Wait, ARM, the heck is this?

[TerLoki]

So I started a new career for 0.23.5, and as I go along I check the tracking station periodically for interesting asteroids and tag them for when I get the claw unlocked, so I can have a bit of variety. Well one time went I did this, and I'm an idiot for not taking a screenshot, an E class asteroid spawned in orbit around Kerbin. I just look, and there it is. It's highly inclined and REALLY eccentric (like ~300km peripasis with an apoapsis just inside Minmus), but stable.

Has this happened to anyone else?

[electronicfox]

Asteroids that pass by Mun or Minmus can be pulled into a stable orbit. If left to its own devices, it will (perhaps after thousands of years) most likely be re-directed by whoever dragged it into orbit again, and be shot off into space.

I have 2 in a stable orbit, a class A and E.

[TerLoki]

I thought about that, but there are two things that don't add up:

One: As far as I know asteroids and any other out-of-focus objects are simulated "on-rails", meaning their orbits can't be changed like that.

Two: This thing's orbit is REALLY inclined away from both muns, at least 45 degrees, its ascending and descending nodes with the Mun are way too close to Kerbin. I don't really see how it would have interacted with them in the first place.

I guess maybe that's why the game spawned it so close, but I don't see how it could have been captured naturally.

[electronicfox]

Both of my auto-captures were amost polar, and both highly inclined, and constantly on-rails. I didnt actualy see the capture moment for either of them, but I did track them both. Not sure how the orbits are processed for asteroids, but I believe their spawns are randomised within a certain range of Kerbin. Perhaps this one just spawned on the edge of Kerbins SOI.

[SofusRud]

I thought about that, but there are two things that don't add up:

One: As far as I know asteroids and any other out-of-focus objects are simulated "on-rails", meaning their orbits can't be changed like that.

Two: This thing's orbit is REALLY inclined away from both muns, at least 45 degrees, its ascending and descending nodes with the Mun are way too close to Kerbin. I don't really see how it would have interacted with them in the first place.

I guess maybe that's why the game spawned it so close, but I don't see how it could have been captured naturally.

Actually, just because it is on rails doesn't mean it can't be affected by gravity and SOI changes. I have had craft in what i thought were stable orbits around Jool, only to leave them on rails and later find out that Tylo slingshotted them out of the system.

As for the inclination, I got nothing, so I'll say the Kraken did it

[DeMatt]

I'm fairly sure that asteroids are treated like your spacecraft/stations/debris/lost EVAs etc. Their on-rail trajectory is determined by the sphere of influence they're in, and with the abrupt SOI transitions we get under the current system, they can easily be flung around by encountering a moon.

On the other hand, given the extreme eccentricity you describe, I'd be more willing to bet that they just got generated on a "this would actually already have been captured" vector.

[Ravenchant]

If their starting point and velocity vector are somewhat randomized, they can be already in orbit if spawned with a sufficiently low speed relative to Kerbin and within its SOI.

[Kasuha]

There are two options:

1/ SOI-based implementation of solar system is not accurate and it is therefore possible that a body enters a SOI with just right parameters to enter stable orbit within that SOI that does not exceed its boundary. It is caused by the fact that most points of SOI boundary move through space at different speed than is the true orbital speed at that point.

2/ If an object passes Mun or Minmus orbit it might get gravitationally slingshotted just right to enter stable orbit around Kerbin even though its original orbit would eventually send it out of the SOI again. Such orbit, however, still crosses the trajectory of the moon that caused this, and over time the object will get another gravitational slingshot. In the end it will inevitably either crash into some body within that SOI or exit the SOI again after series of such slingshots but that may happen in very distant future.

[zarakon]

It is caused by the fact that most points of SOI boundary move through space at different speed than is the true orbital speed at that point.

Ahh, that makes a lot of sense.

[cantab]

Timewarping through SOI changes can shift your orbit. Annoying, when you line up the perfect periapsis from a long way away then find you're thrown way off and need to make a delta-V-hungry correction. Whether those shifts can result in an autocapture I don't know for certain, but it seems entirely plausible.

Also possible is that the orbit is just escaping, and the Tracking Station is showing it wrong.