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#11
August 8th 04, 06:44 PM
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How special is the Solar System?
Simple forms of life may evolve into advanced, intelligent forms
of life in a period of several billions of years if they are not exterminated by drastic climatic changes. Stable climate is possible only if the planet's orbit is stable and nearly circular. All the planets of our solar system have stable and nearly circular orbits, but all known extrasolar planets have eccentric orbits except for those close enough to their star to be circularized by tidal forces. The tidal forces also lock the planet's rotation, so one face of the planet is always turned toward its star, just like the Moon always keeps the same face turned toward the Earth. The bright side of the planet is too hot for life, while its dark side is too cold for life. Supercomputer simulations of orbital stability are not sophisticated enough to determine if planetary systems made of many planets are stable. It is possible that the absence of massive body in the main asteroid belt stabilizes planetary orbits. Although intelligent forms of life and technological civilizations may be rare, it is unlikely that we are the only technological civilization in the entire universe. 
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#12
August 8th 04, 07:40 PM
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How special is the Solar System? (Forwarded)
Alain Fournier wrote:
Sander Vesik wrote: Alain Fournier wrote: Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. No - its just that that type of objects and star systems are what we can detect best so of course they are most numerous. Oh, and even with a hot super-Jupiter you could get terrestrial planets in habitable zone given favourable presence of smaller gas giants. We can detect large planets close to the star. But why are they in elliptical orbits. We can detect circular orbits as well as elliptical orbits. I agree that there could still be lots of Earth like planets. But it does seem likely that our solar system is atypical, if only because our planets close to the sun are in circular orbits. It still is early to declare what is a typical solar system but we are now getting some data. And that data is not pointing towards our solar system being typical. A lot of these would have been migrations and not as they formed. Alain Fournier -- Sander +++ Out of cheese error +++
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#13
August 8th 04, 11:04 PM
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How special is the Solar System? (Forwarded)
Sander Vesik wrote:
Alain Fournier wrote: Sander Vesik wrote: Alain Fournier wrote: Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. No - its just that that type of objects and star systems are what we can detect best so of course they are most numerous. Oh, and even with a hot super-Jupiter you could get terrestrial planets in habitable zone given favourable presence of smaller gas giants. We can detect large planets close to the star. But why are they in elliptical orbits. We can detect circular orbits as well as elliptical orbits. I agree that there could still be lots of Earth like planets. But it does seem likely that our solar system is atypical, if only because our planets close to the sun are in circular orbits. It still is early to declare what is a typical solar system but we are now getting some data. And that data is not pointing towards our solar system being typical. A lot of these would have been migrations and not as they formed. They still make Earth like planets unlikely. Alain Fournier
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#14
August 10th 04, 05:27 PM
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How special is the Solar System?
Andrew Nowicki ) wrote:
: "How special is the Solar System?" by M. E. Beer1., : A.R. King1, M. Livio2 and J. E. Pringle2 is posted : at: http://arxiv.org/pdf/astro-ph/0407476 : MY COMMENT : The high eccentricity of the extraterrestrial gas giants : implies that all or nearly all extraterrestrial planets : have eccentric orbits and that solar system is uncommon. Could this be due to us having several gas giants and that Jupiter and Saturn are both large? Or that the measurements from AU are much better than from LY, and that if we were actually near these extraterrestial planets would be much more like our own? Further, does our solar system from a few LY appear to have a 20 year wobble that coincides with Jupiter and Saturn's synodic period? Since Jupiter's period is 12 years this 8 year anomaly might make the orbit seem more eccentric. : In addition to the nearly circular orbits (except for : Pluto), the solar planets are almost evenly distributed : as predicted by the Titius-Bode Law. The Titius-Bode Law : also works for moons orbiting solar planets, but does not : work well for Neptune and Pluto: : http://astrosun2.astro.cornell.edu/a.../bodes_law.htm : Apparently the solar system accretion disk was not : disturbed by interlopers when planets and moons : formed 4.5 billion years ago, except for the most : distant planets: Neptune and Pluto. We still do not : know if planetary orbits are inherently unstable. We know that they are stable and have predicted when the perhelion points move as well. See: http://ssd.jpl.nasa.gov/elem_planets.html : It seems that planetary systems having many planets : should be less stable than planetary systems having : few planets. The absence of massive bodies in the : middle of the solar system (known as the main : asteroid belt) may have stabilized the solar system. : If planetary orbits are inherently unstable than solar : system is uncommon and SETI is a waste of time. Simple : forms of life may survive on a somewhat unstable planet, : but they cannot create a technological civilization. My guess is that our solar system is typical of others, at least others that have only one star. : We need better computer simulations of orbital : stability -- these simulations are more important : than all the microwave SETI research. Right, you cannot infer AU-based data with other data like it at LY-based data. There is simply too much room for error. Eric : PS. I wonder if the Moon (Luna) acts like a vacuum : cleaner in a sense that it hurls deadly asteroids : away from the Earth. : __________________________________________________ ______________ : RELATED ARTICLES : Computer simulations of orbital stability are difficult. : For example, the following paper is based on simulations : made on a supercomputer having 128 processors, and yet it : neglects possible inclinations as well as planetary systems : having more than 3 planets: : Stability of Terrestrial Planets in the Habitable Zone of : Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208 : http://arXiv:astro-ph/0403152 : Excerpt from "The Stability Of The Orbits Of Earth-Mass Planets : In And Near The Habitable Zones Of Known Exoplanetary Systems" : by Barrie W Jones, David R Underwood, P Nick Sleep, : http://www.astrophys-assist.com/educate/cgino617.pdf: : "We have shown that Earth-mass planets could survive in : variously restricted regions of the habitable zones (HZs) : of most of a sample of nine of the 93 main-sequence exoplanetary : systems confirmed by May 2003. In a preliminary extrapolation : of our results to the other systems, we estimate that roughly : a third of the 93 systems might be able to have Earth-mass : planets in stable, confined orbits somewhere in their HZs." : This is a poor quality article. It does not explain : how they calculated the orbital stability. : Excerpt from "Dynamical Stability and Habitability of a : Terrestrial Planet in HD74156" by M. Colleen Gino, : http://www.astrophys-assist.com/educate/cgino617.pdf: : "The dynamical stability of the system must be taken into : account as well, particularly in light of the impact that : large planets can have on the orbit of the terrestrial planet. : For a terrestrial planet to remain habitable, there is a : dynamical requirement that other planets in the system don’t : gravitationally perturb the planet outside of its habitability : zone. In a recent study involving 85 of the known extrasolar : planetary systems, Menou and Tabachnik (2003) found that more : than half of these systems, primarily those with distant : eccentric giant planets, are not likely to support terrestrial : planets and are therefore dynamically inhabitable. Marcy and : Butler (2000) give similar evidence for the likelihood of : terrestrial planets to be scattered gravitationally from the : high eccentricity of Jupiter-like planets that exist between : 2 – 3 AU. Under such circumstances the circular orbits and the : long term survival of terrestrial planets is not guaranteed."
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#16
August 10th 04, 05:42 PM
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How special is the Solar System? (Forwarded)
Greg D. Moore \(Strider\) ) wrote:
: "Alain Fournier" wrote in message : ... : : Yes there is evidence against it. The evidence isn't very strong : but we are now getting some serious data on the matter. Well : the evidence is somewhat strong that our solar system is : fundamentally different from the majority of planetary systems : around stars. It is much weaker about Earth-like planets being : very rare. Most planets found to date are Jupiter sized or bigger : in an elliptical orbit with periapsis less than 1 AU. If Jupiter : had an elliptical orbit with periapsis less than 1 AU, then : Earths orbit wouldn't be stable and Earth wouldn't be. : : Keep in mind that most of the techniques used are more LIKELY to find that : sort of system than ours. : Mostly they focus on the wobble of a star, a star with a Jupiter class : planet close in will have a more easily detectable wobble than one further : out, for two reasons: : 1) Mass closer causes a larger effect. : 2) Shorter orbit causes wobbles more often. Synodic periods of large planets (i.e. Jupiter ans Saturn)? That period is 20 years even though Jupiter's period is 12 years and Saturn's is 29. Who is to say that these extrasolar planets don't have a similar makeup like Jupiter and Saturn? Eric : Alain Fournier :
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#17
August 10th 04, 05:45 PM
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How special is the Solar System? (Forwarded)
Alain Fournier ) wrote:
: Sander Vesik wrote: : Alain Fournier wrote: : : : Sander Vesik wrote: : : Alain Fournier wrote: : : : Yes there is evidence against it. The evidence isn't very strong : but we are now getting some serious data on the matter. Well : the evidence is somewhat strong that our solar system is : fundamentally different from the majority of planetary systems : around stars. It is much weaker about Earth-like planets being : very rare. Most planets found to date are Jupiter sized or bigger : in an elliptical orbit with periapsis less than 1 AU. If Jupiter : had an elliptical orbit with periapsis less than 1 AU, then : Earths orbit wouldn't be stable and Earth wouldn't be. : : : No - its just that that type of objects and star systems are what : we can detect best so of course they are most numerous. Oh, and even : with a hot super-Jupiter you could get terrestrial planets in habitable : zone given favourable presence of smaller gas giants. : : : We can detect large planets close to the star. But why : are they in elliptical orbits. We can detect circular : orbits as well as elliptical orbits. I agree that : there could still be lots of Earth like planets. But it does : seem likely that our solar system is atypical, if only because : our planets close to the sun are in circular orbits. It : still is early to declare what is a typical solar system : but we are now getting some data. And that data is not : pointing towards our solar system being typical. : : : A lot of these would have been migrations and not as they formed. : They still make Earth like planets unlikely. Has anyone tried to simulate what our solar system would like like from 5-10 LY? Does it look radically different that what we see at 5-10 LY from other star systems? Eric : Alain Fournier
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#18
August 12th 04, 04:50 AM
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How special is the Solar System?
Andrew Nowicki wrote in message ...
all known extrasolar planets have eccentric orbits except for those close enough to their star to be circularized by tidal forces. Not entirely true: http://www.obspm.fr/encycl/cat1.html I count five planets with semi-major axis 1 AU or greater, and orbital eccentricity less than 0.1: HD 28185b, 1.00 AU, ecc = 0.06 HD 27442b, 1.18 AU, ecc = 0.07 HD 4208b, 1.67 AU, ecc = 0.05 HD 12661c, 2.56 AU, ecc 0.1 47 Uma c, 3.73 AU, ecc 0.1 For comparison, Jupiter's eccentricity is 0.048, and Saturn's is 0.056. Ecc of Mars is 0.093.
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#19
August 18th 04, 10:50 PM
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In article ,
(Eric Chomko) writes: : The high eccentricity of the extraterrestrial gas giants : implies that all or nearly all extraterrestrial planets : have eccentric orbits and that solar system is uncommon. Could this be due to us having several gas giants and that Jupiter and Saturn are both large? Or that the measurements from AU are much better than from LY, and that if we were actually near these extraterrestial planets would be much more like our own? I don't see why there should be any doubt about the derived eccentricities, which are based on the radial velocity curves. The problem is selection effects. It's much easier to detect systems with heavy planets close to the star than systems like ours, where the heavy planets are distant from the star. Observations so far are incapable, or at best just barely capable, of detecting solar systems like ours. Further, does our solar system from a few LY appear to have a 20 year wobble that coincides with Jupiter and Saturn's synodic period? No. With sufficient observations -- which would have to span a few decades -- both periods would be seen. Try plotting the sum of two sine waves with different amplitudes and periods. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.)
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#20
August 19th 04, 09:27 PM
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Steve Willner ) wrote:
: In article , : (Eric Chomko) writes: : : The high eccentricity of the extraterrestrial gas giants : : implies that all or nearly all extraterrestrial planets : : have eccentric orbits and that solar system is uncommon. : : Could this be due to us having several gas giants and that Jupiter and : Saturn are both large? Or that the measurements from AU are much better : than from LY, and that if we were actually near these extraterrestial : planets would be much more like our own? : I don't see why there should be any doubt about the derived : eccentricities, which are based on the radial velocity curves. The : problem is selection effects. It's much easier to detect systems : with heavy planets close to the star than systems like ours, where : the heavy planets are distant from the star. Observations so far are : incapable, or at best just barely capable, of detecting solar systems : like ours. : Further, does our solar system : from a few LY appear to have a 20 year wobble that coincides with : Jupiter and Saturn's synodic period? : No. With sufficient observations -- which would have to span a few : decades -- both periods would be seen. Try plotting the sum of two : sine waves with different amplitudes and periods. My understanding is that when Jupiter and Saturn are near conjunction, the barycenter between them and the sun is about 100K miles away from the solar corona in the direction of the planets. I believe that Asimov discussed this in his book, "Jupiter". Also, don't we know about the existence of planets outside the solar system due to the relationship between the barycenter of the star and its apparent motion related to it? Eric : -- : Steve Willner Phone 617-495-7123 : Cambridge, MA 02138 USA : (Please email your reply if you want to be sure I see it; include a : valid Reply-To address to receive an acknowledgement. Commercial : email may be sent to your ISP.)
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