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Ikkakujyu
June 25th 03, 04:42 AM
I've been pondering the use of a planet around Sirius as a device in
science fiction for a little while, and I wanted to make sure I have
my facts straight.

The idea is to have a terrestrial planet orbiting Sirius in a fairly
circular orbit at a distance of about two astronomical units. This
would give it a temperature range not unlike Earth's, and the
possibility of liquid water. Support of life is not expected and not
required, though its water would be a valuable fuel for fusion
reactors.

The existence of Sirius B complicates things a little, at least for
me. Since it was much larger in the past, it might have interfered in
this planet's development, or would have pulled it into orbit around
it. This being the case, our planet would be in a relatively far orbit
after its collapse, and liquid water would be impossible.

Assuming that the planet orbits Sirius A, the passing of Sirius B
every fifty years would cause especially hot summers. Not a problem,
just a peculiarity.

Anything I'm forgetting, or do I have anything wrong?

Odysseus
June 25th 03, 06:28 AM
Ikkakujyu wrote:
>
> I've been pondering the use of a planet around Sirius as a device in
> science fiction for a little while, and I wanted to make sure I have
> my facts straight.
>
> The idea is to have a terrestrial planet orbiting Sirius in a fairly
> circular orbit at a distance of about two astronomical units. This
> would give it a temperature range not unlike Earth's, and the
> possibility of liquid water. Support of life is not expected and not
> required, though its water would be a valuable fuel for fusion
> reactors.
>
> The existence of Sirius B complicates things a little, at least for
> me. Since it was much larger in the past, it might have interfered in
> this planet's development, or would have pulled it into orbit around
> it. This being the case, our planet would be in a relatively far orbit
> after its collapse, and liquid water would be impossible.
>
I think it complicates things a lot! Beside the problem of arriving
at a stable orbit, a critical period would have been when Sirius B
went through its red-giant stage, swelling up to many times the size
of the 'primary' and making the inner regions of the system much too
hot for water to exist on the surface of a planet. But of course
things have cooled down since then (except for the white dwarf
itself, which is still extremely hot), and lost surface water could
have been replenished from the planet's interior.

> Assuming that the planet orbits Sirius A, the passing of Sirius B
> every fifty years would cause especially hot summers. Not a problem,
> just a peculiarity.
>
I don't think Sirius B would have a very noticeable effect on your
planet's climate any more; at something like 2% the luminosity of the
sun and an opposition distance of some five or six AU the additional
radiation wouldn't be very significant -- except that there'd be
quite a bit in the form of hard UV and even X-rays. OTOH the dwarf's
gravity -- although it's much diminished from its 'glory days' it
still has a mass comparable to our sun's -- would continue to perturb
the planet, especially strongly at each 'encounter'. Some sort of
resonance would likely have to develop between the two orbital
periods to be even 'metastable'. In general the closer the planet is
to Sirius A the safer it's likely to be, it seems.

> Anything I'm forgetting, or do I have anything wrong?

Well, some would consider planets and binary star systems so
incompatible as to make the whole notion implausible. For example see

<http://www.sciencenet.org.uk/database/Physics/9812/p01204d.html>.

--Odysseus

khufu
June 25th 03, 11:57 PM
>Well, some would consider planets and binary star systems so
>incompatible as to make the whole notion implausible. For example see
><http://www.sciencenet.org.uk/database/Physics/9812/p01204d.html>.

But see "Planetary orbits in the elliptic restricted problem: II. The
Sirius system" by D.Benest. The full paper can be found by searching
at
http://adsabs.harvard.edu/abstract_service.html
This paper investigates the various planetary orbits which are
possible in the sirius system.

Bill Nunnelee
June 26th 03, 03:19 AM
It's even worse than that. Sirius B is the less massive of the two
components, yet it is the most highly evolved star. This leads to the
conclusion that there must have been an exchange of matter in the past,
during the giant phase---very problematic for any planet in between.



"Odysseus" > wrote in message
...
> Ikkakujyu wrote:
> >
> > I've been pondering the use of a planet around Sirius as a device in
> > science fiction for a little while, and I wanted to make sure I have
> > my facts straight.
> >
> > The idea is to have a terrestrial planet orbiting Sirius in a fairly
> > circular orbit at a distance of about two astronomical units. This
> > would give it a temperature range not unlike Earth's, and the
> > possibility of liquid water. Support of life is not expected and not
> > required, though its water would be a valuable fuel for fusion
> > reactors.
> >
> > The existence of Sirius B complicates things a little, at least for
> > me. Since it was much larger in the past, it might have interfered in
> > this planet's development, or would have pulled it into orbit around
> > it. This being the case, our planet would be in a relatively far orbit
> > after its collapse, and liquid water would be impossible.
> >
> I think it complicates things a lot! Beside the problem of arriving
> at a stable orbit, a critical period would have been when Sirius B
> went through its red-giant stage, swelling up to many times the size
> of the 'primary' and making the inner regions of the system much too
> hot for water to exist on the surface of a planet. But of course
> things have cooled down since then (except for the white dwarf
> itself, which is still extremely hot), and lost surface water could
> have been replenished from the planet's interior.
>
> > Assuming that the planet orbits Sirius A, the passing of Sirius B
> > every fifty years would cause especially hot summers. Not a problem,
> > just a peculiarity.
> >
> I don't think Sirius B would have a very noticeable effect on your
> planet's climate any more; at something like 2% the luminosity of the
> sun and an opposition distance of some five or six AU the additional
> radiation wouldn't be very significant -- except that there'd be
> quite a bit in the form of hard UV and even X-rays. OTOH the dwarf's
> gravity -- although it's much diminished from its 'glory days' it
> still has a mass comparable to our sun's -- would continue to perturb
> the planet, especially strongly at each 'encounter'. Some sort of
> resonance would likely have to develop between the two orbital
> periods to be even 'metastable'. In general the closer the planet is
> to Sirius A the safer it's likely to be, it seems.
>
> > Anything I'm forgetting, or do I have anything wrong?
>
> Well, some would consider planets and binary star systems so
> incompatible as to make the whole notion implausible. For example see
>
> <http://www.sciencenet.org.uk/database/Physics/9812/p01204d.html>.
>
> --Odysseus
>