What is the deal with these two iron planets??

[Tee Mcgee]

So I popped into a system that immediately was something unusual, several nested orbitals:

Zooming in closer in the A star system you'll see this:

Click for stats: (Both planets are nearly identical, one is 0.1G less mass)
Now the weird parts:
The two planets move incredibly fast along their orbital (0.2 day year, moving at a whopping 250km/s and fleeing rapidly from you in supercruise) but never rotate around each other. Rather, they rotate in space (in the same direction, it looks like) but always remain perfectly distant away from the sun. They always remain at an exact angle.

Secondly, despite having only 0.3~ G's, when I went to land on one, at around 500km it slammed my ship Orca down to the planet and I ricochet'd off, with my upward thrusters doing nothing to stop me. I also saw this weird red fog effect when one of many eclipses happened:

So what's going on with these planets? Does ED actually simulate magnetics? Why aren't they orbiting each other? Why is their speed so insanely fast?

 

[varonica]

So what's going on with these planets? Does ED actually simulate magnetics? Why aren't they orbiting each other? Why is their speed so insanely fast?

Expected orbital speeds are easy to work out, there's a thing called a Roche Limit where bodies will break up if they get to close together, different materials will affect the Roche Limit of the the bodies, so two similar sized metalic bodies can get fairly close before they break up and they can pick up quite a speed when they get close together.

 

[Sapyx]

"The deal" is all about how ED simplifies gravity in its simulation of a star system. Out there in the real universe, the net gravitational field you feel at any given moment is a combination of the gravitational fields from all the nearby objects large enough to possess a detectable gravitational field. Thus, a satellite orbiting Earth feels primarily the Earth, but also the Sun, Moon and (to a diminishly smaller extent) all the other planets. The net effect is difficult to accurately model, even with our best supercomputers. So ED simplifies things, and you (your spaceship) only ever "feels" the gravity from one object at a time: the object which it calculates has the greatest effect on you at your given location. So, a satellite (or a spaceship) orbiting the Earth in ED only ever feels the Earth; all other objects are ignored, while that satellite remains within Earth's gravitational sphere of influence.

The "insanely fast speed" of your two planets is caused by their orbital velocity. They are fairly small planets, right up close to a very large sun - so they have a very small gravitational sphere of influence. When you are in the gravitational sphere of influence of a star, your speed is measured relative to the star - so if you are at idle speed (30 km/s), that's relative to the star, not any nearby planets. To get into the sphere of influence of those planets (and stop them from running away), you'll have to get closer.

You can tell which sphere of influence you're in, by which object is named at the bottom of the bottom-left panel in the main cockpit view. For example, here I am, just after Arrival in the Trante system:

Look down in the bottom left corner of the screen - you see the name "Trante". That's my current sphere of influence - the star Trante.

The Trante system has a rather large HMC planet which I've selected here as my nav target: Trante 1, in a very close orbit around the star - 2.5 days orbital period, around a star that's bigger and brighter than Sol. Trante 1 has over 16 Earth-masses and nearly 4 G surface gravity - so it's a big planet, with a correspondingly big gravitational sphere of influence. Suppose I want to visit Trante 1; Let's start moving towards Trante 1, and watch when the sphere of influence changes.

Here I am, at 1.28 Ls from the planet - that's closer than Earth's moon is to Earth.

But look, the name of the current sphere of influence at the bottom right is still "Trante". So my speed is still being measured relative to the star, not the planet, because the star still has stronger gravitational pull at that location. If I come to a dead stop at this point, the planet will visibly move away from me, as it is travelling quite fast in its orbit. Let's get closer, to try to catch this runaway planet.

Here I am at the sphere of influence transition - at just about 0.44 Ls distance, the sphere of influence switched from "Trante" to "Trante 1".

Now that I'm in the planet's sphere of influence, if I come to a dead stop, the planet will remain stationary - I would now be "orbiting" the star, along with the planet, travelling at the planet's speed relative to the star - and I'll barely notice this, because the speed on my speed gauge is now measuring speed relative to the planet, not the star, and the star's gravity and even its very existence is now ignored, from my spaceship's point of view.

Your little tiny planets will probably have a much, much smaller sphere of influence than Trante 1 - so you'll have to get a lot closer than 0.45 Ls to catch them - or rather, for them to catch you.

 

[Tee Mcgee]

Interesting, thanks for that explanation. It doesn't quite explain everything, but most of it. I've landed on who knows how many hundreds of planets and I've never, ever seen a 0.36G planet that made me drop so fast. I started holding ascending thrust at 500m while horizontal and it still plowed me straight into the ground (it seemed I descended much faster < 100m), it felt like it was a 5G planet, not 0.3. Need to go back and do more astrophysics testing..