mass of Earth, is a “Pluton” for crossing paths with Pluto? Does the Earth cease to be a planet whenever an asteroid flies past it? Did Jupiter stop being a planet while the fragments of comet Shoemaker-Levy 9 pummeled it? What about other solar systems? A young solar system can have gas giants larger than Jupiter sharing an orbit with massive amounts of space-debris. It could take millions to billions of years for these enormous celestial bodies to clean up their orbital paths. What happens if astronomers observe a celestial body as meeting this criteria, but then later discover other objects in its orbital path? With our perpetual advances in astronomical observations, we will have objects falling in and out of “Planet” status all the time.
Where are the concrete numbers in this third criteria? There is no ratio of orbital-length to acceptable amount of debris in the orbit for an object to qualify as a planet. What about mass ratios? How much more massive must one body be to another in the same orbit for the smaller object not to count as debris?
This criteria has raised far more questions than it has answered, and the answers to these questions will require such volumes of technical jargon to define them as to only make matters worse. The scientific principle of Occam’s Razor advises minimalism and simplicity in scientific theories. It is the K.I.S.S. (Keep It Simple Silly!) method for scientists, and the IAU’s third criteria completely flunks this principle. It’s as if this were an attempt by the IAU’s academics to make their field so complex as to exclude all but the most pedantic of intellectuals, when they should be opening the field to more amateurs in the interest of popularizing Astronomy.
Of the IAU’s 10,000 members, only 4% were present for the vote, which was cast on the last day of the conference after many members had already left. The vote was essentially hijacked by a group of dynamicists, astronomers who study the motion and gravitational effects of celestial objects, who were offended that planetary geologists had so much influence on the previous week’s definition (source). Galileo must be spinning in his grave at this illogical and highly political decision.
The original definition added three new planets to our solar system, rather than eliminating a heavenly body we’ve accepted as a planet for 76 years—for the simple reason that it is round and orbits the sun. The new definition is confusing, illogical, and will muddy scientific waters at a time when we need to be making science more accessible to the public.
What’s more confusing: 12 Planets with the possibility of finding dozens more in our solar system? Or 8 planets, with 10-20 vaguely defined “Plutons.” Not to mention asteroids, comets, moons, Kuiper-belt, and Oort Cloud objects?
People must realize that this is not a so much a factual as a semantical debate. The English dictionary evolves and adapts to our evolving use of language. There is no reason an informed public cannot have a say in our shared understanding of what constitutes a “planet.” Carl Sagan said, “There are no authorities, at best there are experts.” The 400+ minority of IAU members who voted to demote Pluto are not an authority, and we don’t have to accept their spurious logic simply because of appeals to authority.
Pluto, Charon, Ceres, and UB313 all have sufficient gravity to pull them into a round shape and they do not orbit other planets; therefore, they are planets. There are 9,500 other astronomers who were not allowed to vote on this issue because they were not in attendance, making this a clear-cut case of “Tyranny of the minority.” The IAU must reinstate Pluto as a planet immediately before its credibility suffers and future generations of scientists look back on the 2006 conference as the day scientific integrity was abandoned because of intellectual hubris.
Getting Active
The Online Community is in the process of getting organized on this issue. In the meantime, you can sign one of the many online petitions and join the debate:
http://pleasesavepluto.org/
http://www.saveplanetpluto.org/
http://www.save-pluto.de/
http://savingpluto.org/
http://www.save-pluto.org/
http://www.save-pluto.net/
A Glimmer of Hope for Pluto
Reinstate Pluto as a Planet
Or you can write the IAU directly:
Counter Points:
From: Kevin Heider
Did Jupiter stop being a planet while the fragments of comet Shoemaker-Levy 9 pummeled it?
Actually this is one of the rules (clearing it’s orbit) that makes Jupiter a Planet and not a Dwarf Spheroid.
What’s more confusing: 12 Planets with the possibility of finding dozens more in our solar system?
Planets should be dominant objects in a solar system. Pluto does not dominate his fellow KBOs. And even the current definition allows us to find A LOT of planet with IF there mass is great enough to control their region of space. And yes, I am sure they will refine the defintion if we find a couple of grey areas with Planets roughly Mars size. The planet Neptune has 8600 times the mass of Pluto!! (the largest body that crosses its orbit and it not in direct orbit around Neptune.) This is why Pluto orbits in a 3:2 orbital resonance with Neptune. One of Nepune’s moons (Triton) is larger than Pluto, but we do not call it a planet because it orbits Neptune.
Or 8 planets, with 10-20 vaguely defined “Plutons.”
Not to mention asteroids, comets, moons, Kuiper-belt, and Oort Cloud objects?
Plutons and Plutinos (orbital resonance with Neptune) will be used regardless of how many Major Planets we define.
Asteroids, Comets, and KBOs will be around regardless of how many Planets we define.
There are 19 moons (7 BIG & 12 smaller) in the solar system that are worthy of being called planets, but we do NOT call them planets because they orbit around DOMINANT spheroids that we do call Planets.
Saturn moon Titan is a great example. With it’s thick Nitrogen atmosphere resembling what the Earth was probably like billions of years ago, it is the most EARTH-LIKE spheroid in the Solar System. Yet, by either propsed definition, it is a satellite, not a planet!
If they really want to be all inclusive they have to open up the defintion of Planet to include the current 19 moons that would be Planets except that they are not GRAVITATIONALLY DOMINANT in their orbit.
Food for thought.
— Kevin Heider
Counter Points
From: Kevin Heider
Did Jupiter stop being a planet while the fragments of comet Shoemaker-Levy 9 pummeled it?
Actually this is one of the rules (clearing it’s orbit) that makes Jupiter a Planet and not a Dwarf Spheroid.
What’s more confusing: 12 Planets with the possibility of finding dozens more in our solar system?
Planets should be dominant objects in a solar system. Pluto does not dominate his fellow KBOs. And even the current definition allows us to find A LOT of planet with IF there mass is great enough to control their region of space. And yes, I am sure they will refine the defintion if we find a couple of grey areas with Planets roughly Mars size. The planet Neptune has 8600 times the mass of Pluto!! (the largest body that crosses its orbit and it not in direct orbit around Neptune.) This is why Pluto orbits in a 3:2 orbital resonance with Neptune. One of Nepune’s moons (Triton) is larger than Pluto, but we do not call it a planet because it orbits Neptune.
Or 8 planets, with 10-20 vaguely defined “Plutons.”
Not to mention asteroids, comets, moons, Kuiper-belt, and Oort Cloud objects?
Plutons and Plutinos (orbital resonance with Neptune) will be used regardless of how many Major Planets we define.
Asteroids, Comets, and KBOs will be around regardless of how many Planets we define.
There are 19 moons (7 BIG & 12 smaller) in the solar system that are worthy of being called planets, but we do NOT call them planets because they orbit around DOMINANT spheroids that we do call Planets.
Saturn moon Titan is a great example. With it’s thick Nitrogen atmosphere resembling what the Earth was probably like billions of years ago, it is the most EARTH-LIKE spheroid in the Solar System. Yet, by either propsed definition, it is a satellite, not a planet!
If they really want to be all inclusive they have to open up the defintion of Planet to include the current 19 moons that would be Planets except that they are not GRAVITATIONALLY DOMINANT in their orbit.
Food for thought.
— Kevin Heider
Ryan Responds:
Hello Kevin,
Thanks so much for your counterpoints.
As far as moons go, the original criteria covered those. Moons are moons without the third criteria. As I mentioned in my article, Charon would become a planet under the first two criteria, despite the fact that we traditionally considered it Pluto’s moon, because the center of gravity is between Pluto and Charon and not inside one of them. The center of gravity between Triton and Neptune resides within Neptune; therefore, Triton is inarguably a moon of Neptune.
Of course, this definition raises another complication: What about stars that “wobble?” In recent years astronomers have detective massive planets by observing the gravitational influence they exert on their star. No one is suggesting these stars should be demoted to some lesser-star status because they are not the gravitationally dominant object in their solar system.
We define stars based on their immediately and easily observable physical characteristics. We have to because we lack the technology to observe the characteristics of their solar systems. Their gravitational dominance does not factor into the equation.
In the case of planets in other solar systems, we are indeed defining them planets based solely on their observable gravitational effects; however, these gravitational effects are strong enough to assure us the planet in question meets the first two criteria. We know absolutely nothing about whether or not these planets, which we cannot observe directly, have cleared their orbits.
You argue that Jupiter’s recent collision with comet Shoemaker Levy 9 strengthens Jupiter’s status as a planet because we are actively observing it clearing its orbit, but the definition specifically uses the word “cleared.” The object must have cleared its orbit. So Jupiter is still actively clearing its orbit. In fact, Jupiter’s orbit is one of the most cluttered in our solar system, as we can see in the many Trojan Asteroids that share its orbit.
So the third criteria inarguably fails. Jupiter is a planet and it has not cleared its orbit. It’s back to the drawing board for the IAU. They have flunked their science test and no amount of clarification will correct the problem.
To understand why they cannot refine their definition enough to correct the problem, we must look at Solar System Formation. Stars condense out of clouds of hydrogen, forming Stellar Disks. The planets condense out of these disks, sweeping their orbits clean, until the central star ignites and its solar winds push away the remaining dust.
So we must define an exact point in the accretion process when the object becomes a planet. I’m sure the IAU’s members are capable of establishing a sufficiently abstruse definition that will surely scare many budding amateur astronomers away from the field, but what they will not be able to provide is the technology and means required to accurately determine if a potential planet meets the criteria. Jupiter might obviously out-mass the asteroids that share its orbit, and 1 Ceres, the largest object in the asteroid belt, may not, but we must be able to accurately determine the mass of the potential planet and compare it to the mass of objects sharing its orbit. That is an impossible task when we are perpetually discovering more objects in these orbits.
The third criteria is being inconsistently applied, as we see in Jupiter remaining a planet. To make the third criteria work will require an unnecessarily complex definition. Whatever that definition, it will require observational techniques beyond our current capabilities to enforce it. The third criteria for defining a planet does not work and must be recalled.
Also, as my friend Kris points out, the band 2 Skinnee J’s has a song out stating that Pluto is indeed a planet. What more do you need?
More Counter Points
Hello Ryan;
As far as moons go, the original criteria covered those. Moons are moons.
You are right that moons are defined by their surrounding DOMINANT (more massive) Planet. But currently (for better or worse) we define both planets and moons by their surroundings.
You argue that Jupiter’s recent collision with comet Shoemaker Levy 9 strengthens Jupiter’s status as a planet because we are activelyobserving it clearing its orbit, but the definition specifically uses the word “cleared.” The object must have cleared its orbit.So Jupiter is still actively clearing its orbit.
Yes, the IAU needs to work on the wording, but the concept is sound. The proposal should have said the difference between a Planet and a ‘Dwarf Planet’ is: “and (c) dominates the neighborhood around its orbit clearing it of comparable objects.”
Comets are insignificant in comparison to a Planet. When you are the most massive, and thus most gravitationally dominant Planet, you will naturally attract the most objects.
All of the Planets and even the Sun are still clearing their orbits. What do you think a shooting star is? Meteor Showers are are caused by the Earth passing through cometary debris left behind by comets passing through the inner solar system. “Clearing the orbit” is and has to be an on going process.
Regardless of the definition of a Planet, let’s hope that the Earth does not clear it’s orbit of any 1+km objects in the foreseeable future. 🙂
In fact, Jupiter’s orbit is one of the most cluttered in our solar system, as we can see in the many Trojan Asteroids that share its orbit.
The Jupiter trojan asteroids (1826 of them) are kept at Lagrange points (that lie 60° ahead of and behind Jupiter in its orbit) were the gravitational pull of the Sun and Mighty Jupiter is balanced. Since they are held in position by Jupiter’s gravity, they can not be cleared from Jupiter’s orbit. A ‘Dwarf Planet’ like Pluto would not have enough gravity to trap so many ‘Small Solar System Bodies’.
we must be able to accurately determine the mass of the potential planet and compare it to the mass of objects sharing its orbit.That is an impossible task when we are perpetually discovering more objects in these orbits.
As we learn more about our solar system and other systems we will be able to infer with reasonable accuracy how much debris is between dominant Planets. I suggest reading Steven Soter’s 22 page article at:
http://arxiv.org/abs/astro-ph/0608359
Rather you agree with it or not, it makes for excellent reading.
Ceres, Vesta, Juno, and Pallas had their planetary status removed in the 1850’s because asteroids were becoming very common and they were not considered big enough. Yet modern technology has shown Ceres to be a spheriod. See:
http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html
I believe we are much better off today than were back when Planets were known as wanderers in the sky. Pluto is unfortunately a victim of technology. As our technology became better we realized that Pluto was not 6.6x more massive than the Earth as “Lowell required Planet X to have seven Earth masses to produce the effects on the other planets”. But Pluto turned out to be 500x less massive than the Earth. Pluto does not effect the orbit of Neptune as was originally assumed in 1930. Pluto just happened to be a wandering object in the right place, at the right time. Pluto was made a Planet in haste.
— Kevin Heider