| Gaeliccrossed1 wrote: |
It is still a PLANET whether large or small-the problem THEY are having is classifying everything, it is a HUMAN trait to classify everything into categories, to pigeon-hole everything as it were. Just recently, astronomers started classifying every large or small body they found ( and are still finding) in the Kuiyper Belt, the problem arose because Pluto doesnt fit into THEIR categories anymore. It is still a PLANET. Astronomy is basically arguing over the terms BIG ,LITTLE and SHAPE. I cant wait till New Horizons gets to Pluto and more data comes in, there has to be something more constructive than arguing over size!
Pluto is still very important. But I have to admit, with all the important stuff going on in the universe we cant just leave Pluto alone and move on- I wasnt aware that there was a quota on the number of "classical" planets. If you ever look at the planet depictions in Sumerian and Assyrian tablets theres more that 8 planets depicted there! |
Gaeliccrossed1 nailed this right on the head. All that the IAU is saying is that it does not meet the 21st century technical description of a planet. That really doesn't mean a whole lot. It is a round body of sufficient mass to orbit the sun. It has a satellite orbiting it. Whether it's a dwarf planet or planet is just an arbitrary limit set by the scientists.
Here's something to consider. A definition of a planet is that it only answers to the sun in terms of gravitation. The satellite Ganymede, for example, which is large enough to be a planet, is not one , because the pull of Jupiter's gravity (which Ganymede orbits) is much stronger than that of the sun in the vicinity of Ganymede. Technically the two (Jupiter and Ganymede) orbit a common center, although that center is buried deep with Jupiter, so Jupiter sort of wobbles around that point. Is this important, yes, as I will show shortly, so keep that in mind, but also the important 21st classification is that Jupiter's gravity is stronger than the Sun's at Ganymede, so Ganymede is a moon, not a planet.
Now let's consider the Earth's moon. The Earth is more massive so the moon orbits the earth while the earth wobbles around the earth-moon center which is inside of the earth. But the earth is not as massive as Jupiter and the moon is much closer to the Sun than Ganymede. What does that mean? Simply that the Sun's gravitational influence on the Moon is TWICE that of that of the Earth upon the moon. I'm not making this up; I will gladly supply the equations that support this. But the bottom line is that Earth's pull on the moon is only 46% of the Sun's pull on the Moon. Bottom line: If we strictly adhere to the new classifications of what constitutes a planetary body, the moon would be a planet and the Earth-Moon would comprise a double planetary system.
Well, no one at the IAU has proposed this. Probably because no one would accept it. Technical definitions don't change what common sense tells us. We see the moon as a satellite, not as a planet, and we see Pluto as a planet. Anything else is just arbitrary nonsense.