Re: Old colony obiting type F star?

On 17 mai, 23:37, David Johnston <da...@xxxxxxxxx> wrote:
On Sat, 17 May 2008 15:42:10 +0200, Peter Knutsen

<pe...@xxxxxxxxxxxxxxxx> wrote:
I've decided that one way to get blue plants on my planet is to have it
orbit a type F star, and I'm thinking something in the mid-range of the
F, or blue-white, span, perhaps F5 or so. Our sun is, as I understand
it, a yellow star at the high end of the G span. G2 IIRC, so this star
would be around 2/3 of a spectral class warmer.

But what is it like living on a planet orbiting such a bright star?

Clearly the planet would have to orbit much more than 1 AU away, so the
year would be longer. Would a long day cause problems?

The length of the year has no relationship to the length of the day.

Would a long day

of, say, 60 hours or more cause the colonization agency to dismiss the
planet as useless, because the slow rotation causes overheating?

Assuming the planet has air and oceans, that isn't really an issue.
Parts of the planet might end up with nasty variations between noon
and midnight, but only in areas far away from the moderating influence
of bodies of water. Even there, air circulation will keep things from
getting too far out of the way.


Also consider Coriolis forces. On Earth, air cannot blow directly from
cold spots to warm spots because Coriolis forces deflect it to blow
along isobars and only slowly leak into cyclones due to friction. On
Venus with little physical rotation, air freely flows and carries heat
around. Slow rotation would mean weaker Coriolis force and more
effective heat transport by air and water.


The colony is old, and has grown into a full civilization, covering
almost all habitable areas of the planet's surface, and has also
survived at least one Asimov-style interregnum, where the entire
galactic society degenerated to at technological stage equivalent to the
middle ages, or possibly lower.

Where can people live, on such a planet?

I was thinking domed cities at first, with huge domes of a mostly
transparent material that filters out a lot of the light (including most
of the UV), letting just enough through for the light level to be
comfortable for humans. But can such domes, each several kilometers in
diameter, remain largely intact a period of 500 or 1000 or even 2000
years with no maintenance?

Not unless it's a tectonically dead world which is unlikely since it
won't be a hugely old world.

Mars is tectonically much less active than Earth. Young Mars was more
active than old Mars (formation of Vallis Marineris et cetera) but
less active than young Earth (little trace of continental drift on
young Mars). So, if you have a young world less active than Earth, you
could well have modest activity levels.


Obviously I could invoke superscience materials, like with Niven's
Ringworld or Banks' Orbitals, and while I do that in other situations, I
don't want to do it here. So domes are out.

Would people be forced to live near the poles, and staying far away from
the equator?

Probably not, unless it was a little too close for comfort.

If the atmosphere is thick enough, it could filter out a lot of UV, so
that you wouldn't have to be black-skinned to surive, I'm thinking. If I
make the planet somewhat smaller, with a lower gravity than Earths, but
not so low that the planet is passed over by the Colonization Agency,
the atmosphere would extend further out.

Extend further out? No, lower gravity doesn't cause that.

It does. See Titan for most extreme.

.

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