The Pluto Files: the Rise and Fall of America’s Favorite PlanetBy Neil deGrasse Tyson
W.W. Norton, 2009. 194 pgs. Young Adult Nonfiction
Quoting reasoned scientific opinion and impassioned letters from elementary students – “Why do you think Pluto is no longer a planet? I do not like your anser!!! Pluto is my favorite planet!!!!," Tyson documents the controversy surrounding the definition of a planet established by vote of the International Astronomical Union in 2006. This hotly contested definition officially demoted Pluto to the status of a “dwarf planet.”
The political cartoons, photos, song lyrics and scientific illustrations make this book a delight to browse or read. I highly recommend this book to teens or adults with an interest in science or popular culture.
SH
1 comment:
Planet Pluto has not "fallen," and the IAU was never "forced" to define the term planet, an act many members now regret. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds. These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned. The requirement that an object must "clear its orbit" to be a planet was concocted specifically to exclude Pluto, and there is no reason for it.
This isn't about resistance to change; it's about resistance to bad change. Not all change is good. In this case, the IAU decision went in the wrong direction, narrowing rather than broadening the definition of planet even while we are discovering more and more diverse planets in this and other solar systems.
Pluto actually has a lot in common with the other eight planets. In fact, it could be said to have more in common with Earth than Jupiter does. Pluto and Earth both have solid surfaces, are geologically differentiated into core, mantle, and crust, have weather, and have a large moon formed from an impact. Unlike asteroids and shapeless Kuiper Belt Objects, Pluto, Haumea, Makemake, Eris, and Ceres all are shaped by gravity--a characteristic of planets.
For the other side of this very much ongoing debate, check out "The Case for Pluto" by Alan Boyle, "Is Pluto A Planet?" by Dr. David Weintraub, transcripts of the Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in August 2008 in response to the IAU decision (transcripts are here: http://gpd.jhuapl.edu/ and my Pluto Blog at http://laurele.livejournal.com
In spite of what the IAU claims, dwarf planets should simply be considered a third class of planets, in addition to terrestrials and jovians. They are planets because they are in hydrostatic equilibrium but of the dwarf subclass because they do not gravitationally dominate their orbits. Using this definition, we have 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.
Post a Comment