I’m pretty sure Pluto doesn’t orbit a planet, so it’s not a moon. And the Moon, not only is it named a moon, but also orbits a planet, so therefore is a moon. One is a moon and the other is not a moon. Moon, not moon.
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traches@sh.itjust.works 3 days ago
And the IAU got it wrong when they reclassified Pluto. Jupiter and mercury belong in the same category but the moon and mercury don’t? Get the fuck outta here
sbeak@sopuli.xyz 2 days ago
traches@sh.itjust.works 2 days ago
Why does the definition involve location? Intrinsic properties make more sense. Who cares what it orbits or what else is is in a similar orbit?
sbeak@sopuli.xyz 2 days ago
Moons are defined as naturally-formed objects that orbit a planet. Natural satellites, basically. What’s wrong with that definition? The Moon is a moon, but Pluto is not. Moons don’t have to be a fixed size, Earth’s moon is relatively big compared to the planet it orbits, Ganymede is larger than Mercury, and some moons are teeny tiny. If you tried to classify them based on size, you’d have a million different categories.
traches@sh.itjust.works 2 days ago
I’m saying that (most) moons are planets too. Anything big enough to be round, but not big enough to burn hydrogen, should be a planet regardless of where it orbits.
Tlaloc_Temporal@lemmy.ca 2 days ago
Pluto and Charon orbit each other. The barycentre (the center of mass they both orbit) is far outside of Pluto. The Earth-Moon barycentre is still inside Earth, though this could be changed by moving the Moon further out.
Either way, Earth, the largest rocky planet, could be made into a moon by sending it to Jupiter, so I don’t think being a moon should disqualify a celestial body from being a planet.
sbeak@sopuli.xyz 1 day ago
One of the main criteria for a planet is that it orbits a star. Moons don’t orbit stars and hence not planets. If Earth was orbiting Jupiter, it would be a moon but not a planet. Moons could harbour life too! Titan (which orbits Saturn) has an atmosphere, and Europa could have subsurface oceans under all that ice.
Tlaloc_Temporal@lemmy.ca 1 day ago
That definition means a planet has nothing to do with physical state, and everything to do with the proximity of your neighbors. We could promote the Moon to a planet by pushing it further away, or demote Earth from being a planet by slinging it a bit closer to it’s hungry uncle Jupiter. We could demote all planets by extinguishing the Sun! Then the entire system stops working and it’s all just asteroid or something.
That arbitrarily chosen definition doesn’t describe the object, only it’s place in the malleable hierarchy. With this, the title of planet tells us nothing about the object itself, except that it’s orbit is only dominated by a star.
Even worse, the IAU definition is extra arbitrary, as it only counts objects that orbit specifically the Sun, so the vast majority of bodies in hydrostatic equilibrium that don’t fuse hydrogen aren’t planets. They also play very lose with hydrostatic equilibrium, as Mercury isn’t in hydrostatic equilibrium, yet is explicitly classified as a planet. And “clearing it’s orbit” is also rather indistinct, with no method to determine this is given. It’s up to argument if Neptune is a planet, as many plutoids intersect it’s orbit.
Even more worse, the barycentre of our solar system is sometimes outside of the sun! That means sometimes the Sun is co-orbiting with the rest of the solar system bodies, and therefore by this definition nothing is a planet! It’s a definition so arbitrary that it periodically stops existing!
I’m not just saying I disagree with the IAU here, but that their definitely is objectively poor, and poorly used. I agree that Pluto, Eris, Ceres, and many others should be in a different category from Jupiter, but make some categories that make sense, please!
rockerface@lemmy.cafe 2 days ago
It’s either remove Pluto or add a dozen other “planets” to the list, most of them in the middle
traches@sh.itjust.works 2 days ago
They should have done that
lemmyartistforhire@lemmy.world 2 days ago
Yes they should have. Fuck Mike Brown.
frezik@lemmy.blahaj.zone 2 days ago
I’ve heard (from people who have credentials in this stuff) that the people in the room at the time were mostly orbital mechanics people. The planetary scientists weren’t there. That’s why you have this “cleared its orbit” rule. If there were more planetary science people in the room, Pluto might still be considered a planet. And it may yet change back.
craftrabbit@lemmy.zip 1 day ago
You sound like a lunatic traumatised war veteran. The war has been over for a long time, the decisions have been made and there is no going back, my friend.
sbeak@sopuli.xyz 2 days ago
And to add,Jupiter and Mercury belong in the same category as in they both orbit a star (the Sun in this case), both have enough mass to be spherical, and both have clear most of their orbits.
But the category of planets has sub-categories. Mercury is a rocky terrestrial planet while Jupiter is a gas giant as the former is smaller and rocky while the latter is large and made of mostly hydrogen and helium gas. Gas giants can also be called “Jovian planet”, but Jove is just an alternate name for Jupiter (the god) so you’re basically calling Jupiter a “Jupiter planet” which I think is a bit ridiculous but whatever it’s fine. Both are still, of course, planets. It’s like a large tree and a sunflower. Both are still considered plants, but certainly in different subclasses of the category of plant.
Dwarf planets, although not proper planets, are still very interesting objects that could even harbour life in oceans below their icy surfaces. Also, Pluto is not alone in the dwarf planets classification. There’s also Eris, Ceres, Makemake, and probably thousands more we haven’t discovered yet!
Tlaloc_Temporal@lemmy.ca 2 days ago
There’s also plenty of classifications of plants based on form! Non-vascular plants, woody plants, herbaceous plants, algae and lichen…
Most of our “rocky” planets are pretty wet though. Mars is drying out, but Venus is caked with volatile chemicals and Earth is downright infected. Only Mercury is really barren, partly due to it’s small size. I could easily see three categories for gravitationally rounded bodies that can’t fuse hydrogen: Dry planets (usully smaller), Wet planets (usually larger), and Gaseous planets (gas giants).