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[WIP] Planet Jam 2: The Ilio-Pyri System. 15 Modders, 91 Worlds, (initially made in) 2 weeks.

Whirligig Girl

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So we haven't figured out a name yet! This is the development showcase thread for Planet Jam 2 (the sequel to Week World Planet Jam: Sauwel System)

After the success of Week World Planet Jam, where 10 planet modders made a 31-planet solar system in 1 week, some of the WWPJ creators had been brainstorming how we might run a second planetjam in a similar format. We kept the things which were most fun about making WWPJ and got rid of some of the worst parts--namely the lack of collaboration, and the deadline which was just right for some but too short for others. This time we would have two weeks and up to two orbits per person, rather than one orbit per person. Cross-collaboration would be allowed. It ended up actually being quite a complicated thing to set up the allotments because this time the system layout would reward many gas giant planets and some contributors did not want to make gas giant systems, but when all was said and done we had 15 contributors and 15 orbit slots to be filled in. Most of the slots had a specific mass allotment that had to be filled exactly, but could be split up into a planet and moons, or coorbital planets, or left as a single planet.

We started on Saturday, 2022-October-21, and the initial "Deadline Version" was compiled two weeks later on a red-letter date in the history of planet modding: November 5th 2022. Yes... of course, November 5th twenty twenty two... hahaha... that was the day I compiled the deadline version! I remember it vividly. I was standing on the edge of my toilet hanging an orrery--the porcelain was wet, I slipped, hit my head on the edge of the sink! And when I came to I had a revelation! A vision! A picture in my head! A picture of THIS!


This is what makes Planet Jam 2 possible: the Ilio-Pyri system! It's taken me over 30 days and my entire family fortune to realize the vision of that day... My god has it been that long.

Things have certainly changed around here. I remember when this was all Jool Templates as far as the eye could see...

uh. well. anyway. Back To The matters at hand...

The Ilio-Pyri system is a ternary system which is superficially similar to the layout of Whirligig World, with each of the three stars being at interplanetary rather than interstellar distances. The main difference to Whirligig World's stars is that Pyri is close in enough that circumtrinary planets are possible and relatively reasonable--the entire system is about as compact as the stock + OPM system overall.

Let's zoom in on the center of the system to look at the Inner Ilio System.


Ilio-Phosphol and Ilio-Vespol are not quite twin suns--one is a G2V and the other K2V, but combined together their luminosity and mass are both exactly 2 times that of the Sun. Around them are four planets, the smallest of which is innermost Ollo, then equal mass large planets Kilna and Alkin, then small Gerro-Sandevistan. If this arrangement looks familiar, do not fret, I haven't stolen the real solar system--all of these planets are gas giants, with Alkin being nearly the same mass as Jupiter (accounting for KSP's minuscule scale--there's no rescale trickery going on here).

Now let us zoom in on Pyri--a red dwarf star 0.08 solar masses. Note in the zoomed out view it is small enough compared to its twin sun parents to hold onto two trojans!

2fyst7Q.pngThe inner Pyri system, with Armstrong, the Early Game Asteroid Belt (if this looks cluttered to you, do not worry. I added periapsis and apoapsis indicators to each orbit so now it's even worse! But more helpful.), Haut-Oklo, and gas giant Zhandar with its trojan double-planet Beddul-Dopale.


Zooming out a little we can see the outer planets, Bifrost and Sinacin, which are giant planets.

The entire system layout is here, in the spoiler:



Ilio AB System Barycenter

  • Ilio A Ilio Phosphol

  • Ilio B Ilio Vespol

  • Ilio ABb Ollo

    • Ilio ABb I Olu
    • Ilio ABb It Soval
    • Ilio ABb II Fourcroy
    • Ilio ABb III Conscience
    • Ilio ABb IV Fish
  • Ilio ABc Kilna

    • Ilio ABc I Smeezobbler
    • Ilio ABc II Solin
    • Ilio ABc III Floryet
    • Ilio ABc IV Arach
    • Ilio ABc V Drae
    • Ilio ABc VI Whayt
    • Ilio ABc VII Hemantreeantbumbalo
  • Ilio ABd Alkin

    • Ilio ABd I Squangus
    • Ilio ABd II Marith
    • Ilio ABd III Radlun
    • Ilio ABd IV Ulen
      • Ilio ABd IVb Ilmar
  • Ilio ABe Gerro-Sandevistan Barycenter

    • Ilio ABe A Gerro
      • Ilio ABe A I Somna
    • Ilio ABe B Sandevistan
  • Ilio-Pyri L4 Tritonis

    • Ilio-Pyri L4 I Andro
    • Ilio-Pyri L4 II Arterr
    • Ilio-Pyri L4 III Trithus
  • Ilio-Pyri L5 Millie

    • Ilio-Pyri L5 I Casy
    • Ilio-Pyri L5 II Eron
  • Ilio C Pyri

    • Asteroid 1 Dord
    • Pyri b Armstrong
      • Pyri b I Buzz
    • Pyri-Armstrong L4 Garner
    • Pyri-Armstrong L5 Lu
    • Asteroid 2 Welkendon
    • Asteroid 3 Weegletoss
    • Asteroid 4 Naharosmank
    • Asteroid 5 Morhomlo
    • Asteroid 6 Schmev
    • Asteroid 7 Gershmurzelen
    • Asteroid 8 Raft
    • Asteroid 9 Rider
    • Asteroid 10 Quank
    • Asteroid 11 Ogoquo
    • Pyri c Haut-Oklo
    • Pyri d Zhandar
    • Pyri-Zhandar L4 Beddul-Dopale Barycenter
      • Pyri Zhandar L4 A Beddul
      • Pyri Zhandar L4 B Dopale
    • Pyri e Bifröst
      • Pyri e I Máni
      • Pyri e Iq Ljós
      • Pyri e It Bil
      • Pyri e II Heimdall
      • Pyri e III Þórr
      • Pyri e IV Jötunn
    • Pyri f Sinacin
      • Pyri f I Rangon
      • Pyri f II Glice
      • Pyri f III Caua
      • Pyri f IV Alia
        • Pyri f IV i Jones
  • Ilio ABCb Oynag

    • Ilio ABCb I Viszra
    • Ilio ABCb II Jejunum
    • Ilio ABCb III Acic
    • Ilio ABCb IV Atrium
      • Ilio ABCb IV i Cuspid
    • Ilio ABCb V Fundus
    • Ilio ABCb VI Cricoid
  • Ilio-Oynag L4 Descry

    • Ilio-Oynag L4 I Zeppeli
    • Ilio-Oynag L4 II Pendle
  • Ilio-Oynag L5 (1) Zziezel

    • Ilio-Oynag L5 (1) I Skle
  • Ilio-Oynag L5 (2) Xeititit

  • Ilio ABCc Tobalk

    • Ilio ABCc I Turtlestar
    • Ilio ABCc II Hysnoon
    • Ilio ABCc III Hidalgo
    • Ilio ABCc IV Pi
  • Ilio-Tobalk L4 Hadfield

  • Ilio ABCd Kialla

    • Ilio ABCd I Blitzø
    • Ilio ABCd II Nevig
    • Ilio ABCd III Phyre-Wepor Barycenter
      • Ilio ABCd III A Phyre
      • Ilio ABCd III B Wepor
    • Ilio ABCd IV Twilight

Oh by the way did I mention you start on the innermost planet of Pyri?



Armstrong's description:

Armstrong's Limit was discovered by heavyweight arm wrestler and amateur pilot Harriette "Arm Strong" Kerman thousands of years ago on the original homeland, Kerbin. It was the limit at which blood would boil at body temperature, at an atmospheric pressure of 0.0618 times that of Kerbin's sea level. Our world's sea level pressure is 0.068 atmospheres--barely above that limit, hence the name Armstrong. One wonders why our ancient ancestors--diverse and multiplanetary as they were--ever settled this planet, but for one reason or another, they did, and so that's why you have to put on a pressure suit to go to the pharmacy if you're running a fever. Some other complaints about our home, while we're at it:

  • It's too dry. My lips are chapped all the time.
  • The gravity's too high. I keep thinking I can manage to go for a run but I end up with terrible joint pain. 1.0 G sounds just right. 1.3 might be a healthy compromise. But 1.75G? Are you kidding? I don't think I can stand it.
  • Only half the planet is livable. One half of the planet is full-time facing a glowing red hot orb that occasionally flares up and emits deadly radiation, only half has a nice day-night cycle.
    • though it's better than if the planet were spinning properly I guess.
  • It's too cold! I'm gonna say it! It's too cold. You look at those beaches and you think "time for a nice swim!" No! Not a chance! That stuff is barely water and it will freeze you to your CORE!
    • though, again, I have to admit that at the very least it is better than the other half of the planet.
  • The fashion sense. NOBODY KNOWS HOW TO DRESS! You see pictures from the ancient times and you're like "WOW! Now there's some style!" But then you look at what everyone is wearing these days and it's like "are you really going to pair--

[Ed note: We had to stop the previous author before they went on a tirade about thigh-high socks and sandals, which are beloved to us.]

Surface gravity 1.75G. Radius 950,000m. Atmospheric pressure 0.068atm.

Delta-v to orbit is comparable to a roughly 2.5x rescale, but with higher thrust required to liftoff. Historical rocket parts mods such as Bluedog Design Bureau or Tantares, play interestingly with Armstrong. Often you can use real designs, as long as you stuff extra engines or boosters on them to get the thrust you need. Players who find Armstrong difficult may want to install SMURFF to make rocket part mass ratios more forgiving.



launch of an Explorer satellite on a weird Dual-Engine Redstone. BDB's comically-high-thrust A-7 Quad ("Feldspar") engine cluster really comes in handy in the early game.

Armstrong's atmosphere is inspired by the Seven Minutes of Hell entry descent and landing sequences of real Mars missions, and by a planet mod I helped maintain years ago, Little Green Men From Mars. That is--the atmosphere is thick enough that entry heating is a serious concern, but thin enough that it won't really slow you down much. Landing on Armstrong is challenging, but it is rewarding to get it right and make it reliable. The InlineBallutes mod and Trajectories come in handy.

Armstrong is a two-sided planet--a scorched desert on one side and a frigid desert with some isolated chilled seas on the far side, kept warm more by wind blown in from the scorched side than the meager sunlight that reaches its far side from the twin suns. Those twin suns are nevertheless plenty bright enough to see by, so Ilio Phosphol and Ilio Vespol are used to tell day from night. Armstrong happens to orbit Pyri every 6 hours--handy for Kerbin timekeeping.

Eventually planned are two homeworld swap configurations which allow you to play from either Dopale (in the Pyri system) or Ilmar (in the inner Ilio system). These are substantially more Kerbin-like worlds, which kind of takes out half the fun of system replacer mods if you ask me.


Like Whirligig World, Planet Jam 2 is going to reward infrastructure building. The early game belt has a few asteroids placed just right for you to climb up to them with a relatively reasonable rocket, refuel there, and then reach the gas giant Zhandar. (Armstrong will have satellites in low and medium orbit to help facilitate this as well, and like in Whirligig World, rudimentary fuel mining and refining parts will be unlocked earlier than in the stock KSP tech tree).


Once there, a flyby of Zhandar can put you on an orbit which will encounter Bifrost--which, being a superjovian, can send you pretty much anywhere in the system if you're clever with it.

Bifrost? Oh you know.


just the Burning Rainbow Bridge to the Heavens that can be resolved easily with the unaided eye from Armstrong. No big deal.

I shall not spoil Bifrost because it and its satellites are genuinely some of the coolest things I've seen in any planet mod--kudos to Sabine for that one.

I definitely need to make some good "Astrophotography" images of the objects in this system--a sort of non-spoilery view of the planets that represents what you'd be able to see in a telescope from the ground. I don't want to share any screenshots up close because these planets are genuinely so good and interesting that you are going to have a lot more fun if you see them up close for the first time with a spacecraft. Don't go tabbing through the tracking station, trust me!


Bellyflop (a funky winged entry system designed to get enough drag to slow down in the thin upper atmosphere) landed on Buzz, Armstrong's closest moon, which orbits. (checks notes) well below the roche limit. Huh? Well there's your first mystery to investigate I suppose.

A few teaser images. (Spoilers!)



Beddul and Dopale, by Caps Lock



The largest and most massive planet of Pyri, Bifröst is a world of mystery and extremes. Nearly big enough to be a binary companion of its star, it has managed to collect a number of moons, while its gravitational influence is felt far and wide.

When viewed through a telescope, or just a keen eye alone from a dark enough site, its most striking and distinctive feature becomes visible: the so-called chromatic disk. Just what it is remains a mystery, but to many it feels distinctly unnatural (though scientists claim otherwise), and it is important to most mythologies. It is believed by many that the legendary Kraken resides somewhere around here.



Here's one that's so cool I'm hesitant to even show it up close!


Oynag is a monster. Or, at the very least, it was named for one. Mythologies aside, this giant lives up to its name. Swirling storms, orderly latitudinal rows of billowing clouds, a kingdom of orderly moons and rings held in formation by gravity. These are features that make a gas giant recognizable, that make them identifiable at a glance.
Oynag has none of these things. Oynag’s features have been compared to melting faces by some astronomers.

-Wolf-Rayet AKA Exo's Lab


Ollo (the innermost planet of the inner Ilio system) with its moons Olu, Soval, Fourcroy, Conscience, and Fish.  -SnailsAttack


Release Date:

Planet Jam 2 is still under active development but it's getting close to release; we hope for it to be available before the new year! Though PJ2 started as a two-week afair with perhaps a couple weeks or a month for lightweight polishing, it has turned into something much more. Not merely an experiment in exoplanetary expediency, but an incredibly cool planet mod in its own right. That change in scope has lead to it taking longer than we expected! It's going to be worth it in the end though.


Note: some objects are credited to multiple people.

  • Luna/Gregrox: Project coordinator. System layout planner. Ilio Phosphol, Ilio Vespol, Somna, Pyri, Dord, Armstrong, Buzz, Weegletoss, Lu, and Zhandar.
  • SnailsAttack: Ollo, Soval, Fourcroy, Conscience, Fish, Raft, Quank, Ogoquo, Tobalk, Turtlestar, Hidalgo, Pi, Hadfield
  • Cloverdove: Olu, Millie, Casy, Eron, Sinacin, Glice
  • The Orios: Cloud textures for Kilna, Alkin, and Arterr
  • Techo: Squangus, Marith, Radlun, Ulen, Ilmar, Tritonis, Andro, Arterr, Trithus
  • Mh: Kilna, Drae, Arach, Radlun, Ulen, Ilmar
  • Interplanet Janet: Gerro, Somna
  • Marshall (Myth): Sandevistan
  • Wolf-Rayet: Smeezobbler, Solin, Floryet, Whayt, Hemantreeantbumbalo, Dord, Garner, Naharosmank, Welkendon, Morhomlo, Schmev, Gershmerzelen, Mani, Jotunn, Oynag, Viszra, Jejunum, Acic, Atrium, Cuspid, Fundus, Cricoid, Descry, Zeppeli, Pendle, Zziezel, Xeititit, Hysnoon, help with a settings file.
  • Tholin: Haut-Oklo
  • Caps Lock: Beddul, Dopale
  • Sabine: Bifrost, Bil, Ljos, Heimdall, Thorr
  • Triston: Sinacin, Rangon, Caua, Alia, Jones
  • JoQueeb: Kialla
  • ElectricPants: Blitzo, Nevig, Phyre, Wepor, Twilight
  • Special thanks to Adstri for help during development, and Levana for playtesting and writing D or d's description.
Edited by GregroxMun
release thread
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I love this mod and hate Armstrong (Not conceptually,  conceptually I love it to bits it's just an annoying bugger to launch and land from)

Seeing Bifrost rise from Low Armstrong Orbit made me go "HOLY excrements HI BIFROST"

And there are a lot of funky things all around to keep you interested.

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  • 2 weeks later...

We're getting very close to release now.

Here's a spoiler-free set of scale comparisons. For reference, Alkin is very close to the size of Jupiter, Armstrong is 950km across, and Beddul is very close to the diameter of Kerbin.


Giant Planets and Stars of the Ilio-Pyri System


The Inner Pyri System's rocky planets & largest asteroids.


Just the asteroids in the Arriprit Belt (The Early Game Asteroid Belt), plus Garner, an Armstrong trojan.

The system is more complex than these three graphics imply. There are now 100 worlds (since the count in the OP of this forum thread, Gwargin and its five moons, an extra Armstrong moon, and two Sandevistan moons have been added), which is like, so many that I am genuinely worried it might be too much. Like my game still runs alright, but wow. That's a LOT of planets. Almost all of them are finished--Sandevistan and the 100th object, one of its moons, is still a work-in-progress. Mostly what remains to be done is scatterer support for the Gerro-Sandevistan System, the Oynag Mess, and the Tobalk-Turtlestar system, a few more science defs (though the science defs won't be as complete as I'd like), and to make sure all the scaledspace textures are in the dds format and use Kopernicus' LoadOnDemand system to cut down RAM use. (Seriously, OnDemand loading is the main reason PlanetJam 2 works at all).

I am so frickin proud of the work everyone has put into PlanetJam 2, both during the "jam" itself and after the deadline version.

Spoilers for Desmet, Armstrong's second and outermost moon (created by myself).



This deep impact basin gets no light from any suns. What could be hidden in the dark?


Edited by GregroxMun
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One of my newest contributions to this pack was Gwargin, spoilers attached


Gwargin is by far one of the best planets I've ever done, being entirely hand-painted but given careful thought throughout. Most all of Mars' features are represented, but in all of the wrong places. Gwargin also provides a thematically important comparison between our own Solar System's hypobaric world, Mars, and this pack's hypobaric (but far larger) homeworld, Armstrong.

I am incredibly excited for this pack's official full release, I alongside many others have contributed many hours of love and care into delivering this gift to the community!


Edited by Exo's Lab
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4 minutes ago, ffx said:

Im just asking but why does zhandar have the trans flag for the surface color?

Rather than answer your question, I'm going to simply copy the in-game description of Zhandar which i encourage you to read out loud.


Zhandar is a gas giant planet orbiting Pyri at such a distance that it might actually be comfortable to live at, for a change. The discovery that it was made in large part of hydrogen and helium helped bolster the ancient and well-respected theory that the universe is made up of concentric shells orbiting a Central Fire, made of lightweight ethereal matter that doesn't unbalance the cosmos too much. The fact that all that lightweight, ethereal hydrogen gas added up to be more than a dozen times heavier than Armstrong was, somehow, considered unimportant. Unfortunately, due to its water and hydrogen-rich composition, Zhandar doesn't actually have a surface you could land at and walk on, so mission planners see it instead as a huge mass that a spacecraft could do a gravity assist off of.

Such trans-Zhandar trajectories would allow access to the rest of the Pyri system, and even the Ilio system, with considerably less rocket fuel than if it were avoided altogether.

-Luna Gregoria


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1 hour ago, Leganeski said:

Bifrost appears to be larger (in terms of equatorial radius) than the star it orbits. I don't think I've ever seen a planet like that before!

Objects being larger than the object they orbit turned out to be a surprisingly common theme in PJ2. Something which has more or less never been seen before actually has happened (on purpose) twice in PJ2--Sinacin is smaller than its moon Glice and Tobalk is smaller than its moon Turtlestar. That it happened twice is actually a coincidence; it was an idea both SnailsAttack and Triston came up with independently!

Pyri and Bifrost are both near the sort of common asymptote of Jupiter-sized objects that you get with most objects between about 1 and like 90 jupiter masses; but since Bifrost is oblate due to its rapid rotation, it's wider than Pyri.

It seems like it shouldn't be that uncommon to find things like hot puffy jupiters with super low densities and high radii orbiting very nearby smaller red dwarf stars, somewhere in the universe. Though I dunno how common Hot Jupiters are around ultracool red dwarf stars.

And like, most white dwarfs with planets probably have planets that are larger than them. But those aren't technically true stars.

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15 hours ago, GregroxMun said:

Objects being larger than the object they orbit turned out to be a surprisingly common theme in PJ2. Something which has more or less never been seen before actually has happened (on purpose) twice in PJ2--Sinacin is smaller than its moon Glice and Tobalk is smaller than its moon Turtlestar. That it happened twice is actually a coincidence; it was an idea both SnailsAttack and Triston came up with independently!

Pyri and Bifrost are both near the sort of common asymptote of Jupiter-sized objects that you get with most objects between about 1 and like 90 jupiter masses; but since Bifrost is oblate due to its rapid rotation, it's wider than Pyri.

It seems like it shouldn't be that uncommon to find things like hot puffy jupiters with super low densities and high radii orbiting very nearby smaller red dwarf stars, somewhere in the universe. Though I dunno how common Hot Jupiters are around ultracool red dwarf stars.

And like, most white dwarfs with planets probably have planets that are larger than them. But those aren't technically true stars.

It’s been seen before in galaxies unbound as well as light levels

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11 minutes ago, ffx said:

So, what did you make for the planet jam?

Techo had a huge hand in creating the moons of the inner gas giant Alkin, and as I understand it made the inner rocky planet Sandevistan's larger moon as well as the Tritonis system (a trojan of the star Pyri with a few moons) himself.

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  • 3 weeks later...
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