In this animated conversation, the always charismatic astrophysicist Neil deGrasse Tyson explains the reasons that Pluto recently got demoted from the status of a full-fledged planet to that of the first dwarf planet in the Kuiper Belt, the criteria that a celestial object must meet in order to count as a planet, the unexpected and intense reaction this news created, the political attempts by some to restore Pluto to what they see as its rightful place, and all the hate-mail he's received from third-graders...Did you ever think you'd see third-graders get so worked up on a scientific topic?
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Third graders are not the only ones. Many astronomers, both professional and amateur, believe the demotion of Pluto is wrong, for the following reasons.
ReplyDelete1. Pluto as a planet is not in a category of one. There are several of these smaller
planets that need to be distinguished from asteroids because their makeup is exactly like
that of planets in that they are in a state of hydrostatic equilibrium. This means they
have enough self gravity to pull themselves into a round shape, which makes them
geologically like the larger planets and unlike shapeless asteroids and
comets. Tyson never discusses hydrostatic equilibrium and blurs this crucial distinction
by lumping Pluto and other small Kuiper Belt planets with comets and asteroids.
2. The scientific community has not made a final decision on this matter. This definition
was adopted by only four percent of the IAU, most of whom are not planetary scientists.
No absentee voting was allowed. It was done so in a highly controversial process that
violated the IAU’s own bylaws, and it was immediately opposed by a petition of 300
professional astronomers led by Dr. Alan Stern, Principal Investigator of New Horizons,
saying they will not use the new definition, which they described accurately as “sloppy.”
Also significant is the fact that many planetary scientists are not IAU members and
therefore had no say in this matter at all.
Many believe we should keep the term planet broad to encompass any non-self-luminous
spheroidal object orbiting a star.
3. Tyson's comparison of Pluto with comets is a red herring. Yes, if brought into Earth's
orbit, Pluto would begin sublimating and appear to grow a tail. However, so would any
planet brought close enough to its parent star. If Earth were placed in Mercury's orbit,
it would appear to grow a tail as well. Pluto is also far larger than any comet, and its
orbit never takes it into the inner solar system. Significantly, a large exoplanet, HD80606b, was just discovered, which is four times the size of Jupiter and orbits its star in only a few days, yet has a comet like orbit. Is this object, which is bigger than any in our solar system, not a planet but a comet because of its elliptical orbit? Clearly,
"comet-like" orbits alone do not make objects comets instead of planets.
I plan to write a book of my own on Pluto, explaining why it is a planet and documenting worldwide support for its planet status. Notably, even now, many professional astronomers and lay people are working to get the controversial demotion overturned.
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