Boffins discover new dust clouds in the Solar System, Mercury has a surprisingly filthy ring Scientists have spotted, for the first time, gigantic dust rings circling the Sun alongside the orbits of Mercury and Venus. The Solar System is nothing but our star, a few planets, some satellites, lots of little rocks, and a load of dust. As asteroids collide and comets burn up, leftover crumbs are scattered around space, …
Look again at the picture in the article. You can clearly see that the immediate neighbourhood around the planets (to several diameters) is cleared. I'm not sure what the exact definition of 'neghbourhood' is in these terms, but I'm pretty sure they all make the grade.
I appreciate that the picture is illustrative and clearly not to scale, but the reasonable implication here is that the dust rings orbit the sun at the same rate as the planets (any slower, and they would fall towards the sun, and faster, they would move away), so the bits that are not close to the planets never will be.
https://en.wikipedia.org/wiki/Clearing_the_neighbourhood
By the above definition, the whole orbit of the planet must be cleared and therefore none of Mercury, Venus or Earth are planets, as their orbits are not cleared. This is the definition used by the IAU. So, the original poster is quite right. By current terminology, none are planets.
"https://en.wikipedia.org/wiki/Clearing_the_neighbourhood
By the above definition, the whole orbit of the planet must be cleared and therefore none of Mercury, Venus or Earth are planets, as their orbits are not cleared."
There's more to the definition, size matters: "there are no other bodies of comparable size other than its natural satellites or those otherwise under its gravitational influence." Therefore dust & small rocks don't count and don't have to be cleared. By current terminology, Mercury, Venus and Earth are planets in dusty orbits.
I was paying attention in school which is why I know that the mass IS relevant. Speculation on my education aside, you might want to refresh your memory on Kepler's laws of motion, I'll even supply a quick primer http://homepages.wmich.edu/~korista/Newton-Kepler.html
Thank you for the link, but my reading of the page is that it is contrary to your understanding. Could you draw attention to the parts that support your argument that orbital velocity in a solar orbit is a function of the mass of the orbiting body?
From the web page referenced:
So does the mass of the planet have a significant impact upon its orbital period (or orbital speed) about some star? Given that planets are by definition almost always much less massive than the stars they orbit, the practical answer is "NO."
By this (laughable, but officially accepted) definition, Jupiter isn't a planet. Jupiter has two groups of asteroids leading and trailing it's orbit. Jupiter's orbit is not clear, thus, it is not a planet.
This is why people are getting upset with the IAU. The 'definition' was railroaded through by a small minority of members who seem to have got their diplomas from poundland.
Like it or not, but this is not what the definition entails. "Clearing the neighbourhood" was never intended to mean and does not mean that the neighbourhood should be completely empty. That will be an impossible standard for a number of reasons, the obvious one are the moons. A little harder to grasp is all the minor objects that will end up in the stable Lagrange points L4 and L5 or orbit both in a horseshoe orbit. And I suspect most of this dust have in fact a horseshoe orbit. Read more about it:
https://en.wikipedia.org/wiki/Horseshoe_orbit
Third we have the orbital resonances of some bodies. Pluto is in such a resonance with Neptune, but so is Orcus which have the exact same orbit as Pluto.
And this is exactly the point of all these examples. Remove Neptune and Pluto will eventually pull Orcus in and they will merge. As of now their orbit is not their neighbourhood, it is Neptune's. The Trojans are not merging because of Jupiter. The same with the asteroid belt etc. They obviously was aware of this, and no they have not made a definition that excludes Jupiter and Neptune by mistake.
Personally I think we should remove the criteria and have a larger number of planets and instead call the eight major planets or something. I really fail to see why it was an argument that they had to because if Pluto should be a planet then a lot of other bodies would be planets to. So what? Regardless the definition they have now stands perfectly well. But I bet it will exclude exoplanets at some point that we would really think of as planets.
“The dust close to the Sun just shows up in our observations, and generally, we have thrown it away,” — Russell Howard, US Naval Research Laboratory
"Pol was finally discovered when someone decided to write down the location of the pollen, after having given up on yet another failed attempt to be rid of the smudge." — Kerbal Astronomical Society
https://wiki.kerbalspaceprogram.com/wiki/Pol
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