metaphor

It is written for our solar system since that's the only one we have any data on. We haven't discovered any small bodies around other stars so it doesn't make sense to have a definition based on a supposed distribution of bodies that might or might not exist. If we get a lot more data on other stellar systems and find that our current definition isn't generalizable, we'll revise it to take that data into account. Planets form by clearing their orbit. They are also generally able to clear their orbit after migrating to another orbit. The Stern-Levison parameter measures the approximate time in which a body would be expected to clear its orbit (by scattering other planetesimals). There is a big difference between Mars and Jupiter (something explained by the Grand Tack model), but that range contains the other 6 planets. The gap between Mars and Eris is just as big but doesn't have anything in it, that's why it's clear-cut. It's possible that that gap might not just exist in our solar system, but also in other star systems, assuming exoplanets form in a similar way to the solar system planets. We don't really know yet though. If we find that the gap is just a big local coincidence and doesn't exist in other star systems, we'll have to revise the definition. But first we have to get a lot more data.

The Mun is much bigger and closer compared to Kerbin than the real Moon is to the Earth. Minmus is also pretty far out in Kerbin's SOI. In an n-body simulation I would expect Minmus's orbit to be unstable, so maybe that's what's happening there.

I would say the Stern-Levison parameter is better than Soter's discriminant. It's based on quantities that are easily observed even in extrasolar planets, and is less variant over the history of a solar system. If you plot it on a log scale, you can see that there is a much bigger gap between planets and non-planets than there is between gas giant planets and rocky planets for example. I don't think the first characteristic of the IAU planet definition (that it should be round) is needed at all, the "clearing the orbit" part pretty much excludes non-spherical objects (and it's a pretty fuzzy characteristic anyway). Mars in a way is in fact smaller than it should be, given the usual models of planetary formation. That's the main problem that the Grand Tack model solves, and it has to do with Jupiter migrating inward then outward again in the very early solar system.

Most real-life RTGs use plutonium 238 with a half-life of about 90 years (half the power is decayed after 90 years), but there's other parts besides the plutonium that degrade faster. Maybe ~40 year half-life would be more reasonable.

The current classification of a planet is based mainly on orbital characteristics. "Clearing the neighborhood" is a pretty good dividing line between planets and non-planets in the solar system, it's very clear-cut (look at something like the Stern-Levinson parameter), it's generalizable to exoplanets, and it has to do with the way planets form in the first place. But you could also make another classification based on physical characteristics. For example, a "world" could be anything that's large enough to be rounded by gravity, and isn't a star. So Pluto and Ceres would be worlds (but not planets), and so would Europa and other large moons. I do think kids in school should learn, along with the planets, at least the 7 major moons in the solar system (Moon, Io, Europa, Ganymede, Callisto, Titan, Triton), since they're relatively unique objects that each have a different story. Also the Kuiper belt along with the asteroid belt. Pluto could be given as a representative KBO once we image it close up next year.

Yeah, the asteroid belt is a tiny portion of the mass of the solar system. The difference in mass between Eris and Pluto (Eris is 27% more massive) is larger than the entire combined mass of the asteroid belt. The Kuiper belt is really more important than the asteroid belt, it's about 100 times more massive, extends across a much larger volume, and contains larger objects. And yet only a tiny portion of the people who learn about the asteroid belt know what the Kuiper belt is (although that might have changed in recent years as textbooks got updated). I'm guessing one of the reasons is that we don't have any good pictures of any representative objects, but that should change next year. I do think kids should learn about the major satellites of the solar system in school, at least Io, Europa, Ganymede, Callisto, Titan, and Triton.

Neptune did clear its zone. Pluto's mass is about 0.01% of Neptune's mass, which is insignificant. Not to mention it was forced into a resonant orbit by Neptune, along with other KBOs. The definition is written to be applicable to our solar system, because it's the only one for which we have any data regarding the existence of small bodies. Every single planetary object discovered so far around another star is clearly a planet, with a Stern-Levinson parameter greater than Mars's (which you can calculate from mass and semimajor axis). At least in our solar system, there is a physical reason for which there exists a clear dividing line, and it has to do with the way planets form. It's not known so far if there is such a clear dividing line between planets and small bodies in other systems, since we don't have any data. If we find that not to be the case, we'll probably revise the classification.

The edge of objects being "round" is a lot blurrier than the edge of objects which have or have not cleared their orbit. The latter is a very sharp edge, there's no question of what side of it every planetary body in the solar system lies on. By any reasonable measure of "clearing the orbit", the planets differ by at least 5 orders of magnitude from the dwarf planets (and any other small bodies). (Also, dwarf planet is a pretty confusing name, they should have named that category something different, like planetoid.)

That's not at all as clear as the current definition of planet. There's lots of things that are right at the edge of being round, like Vesta for example. The current definition is pretty clear-cut, at least with the objects we have discovered so far. There's the planets, which are the large, singular objects in roughly circular orbits without any chance of an orbit-altering encounter with another body; and there's the asteroids, KBOs, and comets, which are all part of families of similar objects orbiting in similar orbits (which are usually highly inclined and eccentric). The current classification says a lot about the history of those bodies, since all the planets formed on nice round orbits, and scattered everything else into inclined eccentric orbits. - - - Updated - - - Not much of one, since Pluto is currently very close to its ascending node with respect to the ecliptic.

Even though multiple landers are allowed, I thought I would go another way... no dockings at all, just a single probe core and kerbal with things decoupling off it. To Eve and back, and then to Eve again and back again... Just after I get this 1500-ton 800-part rocket to orbit.

Any classification of physical objects is arbitrary in some way. But the current definition of planet works pretty well, it's pretty clear-cut for all the objects we know about. Whenever we discover something that's not clear-cut, we'll change the definition to better classify things (which is what has happened in the past).

It's too bad there's no 180-year-olds alive today, who grew up with Ceres and a few others being planets. I bet they said the same thing when that changed. Anyway, there's two conflicting ways to categorize a body: based on its orbital characteristics, or based on its physical characteristics. The current definition of "planet" is based on orbital characteristics, which have to do with the formation of celestial bodies (the bodies which grew first and fastest became larger and cleaned up their orbit). I would propose another classification system based on their physical characteristics instead of orbital characteristics. Anything that's round and not a star would be called a "world" (or some other word that's not already taken...). An object being round basically means that it's large enough that it's differentiated on the interior. So we would have two classifications, one having to do with orbital characteristics and one having to do with physical characteristics. Pluto would be a world and also a dwarf planet, Earth would be a world and a planet, Titan would be a moon and a world, etc.

No, PQS is a KSP thing. But that file only shows some representative planet values for each PQSMod, so Minmus could also have any of the other ones as well.

I don't know which PQSMod Minmus has that's causing it to act like that, but here is a partial list of the possible PQSMods in the game, that I got from Kragrathea, the maker of Planet Factory. I'm not sure how many of these are implemented by RSS.

Well here are the orbital elements for Neptune and Triton using the same data as the other planets (1950 epoch, relative to Earth equator, etc). Let me know if you need any others. Neptune Orbit { // Target body name: Neptune (899) // Center body name: Sun (10) // Center-site name: BODY CENTER semiMajorAxis = 4497455831858.165 eccentricity = 0.008090397956671817 inclination = 22.30735942219246 meanAnomalyAtEpochD = 162.0995472049553 LAN = 3.512610707556779 argumentOfPeriapsis = 29.81485499342245 referenceBody = Sun } Triton Orbit { // Target body name: Triton (801) // Center body name: Neptune (899) // Center-site name: BODY CENTER semiMajorAxis = 354767243.5407871 eccentricity = 0.00001688014345366826 inclination = 112.3356618078263 meanAnomalyAtEpochD = 358.6561874819175 LAN = 197.1953239787470 argumentOfPeriapsis = 220.4523291697835 referenceBody = Neptune // change this to body name } The data in the Planet Factory config isn't anywhere near as reliable (also it doesn't account for inclination of the Earth's equator to ecliptic, and is for the wrong year).

You can use JPL's Horizons database to calculate orbital parameters. What planet(s) do you want them for?

Can there be more than one lander for the same body? For example, going to Eve with two identical landers, using one to get to the surface and back, then landing the mothership + other lander on Kerbin, then returning to Eve and using the other lander to get to the surface and back?

Nice pic tygoo7. Here's one of Minmus: Not sure how to make the mountains smaller...

Just in case people here haven't seen it, the amazing Venus crewed return mission by maccollo: Definitely worth watching the whole thing.

Don't forget Vesta (for which we actually have good surface maps). It's possible to have as many planets as you want with Kopernicus. I would say at least the major moons of the planets: Amalthea and Himalia for Jupiter maybe (the next 2 largest moons after the big 4); Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus, Phoebe for Saturn; Miranda, Ariel, Umbriel, Titania, Oberon for Uranus; Triton, and maybe Nereid and Proteus for Neptune; Charon for Pluto. And then some of the important minor planets: Ceres, Vesta, Eris, Haumea, Makemake, Sedna, maybe Chariklo/Chiron and Halley's comet.

Yes, this is a configuration for RSS that has the stock planets but at 1/10th the stock size. That means Kerbin has a 60 km radius, its atmosphere ends at 7 km up, the Mun orbits at 1140 km, etc. The orbital and rotational periods are also scaled to match, and the surface gravities should be the same as stock. Still having some problems with the terrain of some planets (Minmus looks pretty cool though). But Kerbin itself should actually be OK. It's pretty fun, like KSP on easy mode. DOWNLOAD Installation instructions: Put this file into your KSP/GameData/RealSolarSystem folder, and remove the file "RealSolarSystem.cfg" from that folder. A time control mod is recommended, since the default altitudes for time warp are way too high now. Known bugs: -Kerbin's atmosphere seems to cut off rather abruptly when viewed from the ground. -lots of exaggerated terrain, mainly on the smaller bodies -Laythe suddenly has lots of small islands -Gilly and Bop seem to lag a lot as you get close to them edit: Renegrade has a RealSolarSystemSettings.cfg file for balanced solar power generation in post #6 below.

10. Although I've never played without revert/reload. It would be way too frustrating to start a mission over after the Kraken crashes the game. Also, I'm horrible at building spaceplanes. Maybe that should count for some points since a lot of people seem to be skillful at that (like Scott Manley).

I have to agree, getting periapsis at Minmus's orbit in the Kerbin system without gravity assists is more impressive than landing on Eve.

So.. what happens if you do include mass for every body in the system? Does Vall crash into Jool? Does Minmus get ejected into interstellar space?

Cool. Yeah we don't have any good textures for the moons of Uranus and Neptune since the only spacecraft to see them was Voyager 2 on a flyby (and only one side of them). But there's other realistic-looking textures made by people, including some from Celestia. Height maps are going to be harder to come by. Let me know if you want orbital parameters or something like that.