The Great Planet Standoff, What's Next for Pluto?

August 16, 2008

The Great Planet Debate here at the Johns Hopkins University's Applied Physics Laboratory in Maryland has been a seesaw of presentations between the two Pluto camps. But as expected there is no resolution. And, even if there was, the group of attending planetary astronomers is too small for it be called any kind of consensus in the astronomy community.

The camp called the  “dynamicists” is made up of those astronomers who want an object’s planetary status determined by how it gravitationally dominates its orbit by sweeping up debris.

Therefore, a planet’s location from its star is important. Does it reside in a debris disk like Ceres and Pluto, or has it gravitationally swept out a clear zone like Earth and Jupiter?

This is at the heart of the contentious International Astronomical Union  (IAU) definition for a planet. (By the way, the IAU definition only applies to planets orbiting our sun. To try and apply it to extrasolar planets is opening a Pandora’s box because exoplanets are so weird they would challenge the IAU planet definition. In wording the definition the authors did not want to alienate exoplanet astronomers, according to one attendee, because the IAU needed their votes.)

Critics say that the dynamical approach biases you to considering only the largest planets in a star system. Also, a strictly dynamical description would rule out Earth as a planet if it were in the Kuiper belt. A black hole orbiting a star could be called a planet by this definition.

The “geophysicists” camp instead wants a physical definition for a planet. This begins with an object in hydrostatic equilibrium. In other words, round. When an object has enough gravity pull itself into a sphere, it can be geologically interesting. It can be differentiated and have oceans (either on the surface or subsurface), an atmosphere, volcanic processes, and a biosphere. There are many geophysical commonalities among planets in diverse locations.

Alan Stern, the principle investigator on the New Horizons mission to Pluto, gave by far the most insightful and eloquent presentation. This got to the heart of the debate and it was much more informative than the earlier Tyson-Skyes faceoff which was science vaudeville at best.

Stern dismissed the dynamists’ arguments by asserting, “location is for realtors!” High density and low-density neighborhoods don’t diminish the intrinsic architectural qualities of a house.

Certainly stars are still stars regardless of where they live in the galaxy: in spiral arms, galactic core, or dense globular clusters.

Defining a planet by its physical description is less ambiguous, embraces diversity, and one doesn’t have to do a census of the planetary system. What's more, the planetary objects don’t need reclassification if you move them to a different orbit.

Stern argued for a “Captain Kirk” test for identifying a planet.

Imagine a Star Trek scene where Kirk and Science Officer Spock look at an undiscovered world on their view screen.

Kirk: “Tell me about this world, Spock.”

Spock: “Well captain, despite the fact it has clouds and oceans we don’t really know if it is a planet. We must fist make dynamical calculations and do supercomputer simulations to see if it dominates its orbit.”

Kirk: “Get real Spock!”

This approach would never work on the Enterprise or deter Kirk and crew from “exploring strange new worlds.”

The reality of the Kuiper belt has forced astronomers into a transition from a quaint classical solar system dominated by Jupiter to a more rambunctious Wild West environment where smaller planets are much more numerous and whirl around in elliptical, inclined orbits.

The meeting ended on a poignant note that put this whole debate into a larger, emotional perspective. Members of Clyde Tombaugh’s family were in attendance. Tombaugh discovered Pluto in 1930 and some of his ashes on on board the New Horizons craft.

The family’s attendance at the conference was like that of a love one wanting to find out how a family member died. They wanted to listen to what exactly happened to their beloved Pluto.  They related how the local community wanted to take Tombaugh’s name off of a school, street signs and other mementos following the IAU demotion. Learning that the IAU decision was a crafted by last-minute back room politics and hidden agendas, according to some speakers, could not have made them feel very good.

The sad thing is that if the IAU stuck with its original plan to keep Pluto a planet, the headline could have read, “Pluto Discoverer Tombaugh Found the Archetype of a Third Class of Planets in the Solar System.” The articles would have gone on to describe that Pluto was and oddball for 70 years. But When Kuiper Belt Objects (KBOs) were discovered Pluto logically fell into place. Observations of Kuiper belt structures around other stars show that the icy planets are the most common type of planet in the galaxy.

Instead, the dour story from the IAU conference was simply “Pluto ‘Dissed’.” Culturally, This flies in the face of our emphasis on inclusion and acceptance of diversity.

In hindsight the Pluto debacle is a textbook demonstration how some scientists are insular and out of touch with the impact of these decisions on the public. They dive into graphs and charts and nerdy details but don’t step back to see the cultural picture.

Pluto is a cultural icon. Demoting it was like shooting the dog Old Yeller in the 1957 Walt Disney movie. The word “planet” carries a cache’ and bestows importance. Calling it a Kuiper Belt Object sends people scurrying to the dictionary.

Pluto will remain in planet limbo as the standoff between astronomy camps simmers with no end in sight.

It’s very doubtful the IAU will revisit their vote, though some astronomers at the meeting want to petition for the IAU planet definition to be withdrawn. Many astronomers and college professors will ignore the Pluto demotion. But elementary and middle school teachers will be flustered as to how to describe Pluto as a KBO to students. It might be best used in teaching student how to “question authority.”

What is needed, which I discussed with planetary astronomer Heidi Hammel at the meeting, is to develop a classification scheme for all planets much like the classification scheme for stars

I alluded to this in a previous posting that described a 1966 Star Trek episode that had an alphabetical classification for planets. You might chart planet mass and distance from a star, among other parameters. Perhaps some alphabetical system could be developed for different planetary types. When you see a weird planet around another star you drop it into the chart and see what class it falls into: gas giant, rocky world, icy dwarf etc.   This would integrate planets into a coherent scheme.

The year 2015 will be “ The Year of the Dwarf Planets.” NASA's Dawn mission reaches Ceres, and the New Horizons probe flies by Pluto. We will see Pluto up close for the first time and it will become a real place and not just a dot on a scatter chart.

Like Kirk standing on the bridge of the Enterprise, we will behold a world and will intuitively know it is rightfully a planet.

As young adults in 2015, today’s elementary school children will say, “Oh I remember being taught Pluto wasn’t a planet, how silly.”

The Great Planet Debate will then become merely a footnote in science history.

Photos, top to bottom: Ray Villard; NASA

The Great Planet Debate Kickoff

August 14, 2008

The “Great Planet Debate” has kicked off here at the Johns Hopkins University Applied Physics Laboratory near Columbia, Maryland with some review and soul-searching.

At the start, participants largely agreed that all of the fuss leading to this meeting is simply over semantics -- the meaning of the word “planet.”

In hindsight, the feeling of some participants is that the International Astronomical Union "crossed the Rubicon" in trying to redefine a scientific term. This is unprecedented. (And the IAU will probably never try it again!) 

The IAU is the official world body for naming celestial objects. The IAU astronomers were motivated by simply trying to address how to name Kuiper Belt objects, of which Pluto is one of the largest members.

This backfired into a debate of where to draw the line on the number of planets in the Solar System. And, in a 12-hour revolt at the IAU’s August 2006 General Assembly, Pluto got kicked out as a full-fledged planet.

The other criticism is that this was not consensus-building at the IAU meeting, but rather an arbitrary, dogmatic vote. Folks also argue that a scientific definition can't be “voted on.”

Nevertheless, people admitted that the IAU must be recognized as the astronomical authority, otherwise there will be anarchy in astronomy education. And now the number of planets will vary widely from textbook to textbook.

My favorite anecdote from the meeting so far is from a chat I had with New Horizons Pluto mission lead investigator Alan Stern. “My son said there were nine planets on a test and the teacher marked him wrong!” he griped -- that’s because the state of Colorado education curriculum was revised following the IAU decision to demote Pluto to a dwarf planet.

Stern says "size doesn’t matter" when it comes to planets. Mice and elephants are mammals, and grains and boulders are part of a continuum. “It’s as if biologists grew up on a island with certain fauna. When they discover other plants on the mainland they refuse to include them in their definition of plants,” Stern says.

Early in this week's conference, two key planet definitions from the IAU resolution were discussed and debated:

1. that a planet must be big enough to have enough gravity to pull itself into a sphere, and
2. that a planet must be in an orbit swept clean of smaller debris -- the more contentious requirement, as Pluto is embedded in the Kuiper belt.

Hal Levison of Southwest Research Institute acknowledges that the big problem with the IAU definition is that Earth would not qualify as a planet if it were in the Kuiper belt.

Levison underscores that this is a hypothetical problem whereas the number of round planets is a challenge.

The problem with only using this definition of the “roundness” of an object is that all bodies in the Solar System, down to the size of Saturn’s moons Mimas, would be round. This would lead to 1,000 planets in the Solar System, says Levison. Try naming them all!

But I’d say this is a moot point when one considers the moons of Jupiter. Galileo discovered four major moons in 1609. Since then a total of 64 moons have been discovered.

Students aren’t required to know the names of all of Jupiter’s moons, and they are not terribly interesting or relevant. But there was never an IAU debate of what is a moon and what is not a moon. We even call man-made satellites "artificial moons."

When you look at the hierarchy, I would argue that scaling of the planets in the solar system by a fact of ten, to a total of 1,000 is not terribly unreasonable.

Levison argues for a more precise definition of a planet. But in another presentation educator Larry Lebofsky of the University of Arizona argued the many of these concepts are too esoteric for students. He wants a simple definition.

More to come . . .

Photos: Ray Villard

Pluto: Countdown to the Big Showdown

August 13, 2008

Think of whatever military standoff you can imagine: the Monitor vs. the Merrimac, the Spartans vs.the Persians, Napoleon at Waterloo, the North vs. the South at Gettysburg.

Just 50 miles from Gettysburg, here in the Maryland suburbs at the John Hopkins University's Applied Physics Lab, astronomers are drawing battle lines for a three-day conference entitled: "Great Planet Debate: Science as Process.”

You’ll have the Plutoid Promoters (who want to keep Pluto strictly second-class) vs. the Pluto Huggers (who want to reinstate Pluto's planetary status) duking it out. News stories, TV talk shows, and Internet blogs are building to this event like the lead-up to a prizefight.

For the past two years we’ve been waiting for the other shoe to drop on the hot debate over the status of cold, diminutive Pluto.

In 2006 the International Astronomical Union kicked Pluto out of the exclusive Planet Club and voted that there were only eight serious planets in the solar system. The demotion was decided on a vote by 424 astronomers out of approximately 10,000 professional astronomers around the world.

Why did they go after something that’s been in the astronomy texts for over 70 years?  Because an object even bigger than Pluto had been found in the outer fringes of the solar system. Some astronomers worried that they’d run out of fingers for counting planets if this got out of hand. So, enough was enough.

The public and especially school children, who just love underdog Pluto, decried the decision.   To many planetary astronomers the vote prematurely marginalized the class of objects that dwell in the largest piece of real estate in the solar system, the Kuiper Belt.

Round One in this battle actually started in 2000 when New York City’s American Museum of Natural History (AMNH) decided not to include Pluto in the planets display in its spanking new Rose Center.

Three AMNH staff astronomers thought that time was overdue to retool the solar system and drop Pluto because it lives in the Kuper belt, which is a cluttered and messy place with tens of thousands of sizable icy objects.

They skirted the issue of whether Pluto was truly a planet, it was simply described as a Kuiper belt object (KBO) in the exhibit. The AMNH astromers correctly predicted that larger KBOs would eventually be discovered, and that would make things even more confusing for Pluto's pedigree.

So the AMNH had a defacto solar system display of no more than eight planets. But the unilateral decision to marginalize Pluto like an unwelcomed  relative eventually got noticed by the New York Times.   Pluto's omission ultimately exploded with public derision. If any other museum had done this switcharoo nobody would have cared or paid much attention. But not the venerable AMNH, which historically has been “Astronomy ‘R Us” for the public.

Now we’re at Round Three at tomorrow's APL meeting. The first cannon fire already started on August 12 in a press release launched by Mark Sykes, Director of the Planetary Science Institute.

Sykes isn’t pulling any punches: "The IAU damaged the public perception of science by the high-profile spectacle of imposing, by vote, a controversial definition of a commonly used term. Too often, science is presented as lists of facts to be learned from authority, instead of the dynamic open-ended process that it really is. The IAU reinforced this misconception of science.”

Under a revised planet definition supported by Sykes, he is lobbying for our solar system to have 13 planets. The new members would be Pluto-Charon (a double planet), Eris (which is slightly larger that Pluto), Makemake, and Ceres, the largest member of the asteroid belt and a suspected Kuiper belt refugee.

On Thursday Aug. 14 Sykes will debate with Neil deGrasse Tyson of the AMNH, and host of NOVA Science Now. Since 2001 Tyson has been stoic -- though some might say obstinate -- in standing by the Pluto demotion in the face of withering public ridicule. To Pluto Huggers Neil is the Grinch that refused to add a Pluto ornament in the hallowed planet gallery of the Rose Center.

I’ll be reporting from ringside on Thursday.

Photos, top to bottom: Associated Press; American Museum of Natural History/Rose Center

What’s in a Name When You’re Just a Plutoid?

July 17, 2008

Composer Gustav Holtz’s magnificent orchestral suite The Planets has seven individual compositions for each of the solar system’s planets. There is Mars the Bringer of War, Jupiter the Bringer of Jollity, and Neptune the Mystic. Each movement is intended to convey ideas and emotions associated with the human psyche.

But would Holtz have been inspired to do compositions for planets with names like Quaoar, Eris, and Makemake?

The largest of the icy dwarf worlds on the outer rim of our solar system are being assigned names by the International Astronomical Union (IAU). The astronomers who discovered them have the right to pick a name and get it officially sanctioned by the IAU.

You’ll remember that the IAU recently categorized these Kuiper Belt Objects (KBOs) as Plutoids in a miserably failed PR attempt to placate Pluto huggers.

Pluto remains the only KBO that is named after a Roman god in accordance with the seven other major planets. Pluto is the Roman god of the Kingdom of the Dead – not the Walt Disney cartoon dog as so many school children think. The first two letters PL also are the initials of the astronomer who inaugurated the search for Pluto in 1915, Percival Lowell.

When Pluto’s moon Charon was discovered in 1976 I was hoping that the astronomer who uncovered it, James Christy, would call it Cerberus after the god of the underworld’s three-headed dog. A planet named after a dark lord and his pet monster was sure to captivate childrens’ imaginations. But nope, Christy has a wife named Charlene and her nickname is “Char.” so he was thinking of her when he picked Charon, the boatman who ferried dead souls to Pluto across the river Styx.

When astronomers found Pluto’s much smaller pair of moons in 2006, I though of names like Abbot and Costello, Thelma and Louise, or Beavis and Butthead. These would be hip and cute, but terribly inappropriate for the IAU crowd.

The New Horizons team who made the discovery using Hubble Space Telescope toyed with dric and drac (not Frick and Frack) the coins the Romans put on the eyes of the deceased to pay Charon for the river crossing.

Instead, the names Nix and Hydra were picked because they are the initials of the Pluto-bound New Horizons spacecraft.  How cheesy can you get? In mythology Hydra is a nine-headed serpent-monster, and Nix is the goddess of darkness and night and the mother of Charon.

Caltech astronomer Mike Brown has had the fun of naming the other KBOs he has discovered. The KBO designated UB313, later found to be slightly larger than Pluto, was Nicknamed Xena after the television Warrior Princess from the mid 1990s. A small satellite companion was named Gabriella, Xena’s sidekick.

The names had to go because of their high “giggle factor.” In fact, I got one slightly risqué e-mail from an amateur astronomer: “The size estimates are continuously changing [for Xena].  Xena seems to be breathing or something.  Maybe not as exciting as Lucy Lawless, but interesting nonetheless.”

In 2006 the IAU renamed UB313 Eris and Dysnomia, as selected by Brown. Eris is named after the Greek goddess of strife and discord. Dysnomia is Eris's daughter, the goddess of lawlessness. Brown thinks the names are appropriate considering that the KBO’s discovery was instrumental in demoting Pluto to dwarf planet status.

In 2002 Brown discovered another big KBO designated 2002 LM60. In preparing a press release on this I wrote to Mike an urged him to give it a nickname so it became a place in people’s imaginations. What would the Star Wars films be without the exotic worlds of Hoth, Tatooine, and Dagobah? Conversely, who, if anyone, remembers the planet Altair IV in the 1956 classic film Forbidden Planet?

A day later Brown e-mailed me to report his name selection. I slowly read it off the computer screen: Q-U-A-O-A-R. Huh?? I wondered.  Sorry, you’d never find this planet in the Star Wars galaxy.

Quaoar (pronounced KWAH-o-ar) is the name of an asexual creation deity of the Native American Tongva people who lived in Southern California.

Internet chatter soon bubbled up:

“Quaoar? It’s a name only Barbara Walters could pronounce.”

“Quaoar? I don’t like pronouncing something that sounds like I just finished having dental surgery.”

“Quaoar? Probably a bunch of astronomers were playing Scrabble and they ran out of consonants.”

To keep his naming record consistently imaginative -- if not unpronounceable -- Brown has named a third KBO, formerly know as 2005 FY9. Ready? It’s called Makemake, after a god in the culture of Easter Island. This was officially sanction by the IAU just recently.

The Next plutoid on the list for a name is 2003 EL61. Brown has nicknamed it Santa. But there has been ongoing battle between Brown and Spanish astronomer Jose-Luis Ortiz Moreno as to who rightfully saw the KBO first.

I say, let the astronomer with the coolest planetary name win. 

Photos, top to bottom: NASA/Adolf Schaller; NASA; GFDL

Does the Solar System Have a Case of the Plutoids?

June 12, 2008

Quiz for today: “what is a plutoid?"

a. Something the doctor has to surgically remove.
b. A new Transformers action figure.
c. A throat lozenge.
d. The name for the most abundant type of planet in the solar system.

If you guessed “d” you’re right.

Pluto, the Rodney Dangerfield of the solar system, is now officially a “plutoid' according to a June 11 announcement by the International Astronomical Union (IAU) Committee on Small Body Nomenclature.

You’ll remember that underdog Pluto was unceremoniously demoted to a “dwarf planet” in a raucous IAU General Assembly meeting in 2006 that shrunk the solar system to eight normal planets. This triggered a public backlash with protest slogans like: “size doesn’t matter!”

The General Assembly debated whether Pluto fulfilled all the definitions of a planet. It almost did, except for one sticking point. Pluto doesn't sweep out a clean orbital path but instead lives in a cluttered neighborhood. Pluto is one of the largest know members of the Kuiper belt, an outer debris field of perhaps as many as 100,000 icy bodies extending 2 billion miles beyond Neptune, which is the outermost of the “normal” planets according to the IAU.

The clunky term plutoid is not only intended for Pluto, but also anything out there like Pluto. In other words an icy body that is big enough to have enough gravity to be spherical. So, the IAU has also called Pluto’s slightly larger cousin Eris (aka Xena) a plutoid too.  And, the IAU says there will be more.  Astronomers are just beginning to plumb the depths of the Kuper belt. By my count at least nine other Pluto-sized icy dwarf Kuper belt objects should qualify as plutoids at present. Some experts predict there could be over 100 plutoids out there.

This latest move by the IAU adds insult to injury for Pluto supporters everywhere. Textbook authors will have to go into more revisions – if they so choose. Elementary school kids will have something else to memorize. And, the SAT exams just got harder.

Actually, I think the new term will be largely ignored and only fuel further debate over Pluto's planetary pedigree.

The bottom line is that getting preoccupied with nomenclature for solar system bodies is unnecessary, irrelevant, scientifically meaningless, and confusing for the public. You would think that the discovery of over 275 wild and exotic planets circling neighboring stars would be humbling enough to antiquate long-held notions of what is and what is not a planet.

The Pluto debate marginalizes one of the new revolutions in planetary astronomy: the discovery only 16 years ago of the “third solar system," the Kuiper belt. This vast outer rim is the largest piece of architecture in the solar system, and has the biggest collection of objects.

So, the irony is that the Kuiper belt is home to the most abundant class of planet-like objects in the galaxy -- whether you chose to call them plutoids, icy dwarfs, or just plain planets. We know this simply because Kupier belt type structures are common around stars with circumstellar disks.

Locking the largest KBOs out of the exclusive "Planet Club"  just gives the public the impression that some astronomers can’t count past the number 8.

Stars vary is size by four orders of magnitude, from white dwarfs to red supergiants. But they are all called "stars." The same should hold true for planets, big and small. If the object is big enough to be spherical, it likely is differentiated like Earth, with heavier elements at the core and lighter elements at the surface. This means that Pluto could be a geologically diverse and interesting world -- planet or not.

I anticipate that when NASA's New Horizons probe arrives at the Pluto system in 2015, it will make a number of fascinating discoveries that will show Pluto is one of the most intriguing objects in the solar system. This will bury the present debate in the ashes of history.

Photos, top to bottom: IAU; NASA