Hubble spots another moon around Pluto! I knew about Charon, but had never heard of the other one until just now.
So how should planets be determined, number of moons, 'who grew up with it being a planet and got used to it', or some more sensible measure ?
They demoted Pluto based on this "not having cleared its neighboring region of planetesimals". I never understood this. Are there any planetesimals anywhere remotely near the orbit of Pluto? Also, when Pluto was demoted to Dwarf Planet, it was widely thought that the newly discovered Eris was larger than Pluto. Now, I've heard that Eris is not nearly as large. I think Pluto should be declared a planet again. Extra moons help I think as it indicates Pluto's gravitational dominance over its local space.
Could it have to do with the fact that Pluto revolves closer to the sun than Neptune at certain points? In other words, it hasn't quite cleared Neptune's orbit?
No. Neptune and Pluto's never intersect. Different planes. And a number of the newly discovered extrasolar planets have eccentric orbits as Pluto does.
So Ceres, Pallas, Juno and Vesta should be counted as planets as well since there was an entire generation who grew up with them being classified as such?
Of course, as one astronomer pointed out, if a Jupiter sized body were discovered outside the orbit of Pluto, it would fail to meet that definition as well. I'm wondering what we're going to do when we discover an Earth sized moon orbiting a gas giant. Shouldn't it be considered a planet?
Ganeymede and Titan are already larger than Mars IIRC. No, an Earth sized moon would still just be a moon because it is gravitationally bound to a much larger body that circles a star.
Me neither. I've followed New Horizons from a decade before it was launched when it was inspired by a postage stamp. The U.S.P.S. issued postal stamps with each planet on them and the first spacecraft listed that explored each. But for Pluto all they could put was "Not Yet Explored". A decade later or so, after two other proposed Pluto missions were canceled, New Horizons was launched. Just goes to show that sometimes things go right for the U.S.
They probably aren't spherical. At least Vesta isn't, according to the shots we're getting from the Dawn probe. I'll change my mind about Pluto if it isn't spherical either, but we won't know until 2015.
Well technically, I don't think Charon would be classified as a moon of Pluto. Charon and Pluto orbit a common center of mass that is between them (though closer to Pluto)
