Colorized photo of Pluto


Originally published at:


It appears to be fully festooned for the military parade. When do we send them?


I find this enhancement more realistic:


Sure looks like a planet to me.


Pretty. All lies, of course, but pretty none the less.


If you spin Pluto around to its back side it looks like a total eclipse of the sun. I think I just blew my mind.


I see what you did there.


I wish it really did lok like that. I’d move there.


Huh? I thought this was a photo of Pluto.


I find it amusing that scientists still can’t articulate any convincing argument for declassifying Pluto as a planet beyond “but if Pluto is a planet that means other bodies like Ceres are also planets!”

To which most people respond: “So?”


Yes, but think about how many planets schoolchildren would have to memorize and how cluttered their models of the solar system would have to be to accommodate all these smaller planets, something no astronomers considered in their decision to take away Pluto’s planetary status and honestly I’m starting to wonder myself what the problem would be.


the greys told us we need to standardize our terrorial claims in keeping with the rest of the universe DUH


So we can’t get people to memorize 9, much less others. :wink:

Where is the cut off? When does it go from a planet to dwarf planet to asteroid? I dunno, so much of science and classification has so much grey area. So despite my initial reservations, I have let it go. Since it is dwarf planet and there are many others, seems like we could just add another chapter or lesson to the books, just before asteroids and comments about the different dwarf planets.


If the reclassifiers just admitted the cutoff was completely arbitrary I’d probably be OK with it, but it seems silly to me that the cutoff has more to do with location than with the physical properties of the body in question. If you organized the objects in our solar system by size, composition and other physical properties the Earth has more in common with Pluto than with a Jupiter, yet Earth and Jupiter are classified as one thing and Pluto as another.

It would be kind of like biologists saying “Emperor Penguins don’t really count as birds because they live all the way down in Antarctica.”


One of the more bizarre definitions of a planet is its ability to clear its orbit of any other celestial bodies and to be classified as a planet Pluto would have to meet very one of the requirements including this one. The strange thing is, a few years ago they discovered the Earth has a satellite trailing in its orbit. By definition this should declassify the Earth as being a planet. Where does it stop!!!


Looks like a big old poké ball.


“Planet” has several sub-categories that do clarify those distinctions. Jupiter is a gas giant, and Mercury through Mars are terrestrial planets. Pluto picked up the planet designation because at the time it was discovered, it was the only Kuiper Belt object large enough to be visible, but as a planet, it was always the weird (dare I say Goofy) odd man out, with a highly inclined and highly elliptical orbit that intersected with Neptune’s, and a companion so comparatively massive that the two bodies actually orbit each other. Since advances in astronomy have made it possible to spot more of Pluto’s solar neighbors, its behavior and characteristics put it more in line with being a large Kuiper Belt object, rather than a wonky, rinky-dink planet.

The distinction between what is a planet and what is a dwarf planet also isn’t strictly location-based, but dwarf planets are statistically more likely to crop up in certain places simply because of how solar systems are formed. Especially out in the nether-regions of the solar system, it’s difficult to cobble together enough material to make a gravitationally-compressed spheroid body, and things are so far apart that it’s also difficult for any one object to sufficiently clear its orbit of debris. However, not every dwarf planet is so far-flung. Ceres, notably, is just past Mars in the asteroid belt, where there was insufficient material present to build up a proper single body. Up until the 1850s, it was actually considered to be a planet, but later discoveries of objects in the asteroid belt knocked it out of the pantheon, demoting it to merely an asteroid. The creation of the “dwarf planet” designation in 2006 actually boosted Ceres’s standing by recognizing the ways in which it stands out from other asteroids.

I’ll grant that the “cleared orbit” condition is fuzzy, but it’s a bit clearer if you go by the more technical definition which states that the body be gravitationally dominant within its orbit. Due to resonances in orbital mechanics, it’s also technically impossible to clear trojans occupying the L4 and L5 Lagrange points, which even Jupiter has failed to do, and so those bodies aren’t considered in the “cleared orbit” determination. Thus, Earth is a planet because it is gravitationally dominant despite the technical existence of other minor debris, while Ceres, Vesta, Pluto et al. are not, because they exist in the vicinity of other similarly-dominant bodies. The definition of a planet gets fuzzy at the upper boundary too, where gas giants start to look more and more like stars that flunked out of nuclear fusion class. Jupiter itself sometimes sits at the bottom end of that scale, depending on who you ask and whether they’ve read Clarke’s 2010.

A lot of things in astronomy end up being fuzzy, really, as happens in any physical science where reality refuses to be put into neat little boxes - “dwarf planet” is just the latest addition to the ever-growing box collection. The previously-hosted-by-Stephen-Fry BBC panel show QI has gotten a lot of mileage out of the question “how many moons does the Earth have?”, because “moon” is a squidgy term that could be interpreted classically to mean we only have one (The Moon), or it could be interpreted literally to include any natural object orbiting the planet, in which case there’s dozens or even hundreds of tiny clumps of rock that technically qualify. Given the relative size of the Moon to Earth, you could even make the case that this is a twin-planet system, rather than a planet-moon system, and thus the Earth technically doesn’t have a moon at all. Depending on how you want to define the cut-off between moon, moonlet, and “whatever is smaller than a moonlet” (which so far astronomers have neglected to do), Saturn has between 13 and 62 moons - or millions if you count each ring particle separately.


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