Are Rask and Rusk planets

[K^2]

10 hours ago, Maria Sirona said:

Well then i am too. If Sun's gravity is stronger on the Moon than Earth's then how does that not contradict the Moon orbiting the Earth

First, it's important to make sure you are convinced that this first part is, indeed, true. Gravitational parameter for the Sun is 1.33x10²⁰ m³/s² giving gravity at 1AU of about 0.006 m/s². Earth's gravitational parameter is 3.99x10¹⁴ m³/s², and at a distance of 362,600km, the perigee, results in gravity of 0.003 m/s². So Sun's gravity is almost exactly twice the Earth's. This ratio varies ever so slightly due to both orbits not being perfect circles, but it's never far off.

So now for the conceptual part. First, whether we think of the Moon as actually orbiting the Earth is kind of matter of semantics and your frame of reference. If you look at the trajectory of the Earth and the Moon around the Sun, they are both racing around at nearly 30km/s. The Moon's speed varies by only about 1km/s relative to that, sometimes leading the Earth, and sometimes lagging behind. That is not a huge amount of variation. Yes, from perspective of someone standing on the Earth, this wobble looks like the Moon making circles around the Earth, but from perspective of any other planet, it's two objects pretty much sharing an orbit around the Sun, with the Moon's orbit being a bit wobblier than the Earth's.

Still, the Earth and the Moon are clearly orbiting in concert. The movement is not chaotic in the least. The path of the Moon relative to the Earth follows Kepler's laws pretty closely and in every way appears to be an orbit around the Earth. And, of course, there is mathematical beauty to why it works this way. To a high degree of precision, you can think of the center of mass of the Earth-Moon system as traveling around the Sun as if it was a single planetary body of combined mass. It is not exactly so, due to tidal effects, but it's close enough. So you can think of Earth-Moon barycenter as being in free-fall with respect to the Sun. We can attach our frame of reference to the barycenter. It is an accelerated frame of reference - much like being on a Devil's Wheel, or any other rotating platform. So if we want to describe motion of the Earth and the Moon relative to that barycenter, besides the Sun's gravity you also have to consider the centrifugal force and the Coriolis effect. The centrifugal force cancels out Sun's gravity almost exactly. It is not a perfect cancellation, because the Sun's gravity is a bit stronger closer to the Sun and weaker further away. However, this correction is now much, much weaker than Earths' gravity. Likewise, Coriolis effect is fairly significant, but the main contribution is going to be reducing effect of gravity between Earth and the Moon. The net effect is that the Moon completes almost exactly 12 orbits around the Earth in a year, corresponding to the 12 lunar Months. Whereas, of course, from perspective of an inertial frame of reference, the Moon wobbles around the Earth 13 times in a year. Likewise, the Coriolis effect results in the Moon's orbit appearing to precess, completing one precession revolution in a year. Therefore, exactly matching the orientation of the Moon's orbit staying relatively fixed from perspective of an inertial coordinate system.

tl;dr, when a pair of objects orbit close enough to each other in presence of a third much, much heavier body, they can still behave as if they are orbiting just each other, because their mutual center of mass is in free fall with respect to the third body.

There is a limit to this, of course. As the Moon recedes from the Earth, various perturbation effects are getting stronger. Eventually, unless both are swallowed by the Sun inflating to red giant first, the Moon will be too far away and these perturbations will knock it out of the Earth's vicinity entirely. What happens after that would depend on a lot of factors. The Moon might crash into the Earth eventually, or it might get knocked out into a different orbit. But that will be billions of years from now.

[PlutoISaPlanet]

Not sure if anyone said this, but Pluto and Charon are considered a Binary pair.

[K^2]

2 hours ago, PlutoISaPlanet said:

Not sure if anyone said this, but Pluto and Charon are considered a Binary pair.

Yeah. If Pluto was to be reclassified as a planet again, it would have to be so along with Charon, making it a double planet based on current definitions.

[SSTO Crasher]

A new page of intense debate 

[AtomicTech]

egap wen kool yeh

[PlutoISaPlanet]

14 hours ago, K^2 said:

Yeah. If Pluto was to be reclassified as a planet again, it would have to be so along with Charon, making it a double planet based on current definitions.

#plutoisaplanet

[Omni122]

On 1/20/2022 at 4:31 PM, intelliCom said:

There's a new definition for planet being proposed, which would essentially consider moons to also be planets of their own, ignoring the "clearing of the neighbourhood".

Also, as an important note: If a planet could only be a planet if it's cleared its neighbourhood, would this make Saturn a dwarf planet?

Clearing it's neighborhood has nothing to do with whether or not their are objects in something's orbital path, it is the ratio of an object to the mass of all other objects in it's orbit combined. Saturn is not a dwarf planet by the current  definition. 

 

This thread is ridiculous, some people are actually arguing that the Moon orbits the sun. Oh my god

On 1/20/2022 at 9:35 PM, K^2 said:

I'm absolutely in favor of classifying the Moon as a planet. While Earth is massive enough of the two that the Earth-Moon barycenter is entirely within Earth's surface, Earth's gravity is still weaker than the Sun's as far as effects on the Moon. That is, Moon primarily orbits the Sun, not the Earth, and merely co-orbits the Earth. Another way to look at it is that Moon's trajectory around the Sun is everywhere convex - it is always accelerating towards the Sun. This isn't true for any other moon in the Solar System. All of the other moons are pulled by their primary with enough force that sometimes they are pulled away from the Sun. That really shows that the moons are bound to their planet. Since this is not the case for the Moon, it really doesn't make sense to say that it orbits the Earth as its primary.

I would also argue that barycenter situation is temporary, as the Moon is receding, and this will eventually resolve itself. Yes, it's billions of years in the future, but I think it's a good enough example to use the tug-of-war definition instead of the barycenter one.

There might be some naming confusion. But if it gets too confusing, we can start referring to the Moon as Luna, clearly distinguishing it from various moons of the solar System. But that's optional. Proper classification is the important bit here.

Even if the Moon did orbit the sun (it doesn't), the moon still wouldn't have cleared it's orbit and would be a dwarf planet.

Edited January 29, 2022 by Omni122

[intelliCom]

3 hours ago, Omni122 said:

Clearing it's neighborhood has nothing to do with whether or not their are objects in something's orbital path, it is the ratio of an object to the mass of all other objects in it's orbit combined.

A ratio? What's the ratio?
Who gets to decide what the ratio is?
Is it specific, is it a range?
If it's specific, what happens if we find a planet that perfectly sits on that exact ratio?
Why does the presense of debris decide a planet's status? If we found a planet the size of Earth, but it's 'neighbourhood' resulted in a dwarf planet's ratio, is it a dwarf planet- not because it's undersized- but because it's "not big enough"?

There's too much vagueness with the current definition. Too many unknowns and confusion. It's easiest to consider a "planet" as an object whose orbit is locked to a sun. Sub-planets are objects whose orbit is locked to a planet. Yes, this would also make asteroids planets, but not large enough to be considered important. Many asteroids are considered "Moons" anyways, so what's wrong with considering them planets if they orbit the sun? 

3 hours ago, Omni122 said:

Even if the Moon did orbit the sun (it doesn't),

Technically, the Moon orbits the sun with the Earth. It's not like you're outside the sun's gravitational field just because you're in Earth's gravitational field. Mapping the moon's orbit as the earth moves around the sun looks like it has a similar orbit to the Earth, but oscillating from side to side due to its motion around Earth. If the Earth just disappeared, the moon would continue to orbit at the same speed and position as the Earth used to. So, technically, all moons orbit the sun, it's just that their motion is affected by the planet that they also orbit at the same time.

As for @K^2's reasoning to consider the Earth's moon a planet because the sun has a more significant effect than the Earth, I'm not so sure about that. The moon's orbit forms a proper loop around its parent planet- Earth- so it is a satellite to Earth, therefore not a planet.

Edited January 29, 2022 by intelliCom

[SSTO Crasher]

The current definition would classify a celestial object the is the dominant object. It has to be the main influencing factor. Like for example Neptune, everything is Neptune’s orbital path is controlled by Neptune, and by that I mean Neptune ejected the vast majority of them into the Kuiper belt. And Neptune has the most mass in its orbit. 

[intelliCom]

8 hours ago, SSTO Crasher said:

The current definition would classify a celestial object the is the dominant object. It has to be the main influencing factor. Like for example Neptune, everything is Neptune’s orbital path is controlled by Neptune, and by that I mean Neptune ejected the vast majority of them into the Kuiper belt. And Neptune has the most mass in its orbit. 

Pluto has more mass than Charon, so then it should be a planet under this definition, right? What would this make Charon? A moon?

[K^2]

On 1/28/2022 at 7:38 PM, Omni122 said:

Even if the Moon did orbit the sun (it doesn't), the moon still wouldn't have cleared it's orbit and would be a dwarf planet.

In what possible world is the Moon not orbiting the Sun? It's trajectory around the Sun is almost a perfect circle. If I give you a plot, you will not be able to distinguish it from a circle even if I plot a matching circle next to it.

As for clearing the local neighborhood, Stern–Levison's Λ for the Moon would be 23, which is significantly greater than 1, meaning, the Moon alone would be capable of clearing local neighborhood without any help from Earth. Other similar parameters for planethood are even higher for the Moon. It would absolutely not be a dwarf planet under any existing definition. If the Moon was in its exact current orbit, but the Earth was not here, the Moon would be a planet of a solar system following current definitions of the IAU. That is a demonstrable fact.

On 1/28/2022 at 10:48 PM, intelliCom said:

The moon's orbit forms a proper loop around its parent planet- Earth- so it is a satellite to Earth, therefore not a planet.

In what coordinate system? If you mean from perspective of the Earth, then from perspective of the Moon, the Earth makes a complete loop around the Moon, and therefore, is the Moon's satellite. This cuts both ways.

 

The only factor that makes the Moon a moon of the Earth is the fact that barycenter of the Earth-Moon system is within the Earth's surface. Unfortunately, that is the factor that IAU chose to define a moon by. It is ridiculous, because by absolutely every other standard, the Moon is a planet, and the Earth-Moon system is a double planet.

The definition in use is a bad one, because it falls apart the moment you start considering other potential planetary systems. A potential moon of a potential exoplanet whose orbit is elliptical and whose barycenter only sometimes passes through one of the bodies, is that really a moon? Well, how often does it have to happen? What if it only happens under influence of other bodies? This is a bad definition, and the only reason we're clinging to it, is because we're used to saying that the Moon is a moon of Earth, and we want a definition that keeps it so. It's the same reason we clang to the old definition of a planet with Pluto, to make sure it stays a planet. And so we should change the definition of a moon for the same reason we changed the definition of a planet - to make sure we can apply it generally. Convexity of orbit around parent star is a good definition. It fully encapsulates the relationship between the star, the planet, and the moon, while being rigorous even when the orbits are potentially complex. And by that definition, every moon of the Solar system that is currently a moon gets to stay one. All except for the Moon. Because the Moon really does have more in common with planets than other moons.

[intelliCom]

27 minutes ago, K^2 said:

In what coordinate system? If you mean from perspective of the Earth, then from perspective of the Moon, the Earth makes a complete loop around the Moon, and therefore, is the Moon's satellite. This cuts both ways.

Touché. Didn't consider that. How about a more extreme case? Between Amalthea and Jupiter, could Jupiter be considered a satellite of Amalthea if you consider Jupiter's motion relative to Amalthea? If not, why?

Quote

The only factor that makes the Moon a moon of the Earth is the fact that barycenter of the Earth-Moon system is within the Earth's surface. Unfortunately, that is the factor that IAU chose to define a moon by. It is ridiculous, because by absolutely every other standard, the Moon is a planet, and the Earth-Moon system is a double planet.

A potential moon of a potential exoplanet whose orbit is elliptical and whose barycenter only sometimes passes through one of the bodies, is that really a moon? Well, how often does it have to happen?

If I recall, the Earth-Moon pairing has one of the closest ratios between the mass of two celestial bodies (ignoring Pluto-Charon). By the IAU's definition, if the Moon was orbiting just a bit further away, am I correct that the barycenter would no longer be in Earth? If this is the case, then an exoplanet with the same altered conditions that I mentioned would then be a binary planet pair. Larger with the same mass as Earth, Smaller with the same mass as the Moon, but they're further apart. This would mean that the difference between the Moon being a satellite and a planet is its distance from Earth. Just because its a bit closer means its a Moon?

Quote

This is a bad definition, and the only reason we're clinging to it, is because we're used to saying that the Moon is a moon of Earth, and we want a definition that keeps it so. It's the same reason we clang to the old definition of a planet with Pluto, to make sure it stays a planet. And so we should change the definition of a moon for the same reason we changed the definition of a planet - to make sure we can apply it generally. Convexity of orbit around parent star is a good definition. It fully encapsulates the relationship between the star, the planet, and the moon, while being rigorous even when the orbits are potentially complex. And by that definition, every moon of the Solar system that is currently a moon gets to stay one. All except for the Moon. Because the Moon really does have more in common with planets than other moons.

Is there anything relevant about the mass of various other moons exceeding our moon? Titan and Ganymede for instance, are those satellites just because they're nearby a larger body? If you got Earth in orbit of Jupiter, would it be a moon of Jupiter?

Edited January 30, 2022 by intelliCom

[K^2]

2 hours ago, intelliCom said:

If I recall, the Earth-Moon pairing has one of the closest ratios between the mass of two celestial bodies (ignoring Pluto-Charon). By the IAU's definition, if the Moon was orbiting just a bit further away, am I correct that the barycenter would no longer be in Earth? If this is the case, then an exoplanet with the same altered conditions that I mentioned would then be a binary planet pair. Larger with the same mass as Earth, Smaller with the same mass as the Moon, but they're further apart. This would mean that the difference between the Moon being a satellite and a planet is its distance from Earth. Just because its a bit closer means its a Moon?

Yeah. The maximum elevation of the barycenter is when the Moon is at the apogee. You take that apogee of 405,400km, multiply by the Moon's mass, and divide by combined mass of the Earth and the Moon and you get 4,927km. Earth's equatorial radius is 6,378km, so the Moon would only have to be about 30% further away for the barycenter to end up above the Earth's surface. And the Moon will get there in another 4 billion years or so. So under current IAU definition, the Moon will be a planet in the future. It's pretty much a certainty, unless Sun expands to the red giant stage a bit faster than anticipated.

But that's just one more reason I'm not happy with current definition. "The moon is a moon. For now!" I get that things move around and status of celestial objects can evolve, but a moon predestined to become a planet is a bit much.

2 hours ago, intelliCom said:

Is there anything relevant about the mass of various other moons exceeding our moon? Titan and Ganymede for instance, are those satellites just because they're nearby a larger body? If you got Earth in orbit of Jupiter, would it be a moon of Jupiter?

Well, the thing is, if you arbitrarily place something somewhere else, you can get bizarre combinations. But there's a reason why the situation with the Moon is unique. Usually, moons form from protoplanetary disk, so as you move further out, you end up with less and less stuff to make these moons. As a result, the heavier moons are closer to parent body, where the gravity of parent body is also stronger. So you end up with a situation where the gravity of the planet dominates for any naturally formed moon. Likewise, captures tend to be light in general, and a heavier capture requires a stronger interaction, so it also likely to end up being closer in. There just aren't a lot of ways in which what we typically think of as a moon can end up being both fairly heavy and fairly far away from the planet.

Earth-Moon situation is special and it reflects the special way in which the two bodies formed. That, of course, being an impact of two planetary bodies, proto-Earth and Theia. An impact like that can easily produce just one large planet, a planet and a bunch of moonlets or, as it happened in this case, during a glancing impact, two planets in - two planets out.

So it makes sense for the largest moons of Saturn and Jupiter to be considered moons despite their size, because they formed next to a really massive object and as part of its formation. The Moon wouldn't have been here if it wasn't for an impact from another planet of the Solar System. One which has been almost fully absorbed by the Earth and the Moon.

[intelliCom]

23 minutes ago, K^2 said:

So it makes sense for the largest moons of Saturn and Jupiter to be considered moons despite their size, because they formed next to a really massive object and as part of its formation. The Moon wouldn't have been here if it wasn't for an impact from another planet of the Solar System. One which has been almost fully absorbed by the Earth and the Moon.

Then this begs the question: What should the ratio of mass be between planet and moon be in order to consider the moon as a moon and not a planet? Obviously, we could consider Earth-Moon and Pluto-Charon as binary planet systems, but there's still an important question of where to draw the line.

Why did we consider Pluto a planet and Charon a moon in the first place? Why was Earth considered a planet and the Moon a moon?

Edited January 30, 2022 by intelliCom

[K^2]

11 hours ago, intelliCom said:

Then this begs the question: What should the ratio of mass be between planet and moon be in order to consider the moon as a moon and not a planet?

So I'm fully in favor of tug-of-war definition with a minor modification, that I would use the most favorable arrangement for the planet, where the candidate moon is the closest it ever gets to the planet and the planet is the furthest it ever gets from the star. This takes away some concerns over how to treat elliptical orbits. In other words, to be a moon, the following must hold.

M_S/M_P < R_P²/R_M²

Here, M_S is the mass of the star, M_P is the mass of the planet, R_P is the apoapsis distance between the planet and the star, and R_M is the periapsis distance between candidate moon and the planet. Note that the mass of the candidate moon doesn't factor in at all, and the planet is simply whichever one's more massive of the two. That kind of brings us back to the topic of the thread, because under this definition, depending on how close they are, Rask and Rusk might not be both classified as planets, with the lighter of the two being a moon. Again, because the relative masses don't matter - just the mass of the heavier one and the shortest distance between them.

In the real world, I don't think that's a problem, because arrangements where two very massive objects are going to be orbiting each-other close enough to be each-other's dominant gravitational effect will almost certainly result in the objects merging eventually. Of course, "eventually" is still a long time, so such systems would exist around some stars in our galaxy, but it should be reasonably rare.

One solution that's been thrown around is applying both tests, and qualifying as planet by either makes object a planet. So an object is a planet if it meets other criteria of a planet, such as hydrostatic equilibrium and neighborhood clearing and if either the barycenter is always outside of its partner or the tug-of-war test fails. If we apply that compound definition, then Rask and Rusk are planets by the barycenter test, the Moon is planet by tugo-of-war test, and the Earth is a planet by both tests. Likewise, Pluto and Chaeron would both be planets if both passed neighborhood clearing test.

[intelliCom]

18 minutes ago, K^2 said:

M_S/M_P < R_P²/R_M²

What are the units for mass and distance supposed to be? I realise that it doesn't matter since the ratio between the masses and the distances would result in the same number as long as you use the same units.

So, let's substitute these values with the most relevant ones from Earth-Moon:

M_s = 1 988 500 kg ⋅ 10²⁴

M_p = 5.97 kg ⋅ 10²⁴

R_p = 152.10 km ⋅ 10⁶

R_m = 0.3633 ⋅ 10⁶

1 988 500 / 5.97 < 152.10² / 0.3633² 
1 988 500 / 5.97 < 23 134.41 / 0.13
333 082 < 175 278

The result is untrue, therefore "The Moon" is not actually a moon.
Interesting system. Quickly plugging in various other values here; here's some checks for KSP:

Kerbin-Mun = Yes: 332033.8 < 1284414.3 (Ironic how KSP's analog to the moon is actually a moon but the real one isn't?)
Duna-Ike = Yes: 3885971 < 49249236.32
Jool-Tylo = Yes: 4149.25 < 101125.76

It seems to be a rigid system, if you always make sure to choose the larger mass as a certified "planet".
I wonder how this affects chains of satellites? OPM has Urlum-Wal-Tal for example.

Also, could an artifical object be considered a "moon" because it orbits a planet? If artificial creations don't count, what about dust particles?
An orbiting asteroid the size of a football? An asteroid the size of a car? Tree-sized asteroid? House-sized? At what point does a mass become significant enough to be granted "moon" status?

[K^2]

1 minute ago, intelliCom said:

I wonder how this affects chains of satellites? OPM has Urlum-Wal-Tal for example.

I think similar principles can be applied. There just isn't good terminology on whether a satellite of a moon is still called a moon or something else.

3 minutes ago, intelliCom said:

Also, could an artifical object be considered a "moon" because it orbits a planet? If artificial creations don't count, what about dust particles?
An orbiting asteroid the size of a football? An asteroid the size of a car? Tree-sized asteroid? House-sized? At what point does a mass become significant enough to be granted "moon" status?

A moon is a natural satellite. In fact, that's what formal definitions call them, partially, to sidestep the question of nested satellites like in your example above, I imagine.  So artificial satellites would not be considered moons.

There's no limit on size, either, but informally, sometimes the smaller such objects are called moonlets. I like the idea of making that formal, but I have no idea what to use as a cutoff point. Hydrostatic equilibrium would make a lot of objects traditionally called moons moonlets instead, but maybe that's the right way to go about it? Would we really lose a lot by having Phobos and Deimos being reclassified as moonlets? I'm ok with it. But maybe there's a sensible threshold somewhere bellow that which would be better used for moons. After all, hydrostatic equilibrium is one of the criteria for planets, and maybe it's ok for moons to be smaller? *shrug*

[intelliCom]

7 minutes ago, K^2 said:

I think similar principles can be applied. There just isn't good terminology on whether a satellite of a moon is still called a moon or something else.

I like the term 'sub-moon', or, alternatively, just re-use 'satellite' again. You could call an asteroid "a Moon of Ganymede", which in turn is "a Moon of Jupiter", or a "Sub-Moon of Jupiter."

You could even be silly and say "Moon-moon". The number of "Moon"s is the number of layers that it takes to reach the moon being referred to.

11 minutes ago, K^2 said:

A moon is a natural satellite. In fact, that's what formal definitions call them, partially, to sidestep the question of nested satellites like in your example above, I imagine.  So artificial satellites would not be considered moons.

What if- and this is real science fiction territory we're talking about here- a moon/planet was manufactured by collecting asteroid matter, melting it down into a larger mass of rock, then leaving it in orbit of another celestial body?

If there aren't any significant differences in this artificially produced celestial body compared to other celestial bodies, could it be considered a moon? Do moons/moonlets have to be moons/moonlets just by being primarily made of natural materials like rock or ice? Most technology doesn't really use rocks anymore, so could it be fair to consider a melted down ball of rock a moon?

Sorry if this seems a bit too philosophical, I just trying to get down to the nitty-gritty of what a moon should be.

19 minutes ago, K^2 said:

sometimes the smaller such objects are called moonlets.

Would this technically mean that the moon has billions of moonlets, as there's likely orbiting dust particles?

20 minutes ago, K^2 said:

Hydrostatic equilibrium would make a lot of objects traditionally called moons moonlets instead, but maybe that's the right way to go about it?

Yet again, you end up with the problem of figuring out the cut-off point. How round should a celestial body be for it to be considered "hydrostatic equilibrium"? Does Iapetus's ridge de-classify it as a moon?

[K^2]

1 hour ago, intelliCom said:

What if- and this is real science fiction territory we're talking about here- a moon/planet was manufactured by collecting asteroid matter, melting it down into a larger mass of rock, then leaving it in orbit of another celestial body?

1 hour ago, intelliCom said:

Would this technically mean that the moon has billions of moonlets, as there's likely orbiting dust particles?

I'm bunching these together, because the answer to both is that the astronomical definitions try to be practical. Yes. There are probably some tiny asteroids orbiting Earth that we don't count as Earth's moons, but we can't detect them, let alone track them. As we expand our ability to observe, we'll probably run into this problem and have to decide on what the lower limit needs to be. But we aren't there yet, so I have no idea what that'll be like. Likewise, until we start dealing with these quantities of materials being accumulated via artificial means, or if we find evidence of this happening around some exoplanet out there, which would be huge news in itself, I don't think it really matters.

1 hour ago, intelliCom said:

Yet again, you end up with the problem of figuring out the cut-off point. How round should a celestial body be for it to be considered "hydrostatic equilibrium"? Does Iapetus's ridge de-classify it as a moon?

With pretty much any definition, there's going to be a fuzzy area. Currently, it doesn't matter much, since the only place we use the hydrostatic equilibrium is to determine if something's a dwarf planet or not. There are a few cases where it's a bit fuzzy, including aforementioned Charon, which isn't quite a perfect spheroid. But nothing that really makes the distinction important enough. As we increase number of potential dwarf planets via observation of Kuiper Belt, or if we decide to extend the definition to moonlets, I think the solution will be to replace this loose criterion with a mathematical formula that predicts hydrostatic equilibrium based on the mass, select a threshold, and essentially go with that. In which case, it will become a function of mass and maybe composition of the object. I'm sure it will still be right on the boundary for some objects, but again, until that starts being a problem for classification of something, I don't think it will matter enough to change it.

 

Honestly, a lot of this is very much academic for now, because other than clean classification being useful for studying how planetary systems form by comparing various exoplanetary systems across multiple star systems in our galaxy, there isn't a lot of practical use. This goes double for moons, since we have just a handful of exomoon candidates right now. I do expect this to become a bit more important as we discover more exoplanets and exomoons, but it's still just matter of classification. And it will stay that way until it starts impacting somebody's finances.

And I suspect it will. Mineral rights on planets, moons, and asteroids will probably be a big deal in the future. And I'm sure various laws and treaties will be written using these types of words, and suddenly, it will become very important whether a particular body is a planet or moon. Whether a treaty mentioning asteroids applies to moonlets. Et cetera, et cetera. And I have no idea where this will all end up, but having good, concrete definitions already in use would be a good way to avoid conflict. So for the time being, I'm mostly concerned about consistency, and mostly around the more significant objects of the Solar System.

[Admiral Fluffy]

1 hour ago, K^2 said:

satellite of a moon

I always just called it a moonlet 

[intelliCom]

5 minutes ago, K^2 said:

So for the time being, I'm mostly concerned about consistency, and mostly around the more significant objects of the Solar System.

Good point. Not a good idea to get caught up in the small details when we haven't even cleared up the big stuff yet.

I have realised something about your formula though;

The only reason The Moon isn't considered a moon via the formula is because it's too far away. If it were closer, the ratio between Earth apohelion and Moon perihelion would be greater, resulting in a number greater than the ratio between Earth mass and Sun mass, therefore the Moon becomes a moon by being closer.

[sciencecompliance]

On 1/20/2022 at 6:31 AM, Maria Sirona said:

The third criteria of the IAU planet definition is dumb because Jupiter would then technically not be a planet because of the trojans. 

The trojans are where they are BECAUSE of Jupiter's gravity.  They are located around the Sun-Jupiter L4 and L5 Lagrange points.  Even though there are issues with the IAU definition (as with any attempt to categorize reality into tidy little boxes), this is a poor case against it.

[SSTO Crasher]

Seriously why are we considering the moon as a planet, it is a satellite of the earth. You want the proof, it orbits the earth. 
 

Spoiler

Also we better get back on topic quickly

 

Also, the moon is completely dominated by the earth. The earth keeps it in its orbit, it does not matter how close to circular it’s orbit around the sun looks. Oh gosh what have I done

[K^2]

8 hours ago, SSTO Crasher said:

Seriously why are we considering the moon as a planet, it is a satellite of the earth. You want the proof, it orbits the earth.

Actually, Earth orbits the Moon. I await your proof that this isn't the case. With numbers and criteria of "orbiting," please.

8 hours ago, SSTO Crasher said:

Also, the moon is completely dominated by the earth.

Demonstrated incorrect in this thread with numbers. Sun's gravitational pull on the Moon is twice as strong as the Earth's. If you want to claim otherwise, please, provide figures.

[shdwlrd]

I love threads like this. You end up learning a lot of information you didn't think you would be interested in but, you're learning something new and interesting. I guess it's the KSP way, accidentally learning something new.