nweismuller wrote:I assume that when orbital periods are listed for bodies, the 'days' measuring the period are 24-hour Earth days, rather than whatever the local rotational day is?
I assume so as well, though I haven't looked at the code. The numbers looked okay to me, and they're irrelevant to gameplay, so that's as deep as I got into it. But if I know Sven (and I do), he based them on real mathematical orbital models.
nweismuller wrote:Also: are orbital periods around M-class stars supposed to be that short? I've seen orbital periods shorter than Luna's on some worlds. Are orbits around a more massive central body slower at a given orbital distance? I find it hard to swallow that colonisable planets are orbiting closer to their star than Luna is orbiting to Earth...
The more massive the bodies, the shorter the orbital period at the same radius. M type stars tend to be very small and dim, and so for a planet to be in the habitable zone it would need to be at a roughly similar orbital distance as Mercury, which would usually mean an orbital period of ~80-130 days. However, planets can and do orbit much closer; a known example such as Kepler-186 is an M1V star with its closest planets having orbital periods of 3.9, 7.3, 13.3 and 22.4 days, respectively. The closest of these planets are much farther from the primary than the Earth-Moon distance, but orbit faster because even a small a star is orders of magnitude more massive than Earth.
The numbers that I see looking at a selection of planets look reasonable to me.
nweismuller wrote:Edit: And I just noticed that the orbital period of Fargone I is listed as 3 minutes, which cannot possibly be correct.
There's something obviously wrong there. I'll check it out. I think the preset systems have hard coded values, so there's probably an error there.
The smallest known exoplanet orbit is PSR J1719-1438 b, which has an orbital period of 2.2 hours, and an orbital distance of 0.004 AU (about twice the Earth-Moon distance). It appears to be a carbon planet in orbit around a pulsar.