Planet Generation

[Noven]

I changed the eccentricity from 0.15 to 0.05 so it is a bit more mild.

[Agemegos]

Originally Posted by Noven

Umm, how do I do that? I didn't see that in Space

I see that you worked it out.

It isn't in Space, probably because it is a bit tedious to do it until you automate the sequence and get a computer to crunch the numbers.

If it had been in Space I think playtesting might have driven the authors to reconsider their table for orbital eccentricities. The eccentricities are simply treated as decorative in the RAW. But if you follow the consequences through it makes you wonder about the calculated Habitability ratings for a lot of these planets.

Originally Posted by Noven

Ok I go the temperatures, and wow, maybe I should tone down the eccentricity

I'm really not sure whether the system generation system in Space makes orbital eccentricities too high. The values in our solar system are 0.2056, 0.0068, 0.0167, 0.0934, 0.0483, 0.054, and 0.006. And Mercury's high value is perhaps not randomly-placed: there are orbital interactions that tend to even out the spacings of orbiting satellite, moving the inner ones in and the outer ones out,and they also tend to make the orbits more circular for planets or moons that have something orbiting on each side of them, inwards and outwards. Perhaps a planet in the Goldilocks zone, likely to have another planet in orbit sunwards and another darkwards, should not have a chance of an eccentric orbit anything like Mercury's. Or even Mars's.

One thing that I am pretty sure of is that Space makes "eccentric gas giant" and "episolar gas giant" systems far more common than they are in reality. I understand that it has been established from surveys of nearby stars that no more than 3–6% have detectable (ie. epistellar or eccentric) gas giant planets. If you modify the "Gas Giant Arrangement Table" on p. 107 to

Roll (3d6) g Arrangement
5 or less gapp no gas giant
6 – 15 gapppp conventional gas giant
16 gapgapgap eccentric gas giant
17 – 18 gappp epistellar gas giant

your results will be more realistic and habitable.

Originally Posted by RyanW

A planet functions as a substantial heat sink, so living on an eccentrically orbiting planet won't be quite as extreme as summering on Venus and spending the winter on Mars.

No, but it could be pretty bad. The temperature extremes of day and night are mild compared to those estimated for the dayside and nightside of a tide-locked planet, but they are not negligible. Annual temperature variations due to eccentricity are not as strongly-driven as that, but on the other hand they get more time to build up.

[Noven]

Well I toned it down so it should not really be an issue. With the axis being 7°, how does that affect the seasons exactly. I wish I had a little program I could plug all the numbers from Space that I got and get like an orbital model or something.

Basically, this planet is going to be for a fantasy world that I am making. Basically, homo sapiens idaltu never went extinct. They were removed from the planet by "aliens" when homo sapiens sapiens were on the rise. They were transported to Zeta Tucanae III, where they could evolve unmolested. There are other things, but that is the main gist =).

[David Johnston2]

Originally Posted by Noven

Well I toned it down so it should not really be an issue. With the axis being 7°, how does that affect the seasons exactly. .

7 degrees of axial tilt fundamentally means there are no seasons. Earth has a 23 degree axial tilt and that's what produces our seasons.

[Noven]

Originally Posted by David Johnston2

7 degrees of axial tilt fundamentally means there are no seasons. Earth has a 23 degree axial tilt and that's what produces our seasons.

How much would the axis need to be to have 4 seasons, but mild ones?

[David Johnston2]

Originally Posted by Noven

How much would the axis need to be to have 4 seasons, but mild ones?

Well I was speaking from a Canadian's perspective. For me, there's no difference between having mild seasons and having no seasons. If the snow doesn't fall, you don't have winter. If the trees don't turn yellow you don't have autumn.

[Agemegos]

Originally Posted by Noven

How much would the axis need to be to have 4 seasons, but mild ones?

Be aware that seasons are partly arbitrary and partly an accident of local geography. Some places on Earth have no seasonal variation to speak of, i.e. only one season. Some places (e.g. a stretch from India to northern Australia) have only two: the Wet and the Dry. In Australia south of the Monsoon zone we have perhaps five seasons.

[Figleaf23]

Originally Posted by Noven

How much would the axis need to be to have 4 seasons, but mild ones?

As others have alluded, 'season' generally describes a climatic condition rather a than an astronomical one. Astronomically, even a miniscule tilt will give you equinoxes and solstices, they just won't produce the extremes of climate variance they do if they are larger.

As another poster noted, the eliptical orbit is likely to be a greater contributor to 'seasons' than the axial tilt.

[Pomphis]

Space 1e has a table on p.107sb: minor seasons from 3-18°, earthlike seasons at tilts from 22-32°, major seasons from 33-48° and gross seasons from 49-90°.

[D10]

If you launch an atomic bomb into a planet filled with fuel gases, what would be the result ?