Notices by Prof. Sam Lawler (sundogplanets@mastodon.social), page 2

The idea for this paper came from me looking at an orbital density plot, and wanting a more intuitive way to understand these densities. What does 10^-8 satellites per cubic km even mean?!

The CRASH Clock paper is now peer-reviewed! So to celebrate, my co-authors and I wrote an explainer article (because how better to celebrate one article than by writing another... oh academia...)

It's now published in The Conversation Canada: https://theconversation.com/a-new-crash-clock-measures-the-chance-of-satellite-collisions-and-its-ticking-down-fast-283481

It's so wet the frogs are moving into the barn (I, for one, welcome my new amphibian overlords)

Also it's really hard to take a picture of a frog. I am pretty sure this is a wood frog, which means it was frozen while hibernating a few months ago. Evolution is so cool!! https://en.wikipedia.org/wiki/Wood_frog#Cold_tolerance

I think all the thunderstorms have passed over us, so time for weeding (if the ground isn't completely saturated, which is probably is) or barn-mucking. Deep bedding is fantastic for the winter, but boy it's a lot of work to clean up in the summer... Podcast recommendations?

I weeded until the thunder started, then finished mucking out a barn stall. The last podcast I listened to was an Ologies episode about music and brains and evolution https://www.alieward.com/ologies/biomusicology

And the episode started by talking through the example of the Galilean moons of Jupiter that are in mean-motion resonances with each other (I blathered a LOT about mean-motion resonances last week because of #DDA2026) Very cool stuff!

Wow I am tired.

Purple martins are really neat birds (especially when your bird biologist friend builds you a house that makes it easy to check in on them).

Check out this super cute tidy nest they built! They pick aspen leaves, using the leaves to regulate moisture for the incubating eggs. Look how perfectly they layered the leaves! Evolution is SO COOL.

Sometimes I can't believe how lucky I am to live in such a stunningly beautiful place

Rosemary Pike (Harvard MPC) my friend and collaborator: results from a survey I'm co-PI of, the LiDO survey, 140 new TNOs at 14 degrees or higher inclination.

Hot classical TNO distribution (funny story, this was the most "boring" science case we could think of, but we needed something quick for the survey paper-other for fun science gets its own papers)

We (well, mostly Kat Volk) built a dynamical stability model by mostly filling the hot classical region and eroding (yay REBOUND)

#DDA2026

Time for the outer Solar System! The best dynamics!

Nate Kaib (PSI) talking about dynamically new comets (a>10,000AU), talking about pericenter position relative to node, hard to match sims to observations.

There was a star, HD 7977, that passed within 4000-24,000AU from the sun 2.5 million years ago. This would have perturbed lots of comet orbits, simulations with star passes at 6000-10,000AU match current observations much better. We are still living through a comet shower! Cool!

#DDA2026

Daniel Scheeres (CU Boulder) Binary small bodies are important and frequent. How do they form? Even more fun, how do you make 3 component systems (like asteroid Dinkinesh https://en.wikipedia.org/wiki/152830_Dinkinesh)

Lots of simulations! Found an area of energy/angular momentum space that makes triples very easily. Finds lots of contact binaries.

#DDA2026

Dallin Spencer (BYU) warm classical TNOs are hard to explain, time to run a bazillion integrations! Sees the gap in density distribution at 4-6 degrees - this is right along 2 secular resonance (nu 8 and n 18) https://en.wikipedia.org/wiki/Secular_resonance

Conjunctions pump eccentricity and move them out of this gap. Did this change the boundary of the cold classical belt?

Upcoming paper will have proper elements for all known TNOs.

#DDA2026

Ruth Murray-Clay (UC Santa Cruz) "eyehole libration" in exterior p:1 resonances. We (LiDO) found a 10:1 resonator! I wrote about it for a general audience on page 31 of this pdf: https://www.rasc.ca/sites/default/files/publications/JRASC-2025-10-lr.pdf

In high inclination orbits, p:1 resonances can librate around 180 *or* 0, and switch between these states. Eyehole libration happens when close approach to Neptune isn't at TNO perihelion

I LOVE these beautiful surface-of-section plots Kat Volk makes

#DDA2026

Why is this useful? Tells us about how much the Kuiper Belt was dynamically excited by past planet migration, helps us understand the population we see today and make predictions for future observations.

Our paper (led by Mike Alexandersen) is in review, and will hopefully be accepted and on the arxiv within a couple weeks.

Other LIDO papers that are already out:

https://iopscience.iop.org/article/10.3847/PSJ/adc10c

https://iopscience.iop.org/article/10.3847/PSJ/addd22 (this one will get talked about more in an upcoming talk)

#DDA2026

Fei Dai (IfA U. Hawaii) resonant chains are common, but get disrupted early in planetary systems' history, only young systems have resonant chains.

He's beat the 6:7 resonance (6-7 hehe), with a 9:8 resonant system. How did this form, super short stability timescale. Maybe a captured by a "trap" from evaporation front?

#DDA2026

Agustin Heron (Indiana U. Bloomington) good title "Intruder alert"

20% of Kepler systems have at least 1 pair of planets in or close to resonances. Using planetesimals to slowly change orbits and break resonant chains: time for REBOUND (with added sound effects by speaker haha)

If planetesimals are "recycled" (don't get destroyed/kicked out of system after planet encounters), very small mass (fraction of Earth mass) can change orbits significantly.

Maybe this happened to AU Mic?

#DDA2026

Vaibhav Chhajed (Michigan State U.) pebble collapse simulations - uses many different size pebbles to mroe realistically simulate structures formed. Older sims use same size pebbles which may artificially increase strength of simulated bodies (like a crystal sort of). Wide ranges of sizes actually results in denser planetesimals due to more efficient packing, and makes more oblate shapes, more realistic with observations. Cool!

#DDA2026

Tommy Chi Ho Lau (U. Chicago) planetesimals form and then migrate inwards in disk, are affected by planets. Has code that does ALL of this, wow. Builds up structure of Kuiper Belt using disk dissipation and planet migration. By eye looks like their sim made WAY too many plutinos... Working on eroding after this initial simulation.

#DDA2026

There is one more talk but I have to do other things now. #DDA2026 was super interesting and I learned a lot (though please note I skipped many talks, including all of the galaxy dynamics talks, due to my own bandwidth this week)

I really appreciate getting to learn fascinating astronomy research that's happening - good motivation to keep fighting satellite companies for access to the sky.

Ryan LoRusso (Indiana U.) Cold Neptunes are common, can they help with redistributing planets in resonant chains? 5 Neptune systems migrate inwards in disk and make nice resonant chains, but are broken by planetesimals.

Neptunes/sub-Neptunes are perfect for secular chaos which destroys resonance without too much ejection. Jupiters eject everything.

Predict peak in debris disk activity at 10-100Myr due to this reshuffling.

#DDA2026

Can we all agree not to use this?

(No, we probably can't... also I've already heard from people in the US that some carriers auto-swap over to Starlink sometimes)

The direct-to-cell satellites are the worst for light pollution (they're huge and on low orbits), likely sat working lifetimes will be even shorter than Starlink's 5 yrs (because they're constantly orbit-raising due to friction with atmosphere), and thus more pollution from chucking them into the atmosphere

https://mastodon.social/@arstechnica/116816625892976050