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Pheasability of a star around Sirius
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? |
#2
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Pheasability of a star around Sirius
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 |
#3
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Pheasability of a star around Sirius
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. |
#4
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Pheasability of a star around Sirius
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 |
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