Reading Tyson's "The Pluto Files"

Was I too hard on Dr. Neil deGrasse Tyson in my initial post about The Pluto Files? Several readers thought so and sent me emails with that message. That post was not intended to be a review of the book but a commentary on Tyson’s public statements in various discussions of the planet definition issue.

I do thank Tyson for directing his publisher to send me a copy of the book, which I received last Saturday and read immediately. Going out of his way to make sure that someone who has publicly criticized him gets a chance to read, review, and keep his book is commendatory.

Contrary to some who communicated with me, I do not have any personal animosity toward Tyson. His endearing way of making astronomy accessible to the public is certainly a positive for him.

However, I do see some very real problems, including contradictions, in his public statements about Pluto. As for the seeking of “celebrity” status, I am in principle opposed to the concept of “celebrities” and don’t believe anyone should be paid thousands of dollars for a lecture or “personal appearance.”

And I wish Tyson had stayed for the entirety of the Great Planet Debate in August rather than just attend for his debate with Dr. Mark Sykes. The best of that conference, the rich exchange of ideas, took place mostly in the other, more participatory sessions throughout the two-and-a-half days.

But back to Pluto. My initial use of the word “preposterous” in the earlier entry was specifically aimed at the subtitle “The Rise and Fall of America’s Favorite Planet.” Pluto has not “fallen” from grace. This saga is far from over. Pluto has had its ups and downs, its detractors and supporters, since 1931, one year after its discovery. An assumption that the debate is over, inherent in the title, is unwarranted and in my view, preposterous.

Tyson’s book is a fun, entertaining read, and its pages contain many cartoons and illustrations. It is clearly accessible to children and adults alike. He even cites two songs I referred to in an earlier entry, “Planet X” by Christine Lavin and “I’m Your Moon” by Jonathan Coulton. I like that.

Defining “Planet”:

In an email to me, Tyson emphasizes his conviction that we are not on opposite sides of the planet debate, saying he does not care what the definition of planet is. He notes that he would have no problem with the term planet being defined as anything that is round but then opines that such a classification is not useful pedagogically or scientifically because it would leave us with dozens of planets.

I find those two statements contradictory. The latter sentence indicates he does in fact have a problem with using roundness as the criterion for planethood. Why would having dozens of planets not be “useful” education wise? We have billions of stars and billions of galaxies. Among objects known as stars and those known as galaxies, there are huge variations, which are designated by subcategories. Would it make sense to say the sheer number “devalues” the terms “star” and “galaxy,” and thereby makes these concepts unteachable? The answer is clearly no. Why then, should we have a different standard for planets?

And that is the beginning of where, in spite of recognizing the fun and entertaining tone of Tyson’s book, I disagree with his conclusions.

If Tyson really does not care what the definition of planet is, why then does he proceed to argue against using the criterion of hydrostatic equilibrium--roundness--by saying its resulting in numerous planets makes it not useful? Also, while he rightfully acknowledges the IAU planet definition as flawed, he then muddies the waters by invoking that vote to vindicate his decision to not include Pluto as a planet in the Rose Center display. Which one is it? Either the IAU definition is a step forward or it is not. If he believes it is not, then he should not be citing it to support his choice in designing the planetarium.

On page 132, Tyson states that the IAU “added the word ‘dwarf’ the way astrophysicists have used it for dwarf galaxy (which is still a galaxy) and for dwarf star (which is still a star). But to no avail. As far as anyone was concerned, the IAU killed planet Pluto.”

It seems he has forgotten about resolution 5b--the umbrella resolution that, had it passed, would have made dwarf planets a subclass of planets. Unfortunately, the IAU members participating voted that measure down, meaning they specifically intended to depart from traditional usage by adopting a definition that intentionally said a dwarf planet is not a planet at all.

If the whole “the IAU killed planet Pluto” was just media hype, why then does Tyson title many of his lectures, “How I Killed Pluto, and Why It Had It Coming?” Which one is it?

And, if he truly believes the IAU decision is flawed, why does he then proceed to argue that that vote is representative of planetary scientists around the world--a point widely contested since only four percent of the IAU’s membership voted on this and most are not planetary scientists. Why does he then go on to criticize the petition of scientists who rejected the IAU decision and point out how many signatories were American versus non-American? If he doesn’t care how planet is defined, he should have distanced himself from all sides of the 2006 dispute.

Voting is not the way science is done. If it were, a group of prominent PhDs could vote that the sky is green. Would that make their statement true? Did scientists vote on the theory of relativity? Dr. Alan Stern rightly points out that in science, ideas rise and fall on their own merit. That is a process that takes time. It does not provide instant gratification. It does not give a neat, clean, “planet or not planet” answer in time for
the next newspaper or textbook deadline.

Maybe we need to take the time to study Pluto, the Kuiper Belt, and extrasolar planets in depth before reaching a definitive conclusion. Contrary to the claims of some, children can be taught that sometimes, we just do not have enough information to make a final determination. And even determinations deemed to be final can be later reconsidered.

The point of the petition was to show that within days, hundreds of experts rejected the IAU decision. The only reason the petition had so many American signatories is that most planetary scientists are American.

It’s Not A Comet:

Pluto is a Kuiper Belt Object, but Tyson is incorrect in describing it as a “large comet” and as just another member of the Kuiper Belt. He believes it is a choice to use hydrostatic equilibrium, which is expressed in roundness, as the fundamental criterion in planet definition. This is where his argument falls apart.

Ask anyone to draw his or her conception of a planet. Inevitably, everyone will draw an object that is round. Roundness is universally accepted as the way planets appear. For an object to be in hydrostatic equilibrium, it must be sufficiently massive so that its shape is controlled by gravity rather than by chemical bonds. Pluto clearly meets this criterion, as do Ceres, Haumea, Makemake, Eris, various other objects in the Kuiper Belt, and probably the “asteroids” Vesta, Pallas, and Hygeia. These objects behave like the larger objects in the solar system--the planets--and not like the tiny asteroids and majority of Kuiper Belt Objects.

Planetary scientists measure objects by mass, not volume. Pluto’s mass is 70 percent rock and 30 percent ice. Most of the rock is in the planet’s center and has less volume than the ice. Tyson departs from the convention used by planetary scientists and decides to use volume as an object’s primary characteristic instead. He states, “If volume is what matters to you, then you can rightly declare that Pluto is mostly ice. This fact sits within a long list of properties that are not shared with any other planet in the solar system” (page 33).

So in order to lump Pluto with comets and shapeless KBOs, Tyson must resort to using a different measure than that used as the standard in the field.

And even if by his definition Pluto “is mostly ice,” well, Uranus and Neptune have several Earth masses of ice within them. Are they then not planets?

The reality is that volume has nothing to do with whether or not an object is a planet.
As for his claim that if brought into the Earth’s orbit, Pluto would grow a tail, this is true. But it is also true that any planet brought close enough to its parent star would grow a tail due to the evaporation of its atmosphere. In fact, Earth in its current orbit has a magnetotail. If Earth were brought 30 times closer to the sun than its current orbit--the equivalent of placing Pluto in Earth’s orbit--it too would grow a tail. Some of the “hot Jupiters” found orbiting other stars have visible tails. Many are several times the size and mass of Jupiter. Are they comets rather than planets?

Tyson also argues that Pluto is a big comet because its eccentric orbit matches that of other comets and Kuiper Belt Objects. But Earth’s orbital parameters match those of about a million near Earth asteroids. Is Earth therefore an asteroid?

The answer to all these questions is no because celestial objects are classified by their intrinsic attributes, not by what orbits with them. Otherwise, we’re back to the same preposterous definition created by the IAU in which the exact same object is a planet in one location and not a planet in another.

If Earth were placed in Pluto’s orbit, it would not have enough mass to clear that orbit. This was definitively proven in calculations by Dr. Hal Levison, who interestingly is a dynamicist and therefore a supporter of the eight planet schematic.

Maybe the reality is that it was easier to lay out the Rose Center display into neat categories of terrestrial planets, asteroid belt, gas giants, and Kuiper Belt. After all, it would be a lot more complicated and probably cost more money to name and highlight a few round objects in the asteroid belt and another group, including Pluto, in the Kuiper Belt. Unfortunately for planetarium designers, the solar system is not so neatly arranged, messier than a simple display of four clear categories.

Why Do We Love Pluto?

A final area where I believe Tyson is wrong is his attribution of public affinity for Pluto to the Disney dog. Maybe this is because, as stated in the book’s acknowledgments section, his brother-in-law is a Disney expert. “I could find none,” he says in attempting to find a reason that explains Pluto’s continuing popularity.

Just because he cannot identify a reason doesn’t mean there isn’t one--or many. Most children and adults fascinated by Pluto already have some interest in astronomy and the solar system. When I pointed this out in an email, Tyson stressed that he is referring to the public rather than professionals in the field.

So am I. The public has always had some degree of fascination with the space program, with the discovery of “strange new worlds.” Of the solar system’s known planets, Pluto is one of the least understood. We have never seen images of it up close. We have no other binary planet systems, which Pluto and Charon essentially are. Therefore, Pluto is enigmatic, mysterious, the frontier of our knowledge, at least about our solar system.

That is appealing in the same way that Mars is appealing in that it is both known and unknown, Earth-like, yet different. More science fiction stories have been written about Mars than about any other planet. It is the same reason so many children--and adults--become fascinated with dinosaurs. There is that element of mystery, of something both like and unlike what we know, something remote, either in time or in space.

And yes, there is the appeal of the underdog. Pluto was discovered not by a professional astronomer, but by a Kansas farm boy who at the time had only a high school education. Inherent in that story is an anti-elitism, a conviction that anyone, regardless of the circumstances of his or her birth, can accomplish great things. Notably, Clyde Tombaugh himself was an underdog even once he obtained a formal post-secondary education. Not having a PhD, he was often looked down on by his peers in the field. Perhaps they resented the fact that someone with less formal training than they had had done something they did not--discover a planet.

The IAU decision very likely caused Pluto’s popularity to skyrocket worldwide. Like it or not, we all, scientists included, project our own sentiments onto the world around us. By demoting Pluto and singling it out for exclusion, the IAU effectively made it the Charlie Brown of the solar system. Who has not, at one time or another, identified with that?

As further illustration of Tyson’s generalizing, he comments on page 121 regarding the 2006 IAU decision, “Angry third graders from the year 2000 were now in high school with other (hormonal) priorities to distract them.” Personally, I was somewhat taken aback by his assumption that all the students who had cared enough to write letters in 2000 were now distracted by “hormonal priorities.” How does he know? Not every teenager is all hormones all the time. In fact, some may have maintained their interest in astronomy. How does he know they were not upset by the IAU decision? Their letters at this point would likely be typed on a computer, written in the same language as those of adults, and not include their age or grade. As with the attribution of people’s love for Pluto to the Disney dog, Tyson’s wholesale categorization of high schoolers as walking hormones is a gross generalization, not to mention it is demeaning to teenagers.

Tyson is certainly a highly credentialed astrophysicist, not to mention charming and entertaining. His book most certainly adds to the growing lexicon of literature on Pluto and the planet debate. I would never in any way begrudge him this. His chronicling of popular celebration of Pluto is itself an example of our ongoing fascination with this little world.

But that world has not fallen. It is not dead. The story continues. I believe planet Pluto will rise again, and I still hold out the hope that it will be in 2009.