Between my normal meetings and writing, I'm watching a few talks at the American Astronomical Society's (AAS) Division for Dynamical Astronomy (DDA) annual meeting this week.
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Robin Canup (SWRI) is giving a prize talk on the formation of the Moon. The Moon was definitely formed by a giant impact, but the details are hard! Mars-size impactor makes most sense, but you have to shed a bunch of angular momentum. Can do this with "evection resonance" which keeps the Moon-Earth-Sun in a specific configuration and messes with the Moon's eccentricity. Big problem: matching isotopic composition. Maybe impactor was the same as Earth? #DDA2026
Talks about how tidal dissipation would change as the impact-melted Earth resolidifies.
What about co-accretion? Not for our Moon, but works for jovian planets' large moons. Shows that many generations of moons formed around jovian planets and were eaten by planets during Solar System's planet formation phase. The ones we see today are the last generation before gas disk dispersed.
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Talks about how tidal dissipation would change as the impact-melted Earth resolidifies.
What about co-accretion? Not for our Moon, but works for jovian planets' large moons. Shows that many generations of moons formed around jovian planets and were eaten by planets during Solar System's planet formation phase. The ones we see today are the last generation before gas disk dispersed.
She just told a story about being totally obsessed with Saturn as a middle schooler during the Voyager mission. She wrote a letter to JPL and they sent her a packet of Saturn photos and info! Comments that "I bet they had a good outreach budget back then." SIGH.
Saturn has 1 big moon, did smaller moon get Roche-shredded into the rings? Rings appear to be young, so probably not the right explanation.
Can co-accretion and giant impacts work together to explain Uranus/Neptune moons?
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Talks about how tidal dissipation would change as the impact-melted Earth resolidifies.
What about co-accretion? Not for our Moon, but works for jovian planets' large moons. Shows that many generations of moons formed around jovian planets and were eaten by planets during Solar System's planet formation phase. The ones we see today are the last generation before gas disk dispersed.
@sundogplanets Vored by a gas giant...
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Robin Canup (SWRI) is giving a prize talk on the formation of the Moon. The Moon was definitely formed by a giant impact, but the details are hard! Mars-size impactor makes most sense, but you have to shed a bunch of angular momentum. Can do this with "evection resonance" which keeps the Moon-Earth-Sun in a specific configuration and messes with the Moon's eccentricity. Big problem: matching isotopic composition. Maybe impactor was the same as Earth? #DDA2026
@sundogplanets In the middle of this harsh reality
, we are trying to keep going for our children 
. Please support us by sharing this post so it can reach as many people as possible 
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She just told a story about being totally obsessed with Saturn as a middle schooler during the Voyager mission. She wrote a letter to JPL and they sent her a packet of Saturn photos and info! Comments that "I bet they had a good outreach budget back then." SIGH.
Saturn has 1 big moon, did smaller moon get Roche-shredded into the rings? Rings appear to be young, so probably not the right explanation.
Can co-accretion and giant impacts work together to explain Uranus/Neptune moons?
Peas-in-a-pod exoplanet systems (multiple similar-mass planets closely packed) maybe follow the co-accretion pattern? Simulations with gas migration show a characteristic mass for surviving planets, that doesn't depend strongly on stellar metallicity. Cool!
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Peas-in-a-pod exoplanet systems (multiple similar-mass planets closely packed) maybe follow the co-accretion pattern? Simulations with gas migration show a characteristic mass for surviving planets, that doesn't depend strongly on stellar metallicity. Cool!
Ian Brunton (Caltech) shows that Io and Europa's 2:1 mean-motion resonance can be primordial, but Ganymede's 4:2:1 mean-motion resonance wouldn't have been stable in the primordial disk and would need to fall into place later
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Ian Brunton (Caltech) shows that Io and Europa's 2:1 mean-motion resonance can be primordial, but Ganymede's 4:2:1 mean-motion resonance wouldn't have been stable in the primordial disk and would need to fall into place later
K. Dabroski (U. Idaho) How did Saturn's rings form? Uses only Chrysalis (a.k.a. proto-Hyperion), Titan, and Saturn's J2 as perturbers in REBOUND https://rebound.hanno-rein.de/ Iapetus is important for getting eccentricities high enough for a collision. More sims needed!
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K. Dabroski (U. Idaho) How did Saturn's rings form? Uses only Chrysalis (a.k.a. proto-Hyperion), Titan, and Saturn's J2 as perturbers in REBOUND https://rebound.hanno-rein.de/ Iapetus is important for getting eccentricities high enough for a collision. More sims needed!
Guangyi Zhang (Caltech) Moon-planet tidal system is like a damped harmonic oscillator. 100 bonus points for having a cute animation of a moon on a surfboard "surfing" on the peak "gravito-inertial mode" location as it moves outwards from planet. Applies to Jupiter's and Saturn's moons
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Guangyi Zhang (Caltech) Moon-planet tidal system is like a damped harmonic oscillator. 100 bonus points for having a cute animation of a moon on a surfboard "surfing" on the peak "gravito-inertial mode" location as it moves outwards from planet. Applies to Jupiter's and Saturn's moons
@sundogplanets I may be way off but… it isn’t a damped system, at least not in any meaningful way or the moon would be dropping out of the sky pretty soon I would think
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Guangyi Zhang (Caltech) Moon-planet tidal system is like a damped harmonic oscillator. 100 bonus points for having a cute animation of a moon on a surfboard "surfing" on the peak "gravito-inertial mode" location as it moves outwards from planet. Applies to Jupiter's and Saturn's moons
Wen-Han Zhou (U. Tokyo) why do Saturn A and B rings have such sharp inner rings? Can't be explained by moons. Yarkovsky changes spins through absorbtion and re-radiation of light being in different places (due to rotation). Adding in an eclipse, as for a binary system, changes the average force. This gets REALLY complicated for a ring made of particles all eclipsing each other! Calculate using pkdgrav package, including Saturn radiation. Inner edge is sharp, outer edge leaks outwards
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@sundogplanets I may be way off but… it isn’t a damped system, at least not in any meaningful way or the moon would be dropping out of the sky pretty soon I would think
@rpin42 It's a damped system in that the Earth's spin is slowing down due to tides from the Moon
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Wen-Han Zhou (U. Tokyo) why do Saturn A and B rings have such sharp inner rings? Can't be explained by moons. Yarkovsky changes spins through absorbtion and re-radiation of light being in different places (due to rotation). Adding in an eclipse, as for a binary system, changes the average force. This gets REALLY complicated for a ring made of particles all eclipsing each other! Calculate using pkdgrav package, including Saturn radiation. Inner edge is sharp, outer edge leaks outwards
Should that have been "YORP" rather than "Yarkovsky" ?
Or is this the changes to the ring particle orbits rather than their rotations?
(I am not used to thinking about either past the main belt; but if size is small enough and thermal conduction is slow enough...)
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Talks about how tidal dissipation would change as the impact-melted Earth resolidifies.
What about co-accretion? Not for our Moon, but works for jovian planets' large moons. Shows that many generations of moons formed around jovian planets and were eaten by planets during Solar System's planet formation phase. The ones we see today are the last generation before gas disk dispersed.
@sundogplanets See also "Saturn Devouring His Son" #Goya
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Should that have been "YORP" rather than "Yarkovsky" ?
Or is this the changes to the ring particle orbits rather than their rotations?
(I am not used to thinking about either past the main belt; but if size is small enough and thermal conduction is slow enough...)
@michael_w_busch I'm way out in TNO land where this is not at all significant most of the time, so I probably screwed up the explanation! The initial explanation slides talked about rotations, but then the final slides were about orbits changing, so... I probably wasn't listening carefully enough.
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@michael_w_busch I'm way out in TNO land where this is not at all significant most of the time, so I probably screwed up the explanation! The initial explanation slides talked about rotations, but then the final slides were about orbits changing, so... I probably wasn't listening carefully enough.
Adding in thermal emission from Saturn is yet another complication.
So I will need to go look up what Wen-Han Zhou has been doing.
Thanks for reporting on the meeting!
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Adding in thermal emission from Saturn is yet another complication.
So I will need to go look up what Wen-Han Zhou has been doing.
Thanks for reporting on the meeting!
Seems likely this is about the "binary Yarkovsky" or "eclipse Yarkovsky" effects versus regular Yarkovsky or YORP:
https://iopscience.iop.org/article/10.3847/2041-8213/ae4746/meta
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@rpin42 It's a damped system in that the Earth's spin is slowing down due to tides from the Moon
@sundogplanets @rpin42 And what's more, pushing the Moon *further away* as a result, so in fact the opposite of making it fall out of the sky . . . And am I right in thinking that without internal friction in the earth, the effect wouldn't happen? (I'm guessing that with no friction, the earth's tidal bulge would just stay aligned with the earth–moon axis, so there'd be no sideways force exerted on the Moon and no drag exerted on the earth's rotation.)
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@sundogplanets @rpin42 And what's more, pushing the Moon *further away* as a result, so in fact the opposite of making it fall out of the sky . . . And am I right in thinking that without internal friction in the earth, the effect wouldn't happen? (I'm guessing that with no friction, the earth's tidal bulge would just stay aligned with the earth–moon axis, so there'd be no sideways force exerted on the Moon and no drag exerted on the earth's rotation.)
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Robin Canup (SWRI) is giving a prize talk on the formation of the Moon. The Moon was definitely formed by a giant impact, but the details are hard! Mars-size impactor makes most sense, but you have to shed a bunch of angular momentum. Can do this with "evection resonance" which keeps the Moon-Earth-Sun in a specific configuration and messes with the Moon's eccentricity. Big problem: matching isotopic composition. Maybe impactor was the same as Earth? #DDA2026
@sundogplanets hmm, didn't I read an article a year or so ago about some new earth internal mapping suggesting a deep region of different composition that could be a remnant of an impactor, and that the ejecta could've been all earth material as a result of a more direct hit rather than a glancing blow
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@sundogplanets @rpin42 Thank you for confirming that my brain still works! It was quite fun to think about
