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Astronomer Upset at New Planet Proposal
Jack Horkheimer, director of the Miami Space Transit Planetarium poses in front of photos of planets Wednesday, Aug. 16, 2006, in Miami. Though not approved yet, the 76-year-old lineup of the solar system's planets would grow to 12 under a proposal by leading astronomers. Their recommendation will be decided by a vote of the International Astronomical Union on Aug. 24. Horkheimer's very first book, a full-length cartoon guide to naked-eye astronomy, features an entire chapter on the solar system, the nine-planet version. "My book is out-of-date before it even hits the bookstands," Horkheimer said. "It's kind of like buying a computer. By the time you get it out of the box and get it hooked up, it's already obsolete." (AP Photo/Wilfredo Lee)
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One must wonder how these limits (>500 mile diameter, >1/12,000th mass of Earth) were chosen. Was it to satisfy the current view of our solar system to ensure most objects retain their nomenclature (i.e. moon, planet, etc)? Or was it per some other scientific reasoning (like the minimum mass/diameter that allows self-gravity to shape an object)?
It will be interesting to see how this debate turns out. There is a certain elegance to the whole center of gravity argument that if it lies outside an object that has satellites, then the satellites are considered planets. It really boils down what is orbiting what: a moon and planet (under their current popular definitions) can be considered a single mass orbiting the sun. The dynamics of each planet and its moons is (nearly) independent of its path. As such, it does stand to reason that the definition of a planet should not necessarily stop at "a large object orbiting the sun," but should also include some smaller objects that may or may not also orbit other larger objects and meet certain criteria.
The moon does orbit the Earth, but to a certain extent, the Earth also orbits the moon. Where is the cut-off? Is it size, distance from each other, mass? What would we call two objects of equal size that orbit each other that also orbit the sun? We certainly could not call them both moons. Are they both planets?
After this reflection, I'm not sure if they have properly chosen their limits, but outside of that, I would say that the definitions set forth by the IAU are a step in the right direction.
#1 - Sat Aug 19, 2006 3:17 PM EDTOne of the criteria chosen for the "who orbits whom" scenario is if the center of mass of the system is inside the larger body, the smaller one is a moon by default. Unfortunately, this means that Pluto's moon, Charon (pronounced "kar-on", not "sharron") is a planet, because the Pluto-Charon center of mass is between the two bodies.
I could not agree with Dr. Brown's opinion more, though. A planet does have a special place in a stellar system. These new definitions could very well define any number of asteroids, and (as mentioned in the article), dozens if not hundreds of Kuiper Belt objects. Let us remember that "planets" originally stood out to people because they were special objects in the sky, wandering about the heavens from night to night (originally from the Greek planetes, or "wanderer"). Indeed, apart from Pluto, Mercury through Neptune can be seen by the human eye under the correct conditions.
Moreover, the first eight planets orbit in very circular orbits (quite unlike Pluto, Xena, and company), as well as orbit about in the same plane (Pluto at the very least, has an orbit at an angle to the other eight).
Sadly, Clyde Thombaugh [sic] jumped the gun un 1930 in calling the first discovered Kuiper Belt object a planet, and it might be too late to let Pluto go. Let's keep a planet a planet. At the end of the day, will there be colonies on 2003UB313?
Given the small size of Pluto, they ought to just change the limits of their definitions to keep the inner eight planets as planets and dump Pluto and any other Kupiter Belt outliers.
Personally, this is what I was hoping, as it allows us to keep our current view of the solar system relatively untouched, while setting scientific definitions on what constitutes a planet based on size, orbit, and gravitational center for a given planetary system. Scientifically, though, choosing arbitrary limits to fit our notions of what constitutes a solar system seems too human, when most rigorous scientific definitions lack such quality. Is there any way around this?
Amateur astronomer Jay Manifold at avoyagetoarcturus thinks that the traditional nine planets are enough. His money quote:
I submit that scientists own the science, but laypeople own the narrative. And the narrative of the nine planets of the Solar System is rich in mythology (Mercury, Venus, Mars, Jupiter, and Saturn), serendipity (the discovery of Uranus [pronunciation]), mathematical prediction (the discovery of Neptune), and Herculean effort (the discovery of Pluto). It has been enriched that much further by the stunning imagery of every planet except Pluto returned to us by the Mariner, Pioneer, Viking, Magellan, Galileo, and Cassini probes.
I agree wholeheartedly with Manifold, although I hardly ever see the heavens, as I live in the centre of Toronto where the streetlights outblaze the stars.
#2 - Sun Aug 20, 2006 2:44 PM EDTYou're in Easy Mode. If you prefer, you can use XHTML Mode instead. |
