Prof. Sam LawlerBetween 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
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.
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!
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!
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
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.
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
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.
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
Kaustub Anand (Purdue). Did Mars' moons form from capturing asteroids or a giant impact? Giant impact would make a ring, would cycle with moon - but previous studies ignore collisions within disk. They don't use REBOUND (weird!) they use Swiftest.
Sesquinary catastrophe is the best name! I guess that is caused by moon debris ring re-impacting and destroying the moon. Oo Yarkovsky-Schach effect invoked, constrains ring, helps avoid castrophe
Thea Faridani (U. of Rochester) What if we had another Moon closer-in shortly after Moon formation? Impact-migrate-moonlet-merge. Back to REBOUND again! Early results: mutual inclinations and obliquities are really important for keeping moonlets around.
Raluca Rufu (SWRI) high angular momentum impact could well-mix Earth's mantle and the moon precursor, but then you have to get rid of excess angular momentum. Dumping that depends on internal thermal evolution of Earth, and its spin. Moon's outward migration speeds up after Earth cools enough to re-solidify, how long solidification takes depends on Earth's atmosphere post-collision.
Evection resonance doesn't seem to remove enough angular momentum.
Helena Buschermohle (Instituto Nacional de Pesquisas Espacias) what happens to moons around circumbinary planets? As planets migrate inwards, Hill sphere gets smaller and moons would become unbound. HAHA she calls stable moons "smoons" and a moon that becomes a planet a "ploonet"
All circumbinary exoplanets discovered so far are gas giants, but maybe moons could be habitable, now that we know some moons survive migration.
Now it's a prize talk by Sam Hadden (CITA) about resonant planetary systems, and he's PLAYING MUSIC to demonstrate orbits I love this so much (although I have to say it's not working super great over Zoom, sounds drown out the speaker, oh well). Mean-motion resonances function very much like chords! (This is very well explained in this fantastic website, read it all and enjoy: https://www.system-sounds.com/about/)
Oooo he's got a bunch of orbital sonification on his website! https://shadden.github.io/sonification/
Oooo really neat to hear a chord change during an N-body simulation when stability is lost and a planet swaps to a different resonance.
Resonant chain migration behaves like masses on springs, says it's like vibrato! Cool.
"So that's a lot of fun, but so what?" Unstable modes grow or decay depending on how eccentricities are damped.
Most super earth systems are not resonant (they don't sound so nice), and lots are near-resonant and sound a little out of tune (some sound quite ominous!)
If you throw a few Plutos in to the system, scattering will disrupt the chain that formed, sometimes leaves them near but not quite in the resonance.
Ends with a note to Kepler (the astronomer) who thought the planets should be in perfect resonance, if not now, maybe when formed. Cool!
Leia Shen & Kavi Dey (Harvey Mudd College) current categorization looking for asteroid dynamical families takes ~30 minutes of computation per asteroid. Vera Rubin observatory will discover 10 million more asteroids. Using machine learning and computationally cheaper asteroid properties to find families. Code is available, but they only gave it as QR code not a link...sigh.
David Minton (Purdue): Starts with really cool animation of Moon getting blasted by asteroids! Compares craters to dino footprints. Makes the point that better data (seeing smaller craters) changes the story dramatically
Ben Cassese (MPC): here comes the flood of Solar System small body data! Expect 200 million observations per year from Rubin, + 200 million from NEO Surveyor. MPC has to quickly link previous observations into new orbits, this is hard. Will need machine learning to process everything.
Paul Wiegert (U. Western Ontario): finding interstellar meteors is really hard! Lots of meteors are from comets with high-eccentricity orbits, hard to get good enough data to measure meteor pre-impact orbits. There *are* interstellar meteors, just not as many as that Harvard astronomer (who the speaker did not name) seems to think, and none have been conclusively discovered yet.
Apostolos Christou (Armaugh Obs.) this talk title is hilarious "Larger asteroids stay sober, smaller asteroids get drunk"
Wow what a cartoon!
Small asteroids end up with gaussian distributions around the family centre.
Daniel Durda (SWRI): Overview talk. The asteroid belt is a fossilized collisional system - the size distribution (particularly waves in size dist) tells us about the past. Dust production is "spikey": lots right after a big collision.
Lots of work on Chicxulub impact, where does debris land? (Back into atmosphere, heating it up, burning everything)
Used Ames gun to smash real meteorites and study dust from them.
I should note that this session (and a at least one other) at #DDA2026 are tributes to Stan Dermott, who wrote the Solar System Dynamics bible, and taught a LOT of students.
I guess I have a 1-degree-removed connection here? The postdoc I first worked with, Beth Holmes, who taught me a lot, when I was a baby undergrad, had just finished her PhD with him. (She died from a heart condition while I was still an undergrad)
neville park@sundogplanets we need more scientific illustrations like this
Michael Bacon@sundogplanets Makes me think of the Douglas Adams line:
"You won't like it. It's a bit like being drunk."
"What's wrong with being drunk?"
"Ever ask a glass of water?"
EyeGood on PW for not naming him. That particular astronomer doesn't need any more promotion.
Larry@sundogplanets
Certainly something like the BOINC project.
Certainly something like the BOINC project.
BashStKid@sundogplanets Thanks for today’s threads, it’s been really interesting.
Come On Giant Asteroid!Wait … Harcourt Fenton Mudd conned his way into owning … a *college*??
Alm@sundogplanets respnance may be an objection for KAM theory (and therefore, the stability of the respective solar system), though
poetaster@sundogplanets sadly does not seem the supercollider code is in a repo?
stevenray@sundogplanets this stuff is super fascinating.
Inc Hulk 🧪@sundogplanets Really Cool!
Megan Lynch (she/her)@sundogplanets Does this system work well with the system blind astronomer Wanda Díaz-Merced has developed (based on earlier work, apparently)?
@ml Oh this is cool! This particular sonification just take orbital periods in simulations of exoplanet systems over time and turns them into sound frequencies, so not the same thing.
Red_Shirt_no2@sundogplanets
… we’ve heard the hum of a black hole, now here’s MORE of the “music of the spheres”!
… we’ve heard the hum of a black hole, now here’s MORE of the “music of the spheres”!
Aaron Sawdey, Ph.D.@sundogplanets Of course with the bizarre world definition of planet forced on us .. if those unbound moons just happen to end up in a clear space, they're planets, otherwise .. 🤷🏻♂️
She's routed around the "planet" quagmire and created her own lovely words to describe this new situation, love it.
Dr. Eve Evilpussy@sundogplanets Love a ploonet
Argie@sundogplanets Wow, I think I identify as circumbinary now.
Ryan@sundogplanets you definitely need the under construction sign with a spinning light and the dog running across the bottom. Oh and marquee text.
Blake C. Stacey@fullywoolly @sundogplanets good web design <blink>never</blink> dies
EF@sundogplanets KIS websites should be celebrated not frowned upon or "augmented".
@sundogplanets Sounds to me like you need to add a dancing penguin
Infrapink (he/his/him)@sundogplanets Wait, why don't you have 
?
?
Mark Connolly@sundogplanets But surely it needs to be sprinkled with goat emoji! WIth a good boy looking after them 😀❤️
🐐 🐐 🐐 🐐 🐐 🐕
@sundogplanets Special thanks for the 6-7.
teledyn 𓂀It is 6-11 that we really fear 😅
https://www.tumblr.com/teledyn/816002228085194752/the-tumblr-prophecy?source=share
Esslar2@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.
Roy -- the dull one@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.
@sundogplanets
Do we still have sampling issues? Is “most common planets are super-Earths on very short orbits” because those are easier to detect than super-Earths on longer orbits, or sub-Earths?
Do we still have sampling issues? Is “most common planets are super-Earths on very short orbits” because those are easier to detect than super-Earths on longer orbits, or sub-Earths?
Zombie Gopher 🇨🇦@sundogplanets hot Jupiters in your area... 😁