Sean Raymond (planetplanet.net)

The main challenge is the alternating prograde and retrograde rings of planets.

To build a single ring, I think you's need to pass through a horseshoe constellation phase (see planetplanet.net/2023/04/20/c...) and then damp out the librations. Obviously not feasible for humanity at the moment....

I guess it would be transits, not eclipses, but if the planets had moons they would also be blocking the light from the other planets all the time. A very astronomically-engaging place to be!

New animation of the ultimate engineered solar system for a talk I'm giving tomorrow at a sci-fi convention in Lithuania.

It has 400 rocky planets in the habitable zone of a single Sun-like star

It's perfectly stable (I simulated it out to about a billion years)

planetplanet.net/2017/05/03/t...

AAS members are on the Hill today to #SaveNASAScience and advocate for sustained funding for NASA, NSF, and our nation's other science agencies! Help us amplify their voices by calling and writing to your Congressional offices today: aas.org/action-alert...

See for example this paper : ui.adsabs.harvard.edu/abs/2009ApJ....

Thanks!

If there was a very large amount of internal heat flux from tidal dissipation, it would likely be bad for habitability if the planet is close to the inner edge of the habitable zone, or good if it's beyond (colder).

The planet's orbit would also change (slowly) due to tidal dissipation.

Wild Orbits Prime Planets for Life Looking for habitable worlds? Check the ones with extreme swings.

In my new @nautil.us article, I use a lot of recent research to argue that rocky exoplanets on eccentric orbits are often very good candidates for life.

(At least, eccentric/inclined orbits should not be used as a negative for habitability)

nautil.us/wild-orbits-...

It would be interesting to see what the mass ratio threshold is for stability -- does it have to be 1.000000 or could it be 1.01, 1.1, 2., ...?

Ask away. In terms of stability, eccentric rings are clearly stable for billions of years if left undisturbed. I wrote a paper about the dynamical stability of the circular-orbit case when it's perturbed -- it's more robust than you might think.

ui.adsabs.harvard.edu/abs/2023MNRA...

I haven't studied that carefully for eccentric rings. For circular rings of planets, I wrote a paper about it. The punchline is that they're pretty robust. When kicked, these systems often transition to a horseshoe state, unless they're kicked really hard...

ui.adsabs.harvard.edu/abs/2023MNRA...

That's a great idea to check!

Here's something new and weird -- eccentric rings of co-orbital planets.

They are stable indefinitely, from an orbital point of view.

Could they actually form and exist?

planetplanet.net/2025/09/02/e...

Flashback to 2012 when I ate the Sun

(Photo from the top of Vulcano in Sicily)

a 19th century embroidery sampler showing the solar system, the distance of the planets from the sun, and the length of time it takes each planet to circle the sun

Imagine the complicated and precious genius of the girl who made this embroidery sampler in 1811

The Solar System, sampler, unknown maker, 1811, England. Museum no. T.92-1939. Victoria and Albert Museum, London.

HST Has Conclusively Shown that Avi Loeb is Wrong About 3I/ATLAS The recent JWST observations have firmly shown that 3I/ATLAS is a comet—an interesting and anomalous one in some ways, but definitely not a spacecraft. This has not stopped Avi Loeb from continuing to...

Sigh.
sites.psu.edu/astrowright/...

Next comes a by-now routine dismissal of astronomical observations, in order to claim 3I/ATLAS’s dusty coma (which does exist: de la Fuente Marcos et al.; Seligman et al.; Bolin et al.) does not exist and is just photographic fuzz. What would be bold and novel would be to lean in to the observations of dust and assert that any spaceship coming in hot from the interstellar medium would be very dirty and in need of a wash.

Impacts by interstellar dust particles and interstellar gas particles can easily create a thin layer of dust on the surface of 3I/ATLAS, with no accompanying ices if 3I/ATLAS is not a comet. The interstellar speed of 3I/ATLAS is ~60 kilometers per second relative to the local interstellar medium. Any impacting matter would deliver ten times more energy per impacting proton than required to break a single chemical bond within the solid surface. The microscopic breakup of the surface to super-micron fragments by interstellar impactors, such as dust, gas and cosmic-ray particles, might have led over billions of years to the formation of large dust particles that are released close to the Sun and account for the glow ahead of 3I/ATLAS in its Hubble image.

Still can't get over @deschscoveries.bsky.social parodying Loeb, and Loeb straight-up playing out the parody a 3 days later.

Is Desch a clairvoyant, or did Loeb read this mockery of him and think—hey, that's actually a great idea!—and just plagiarize him?!

There’s No “I” in Team. But There Is One in “ALIENS” Yelling “Tarantulas!” in a crowded movie theater has its time and place. If you’re enduring Madame Web, everyone will be relieved you…

My complaints have not yet been resolved.

medium.com/@steve.desch...

3I/ATLAS. A cat on my balcony (En español  aquí )  S ummary      Recently, a new interstellar object passing through our solar system has been discovered: 3I/ATLAS. Thi...

Loeb’s bad science flies out faster than any one of us should have to deal with it. For a nice explanation of what’s wrong with many of his claims I have not addressed, see @hectorsocas.bsky.social ’s work here: tinieblasyestrellas.blogspot.com/2025/08/3iat...

Me neither -- it's really tricky to understand why our results are different. Either taking the Moon quadrupole into account is critical, or sampling different possible configurations for the flyby is essential.

Every living NASA science chief unites in opposition to unprecedented… The entire past leadership of NASA’s science activities have released a joint statement condemning the proposed 47% cuts proposed to the agency’s science…

Today, *every* living prior leader of NASA's science directorate have released a joint letter condemning the proposed cuts to NASA science. These individuals every administration from Reagan to Biden, and all believe these cuts are insanely destructive: www.planetary.org/press-releas...

Folks need to remember that public funding of science drives economic growth and human quality of life decades into the future.

This is about more than saving jobs on the line now. It's about your future health, and the future of health and well-being for the next several generations.

I suppose I should add that there is a lot more to know about the giant planet instability. I captured some of that in this blog post

planetplanet.net/2022/06/30/t...

NASA science budget over time

Planned NASA mission cancelations

The details are not yet finalized, but the budget bill would devastate NASA science and the future of US exploration in space and astronomy. Among many other things. 🔭🧪

www.planetary.org/articles/nas...

Could the Solar System Lose a Planet to a Passing Star? Close stellar encounters could change the structure of our planetary system, potentially dooming Earth or other worlds to oblivion

Oh hey I didn't know you were here! I wrote about it too. 😄

www.scientificamerican.com/article/coul...

Awesomel! I hadn't seen your article -- much appreciated!

This Is Not the Way We Usually Imagine the World Will End

@nytimes.com article about Nate Kaib's and my recent paper on the future stability of the Solar System when passing stars are accounted for.

www.nytimes.com/2025/06/28/s...

Like dinosaurs, Saturn and Jupiter roamed
They sculpted this system that humans call home

The gas giants roared, the system unstable
An ice giant planet fell right off the table!
A whole ring of comets was launched to the stars
The planets — bombarded — still bear the scars.

YouTube video by Balade Mentale Les planètes tueuses de monde: L’histoire chaotique des systèmes planétaires

I was the scientific advisor for the latest video by Balade Mentale about "World-Killer Planets: The Chaotic History of Planetary Systems" (in French)

youtu.be/_6J9axX3r08?...

The Lindy Effect and the stability of planetary systems.

Here's one way of thinking about why planetary systems go unstable, and when.

planetplanet.net/2025/06/11/t...