Scary thought: Has Kerbin been demoted by .23.5?

[The Destroyer]

IRL there's plenty of asteroids that make flybys of the earth every year. Does this make US not a planet? Didn't think so. I don't think Kerbin is getting demoted any times soon.

That's what I thought too. But it's not just the US, it's the Earth

[problemecium]

By OP's logic, Jupiter isn't a planet either, what with that massive cloud of moons around it.

I say the asteroids around Kerbin don't count as "not cleared" orbital partners, due to their tiny size. Every planet we've been able to investigate has a cloud of tiny neighbors because space turns out to be a rather messy place.

[Tex]

Well, I think I've seen enough! The general consensus seems to be that no, Kerbin has NOT been demoted from planetary status. Hooray!

[LethalDose]

Kerbin is still gravitationally dominant in it's neighborhood. It's fine.

[Tinyboss]

The relevant part of the definition reads "has cleared the neighbourhood around its orbit." In other words, a bunch of crap co-orbiting the sun with Pluto is a problem, while a bunch of crap orbiting Saturn or Jupiter is not.

[Rastaman]

The classification only holds in our solar system, it is likely that elsewhere you still have multiple say Neptune sized bodies in similar orbit and it might take thousands or millions of years to clear the orbit. Are those gas giants dwarf planets? Hardly.

[deadshot462]

No, simply by the fact that Earth is considered a planet and it has just as much debris flying by it (perhaps not as close).

[Nuke]

earth hasn't really cleared its orbit. we still got things like cruithne in there. i have a feeling they will update all the naming conventions again in a few years as more information about what "has cleared the neighbourhood around its orbit" means. its kinda vague and as we find more and more objects, we might find that nothing is a planet because stuff is everything's orbit all the time. i really dont think its a very good definition itself. i think pluto belongs in the not a planet category, just because it crosses into neptune's orbit, but you cant use that as a definition because then neptune wouldn't be a planet either. i wish they had better definition than what they do.

Edited April 20, 2014 by Nuke

[Captain Sierra]

That's what I thought too. But it's not just the US, it's the Earth

Sorry. I was using 'us' as in all people and capitalized for emphasis. If I meant 'U.S.' I would add periods like so.

[NERVAfan]

The relevant part of the definition reads "has cleared the neighbourhood around its orbit." In other words, a bunch of crap co-orbiting the sun with Pluto is a problem, while a bunch of crap orbiting Saturn or Jupiter is not.

Yeah, but it's still based on mass. The trojan asteroids don't disqualify Jupiter (or Mars, which has several also, or Earth, which has one known so far), nor do orbit-crossing asteroids, because the mass is tiny compared to the planet.

Pluto's orbit is really eccentric, but it definitely doesn't constitute most of the mass in the 30 to 50 AU range (which is about its periapsis and apoapsis). For one thing, its periapsis is actually inside Neptune's orbit; plus, there's all the rest of the Kuiper belt out there.

[Tex]

Hey, why all the arguing now? We've all agreed that Kerbin is not a dwarf planet.

[cantab]

I wonder if the Stern-Levison parameter could be calculated for the Kerbin system bodies. It's basically a theoretical prediction of whether a body will clear its orbit, and is given by:

Λ = k M²/a^3/2

Where

Λ is the parameter.

M is the mass of the planet.

a is the semi-major axis of the planet's orbit.

k is a value that depends on the mass of the star and on the orbits of the stuff the planet needs to clear out, and is the bit I don't really understand how to calculate. It should be near-constant for all bodies orbiting a given star though.

In our own solar system, all the planets have Λ >> 1, the lowest being Mars with Λ = 942. All the dwarf planets have Λ << 1, the highest being Pluto with Λ = 0.003

For the Kerbol system, we can at least find Λ/k quite simply, to get a relative idea of how the various bodies measure up.

[table=width: 500, class: grid]

[tr]

[td]Body[/td]

[td](Λ/k) / 10²⁵[/td]

[td]Times greater than the next highest Λ/k*[/td]

[/tr]

[tr]

[td]Moho[/td]

[td]1672[/td]

[td]2.4[/td]

[/tr]

[tr]

[td]Eve[/td]

[td]1537615[/td]

[td]8.7[/td]

[/tr]

[tr]

[td]Kerbin[/td]

[td]176551[/td]

[td]106[/td]

[/tr]

[tr]

[td]Duna[/td]

[td]683[/td]

[td]149[/td]

[/tr]

[tr]

[td]Dres[/td]

[td]1[/td]

[td]N/A[/td]

[/tr]

[tr]

[td]Jool[/td]

[td]99361546[/td]

[td]65[/td]

[/tr]

[tr]

[td]Eeloo[/td]

[td]5[/td]

[td]3.7**[/td]

[/tr]

[tr]

[td]Tylo***[/td]

[td]9936[/td]

[td]N/A[/td]

[/tr]

[/table]

*Not including Tylo

**Yes 5/1 is not 3.7. That's due to rounding errors, I calculated with more precision than I've given here.

***The value is that Tylo would have if it were a planet in its own right in place of Jool, not Tylo's value within the extant Jool system.

Unlike in the solar system where there is a single big divide, in the Kerbol system we have a much more even spread. The divide between planet and dwarf planet in theory still exists, but we'd need to know k to pin it down, and there may well be borderline cases, Duna I think being a leading candidate. Of course it's also possible even Dres is massive enough to clear its orbit, leaving only Eeloo as a dwarf planet by dint of being in its orbital resonance with Jool (which makes its parameter moot).

Also see the example of replacing Jool with Tylo showing how much the orbital distance affect things. Tylo's got 80% of Kerbin's mass, but were it to replace Jool it would only have 6% of Kerbin's "scattering power".

This is all the theoretical approach. One could also take an empirical one, by pre-seeding the system with a whole bunch of small bodies in various orbits, letting the game run for a while, and seeing how well the planets clear them out. However I don't know if KSP's simplified gravity would affect the process too severely for it to be realistic.

[Kruleworld]

+

Because of the addition of asteroids has resulted in Kerbin's orbit becoming cluttered with many, many small bodies, has Kerbin been downgraded to a dwarf planet?

all asteroids are coming from external from Kerbin's SOI, until i capture them...

[UbioZur]

Because of the addition of asteroids has resulted in Kerbin's orbit becoming cluttered with many, many small bodies, has Kerbin been downgraded to a dwarf planet?

It certainly fits all of the criteria, and especially with the asteroids all orbiting in extremely close proximity to Kerbin, do you think that it has lost it's ability to be called a standard planet?

The asteroids does not come from Kerbin orbit but from a solar orbit, some just happen to cross Kerbin SOI.

We only see Asteroids around Kerbins because Kerbin is the only place with a tracking station.

[That guy who builds stuff]

If Kerbin is a dwarf planet does that mean Kerbals are dwarfs?

If so how long until squad releases Kerbal Fortress?

[Ruinsage]

By "clearing the neighborhood around it's orbit" they mean collected the gas and smaller rocks in path of the orbit. This is a major part of planet formation, which is why it's a credential for being a planet. There's always going to be crap floating around in orbits, if the orbits had to be perfectly clean, nothing would be considered a planet.

[KvickFlygarn87]

I believe "cleared its orbit" means that there are no large planets nearby. So we're still good ;-)

[Whirligig Girl]

There are Near Earth objects as well. Jupiter's lagrangian points are filled with space rocks. I think what this means is that if something comes near you, you either fling it out or you collide with it. Kerbin can still have planetary status. Just consider the millions of icy bodies peacefully sharing the orbit of Pluto.

[Superfluous J]

Also, nobody has mentioned this but the IAU's definition of a planet, even if it demoted Kerbin (or Jool even) to "non planet" would have exactly 0 affect on the game.

In much the same way as their changing the classification of Pluto had 0 affect on its orbit, mass, volume, or any other characteristics. All it did was make people sad and caused a few weird laws to be passed in some of the funnier states.

[Matt56]

Ya, as cantab pointed out, there is actually a precise mathematical definition for clearing an orbit. Just as there is a mathematical definition of the neighbourhood of a body's orbit. It's not as wishy washey as the IAU's wording makes it sound.

[zeel]

I believe "cleared its orbit" means that there are no large planets nearby. So we're still good ;-)

It seems like the best definition would be that there is nothing in its orbit of sufficient mass to cause a non-trivial change to its orbit. In other words unless the gravitational or physical effects of another body in the given planetoids orbit could cause a permanent (and greater than the wobble caused by a moon) change in its orbit it is a planet. Thus Kerbin is a planet because none of the asteroids are of sufficient mass to affect its orbit either through gravitational force or impact.

[MalfunctionM1Ke]

Let me just throw my Chart at you again.

Kerbin is in fact a very very tiny planet.

So is Jool as a Gas-"Giant"

But please keep in mind, that the Kerbol-System is not regulated by the IAU at any means

Edited April 21, 2014 by MalfunctionM1Ke