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Dwarf planet versus comet/asteroid hinges on mass, basically its "enough mass to be roughly round" (technically it's called "hydrostatic equilibrium"). Back fr
by mandevil 1y ago
Dwarf planet versus comet/asteroid hinges on mass, basically its "enough mass to be roughly round" (technically it's called "hydrostatic equilibrium").
Back from the 1810's to the 1870's or so, most people considered Ceres, Vesta, and things like that to be planets- they were bodies that wandered around the solar system, that meant they were planets. When the numbers started to get into the 20's, everyone decided to create a new category, "asteroid" (Greek for 'star-like') and put all of the smaller things in that. So when Pluto was discovered in 1930 it was slotted right into the planet category. Pluto was discovered mostly by accident, because Clyde Tombaugh was amazing at working the blink comparator, and finding the one dot that moved in between the two pictures of the night sky a few days apart.
However, by the 1990's and 2000's you had computers and digital cameras, which are even better than Clyde at finding things that move, and quickly the number of planets started to go up- and it was clear that once we had thoroughly mapped the ~~Oort Cloud~~ (meant Kuiper Belt, see below) etc. we would have dozens of planets. And so once again astronomers decided to create a new category, just like they had with asteroids a century earlier. This time they drew the line in such a way that Ceres got moved from asteroid to dwarf planet- it has enough mass to be roughly round, so after over a century of being an asteroid it became a dwarf planet.
This is how things always work in science: we discover something, then we discover more of them, and re-categorize everything based on the new discoveries. It's just more noticeable with Pluto because reciting the planets is done by every schoolkid in a way that they don't for subatomic particles or for species of voles or whatever.
- epicureanideal 1y agoVery informative, thank you!
- AStonesThrow 1y ago> thoroughly mapped the Oort Cloud So it’s interesting that the Oort Cloud is often mentioned as a real thing. Surely there are plenty of bodies discovered which are orthogonal to its existence, but Oort’s “Cloud” itself still enjoys only the status of hypothesis and not reality. https://en.wikipedia.org/wiki/Oort_cloud https://en.wikipedia.org/wiki/Oort_cloud Sadly, even Wikipedia editors seem unable to distinguish between the formal definitions of “hypothesis” vs. “theory” when delivering such a scientific article.
- codethief 1y agoOh wow, looks like I'm one of today's lucky 10,000! Thanks so much!
- mandevil 1y agoYou are correct, I meant to say Kuiper Belt, not Oort Cloud, pulled the wrong thing out of my memory. Unlike the Oort Cloud, we are doing a good job of mapping KBO's as we speak.
- throwaway2k255 1y agoIf the furthest objects of the Oort Cloud are over 3 light years away, it is relatively close to Alpha Centauri. Is there a chance that Alpha Centauri also has its own cloud that overlaps with it? Would AC influence the cloud and adjust the orbit of smaller comets?
- TheOtherHobbes 1y agoThere's a chance, but no one knows for sure. Oort Clouds are mostly empty space, so there wouldn't be much direct interaction. But there would certainly be gravitational effects. My guess (FWIW) is there's more out there than we suspect, likely including plenty of rogue/wandering planets between systems.
- hinkley 1y agoAnd that, boys and girls, is how Neil deGrass Tyson got Pluto demoted. (I kid).
- naikrovek 1y agoI still think he did it because he wanted to have his name on something significant. He’s a science communicator, not a researcher, and he’s not going to be making any discoveries. So he’s gotta change something that already exists to have his name on something that everyone knows. He had the power to change its status, so he did. I think that’s all it was. I hope I’m wrong but I’ve never heard a really GOOD reason to undo something that was so commonly known and taught. The definition for “planet” could change and Pluto could have been left alone, grandfathered in, in a way. There’s a reason it was discovered first. It’s huge compared to other dwarf planets. There’s no reason that Pluto couldn’t have remained a proper planet. It’s big enough to be round and its largest moon is big enough to be round. Mars doesn’t have any round moons. Mars is still a planet.
- XorNot 1y agoIsn't that kind of the issue though? Pluto's moon isn't just round it's about half the size of Pluto itself such that the Pluto-Charon system orbits around a point in space between the two bodies.