Critical Thinking

I finished The Pluto Files this weekend, the latest book by Neil deGrasse Tyson.  Astrophysicist and Director of the Hayden Planetarium at the American Museum of Natural History, Tyson is also a fervent advocate for science and making science understandable to the public.

The Pluto Files tells the story of Pluto’s reclassification, from ninth planet to dwarf planet.  There’s the history of the discovery, along with difficulties involved in planetary discovery in general:

In an embarrassing example from January 1769, the French astronomer Pierre Charles Lemonnier did not discover Uranus six times.

That particular planet had been repeatedly classified as either a comet or a star.  It was not officially recognized as a planet until 1781. As for Pluto, astronomers were searching for a “Planet X” to explain the perturbations in the orbits of Uranus and Neptune (perturbations which later turned out to be the result of poor estimation of the masses of the other planets, and not an undiscovered outer planet).

Tyson’s book describes the remodeling of the planetarium and the decision to classify the solar system by groups of related objects, and what that meant for Pluto in the grand scheme of things.  The second half deals with the public fallout of that decision, from school children wondering where Pluto was in the display of the relative sizes of planets (and hundreds of crayon-illustrated letters to that effect), to other scientists who accused the planetarium administration of going against scientific consensus in grouping Pluto with other objects in the Kuiper belt.  That was until the International Astronomical Union (IAU) voted to clarify the definition of planet. Currently, a planet is defined as a celestial body that:

1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3. has “cleared the neighbourhood” around its orbit.

While Pluto has met the first two criteria, it has not met the third (hence the name Kuiper belt for the region of icy objects where Pluto resides). The funny thing is, we’ve been here before.  Ceres was declared a planet in 1801, and the number of planets in the solar system climbed to 23 as more were discovered.  We later learned that these objects were actually members of the asteroid belt, not planets at all.  Ceres didn’t have the cultural status of Pluto, though, and that’s what I found most interesting about The Pluto Files.

It’s a first hand account of how advances in scientific understanding can have a profound and direct impact on culture (and state legislatures).  Both New Mexico and California passed laws declaring Pluto a planet, though California’s bill is a bit tongue-in-cheek:

WHEREAS, Downgrading Pluto’s status will cause psychological harm to some Californians who question their place in the universe and worry about the instability of universal constants; and…

WHEREAS, The downgrading of Pluto reduces the number of planets available for legistive leaders to hide redistricting legislation and other inconvenient political reform measures….

What should have been celebrated as an advance in human understanding of the universe was instead decried as desecration of a universal constant (that didn’t actually exist).  And that is what makes people so uncomfortable.  Science can change to meet the presentation of new facts, and that’s a good thing.

The following is an conversation that Dr. Tyson participated in at the LA Public Library following the release of The Pluto Files. He’s an entertaining speaker with a wonderful sense of humor, and it’s interesting to hear his perspective on the controversy.