Re: Two suns

In article <MSGID_2=3A240=2F2199.13=40fidonet_4e58efb4@xxxxxxxxxxx>,
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.

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.

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

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.

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.


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Relevant Pages

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