Sean Raymond (planetplanet.net)

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...

YouTube video by Cool Worlds A Dark Age for Space Science

From @davidkipping.bsky.social

www.youtube.com/shorts/L5Ssn...

I know this is getting kind of ridiculous, but I just think it's amazing that this sort of system can exist.

It reminds me of amazing balancing rock piles. Although co-orbital rings of planets are much more stable, because they can survive perturbations, at least up to a point.

A quick update about co-orbital rings of planets.

This setup -- with 42 planets (each the same mass as Earth) sharing an orbit that is the same average distance as Earth (1 au) but super-eccentric -- is stable for at least 5 million years. (I'm running it out to a billion years to test)

Black Holes, Stars, Earth and Mars: Astronomy poems for all ages Black Holes, Stars, Earth and Mars: Astronomy poems for all ages [Raymond, Sean, Raymond, Owen, Tyson, Neil deGrasse] on Amazon.com. *FREE* shipping on qualifying offers. Black Holes, Stars, Earth and Mars: Astronomy poems for all ages

Need a quick book to read in the bath or at the beach?

Even better -- a fun book of astronomy poems to read with your kids to get them interested in science and space?

I humbly offer up my book, illustrated by my son Owen (back when he was 12).

www.amazon.com/dp/B08LFZZWGZ

The NASA planetary science fleet chart. It shows two spirals with missions to Moon/Mars and the Solar System. I’ve crossed off all of the missions that will be cancelled in the president’s budget… and there are a lot of them.

The NASA planetary science fleet chart if the president’s budget is enacted.

See also my blog post here:

(Note the overly dramatic title "Death from the stars"!)

planetplanet.net/2025/05/13/c...

Earth could be flung out of orbit by a passing star Simulations show that the stars’ tug could send Mercury, Venus or Mars crashing into Earth — or let Jupiter eject our world from the solar system.

Nice article about our recent paper (with Nate Kaib) on the future of the Solar System under the effect of passing stars.

www.sciencenews.org/article/star...

Very-wide-orbit planets from dynamical instabilities during the stellar birth cluster phase - Nature Astronomy Giant planets on wide, eccentric orbits—like the putative Planet Nine—may form from dynamical planetary instabilities when stars are embedded in their natal stellar clusters. Simulations suggest a 1–5% chance of such planets forming in exoplanetary systems and up to 40% in the Solar System.

Giant planets on wide, eccentric orbits (like putative Planet 9) may form when stars are embedded in their natal stellar clusters. Sims suggest a 1-5% chance of such planets forming in exoplanetary systems & up to 40% in the Solar System. https://bit.ly/4dD7VOi #AstroSci

Diagram showing the orbits of several distant objects in the solar system, with Planet Nine's proposed orbit highlighted in orange.

"Do you think Planet 9 exists?"

The observational evidence is limited by small number statistics. That's often enough for many to conclude, somewhere between unlikely and no. But, I lean further towards more-likely-than-not, and a new paper out today helps explain why I've thought this way.

1/7

Very-Wide-Orbit Planets Born from Stellar Cluster Chaos In recent years, the search for planets beyond our solar system has unveiled the existence of gas giants residing on remarkably distant and eccentric orbits, often stretching hundreds of astronomical

Some news stories on our paper:

scienmag.com/very-wide-or...

Very-wide-orbit planets from dynamical instabilities during the stellar birth cluster phase Nature Astronomy - Giant planets on wide, eccentric orbits—like the putative Planet Nine—may form from dynamical planetary instabilities when stars are embedded in their natal stellar...

Quick punchline of the paper: There is a ~40% chance that the early dynamics of the Solar System produced "Planet 9". And, one in every ~1000 or more stars should have a very wide-orbit planet.

Authors: Izidoro, Raymond, Kaib, Morbidelli & Isella

Paper (full readable link): rdcu.be/enVEi

Blog post on #planetplanet about the paper: (Exo)Planet Nine strikes back!

planetplanet.net/2025/05/27/e...

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YouTube video by Sean Raymond Capture of "Planet 9" in a simulation of the giant planet instability in the Sun's birth cluster

The most beautiful animation of a dynamical instability you'll see today, showing an early giant planet instability producing a planet nine analog. By Andre Izidoro.

3 different points of view: the cluster (the Sun is pegged at the origin), zoom-in (top right), orbital elements (bottom right)

2/

Very-wide-orbit planets from dynamical instabilities during the stellar birth cluster phase Nature Astronomy - Giant planets on wide, eccentric orbits—like the putative Planet Nine—may form from dynamical planetary instabilities when stars are embedded in their natal stellar...

New paper (Izidoro et al)

We show that planets on very wide orbits -- such as the proposed Planet Nine -- are an inevitable consequence of dynamical instabilities that happen early in planetary systems, still in their (stellar) birth clusters

Paper: rdcu.be/enVEi

Quick thread 1/

Exactly! And there are more (orbital) twists that I'm working on.

No, this is unrelated. But that dwarf planet is super interesting in its own right. We have a paper about how wide-orbit planets like Planet 9 form coming out in Nature Astronomy later today

This seems to be stable indefinitely. Moons would also be perfectly stable (as long as they were at less than 20% of the current Earth-Moon distance), although I haven't included them here.

No spin but it doesn't matter for the orbital stability (in this case).