You know how there's like some mathematician or something, who like did some useful stuff but is primarily known for overshadowing that work by going to great lengths trying to convince people to blow up the moon or something?
I wanna be like that but the hill I'm dying on is that the moon should be considered a planet
Stop tagging this about the Unabomber it's not about the Unabomber, it's about time we give the other fucked up mathematicians some recognition, it's about this fucking guy
OP you're right and you should say it. There are 9 planets in the solar system and two of them are in a binary planetary system. I will die on this hill.
EXACTLY. EARTH-MOON IS A BINARY PLANET SYSTEM. AND I WILL BECOME NOTABLE FOR MY FREQUENT POSTS TO VARIOUS TUMBLR BLOGS AND MY ADVOCACY FOR THE RECOGNITION OF THE MOON AS A PLANET.
Now, dear reader, you might say: "But three of the Jovian moons and Titan are bigger than the Moon!". And to that I say yes, but two of those are bigger than Mercury also and people aren't usually upset about that. Plus all of those are satellites of bodies that are completely incomparable in scale.
Ganymede, the biggest moon in the solar system, is 0.008% the mass of Jupiter. The Moon is a bit over 1.2% of Earth's mass and a solid 27% of its radius. There's no other planet* in the solar system with a satellite anywhere close to the kind of similarity in size that the Earth-Moon system has.
You might also say "Fine but it's literally called 'The Moon' so that's a bit silly". To which I say that I've been calling it that to be more easily understood but it would be extremely easy to switch to calling it "Luna" which is what most people do when they encounter situations where saying "The Moon" creates ambiguity - like when writing sci-fi or a nontrivial amount of astronomical research.
In conclusion, lumping Luna in with the satellites of other bodies is unhelpful because it is geophysically distinct from most of them, and orbitally distinct from all of them. Luna is a planet and it's rad that we can see one so clearly in the night sky.
[*No, Pluto is not a planet, but yes Pluto-Charon is totally a dwarf planet binary]
I'll integrate this into my belief system but only because it's funny
hello???? hello??????????? have we walked into the twilight zone or something??????????? yes, the moon is a percentage (a percentage almost exactly) of earth’s mass, but that doesn’t magically make us a binary system! the barycenter is still well within the diameter of earth! what next, are you going to say that since deimos and phobos orbit mars, they’re actually a trinary planetary system?? you fucking better not!
Hi, I'm an astrophysicist, I am well aware of the IAU (International Astronomical Union) definition of a planet. It is a definition that is relatively controversial and doesn't really make a lot of sense - it was mostly written to prevent the list of planets from getting too long as we discovered more dwarfs. This definition does not include anything to do with barycentres - I'll get back to that.
The IAU definition of a planet has 3 parts:
1. Object in orbit around our Sun
2. Object has reached hydrostatic equilibrium (i.e. it's a sphere, not a potato)
3. Object has cleared its neighborhood around its orbit
Both Earth and Luna satisfy 2. I will accept that 1 is debatable, but the crux of my argument is that Luna is the size of a terrestrial planet (yes, ~1% of Earth's mass, but still huge and of roughly the same order of magnitude as Mercury, which is a mere ~5% of Earth's mass) and exceptionally large relative to its orbital partner compared to any other "satellite", a factor the IAU does not account for.
It's important to note that 1 literally does not permit binary planets - even if both bodies are identical, one must be the "moon". This is major criticism of the IAU definition. It also doesn't account for exoplanets or rogue planets, but that's another story.
3 is where this definition falls apart. You could easily argue that most of the planets in our solar system fail depending on how you interpret it, because it's so fuzzy. The Earth fails, because there's a planet-sized body chilling out in its orbit (Luna), Jupiter fails because it has huge quantities of asteroids trapped in its Lagrange points, etc.
In the latter case, we say that because Jupiter is determining the motion of these bodies, it still counts. For the Earth we simply ignore Luna and say that the rule is more about stray bodies than orbital partners. But by the same logic we can say that for Luna we ignore the Earth, and Luna passes.
So I would argue that the IAU definition is bad, but if you fixed it so that it allowed binary systems to exist, it would readily define Luna as a planet in my view (if you deleted the Earth from the solar system and left Luna, it would unambiguously meet the criteria).
Now let's talk about barycentres.
The barycentre of two bodies in orbit is just their overall centre of mass. People often point to the external barycentre of the Pluto-Charon system to indicate that they are binary dwarfs. However, this is a poor metric in my view, because it's highly dependent on orbital distance.
The centre of mass of the Earth-Luna system is inside the Earth at present, but if Luna simply orbited further away, the barycentre would be in the empty space between them, with nothing about the two bodies individually, or the qualitative nature of their orbits, having changed. In fact, given enough time and pretending the Sun won't consume both bodies in a few billion years, Luna would actually drift far enough away due to tidal interactions for this to happen - it would be silly for it to suddenly be a planet one day when it wasn't the day before.
To answer your question, no. I would under no circumstances argue that the martian moons are planets. They are minuscule space potatoes that are not even large by the standards of asteroids. If Mars were close enough in mass to them for the system to be considered plausibly trinary, it would be far too small to even qualify as a dwarf planet (and there's no way such a system would be gravitationally stable to perturbation by Jupiter regardless).
@hereticalteapot Thank you so much for laying this all out! I totally agree. Something that's motivating to me is the fact that Luna is more gravitationally attracted to the Sun than to Earth- and by that definition is orbiting the Sun, not the Earth. This is not true of any other "moons" in our solar system except some which are not even large enough to become spheres- so this is another way in which it is different from the moons in our system.
It's really frustrating to me when people lash out and say "You're wrong because there's a definition, for the love of god look up the definition" about a topic where I think it's clear my point is that I KNOW the definition and I disagree with it. And that's allowed! Definitions are made up! "Planets" are made up, and I think we should make them up differently!
All the things in our solar system are just different kinds of rocks dancing to each other's gravity- they're all affected by each one's gravity, even in tiny ways. They do not fall neatly into subcategories "planet" and "not a planet" - we made this distinction up because we wanted it. We noticed that some of the bodies in our solar system seemed much more important and dominant than others and we wanted a name for that. But the planets don't know that- they don't have an inherent major distinction between them, nor are they obligated to. When we wanted to come up with a way to clearly decide which bodies were planets, we had to make something up.
What we made up is a little bit vague, and even if it were extremely clear cut, we could still debate whether it was a reasonable or intuitive or useful definition.
In science we have lots of definitions, and they aren't handed down by god, they're made by people, and they are made to be useful, and when they aren't useful or reasonable, they can be and should be and are changed. Knowing which things fit which definitions is part of science, but another part of science is thinking critically about whether things SHOULD be defined, how they should be defined, whether definitions need to be changed, and other things like this- and that's messier than just knowing facts. But that's science.
I hate to say it folks, but my fondness for the "Luna is a planet" argument might not just be because it's silly and I like to be silly. It might be a really convenient training ground for thinking about definitions which are social constructs in other contexts. Like race, sex, gender, disability, economics. These things, like planets, are made up. They are very real, don't get me wrong! They are real because we made them up! But what, exactly, they are... we decided it. And we could decide differently. We have that power. If you don't like something because it doesn't fit a definition- that's not really an argument against it. Because the definition could be changed. Should it be?
This is all great points and you're so right.
Also for any barycenter definition fans - the barycenter of Luna and Jupiter is within Jupiter. I think we can all agree Luna is not a moon of Jupiter.
Something else to note is that IAU bylaws require a new definition to be voted on to be circulating for at least a year in the scientific community. The one voted on in 2006 was drafted the same day. Also, the vote was specifically and carefully planned such that most of the planetary scientists who were only there for specific parts of the conference relevant to their fields had left already. It was rigged and in violation of their own bylaws, so I think its well past time we stop listening to this absurd definition.
What the absolute fuck I can't believe election rigging is part of this story lmfao
Alexander Abian blogging from the dead
Prev I would really like you to explain what you meant by some of this because I think I'm not aware of some physics you're referring to. But. On the other hand. I am SLIGHTLY afraid to ask.
i am Incapable of putting things into words in any reasonable manor so instead i have drawn a handy diagram
Well. I guess that helps.
