Book Review: Is Pluto a Planet?

When people find out I am an astronomer, the next question I am asked is very often "What do you think about Pluto?" Of all my frustrations with the Great Pluto Debacle of 2006, the greatest is that this was a historic opportunity to communicate to the public how science is done, a "teachable moment" at which legions of people were paying attention to astronomy who usually don't -- in fact, people still care about the issue today -- and we (that is, scientists) completely bungled it. We should have said to the public, "Here's how we can expand our view of the solar system, which has a lot of important things in it besides just the planets, and also better understand Pluto's place in it." Instead, the official message was only semi-coherent, and squabbling among astronomers grabbed most of the headlines.

David Weintraub's book Is Pluto a Planet? (Princeton Univ. Press, 2005) makes some worthwhile contributions to the discussion and is well worth reading. In particular, he spends most of the book telling a lively story of the history of planetary astronomy, and the evolution of the term "planet," which he points out has meant a number of different things to different generations. Wider understanding of this story, and of the fact that this is hardly the first time that the meaning of "planet" has shown itself to be elusive, is an important key to getting a handle on this issue.

However, I have three major criticisms of the book:

1) The first part of Weintraub's story (specifically, from the end of Chapter 2 to the first half of Chapter 4) is marred by the simplistic view, which is sadly popular today, of science and religion as being antagonistic to each other, especially during the Medieval and Renaissance periods.

In order to portray hidebound Catholic scholars refusing to look through Galileo's telescope while triumphantly refuting Galileo with passages from Aristotle, Weintraub must resort to an extended quotation from a 20th-century play; this is because scholarly evidence for this legendary event is non-existent. In fact, Magini (one of the characters in the fictitious dialogue) and his associates did look through a telescope in 1610 in the presence of Galileo himself, but were unable to see Jupiter's moons due to the fact that telescopes at that time were notoriously difficult to use properly.

When quoting 16th-century skeptical responses to Copernicus (for example, from Luther and Calvin), Weintraub fails to mention that not until Tycho and Kepler came along would Copernicus' system give a clearly superior fit to the data that would help to justify a paradigm shift of astounding magnitude. Weintraub also does not mention that, while some individuals criticized Copernicus on theological grounds, opposition to heliocentrism was much more fierce among scientists of the day than among theologians, and that no one in the Catholic Church saw heliocentrism as a threat needing an official response until many decades later, when the politically inept Galileo made his splash in the politically fraught context of the Counter-Reformation and the Thirty Years' War.

Weintraub's promotion of the "warfare hypothesis", which is largely discredited among historians of science and religion, is a blot on his otherwise engaging tale that I found hard to ignore. Fortunately, the middle and later parts of his story are free of such problems. For a more scholarly treatment of some of these issues, I recommend relevant chapters of God and Nature: Historical Essays on the Encounter between Christianity and Science, edited by Lindberg and Numbers (Univ. of California Press, 1986). Incidentally, I am looking forward to Ronald Numbers' new book, Galileo Goes to Jail and Other Myths about Science and Religion, due out from Harvard Univ. Press in the spring.

2) Weintraub occasionally gets bogged down by details and momentarily loses his engaging style of storytelling. This is most obvious in Chapter 11, when instead of a fast-paced narrative of the discovery of Pluto's brothers and sisters in the Kuiper Belt, we have several pages listing the names of various astronomers with the dates and alphanumeric code names of their discoveries. I guess he might have been trying to avoid offending anybody by failing to mention them.

3) While Weintraub's book in general lays an excellent foundation for understanding the issues surrounding the word "planet" and what we mean by it, in the final chapter he drops the ball by drawing (in my opinion) the wrong conclusions from that foundation. At this point it must be mentioned that Weintraub's book was published in 2005, a year before the drama at the IAU, so to some extent Weintraub can be forgiven for not giving better consideration to the the definition the IAU eventually adopted. Weintraub actually proposes a better version of the IAU's clunky conclusion, suggesting that "planets are not part of rings or belts around a star", but he dismisses this idea (p.206) because he cannot distinguish between the Asteroid Belt or the Kuiper Belt (the latter of which contains Pluto) and the swarm of Trojan asteroids that share the orbit of Jupiter. The difference, of course, is that giant Jupiter is many many many times bigger than the tiny rocks that share its orbit, and more importantly that Jupiter's gravity strongly controls the orbits of those Trojans while the latter have a no perceptible effect back on Jupiter. Pluto, on the other hand, is fully a member of the Kuiper Belt, though it is a leading member as it is larger than most of its brothers and sisters.

Weintraub would save Pluto as a planet and, for the sake of consistency, would promote several other asteroids and Kuiper Belt objects to planet-hood as well. To the objection that such an inflated list would be too much for schoolchildren to memorize, Weintraub is unsympathetic. "Simple answers are usually wrong," he says, "It is time to start teaching our youngsters something more complicated, with more depth of meaning." To an extent, I agree with that last sentiment. My second-greatest frustration with the Pluto Debacle is that it has been widely viewed as a "subtraction" from the solar system, as if the number of important things to remember changed from nine to eight. Rather, we ought to promote asteroids, comets, moons, and KBOs to take their place as groups alongside the eight major planets. Certainly the solar system is richer than that list of eight or nine, but still it must be recognized that the eight planets have a unique importance to the dynamical functioning of the whole. And, Weintraub to the contrary, there are straightforward physical ways of showing that that is so.

Weintraub quotes a 2002 suggestion by Alan Stern and Hal Levison that we use the term "planetary body" to denote an object big enough to pull itself into a spherical shape, which means that it is geophysically acting like a planet, regardless of what body it orbits. I think this proposal needs to be given much more attention. I strongly oppose any definition of "planet" that would include Pluto but exclude planetary-class moons like Titan, Enceladus, Europa, and even our own Moon. The fact that we have long known that these moons behave geophysically like planets, yet we have never been tempted to call them "planets" rather than "moons," convinces me that the IAU's definition is fundamentally correct (though it could use some wordsmithing). Yet, alongside it, we need a word that we can use to talk about the intrinsic nature of a "planetary body" regardless of where we find it. 

Posted by Matt on 12/29/2008 10:19:00 PM -- Permalink --  11 comments

Matt's "Greatest Hits"

It's been nearly four months now since I last posted to this blog, and I don't feel like that streak is going to be reversed (save for this piece). I had been tapering off for some time, as my growing family and increasingly engrossing job have taken up my time and attention. I'll just say now that everything is well. We moved across town into our new apartment a few weeks ago, and find our new surroundings well worth the trouble of relocation. Isaac and Samuel are growing, and growing more delightful every day. The former picture page is also frozen in time now, but new pictures are being uploaded by Laura to our Shutterfly page, which I invite you to visit.

I think I'll give some closure to this blog by making an index of my personal favorite blog items; out of 188 posts, the ones which I'm most proud of, and/or which give the best snapshots of my life:

• 19 Mar 2003: The Very First Blog Item
  
• 22 Mar 2003: My Opinion of the Iraq War as it was Happening -- I happened to start the blog in the days just before the invasion. Somehow I feel I should get credit for predicting the mistakes Bush would make, but I suppose that doesn't seem useful now.
  
• 11 Apr 2003: John Polkinghorne lecture -- Notes from a public talk on science and faith.
  
• 18 Apr 2003: Good Friday Prayer
  
• 19 May 2003: Mahler's "Resurrection" Symphony -- What the listener/beholder brings to a work of art can have a big effect on how he receives it. Maybe that's not a bad thing?
  
• 5 Jun 2003: Book Report on Bruchko -- Written by a missionary to South America, I love this book not just for the story, but for its message that introducing Christ to a culture should perfect it, not obliterate it.
  
• 13 Jun 2003: Thoughts on Forgiveness
  
• 11 Aug 2003: Review of A Peace to End All Peace -- One of the best books I've read in a while, about World War I and how the Middle East got to be the way it is.
  
• 24 Aug and 8 Sep 2003: The Separation of Church and State -- One of my very favorite posts. Part One Reviews the history of the Supreme Court's decisions on the issue, which I argue have been fairly even-handed. Part Two continues the discussion, responding to a video we had watched in church.
  
• 1 Nov 2003: The Birth of Samuel
  
• 10 Nov 2003: Samuel's Name
  
• 17 Nov 2003: Review of the movie Luther -- With some thoughts on the Protestant Reformation.
  
• 3 Jan 2004: Selected Tidbits from the Cold War -- Moral absolutes can be hard to come by in the real world.
  
• 10 Jan 2004: Visiting "Tricky Dick" -- At the Richard Nixon Library and Birthplace.
  
• 9 Feb 2004: The Bloodwashed Pilgrim -- Some thoughts on a hymn.
  
• 29 Mar 2004: A couple political book reviews
  
• 30 Apr 2004: The Channeled Scabland -- A marvelous place, challenging both "uniformitarianism" and "flood geology".
  
• 8 May 2004: Last Post as a Tucson Resident
  
• 12 and 26 May 2004: The Moving Odyssey: Driving from Tucson AZ to Ithaca NY in the company of a six-month-old boy, Part One and Part Two.
  
• 13 Jul 2004: How we found our church -- We still attend New Life, and are very thankful that God has led us there.
  
• 27 Aug 2004: The Fat Lady Arrives by Post -- Reflections upon receiving my diploma in the mail.
  
• 2 Oct 2004: Book Report Roundup -- A snapshot of what I was reading at that time.
  
• 22 July to 9 Oct 2004: Great Hymnwriters -- A series on my three favorite writers of Christian hymns: Isaac Watts, Charles Wesley, and Fanny Crosby.
  
• 23 Feb 2005: Samuel at 16 Months -- One of the blog's more detailed and enjoyable descriptions of his development.
  
• 25 Mar 2005: Some comments on the Terri Schiavo case -- I tried to be thoughtful and even-handed, pointing out errors on both sides, in what was a very difficult situation.
  
• 9 Mar to 30 Apr 2005: The Trip to Florence -- Laura provided the narration, with pictures at the end. Here is an index:
  
  • Days 1 and 2 (travel and recovery)
    
  • Day 3
    
  • Day 4
    
  • Days 5 and 6
    
  • Days 7 and 8
    
  • Day 9 (return home)
    
  • Pictures
• 8 Apr 2005: The Name of the Pope -- I speculated, not on the identity of the then-future pope, but on what regnal name he might use. I'd like to flatter myself that I did fairly well.
  
• 4 Nov 2005: The Birth of Isaac -- I was already tapering off in my blogging activity by this point, so no conclusions should be drawn from the smaller number of posts about Isaac's infanthood compared to Samuel's.
  

 

Posted by Matt on 8/16/2006 02:54:00 PM -- Permalink --  3 comments

Facts of Life

Samuel: "Where Knit Bear come from?"
Mommy: "Our friends Mrs. Jane and Mr. Ari made Knit Bear, and gave him just for you."
(...cycle through all the other stuffed animals who live in his bed...)
Samuel: "Where Satchel come from?" (Satchel being his favorite companion of all)
Daddy: "Our friend Mrs. Julie in Tucson gave Satchel to you."
Samuel: (Pause) "Where Pamel come from?" (That means Samuel)
Daddy: "Oh, Samuel is very different. You were a baby in Mommy's tummy, and then you were born and we were so happy, and since then you have been our little boy."
(Samuel spontaneously gives Daddy a hug)

First of all, it is amazing how much Samuel understands and can say. It is so much fun to talk to him. But I was just thinking about how little he knows of life, and I guess it will be us who have to teach him. He knows who we are, and he knows his grandparents and others close to us, and he's beginning to understand the relationships between us (the above exchange was followed by questions including "Where Daddy come from?"). But when we get to the point of going beyond that, most of Samuel's great-grandparents are still living, but some aren't. At this point, he has no concept whatsoever of what death means, but at some point (likely years in the future, but still) we'll have to explain that to him. How will that work? It just makes me think about what an amazing thing life is.

New pictures, once again long overdue, can be found at this address. I'll fold this into the Samuel and Isaac Picture Page sometime later. 

Posted by Matt on 4/23/2006 09:54:00 PM -- Permalink --  0 comments

A New Lease, Part 2

There have been some interesting developments since we signed a lease on a new apartment in Ithaca several months ago. It turns out that the people currently living in our erstwhile new apartment didn't actually want to move. While acknowledging that we had a right to force the issue due to the fact that we'd signed a lease, the property managers asked us to look at another unit in the same house. The outcome is that we met them this morning to happily void the old lease and sign a new one.

The new place is on the first floor, so no dragging toddlers up a potentially icy exterior staircase! It's more compactly laid out, with no interior stairs either, and the boys' room is still nicely removed from the main living spaces. It's slightly smaller than our "old new" place, though still significantly larger than our current home, and much of the difference is in items that were somewhat superfluous for us (like a second bathroom). There won't be a dryer hookup (and in fact, a washer hookup is being put in especially to accomodate us), but we don't yet own a dryer anyway. Our laundry situation will be the same as it was in Tucson, which is fine. Moving day will be 8/1, not 7/1, but that just means we don't have to worry about getting out of the final month of our current lease. And while the "old new" place was only barely affordable for us, the new place fits perfectly into our budget.

There's no way we would have even looked at this apartment during our primary home search, because its lack of laundry hookups would have disqualified it. And the landlords wouldn't be so accomodating to us if we didn't have them in a hard place with the lease we'd signed. In all, it's quite the turn of events, and we are feeling very thankful. 

Posted by Matt on 3/08/2006 09:43:00 PM -- Permalink --  3 comments

Snowman, Part 2

You know that thing they say, about how a snowball keeps getting bigger if you roll it? It's not always true!

Samuel has been pining for snowmen ever since we built our first one back in December. But in contrast to last year's deep-freeze foot-of-snow-on-the-ground winter, we've had hardly a snowy day since then! Every now and then, we'll get less than an inch, which pathetically doesn't even cover the grass, and then it's gone again. I'm used to snowless winters, of course, but I feel that if it's going to be freezing, there really ought to be snow to brighten the place up.

Well, yesterday was finally a snowy day, and we still have a good six inches on the ground. So I got out of the house early today to play with Samuel in the snow before work. But wouldn't you know it, the snow wouldn't stick to itself! I gather it has something to do with the humidity as the snow is falling, but some snow is simply better than others. Anyway, we made a little pile of snow, but couldn't put a head on it. Then we got out the sled, but Samuel's still a bit skittish regarding the sled. So, at his request, I put him on my shoulders and walked around the block. I think he still enjoyed the time. 

Posted by Matt on 3/03/2006 07:55:00 PM -- Permalink --  1 comments