Re: Two suns

James Nicoll <jdnicoll@xxxxxxxxx> wrote:
Tina Hall <Tina_Hall@xxxxxxxxxxx> wrote:
James Nicoll <jdnicoll@xxxxxxxxx> wrote:

"Here's an example. We have a planet of jupiter-size (but at about
half the distance) around a sun-like star. Far far away, an
eccentric inclined brown dwarf companion with a semimajor axis of
750 AU - I said far away, right? - orbits the sun.like star. In 300
million years, the Jupiter-mass planet's eccentricity goes from
almost zero to over 0.9, then back to near zero."

That seems a fairly long time, and not that big a change. (But I
don't know what the 0.9 exactly says.)

It means that the distance at closest approach is much smaller
than the distance when the world is farthest from the sun. Pluto, for
example, is considered to have a fairly eccentric orbit but it only
has an eccentricity of about 0.25. I can give you the mathematical
definition if you like.

Better would be actual distances, in AU, and what the 0.9 or 0.25
exactly mean with that.

Or a site that explains that kid-friendly (I don't understand the more
technical explanations).

What this means for a habitable world is that during the periods
when the orbit is highly eccentric, the planet will experience long
cold winters with short and very hot summers. This may well kill off
most of the life on the planet.

Even without the condition being suddenly 'switched on'? I mean there
are millions of years while it gets to the extreme...

If this happens to an Earthlike world, mass extinction seems like
the least that will happen.

With such a gradual change?

I mean, 300 million years? How long ago was it that dinosaurs died
out? I'm looking at the change in species living here in the
meantime (rather than the extinction of dinosaurs).

Dinosaurs bit it 65 million years ago. In fact the largest known
extinction (The Permian, which killed a much larger fration of the
species of the time than died with the dinosaurs) was only about 250
million years ago. The effect of the extinction is that all modern
forms will be descended from whatever happened to be able to make it
through the harsh periods, which could be interesting: all of the
lifeforms might all be descended from hibernators [1].

I have those in mind that, as conditions got worse, gradually adapted to
cope with the huge yearly change in climate.

I actually like that. (My characters, while so far looking like humans,
have an odd reproduction, which looks as if it could fit such an
adaption.)

Perhaps the story is set not quite at the drastic end. (50 million years
before it? How bad would things be then?)

But then, a Jupiter-size planet, at half our Jupiter's distance to the
main sun, wouldn't be habitable, would it?

Less interesting, the extreme periods might kill off all but the
simplest, most hardy species, which would take a long time to recover
from.

But the extreme periods don't jump on the life forms, they change
gradually. Lots of time to learn to cope.

The very dullest option is that the freeze-bake kills all life,
which makes for a very boring planet, at least in terms of possible
characters.

Heh. True.

1: In fact, one can induce a state of torpor in a variety of animals
from mice to nematodes using the same chemical trigger, suggesting
that at some point, our very distant common ancestor found hiberation
a useful trick.

Interesting.

Thanks.

--
Tina
WIP: [Untitled]: 12427 words
WISuspension: Seasons & Elements trilogy | Magic Earth series
Posted to Usenet newsgroup rec.arts.sf.composition.

.

Relevant Pages

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