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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@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
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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
Yurou Liu (Yale): hot-Jupiter hosting binaries are more eccentric, OR hot Jupiters are preferentially aligned with their binaries. They found this through building a bunch of simulated hot Jupiter systems and letting the Kozai effect change the eccentricities and inclinations and looking at the final distributions
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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!
@sundogplanets oh, does this mean that the size of planets in peas-in-a-pod systems scales with the star?
So in these cases we'd expect, what - only earth-sized planets around small-to-mid red dwarfs?
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Yurou Liu (Yale): hot-Jupiter hosting binaries are more eccentric, OR hot Jupiters are preferentially aligned with their binaries. They found this through building a bunch of simulated hot Jupiter systems and letting the Kozai effect change the eccentricities and inclinations and looking at the final distributions
Grant Weldon (UCLA): oh I like this talk title "Saving Doomed Planets". Hot Jupiters like to fall into their stars. But mass loss is important - by losing mass some of them end up not falling into their stars. High eccentricity migration can be survived, but sometimes hot Jupiters turn into hot Neptunes.
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Grant Weldon (UCLA): oh I like this talk title "Saving Doomed Planets". Hot Jupiters like to fall into their stars. But mass loss is important - by losing mass some of them end up not falling into their stars. High eccentricity migration can be survived, but sometimes hot Jupiters turn into hot Neptunes.
@sundogplanets hot Jupiters in your area...
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Grant Weldon (UCLA): oh I like this talk title "Saving Doomed Planets". Hot Jupiters like to fall into their stars. But mass loss is important - by losing mass some of them end up not falling into their stars. High eccentricity migration can be survived, but sometimes hot Jupiters turn into hot Neptunes.
Sacha Gavino (U. Bologna) millions of sims of 3 equal mass earth planets in extremely compact orbits, mapping out 3 body interactions with orbit spacing. Really complex stability structure, depends on initial longitudes of planets. Holy cow that's a complicated map of "the 3-body resonance network", looking at where resonances overlap and chaos happens, and where resonances push planets into higher stability orbital configurations.
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Sacha Gavino (U. Bologna) millions of sims of 3 equal mass earth planets in extremely compact orbits, mapping out 3 body interactions with orbit spacing. Really complex stability structure, depends on initial longitudes of planets. Holy cow that's a complicated map of "the 3-body resonance network", looking at where resonances overlap and chaos happens, and where resonances push planets into higher stability orbital configurations.
Julia Esposito (Georgia Inst of Tech) looking at planet-planet scattering, uses REBOUND TRACE and Reboundx because need close encounters between planets, long integrations, general relativity, and tides (wow). Cold scattering (distances outside 1AU) is needed to produce hot Jupiters. Made lots of eccentric, aligned, warm Jupiters. Predict warm Jupiters should have nearby companions with >30 degree mutual inclinations
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Julia Esposito (Georgia Inst of Tech) looking at planet-planet scattering, uses REBOUND TRACE and Reboundx because need close encounters between planets, long integrations, general relativity, and tides (wow). Cold scattering (distances outside 1AU) is needed to produce hot Jupiters. Made lots of eccentric, aligned, warm Jupiters. Predict warm Jupiters should have nearby companions with >30 degree mutual inclinations
Konstantin Batygin (Caltech): most common planets are super-Earths on very short orbits. How do they not fall into their star? How do they pick which resonance to lock in to? (Bonus points for joke about a system with a 6:7 resonance for everyone with middle-school-aged kids)
Giant equation in a confetti explosion (this guy likes giving talks). Shows that 6:7 resonance requires planets to form simultaneously at 1-3AU: the "planet factory ring"
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Konstantin Batygin (Caltech): most common planets are super-Earths on very short orbits. How do they not fall into their star? How do they pick which resonance to lock in to? (Bonus points for joke about a system with a 6:7 resonance for everyone with middle-school-aged kids)
Giant equation in a confetti explosion (this guy likes giving talks). Shows that 6:7 resonance requires planets to form simultaneously at 1-3AU: the "planet factory ring"
@sundogplanets Special thanks for the 6-7.
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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. They have this fantastic option where you pay US$10 and you can watch all the talks at the meeting. I'll try to share summaries of a few highlights using #DDA2026
@sundogplanets thank you! I like reading these little summaries, even if I don't totally understand the science.
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Konstantin Batygin (Caltech): most common planets are super-Earths on very short orbits. How do they not fall into their star? How do they pick which resonance to lock in to? (Bonus points for joke about a system with a 6:7 resonance for everyone with middle-school-aged kids)
Giant equation in a confetti explosion (this guy likes giving talks). Shows that 6:7 resonance requires planets to form simultaneously at 1-3AU: the "planet factory ring"
@sundogplanets This made me look up again a remarkable series of videos on formation of this solar system by Sean Raymond and Alessandro Morbidelli. They call it "MOJO" or Modeling the Origin of Jovian Planets. I've never seen anything like it.
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@sundogplanets Special thanks for the 6-7.
It is 6-11 that we really fear
https://www.tumblr.com/teledyn/816002228085194752/the-tumblr-prophecy?source=share -
Konstantin Batygin (Caltech): most common planets are super-Earths on very short orbits. How do they not fall into their star? How do they pick which resonance to lock in to? (Bonus points for joke about a system with a 6:7 resonance for everyone with middle-school-aged kids)
Giant equation in a confetti explosion (this guy likes giving talks). Shows that 6:7 resonance requires planets to form simultaneously at 1-3AU: the "planet factory ring"
@sundogplanets
Would 1 AU be a "very short orbit"?Added in edit: (I guess so, for "super-Earths". Is my (very amateur) thinking kinda sorta somewhat right, or am I missing the whole point?)
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Konstantin Batygin (Caltech): most common planets are super-Earths on very short orbits. How do they not fall into their star? How do they pick which resonance to lock in to? (Bonus points for joke about a system with a 6:7 resonance for everyone with middle-school-aged kids)
Giant equation in a confetti explosion (this guy likes giving talks). Shows that 6:7 resonance requires planets to form simultaneously at 1-3AU: the "planet factory ring"
Gabriel Teixeira Guimaraes (National Obs of Japan) more REBOUND sims! Aligned pericenters are important for stability, but absolutely required for higher eccentricity systems.
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Gabriel Teixeira Guimaraes (National Obs of Japan) more REBOUND sims! Aligned pericenters are important for stability, but absolutely required for higher eccentricity systems.
As part of the CV-rejiggering for academic stuff that I previously complained about, I also need to update my academic website (which is embarrassingly simple, but at least I didn't write it in 1999 and it doesn't have a dancing-linux-penguin-gif like Some Other Academics). Will be trying to do that while listening to the next set of #DDA2026 talks
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As part of the CV-rejiggering for academic stuff that I previously complained about, I also need to update my academic website (which is embarrassingly simple, but at least I didn't write it in 1999 and it doesn't have a dancing-linux-penguin-gif like Some Other Academics). Will be trying to do that while listening to the next set of #DDA2026 talks
@sundogplanets you definitely need the under construction sign with a spinning light and the dog running across the bottom. Oh and marquee text.
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@sundogplanets
Would 1 AU be a "very short orbit"?Added in edit: (I guess so, for "super-Earths". Is my (very amateur) thinking kinda sorta somewhat right, or am I missing the whole point?)
@oldclumsy_nowmad it totally depends on the context of who you're talking to! This presentation considered that short.
