Jupiter has 10 more moons we didn't know about(nature.com)
nature.com
Jupiter has 10 more moons we didn't know about
https://www.nature.com/articles/d41586-018-05725-6
111 comments
There really isn't any equivalent of the asteroid/planet split that exists for non-moons. We've known about small, non-spherical moons for over a century and nobody has seriously advocated giving a different name for them and the big spherical ones: Luna, Callisto, Ganymede, Europa, Io, Titan, and Triton. But yeah, astronomers will certianly need to figure out some distinction between chunks of ring and discrete moons.
There is a movement to make anything that isn't a sun capable of being a planet based on only it's own physical characteristics not that of it's location in space.
https://www.sciencealert.com/nasa-scientists-have-proposed-a...
https://www.sciencealert.com/nasa-scientists-have-proposed-a...
I got it! Dwarf moons.
I wonder if discovering lots of tiny moons will lead to a new definition for moon like what happened with the planets.
We also could probably use some adjustments on the other end too: when should a large moon be considered a second planet in the same orbit around their sun as its larger neighbor instead of a moon of that neighbor?
I've seen a couple fairly decent arguments that Earth/Moon should be considered a double planet.
One is that for every moon we know of except for Earth's, the force on that moon from the planet's gravity is more than the force on that moon from the Sun's gravity.
That's not the case for the Moon. The gravitational force on the Moon from the Sun is about twice as much as the gravitation force on it from the Earth.
I could accept a requirement for moon status being that the thing you are a moon of is the thing that has the strongest gravitational hold on you. For the Moon, that is the Sun.
Another argument is based on the shape of the paths of the bodies as seen from the Sun. Planets follow convex paths. Their moons swing them in and out as the moons go around them, but that just reduces the curvature of the planet's orbit. The Moon, for example, turns the Earth's path as seen from the Sun from essentially a circle (the eccentricity of the ellipse is low enough we can ignore it for this discussion) into a regular 12-gon with broadly rounded corners.
Same goes for other planets with moons, except their convex shape is more complicated because they have multiple moons.
When you look at those other moons from the Sun's viewpoint, they are not following convex paths. They are more like something you might have made when you first played with a Spirograph as a kid.
Except for the Moon. The Moon's path as seen from the Sun has the same basic shape as Earth's, a rounded 12-gon. In other words, it looks like a planet path, not a moon path.
(I'm not sure if that is actually another argument. It may follow from the first argument, the relative gravity strength one...I've not tried to do the math to see).
I find both these arguments pretty good, with one caveat. What happens with even bigger moons relative to their planet than the Moon?
Imagine if Earth had a moon that was much closer to Earth's mass, say 70 or 80%, and much closer to Earth?
Going by either the tug-of-war with the Sun criteria, or the convexity of orbit as seen from the Sun criteria, I think we could get a situation where each body would be classified as a moon of the other! I don't think we want to allow a system that is all moons, so we'll need some fiddling so that in this case they are both planets.
(Credits: I'm reasonably convinced I got both of the above arguments from one of Isaac Asimov's books that collected the monthly science columns he wrote for The Magazine of Fantasy and Science Fiction)
I've seen a couple fairly decent arguments that Earth/Moon should be considered a double planet.
One is that for every moon we know of except for Earth's, the force on that moon from the planet's gravity is more than the force on that moon from the Sun's gravity.
That's not the case for the Moon. The gravitational force on the Moon from the Sun is about twice as much as the gravitation force on it from the Earth.
I could accept a requirement for moon status being that the thing you are a moon of is the thing that has the strongest gravitational hold on you. For the Moon, that is the Sun.
Another argument is based on the shape of the paths of the bodies as seen from the Sun. Planets follow convex paths. Their moons swing them in and out as the moons go around them, but that just reduces the curvature of the planet's orbit. The Moon, for example, turns the Earth's path as seen from the Sun from essentially a circle (the eccentricity of the ellipse is low enough we can ignore it for this discussion) into a regular 12-gon with broadly rounded corners.
Same goes for other planets with moons, except their convex shape is more complicated because they have multiple moons.
When you look at those other moons from the Sun's viewpoint, they are not following convex paths. They are more like something you might have made when you first played with a Spirograph as a kid.
Except for the Moon. The Moon's path as seen from the Sun has the same basic shape as Earth's, a rounded 12-gon. In other words, it looks like a planet path, not a moon path.
(I'm not sure if that is actually another argument. It may follow from the first argument, the relative gravity strength one...I've not tried to do the math to see).
I find both these arguments pretty good, with one caveat. What happens with even bigger moons relative to their planet than the Moon?
Imagine if Earth had a moon that was much closer to Earth's mass, say 70 or 80%, and much closer to Earth?
Going by either the tug-of-war with the Sun criteria, or the convexity of orbit as seen from the Sun criteria, I think we could get a situation where each body would be classified as a moon of the other! I don't think we want to allow a system that is all moons, so we'll need some fiddling so that in this case they are both planets.
(Credits: I'm reasonably convinced I got both of the above arguments from one of Isaac Asimov's books that collected the monthly science columns he wrote for The Magazine of Fantasy and Science Fiction)
> I've seen a couple fairly decent arguments that Earth/Moon should be considered a double planet.
It should at least be considered a planet and dwarf planet pair. After all, the Moon is larger than Pluto. The relative size of the Moon compared to Earth is enough to convince me. Binary planet or double planet would make fine nomenclature.
It should at least be considered a planet and dwarf planet pair. After all, the Moon is larger than Pluto. The relative size of the Moon compared to Earth is enough to convince me. Binary planet or double planet would make fine nomenclature.
Yes, perhaps these will be reclassified as satellites and moons will have to be large enough to form spheres under their own gravity. That would mean that Mars would have no moons though.
Can you expand a bit on why a satellite would need the planet's gravity to keep a spherical shape ?
No, we're talking about a satellite forming into a sphere under its own gravity, not the planet's. Given a large enough lump of matter, gravity will overcome structural strength and force the material to flow into a roughly spherical shape. On Earth, this happens with the maximum mountain height being a few kilometers, but on Mars' moons, which are much smaller, the gravity is far too weak to overcome the rock's structure, and they are basically strange shaped rock things.
Mars' moons are really nothing more than captured asteroids. They look like "strange shaped rock things" because that's exactly what an asteroid is: just some random piece of rock.
As for the spherical shape, the term there is hydrostatic equilibrium: https://en.wikipedia.org/wiki/Hydrostatic_equilibrium.
As for the spherical shape, the term there is hydrostatic equilibrium: https://en.wikipedia.org/wiki/Hydrostatic_equilibrium.
> Mars' moons are really nothing more than captured asteroids.
Keep in mind it's not actually possible to just "capture" an asteroid. The object needs to lose speed somehow in order to be captured.
Most likely via collision - something large hitting the planet, or two other moons crashing.
So the story of the moons is much more complicated than just "random piece of rock".
Keep in mind it's not actually possible to just "capture" an asteroid. The object needs to lose speed somehow in order to be captured.
Most likely via collision - something large hitting the planet, or two other moons crashing.
So the story of the moons is much more complicated than just "random piece of rock".
Given enough time [1], all solid objects become perfect spheres, no matter their size.
[1] 10^65 https://en.wikipedia.org/wiki/Timeline_of_the_far_future
[1] 10^65 https://en.wikipedia.org/wiki/Timeline_of_the_far_future
I am comfortable with a definition of "moon" that does not involve extrapolating 10^65 years into the future.
That's what they said about IPv4
Well, then you'd need to define an arbitrary time limit for how long it would take to form a sphere. In which case, you might as well have just defined a size/mass limit in the first place.
I think the definition would be that they're presently a sphere, that was formed under its gravity. That way objects could possibly become moons in the future, but the timescales are so long it's mostly irrelevant
That's technically correct (the best kind of correct!), but I think it's a misleading thing to state. The reason all objects eventually become spherical is because they eventually disintegrate into the nearest significant source of gravity, which will itself be a sphere. It's not as if, hypothetically speaking, an immortal human being floating through space without orbit would eventually morph into a sphere under the pressure of its own gravity. Rather any object is naturally going to decompose into parts which will be spherical or adjoined with an already spherical object.
Even if the conjecture that sufficiently high entropy causes quantum physical effects to dominate macro-physical spacetime is correct, long before that happens there won't be any objects left which aren't already spherical.
Even if the conjecture that sufficiently high entropy causes quantum physical effects to dominate macro-physical spacetime is correct, long before that happens there won't be any objects left which aren't already spherical.
Actually, not always. A mass orbiting close enough to a planet is subject to tidal forces that will rip apart and eventually flatten a round body into a ring.
https://en.wikipedia.org/wiki/Roche_limit
If body is in a strange orbit taking it in and out of the roche limit, it will adopt some strange middle ground between bring a round moon and a flat ring. Inside the limit, material will be ripped away from the body and flattened towards a ring. Outside the limit, that material will fall back nearer to the equator. So you get something like a ball with a belt.
https://en.wikipedia.org/wiki/Roche_limit
If body is in a strange orbit taking it in and out of the roche limit, it will adopt some strange middle ground between bring a round moon and a flat ring. Inside the limit, material will be ripped away from the body and flattened towards a ring. Outside the limit, that material will fall back nearer to the equator. So you get something like a ball with a belt.
Whew, how you can possibly wrap your mind around 10^10^120 is a mystery to me.
I can't wait to be a ball!!
Is the maximum height of mountains on Earth really due to gravity or a limit imposed by geological weathering?
According to quite a lot of comparative planetary geology work, Mt. Everest, Mauna Kea, etc. are pretty close to the height limit imposed by gravity and structural strength. On some objects (like Mercury or the Moon: see https://arxiv.org/pdf/1511.04297.pdf) there aren't any mountains high enough to hit that limit, but Earth seems to have active enough tectonics to push up at that limit despite weathering.
A bit of one, a bit of the other, AFAIK. Of course, having geological weathering is also a function of gravity; small objects don't have the atmosphere for it.
The tallest planetary mountain in the solar system is Olympus Mons on Mars, about 2.5x as tall as Mount Everest (as measured from sea level). This is only possible because Mars has 1/3 the gravity of Earth.
https://en.wikipedia.org/wiki/Olympus_Mons
https://en.wikipedia.org/wiki/Olympus_Mons
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Aren't all moons natural satelites?
Nooo. Don't take away Mars' moons.
Most planets aren't even spherical, they are all elongated at right angles to the axis of rotation.
Most planets aren't even spherical in the same way that a piece of paper isn't even flat.
A fun read about this:
- [Asimov - The Relativity of Wrong](http://chem.tufts.edu/answersinscience/relativityofwrong.htm)
From the link above:
> To put it another way, on a flat surface, curvature is 0 per mile everywhere. On the earth's spherical surface, curvature is 0.000126 per mile everywhere (or 8 inches per mile). On the earth's oblate spheroidal surface, the curvature varies from 7.973 inches to the mile to 8.027 inches to the mile.
> The correction in going from spherical to oblate spheroidal is much smaller than going from flat to spherical. Therefore, although the notion of the earth as a sphere is wrong, strictly speaking, it is not as wrong as the notion of the earth as flat.
A fun read about this:
- [Asimov - The Relativity of Wrong](http://chem.tufts.edu/answersinscience/relativityofwrong.htm)
From the link above:
> To put it another way, on a flat surface, curvature is 0 per mile everywhere. On the earth's spherical surface, curvature is 0.000126 per mile everywhere (or 8 inches per mile). On the earth's oblate spheroidal surface, the curvature varies from 7.973 inches to the mile to 8.027 inches to the mile.
> The correction in going from spherical to oblate spheroidal is much smaller than going from flat to spherical. Therefore, although the notion of the earth as a sphere is wrong, strictly speaking, it is not as wrong as the notion of the earth as flat.
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You're being unnecessarily pedantic. There's a clear difference between oblately spherical and lumpy.
You seem to read my comment as contradicting rather than supplementing.
Sorry, your use of "even" made it seem like you were trying to be contradictory.
Perhaps you meant, "No planets are perfectly spherical"?
[deleted]
Sounds like time poorly spent to me. A waste in fact.
The lay person's mental image of "moon" means something generally spherical, but it's by no means a requirement... Pretty common for moons of any of our gas Giants to be potato shaped or lumpy agglomerations of rock.
The eighth moon sounds exciting... "it travels in the same region of space as the retrograde moons, but in the opposite direction... That means it could easily smash into the retrograde moons, pulverising itself into oblivion."
Setting up science nerds for thousands of years of suspense!
Setting up science nerds for thousands of years of suspense!
This article is a bit incomplete. A planet can not just capture a moon from something that just happened to come near it.
In order for a moon to enter orbit around a planet it must lose energy, there are two ways for it to do this: Crash into another object, or complicated 3-body interactions, which fling another object away.
> It may be the leftovers of a bigger cosmic collision in the past, Sheppard says.
That is the mostly likely scenario: Two objects collided, one shattered into 7 moons traveling in one direction, and the other ended up as this moon traveling backwards.
In order for a moon to enter orbit around a planet it must lose energy, there are two ways for it to do this: Crash into another object, or complicated 3-body interactions, which fling another object away.
> It may be the leftovers of a bigger cosmic collision in the past, Sheppard says.
That is the mostly likely scenario: Two objects collided, one shattered into 7 moons traveling in one direction, and the other ended up as this moon traveling backwards.
Or 3. Dip a little bit into Jupiter or its atmosphere and aerobrake into orbit. Qualifications: played KSP.
Wouldn't it be a spooky experience to stand on one moon, and have another pass close enough for you to touch it? If they were of similar mass my intuition is that you'd go weightless while it was happening. Might be best to be harnessed during something like that.
While I'm thinking about spooky space stories. Jupiter creeps me right the hell out. Thinking about being on one of its moons where Jupiter takes up a HUGE percentage of your visible sky and is just screaming radiation at you. Personify the gas giant a little and you've got a decent proxy for hell. https://solarsystem.nasa.gov/resources/184/simulated-view-fr...
While I'm thinking about spooky space stories. Jupiter creeps me right the hell out. Thinking about being on one of its moons where Jupiter takes up a HUGE percentage of your visible sky and is just screaming radiation at you. Personify the gas giant a little and you've got a decent proxy for hell. https://solarsystem.nasa.gov/resources/184/simulated-view-fr...
> If they were of similar mass my intuition is that you'd go weightless while it was happening.
Remember that they would be attracted to each other, so the orbit would have to be absolutely perfect for this to work.
Imagine an X - each moon traveling on one of the lines, and just barely touching at the center of the X. Their speed would be incredibly high - don't try to touch the other moon, in fact it would be so fast you might not even be able to see it. (In reality X would be very curved.)
Remember that they would be attracted to each other, so the orbit would have to be absolutely perfect for this to work.
Imagine an X - each moon traveling on one of the lines, and just barely touching at the center of the X. Their speed would be incredibly high - don't try to touch the other moon, in fact it would be so fast you might not even be able to see it. (In reality X would be very curved.)
That would be amazing, it looks like Europa travels at 14 km/s or 31,000 mph. With no atmosphere there would be no sound or pressure wave. And the bodies are probably small enough to not shatter because of the gravity interaction. Escape velocity is about 36,000 mph. So you could see a huge Manhattan size chunk of rock flying at you at rocket speeds. Would be amazing to see it pass by 100 feet above you.
> Would be amazing to see it pass by 100 feet above you.
At those speeds, and the necessary angle, I'm not convinced you would be able to see it at all.
The actual encounter would last for too short of a time to see (like trying to see a bullet in flight), and their motion would take them out of your field of view, unless the planet you were on was rotating very fast.
At those speeds, and the necessary angle, I'm not convinced you would be able to see it at all.
The actual encounter would last for too short of a time to see (like trying to see a bullet in flight), and their motion would take them out of your field of view, unless the planet you were on was rotating very fast.
Cool question/objection.
The two moons are going in opposite directions, so the speed guess is really 28 km/s.
For a full second it would be 2km across and 14km or less away (.5 seconds before and .5 seconds after it's overhead). That's 16 degrees of visual angle. The moon is .5 degrees of visual angle, so you get a full second of something 32 times bigger than our moon.
It would be moon sized about 230 km away, which is over 8 seconds away. So you'd get to see a moon grow quite large over 8 seconds.
So you would see it, but would it be awesome?
Lets say our eyes can see things in the 100 ms range (really a bit better). For that 100 ms, the object would be < 1.4km from you and subtend fully 71 degrees of your vision. That's about 2 basketballs width at arms length.
Which sounds cool though maybe not awesome. But hey you are looking at a moon rushing at your face like a basketball, I would totally go.
https://wolfe4e.sinauer.com/wa03.01.html#Calculator
The two moons are going in opposite directions, so the speed guess is really 28 km/s.
For a full second it would be 2km across and 14km or less away (.5 seconds before and .5 seconds after it's overhead). That's 16 degrees of visual angle. The moon is .5 degrees of visual angle, so you get a full second of something 32 times bigger than our moon.
It would be moon sized about 230 km away, which is over 8 seconds away. So you'd get to see a moon grow quite large over 8 seconds.
So you would see it, but would it be awesome?
Lets say our eyes can see things in the 100 ms range (really a bit better). For that 100 ms, the object would be < 1.4km from you and subtend fully 71 degrees of your vision. That's about 2 basketballs width at arms length.
Which sounds cool though maybe not awesome. But hey you are looking at a moon rushing at your face like a basketball, I would totally go.
https://wolfe4e.sinauer.com/wa03.01.html#Calculator
You have to check the angles. Think of the X I posted earlier. Imagine your goal is to stand at the point looking "up" (because that's were they will meet), both moons were traveling bottom to top, and you were on the moon that started bottom left. (So your gaze is at an angle to direction of travel.)
For most of the time the moon will be behind you to your right out of sight. After the interaction, if the other moon was larger than yours, you might be able to see it.
But if it was smaller, then your own moon's horizon would block your view of it.
But it's worse than that - even if you could see it, you would have to turn your head to the left to see it, but it's moving so fast you just don't have enough time to physically move your head before it's far far away.
i.e. It would whiz by across your field of view, not toward it. Which makes it really hard to see.
Edit: I'm tying to visualize how it would look, but I may have missed some detail. It would be cool if someone could program a visualization of this.
For most of the time the moon will be behind you to your right out of sight. After the interaction, if the other moon was larger than yours, you might be able to see it.
But if it was smaller, then your own moon's horizon would block your view of it.
But it's worse than that - even if you could see it, you would have to turn your head to the left to see it, but it's moving so fast you just don't have enough time to physically move your head before it's far far away.
i.e. It would whiz by across your field of view, not toward it. Which makes it really hard to see.
Edit: I'm tying to visualize how it would look, but I may have missed some detail. It would be cool if someone could program a visualization of this.
In the spirit of "could this be awesome" rather than is it likely...
So pretend we stand on the side of the moon facing toward Jupiter so that Jupiter is straight overhead. And pretend the other moon will pass just inside our orbit 100 ft above our head.
Imagine 2 quarters overlapping, representing the orbits. Pushing the top one up a bit keeps the inner moon completely above the horizon for the whole approach. You can also push the top quarter to the left a smidge so that the inner moon orbit is coming from high and to the right. This would be a moon sized object popping up high and right in the sky and then disappearing in a blink below the horizon to your left.
Speed isn't an issue because for the 8 full seconds before it's right overhead it will be our moon sized and bigger. Up to a 2 "arm's length basketballs" when right overhead. You could definitely track the moon across the half the sky over 8 seconds.
So pretend we stand on the side of the moon facing toward Jupiter so that Jupiter is straight overhead. And pretend the other moon will pass just inside our orbit 100 ft above our head.
Imagine 2 quarters overlapping, representing the orbits. Pushing the top one up a bit keeps the inner moon completely above the horizon for the whole approach. You can also push the top quarter to the left a smidge so that the inner moon orbit is coming from high and to the right. This would be a moon sized object popping up high and right in the sky and then disappearing in a blink below the horizon to your left.
Speed isn't an issue because for the 8 full seconds before it's right overhead it will be our moon sized and bigger. Up to a 2 "arm's length basketballs" when right overhead. You could definitely track the moon across the half the sky over 8 seconds.
I was thinking a bit more on this today. Specifically If a moon did this past earth and assuming it was made out of something that wouldn't just break apart in our atmosphere.
The amount compression on the air around you might set you on fire.
That would be interesting.
The amount compression on the air around you might set you on fire.
That would be interesting.
Other recent articles I saw about this said twelve, this one says ten. Anyone know why?
https://www.npr.org/2018/07/17/629396121/galileo-would-be-st...
If you look at Wikipedia's list and sort by year of discovery, 10 would include the ones in 2018 and 2017, while 12 includes two more in 2016. All 12 are discovered by Sheppard et al. Perhaps those two aren't news anymore?
https://www.npr.org/2018/07/17/629396121/galileo-would-be-st...
If you look at Wikipedia's list and sort by year of discovery, 10 would include the ones in 2018 and 2017, while 12 includes two more in 2016. All 12 are discovered by Sheppard et al. Perhaps those two aren't news anymore?
Right, they are talking about roughly the same discoveries but some include 2 more: https://astronomy.stackexchange.com/questions/26999/did-we-d...
Title should read "At least"
A planet as massive as Jupiter will have captured lots(1) of objects.
1. Terry Pratchett Troll counting system.
A planet as massive as Jupiter will have captured lots(1) of objects.
1. Terry Pratchett Troll counting system.
I'm gonna paste this in because pterry was a god (small G), and there should be no point ever where a reference to him shall go unnoticed.
‘Everyone knows trolls can’t even count up to four!’
(In fact, trolls traditionally count like this: one, two, three, many, and people assume this means they can have no grasp of higher numbers. They don’t realise that many can BE a number. As in: one, two, three, many, many-one, many-two, many-three, many many, many-many-one, many-many-two, many-many-three, many many many, many-many-many-one, many-many-many-two, many-many-three, LOTS.)
‘Everyone knows trolls can’t even count up to four!’
(In fact, trolls traditionally count like this: one, two, three, many, and people assume this means they can have no grasp of higher numbers. They don’t realise that many can BE a number. As in: one, two, three, many, many-one, many-two, many-three, many many, many-many-one, many-many-two, many-many-three, many many many, many-many-many-one, many-many-many-two, many-many-three, LOTS.)
I take "lots" in that quote to be 100 (base 4) or 16 (base 10). Then Jupiters 79 moons would be counted as "oodles-many-many-many-three" -- assuming "oodles" as 1000 (base 4) or 64 (base 10).
Presumably because trolls only have 4 fingers on each hand?
There are finger-based counting systems with more than one number per finger. Our average of 10 fingers can handle a lot more than 10 numbers. https://en.wikipedia.org/wiki/Finger-counting
And less than a digit per err digit (thumbs included)
If I recall there was a Native American base 8 counting system which utilized the space between fingers holding sticks or strings as place holders.
Made for a handy octal abacus.
If I recall there was a Native American base 8 counting system which utilized the space between fingers holding sticks or strings as place holders.
Made for a handy octal abacus.
This reminds me of the discussion(s) on BBC QI (Quite Interesting) about 'how many moons does the earth have'.
A video from QI official channel: https://www.youtube.com/watch?reload=9&v=7qZWM8Aatb8
And a compilation of updates over the years. It has Stephen Fry discussing the topic but in recent seasons Sandy Toksvig discussed the topic as well : https://www.youtube.com/watch?v=sGgmmX-dzgU
A video from QI official channel: https://www.youtube.com/watch?reload=9&v=7qZWM8Aatb8
And a compilation of updates over the years. It has Stephen Fry discussing the topic but in recent seasons Sandy Toksvig discussed the topic as well : https://www.youtube.com/watch?v=sGgmmX-dzgU
Awesome, new Eclipse IDE versions!
For reference: https://en.wikipedia.org/wiki/Moons_of_Jupiter
Its gravitational field is so huge that it is basically the vacuum cleaner of the solar system. Also a lot of things that are not in orbit of it are occasionally significantly perturbed in their solar orbits, by Jupiter, such as a number of long period comets.
Its gravitational field is so huge that it is basically the vacuum cleaner of the solar system. Also a lot of things that are not in orbit of it are occasionally significantly perturbed in their solar orbits, by Jupiter, such as a number of long period comets.
How exactly does that work though?
An orbit can't just change from a parabola into an ellipse, without the influence of external forces. Is something slowing down these object so that Jupiter "catches" them? (Rings?)
An orbit can't just change from a parabola into an ellipse, without the influence of external forces. Is something slowing down these object so that Jupiter "catches" them? (Rings?)
You're right that in a two body system this is totally impossible. But for a three body system of Jupiter, the Sun, and our new moon then ballistic capture will baaaasically get you into orbit and then it only takes a small further interaction with another planet, another moon, or whatever to get into orbit the rest of the way.
> the Sun
Jupiter is in a stable orbit about the Sun, I don't think you can use the Sun as the 3rd body, you need another moon or other object.
Jupiter is in a stable orbit about the Sun, I don't think you can use the Sun as the 3rd body, you need another moon or other object.
The important thing, as far as I understand it, is the way the future moon slowly transitions from being primarily under the gravitational influence of the Sun to primarily under the orbital influence of Jupiter.
We've actually used ballistic transport to transition probes from orbit around the Earth to basically in orbit around the Moon with just a tiny braking burn at the far side instead of the serious burn that a Holman Transfer orbit would require. And the Moon is in a stable orbit around the Earth and doesn't have any further satellites.
We've actually used ballistic transport to transition probes from orbit around the Earth to basically in orbit around the Moon with just a tiny braking burn at the far side instead of the serious burn that a Holman Transfer orbit would require. And the Moon is in a stable orbit around the Earth and doesn't have any further satellites.
> slowly transitions
There is no slowly for capturing an incoming object - you get one chance, unless that object is in a similar orbit to your (and in that case the Sun doesn't help).
> with just a tiny braking burn
Tiny is relative here. It's still enough of a burn to significantly change the momentum of the rocket. Moons don't have anything with that kind of energy, except other moons.
There is no slowly for capturing an incoming object - you get one chance, unless that object is in a similar orbit to your (and in that case the Sun doesn't help).
> with just a tiny braking burn
Tiny is relative here. It's still enough of a burn to significantly change the momentum of the rocket. Moons don't have anything with that kind of energy, except other moons.
No, slow is a fair description of this. You need to start out in nearly the same orbit as the target and while you're both traveling around the Sun or Earth fairly quickly you approach the target much more slowly than you would in a Holman Transfer. Then when you're captured you'll be going around the target a number of times before other gravitational perturbances eject you again, giving a long time to do a burn to get into a stable orbit. So yes you have to change the momentum of the rocket but the burn could take place over the course of a week and won't have to be very large. Your burns to achieve an intersect giving you a ballistic capture would typically be much larger than with a Holman transfer but the slowness of the final approach means you're free to use an ion drive, solar sail, or other high efficiency and low thrust drive.
"All the newfound moons are small, between about 1 and 3 kilometres across. Seven of them travel in remote orbits more than 20 million kilometres away from Jupiter"
As a layman with no astronomical credibilty I'd call those satellites, not moons.
As a layman with no astronomical credibilty I'd call those satellites, not moons.
From the above article:
So as it stands, a moon is simply any natural body in orbit around a planet or other non-stellar object (so asteroids can have moons, and it’s even possible for a moon to have its own moon, although none have been discovered so far).
So as it stands, a moon is simply any natural body in orbit around a planet or other non-stellar object (so asteroids can have moons, and it’s even possible for a moon to have its own moon, although none have been discovered so far).
Behemoth ISS is 0.0728 kM across.
But moon anyway mostly just means natural satellite.
But moon anyway mostly just means natural satellite.
Natural satellite == moon.
"Natural satellite" is a subset of "satellite", thus what you'd call them is correct by definition. Let's let the astronomers with credibility play and name the objects.
"Natural satellite" is a subset of "satellite", thus what you'd call them is correct by definition. Let's let the astronomers with credibility play and name the objects.
Do astronomers get as fiery about taxanomy as biologists do? I kind of had the impression they're easy going about naming, just more wary of upsetting young enthusiests. I heard there were many sternly worded letters from 9 year olds, after the demotion of Pluto.
Slightly related, are all the particles in (eg) Saturn's rings wver referred to as moons?
Slightly related, are all the particles in (eg) Saturn's rings wver referred to as moons?
Seems like they do: https://arxiv.org/pdf/1805.04115.pdf
Oh wow. This is basically a paper about astrologists. Was it published under astrology or anthropology?
I agree, however with so many "moons" now known and more being discovered constantly, and so many of those being really nothing more than asteroids and possibly fragments and debris from past collisions, and in light of the change of the definition of "planet", I would not at all be surprised if the astronomers decided to change the definition of "moon" to also include hydrostatic equilibrium, and then captured asteroids like Mars' to be renamed "minor moons" or similar.
So does Saturn have billions of moons?
Instead of moons, maybe they're space stations?
Fun fact, asteroids in the belt can also have natural satellites:
https://en.m.wikipedia.org/wiki/87_Sylvia
https://en.m.wikipedia.org/wiki/87_Sylvia
Incredible.
There goes the neighborhood.
This is a great example of the hubris of scientists that non-scientists can’t stand.
Most believe Pluto is a planet. Moons are rocks in orbit around planets, etc.
Why the obsession to change these names? Brings painful thoughts of our future if this is what they care about.
Most believe Pluto is a planet. Moons are rocks in orbit around planets, etc.
Why the obsession to change these names? Brings painful thoughts of our future if this is what they care about.
Science evolves. Backwards compatibility is good, but then again, the imperial system :D
Sometimes it's a good idea to break with the past.
Regarding Pluto: https://www.youtube.com/watch?v=BKoRt-6pjAE&vl=en
Sometimes it's a good idea to break with the past.
Regarding Pluto: https://www.youtube.com/watch?v=BKoRt-6pjAE&vl=en
The metric system has broken with its own past, though. The breaks were true breaks, not just elaborations, but they were executed with great care for compatibility. 1m has been defined in four or five different ways, depending on how you count.
There's a lesson here: There is a middle ground between preserving legacy and causing problems by deprecation.
There's a lesson here: There is a middle ground between preserving legacy and causing problems by deprecation.
So what are the “problems by deprecation” you see in the current context of redefining Pluto as not a planet? Having to reprint interplanetary tourism guides?
It's just another minor thing to complain about for the people who like to complain about science.
Nothing minor is major. Some of them are minor and worthwhile, some are minor and not.
Nothing minor is major. Some of them are minor and worthwhile, some are minor and not.
The hubris of revising technical definitions that they themselves created to describe their own work? What are you on about?
"Most believe Pluto is a planet" because they were told that by scientists in the first place. Without astronomers, "most" wouldn't even know Pluto existed.
"Most believe Pluto is a planet" because they were told that by scientists in the first place. Without astronomers, "most" wouldn't even know Pluto existed.
Oh sure.
But consider the same issue with different words.
You made your API, you told people outside the company about it, you got it widely used. Are you free to deprecate it? Are you free to change it incompatibly?
You made your postcodes to better sort and deliver letters. That was your only purpose. You told everyone about them and kept telling them until absolutely every database with addresses included your postcodes, and people started using them for other purposes. Are you free to change them if some tweak would improve your ability to sort and deliver letters?
FWIW I don't have an opinion on the matter.
But consider the same issue with different words.
You made your API, you told people outside the company about it, you got it widely used. Are you free to deprecate it? Are you free to change it incompatibly?
You made your postcodes to better sort and deliver letters. That was your only purpose. You told everyone about them and kept telling them until absolutely every database with addresses included your postcodes, and people started using them for other purposes. Are you free to change them if some tweak would improve your ability to sort and deliver letters?
FWIW I don't have an opinion on the matter.
Technically, yes.
And it's happened before, will happen again, and is currently happening all the time.
In the U.S., we had postal zones in certain cities. A two digit code to specify where in a large city, the letter was to be delivered. The modern zip code wasn't widely implemented until 1967. And depending on how an area grows, it's possible for a postal zone to get subdivided changing the zip code for certain areas.
Also, in 1983, Zip+4 was introduced.
So, exactly what you have described has happened.
Same thing with area codes for telephones.
And it's happened before, will happen again, and is currently happening all the time.
In the U.S., we had postal zones in certain cities. A two digit code to specify where in a large city, the letter was to be delivered. The modern zip code wasn't widely implemented until 1967. And depending on how an area grows, it's possible for a postal zone to get subdivided changing the zip code for certain areas.
Also, in 1983, Zip+4 was introduced.
So, exactly what you have described has happened.
Same thing with area codes for telephones.
A better analogy is some sort of third-party API rating system. Consultancies put out big whitepapers about what a "storage service" is, and what the relative quality of things like Amazon/Google/Microsoft's offerings are. The change in definition of e.g.
Pluto might be analogous to that company originally having classified Amazon S3 as a "backup service" before deciding that it was really a new category of service that has now spawned many competitors.
The classification is designed to help us reason and talk about like things. We can all see how Amazon S3 and e.g. Dropbox are fundamentally different categories of service, and they need different names. We shouldn't be afraid of reclassifying things because people will have to change their models. The point of recategorization is that the old models are not as useful as the new models.
Pluto might be analogous to that company originally having classified Amazon S3 as a "backup service" before deciding that it was really a new category of service that has now spawned many competitors.
The classification is designed to help us reason and talk about like things. We can all see how Amazon S3 and e.g. Dropbox are fundamentally different categories of service, and they need different names. We shouldn't be afraid of reclassifying things because people will have to change their models. The point of recategorization is that the old models are not as useful as the new models.
Germany changed postal Codes from 4 to five digits after reunification.
> Reality must take precedence over public relations for nature cannot be fooled - R. Feynman
> Reality must take precedence over public relations for nature cannot be fooled - R. Feynman
“Your only purpose”. As if such standards were set in place and there was no ongoing committee to deal with new cases and scenarios that arise as they inevitably do in any complex system.
It's in the nature of science that sometimes things that were previously believed to be true turn out to be false. The notion that there are nine planets matched what astronomers knew for many decades but with better measurements turned out be be an unsupportable idea.
For centuries there were just 6 planets. Then people discovered Uranus and there were 7. Then people discovered Ceres and there were 8. Then people discovered lots of other main belt asteroids and there were 7 again. Then Neptune and 8 again. Then Pluto and 9. And now we've found all these other big bodies in the outer system and we decided to demote Pluto rather than add a half dozen new planets, just like we did with Ceres.
I don't think anybody particularly objected to the demotion of Ceres since it hadn't been around that long when it happened. But I can only imagine the furor that must have arisen when people tried to claim that Uranus was a planet despite the number of planets being fixed since the time of Homer. Well, Ok, there was the bit when they turned Earth into a planet and we all know about the people like Giordano Bruno literally burned at the stake over that.
So this demotion of Pluto is just another event in the long, long history of scientists revising what counts as a planet. I understand that it's uncomfortable to have to unlearn things you learned as a kid but science is all about changing our view of the world.
For centuries there were just 6 planets. Then people discovered Uranus and there were 7. Then people discovered Ceres and there were 8. Then people discovered lots of other main belt asteroids and there were 7 again. Then Neptune and 8 again. Then Pluto and 9. And now we've found all these other big bodies in the outer system and we decided to demote Pluto rather than add a half dozen new planets, just like we did with Ceres.
I don't think anybody particularly objected to the demotion of Ceres since it hadn't been around that long when it happened. But I can only imagine the furor that must have arisen when people tried to claim that Uranus was a planet despite the number of planets being fixed since the time of Homer. Well, Ok, there was the bit when they turned Earth into a planet and we all know about the people like Giordano Bruno literally burned at the stake over that.
So this demotion of Pluto is just another event in the long, long history of scientists revising what counts as a planet. I understand that it's uncomfortable to have to unlearn things you learned as a kid but science is all about changing our view of the world.
Going further back, the moon was considered to be a planet, in orbit around the Earth, just as all planets were thought to be.
A great { essay / blog post } about this constant churn:
- [Ontological remodeling | Meaningness](https://meaningness.com/eggplant/remodeling)
My favorite bit:
> Jupiter doesn’t go around the sun, and therefore is not a planet by the 2006 definition.
> Don’t believe me? In Newtonian mechanics, two bodies orbit their barycenter, or center of mass. If they have equal masses, the barycenter is the midpoint between them. If one is heavier than the other, the barycenter is closer to it. If one has much greater mass than the other, their common barycenter is located within the larger body, and the smaller object goes around that point. Only then is the smaller body said to orbit the larger one. Otherwise, the two form a binary system.
> Jupiter is ludicrously heavy: it has 2.5 times the mass of everything else in the solar system combined, apart from the sun. The sun is much heavier still—but the barycenter of their mutual orbit is outside it. Jupiter and the sun are a binary system. Their barycenter is, to be fair, quite close to the sun, and informally it may be reasonable to say Jupiter goes around it. But in terms of the formal definition, it doesn’t, so by the IAU criteria, Jupiter is not a planet.
- [Ontological remodeling | Meaningness](https://meaningness.com/eggplant/remodeling)
My favorite bit:
> Jupiter doesn’t go around the sun, and therefore is not a planet by the 2006 definition.
> Don’t believe me? In Newtonian mechanics, two bodies orbit their barycenter, or center of mass. If they have equal masses, the barycenter is the midpoint between them. If one is heavier than the other, the barycenter is closer to it. If one has much greater mass than the other, their common barycenter is located within the larger body, and the smaller object goes around that point. Only then is the smaller body said to orbit the larger one. Otherwise, the two form a binary system.
> Jupiter is ludicrously heavy: it has 2.5 times the mass of everything else in the solar system combined, apart from the sun. The sun is much heavier still—but the barycenter of their mutual orbit is outside it. Jupiter and the sun are a binary system. Their barycenter is, to be fair, quite close to the sun, and informally it may be reasonable to say Jupiter goes around it. But in terms of the formal definition, it doesn’t, so by the IAU criteria, Jupiter is not a planet.
I'm not sure why you would say that A isn't orbiting B if the barycenter of the orbit isn't inside B? We normally talk about Jupiter orbiting the Sun or Charon orbiting Pluto despite this not being true. I can see why someone might want that to be the definition for aesthetic reasons but I'm not seeing any evidence that it's the accepted definition. Wikipedia certainly says "near or within" instead of "within" in the most relevant section and I couldn't find anything clearer or contradicting that.
> I'm not sure why you would say that A isn't orbiting B if the barycenter of the orbit isn't inside B?
If A and B were roughly the same mass then you'd say they're orbiting each other. We don't tho say or write that about Jupiter in my experience.
If A and B were roughly the same mass then you'd say they're orbiting each other. We don't tho say or write that about Jupiter in my experience.
Well that depends on how you define what is inside versus outside the sun. The sun doesn't have a clear outer edge, it just becomes gradually less dense the further out you go. Earth and Jupiter are inside the heliosphere. These definitions are just arbitrary.
Imagine a less convenient example, e.g. a binary star system where the two stars are of roughly equal or similar mass (and the two stars aren't [somehow] 'right next to each other'). We'd say or write that the two are orbiting each other and that the center of their orbits is outside both.
If Jupiter was more massive then that would also be the case, i.e. the center of its orbit would be obviously outside the sun. Unless you're next going to argue that the entire universe is arguably 'inside the sun' because " it just becomes gradually less dense the further out you go".
If Jupiter was more massive then that would also be the case, i.e. the center of its orbit would be obviously outside the sun. Unless you're next going to argue that the entire universe is arguably 'inside the sun' because " it just becomes gradually less dense the further out you go".
Once you reach the heliopause it's pretty clear that you're completely outside the sun.
Are you claiming that it's perfectly reasonable to consider the entire solar system basically as 'inside the sun'?
That's a very non-standard usage.
That's a very non-standard usage.
This article is relevant to most conversations, but very relevant to this one in particular.
http://slatestarcodex.com/2014/11/21/the-categories-were-mad...
http://slatestarcodex.com/2014/11/21/the-categories-were-mad...
Plus, without a lower boundary, pretty much every single chunk of ice in Saturn's rings would count as a moon, so having a formalized definition might come in handy. ;-)