How Many stars have Planets ?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by johnahmed, Feb 6, 2006.

  1. johnahmed Registered Senior Member

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    what proportion of stars have planets ?
    we are told astronomers have discovered the 10th planet orbiting a star thousands of light years away..but what about our nearest star which is only 7 light years away, and other stars closer ? if only 10 or so have been discovered that would mean planetery systems are a rarety ?
     
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  3. James R Just this guy, you know? Staff Member

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    Probably, many stars have planets.

    Most of the planets found outside our solar system so far have been very large planets - Jupiter-sized or similar. Good techniques for finding small, rocky, Earth-like planets are only just now starting to be developed.
     
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  5. Facial Valued Senior Member

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    Astronomers have found so many of them - I don't know how many hundreds or thousands up to date - but the proportion still seems to be small. I'm sure that proportion will become larger as they find smaller rocky planets like JamesR said.
     
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  7. Novacane Registered Senior Member

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    I imagine that the term; small, rocky/water Earth-like planets is more accurate to what I believe the actual planet Earth is like, instead of just calling it a small, rocky, Earth-like planet. Or should we just ignore the presence of the oceans?

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  8. James R Just this guy, you know? Staff Member

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    Well, the Earth has a radius of 6370 km. The deepest ocean is, I think, less that 10 km deep. So, out of the 6370 km, 6360 km is rock, essentially - much of it molten.
     
  9. Laika Space Bitch Registered Senior Member

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    Forgive my pedantry, but the Earth is rock down to a depth of about 2900 km. Below that it's probably a mixture of iron and nickel with traces of lighter elements. Furthermore, of all the rock comprising the mantle and crust only a small volume of it is molten.
     
  10. James R Just this guy, you know? Staff Member

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    Yeah, ok, if you want to be technical about it. The point was: it's not water.

    Really? I thought most of the mantle was liquid, and also the outer core.
     
  11. Facial Valued Senior Member

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    The lower parts of the mantle are plastic. The upper parts are mostly solid, but also heavily laced with hotspots and convenction plumes from the lower mantle / outer core.

    Hope I'm not wrong on this one. Laika?
     
  12. madanthonywayne Morning in America Staff Member

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    Based on my limited knowledge of how stars form, it would seem likely that the vast majority of stars have planets. Now as to how many have truly earth like planets capable of supporting life, a much smaller fraction.
     
  13. Facial Valued Senior Member

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    ...which reminds me, astonomers haven't even settled on the def'n of a planet.
     
  14. Laika Space Bitch Registered Senior Member

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    You're not wrong Facial. The mantle is a plastic solid and it can flow over geological timescales. Even the softest part of the mantle, the asthenosphere, only contains about 5% melt.
     
  15. phlogistician Banned Banned

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    Indeed. I was watching 'The Sky at Night' yesterday evening, and it was about the lengths astronomers go to to detect planets, and what they have discovered so far.

    Now, discovering planets is tricky, but they have found lots of oddities. Gas giants in close proximity to their star, and terrestrial planets in highly elliptical orbits. Good stuff for science, just not great for life.

    But it's early days, and the given the number of stars, we only need a small fraction, and there will be life, somewhere. It's just shame we'll probably never communicate.
     
  16. draqon Banned Banned

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    Are u talking Proxima Centauri?...anyways regarding your question on how many stars have planets...too many to mention...noone will ever know what is the ratio of stars with planets and no planets...is the question directed for the purpose of locating terra-like planets? that is Earth-like? theyve got some databases on the net that have possible extra-solar terra-planet candidates.
     
  17. c7ityi_ Registered Senior Member

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    Are there stars which don't have planets?
     
  18. draqon Banned Banned

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    obviously
     
  19. Xylene Valued Senior Member

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    As for how many stars have planets, probably the majority of the stars in the Universe. As for how many are habitable by Humans, that depends on how many are in the Goldilocks Zone.
     
  20. Clockwood You Forgot Poland Registered Senior Member

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    More than just that. Our solar system has three planets the right distance from the sun to support life.
    It just didn't quite work out in two of the three cases.
     
  21. c7ityi_ Registered Senior Member

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    It's not just about distance though.
     
  22. Xylene Valued Senior Member

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    You're right, ct--it's about whether the parent star stays on the main sequence long enough to allow life to evolve
     

  23. You'd also need to add an active geothermal core producing a magnetosphere for planetary bodies falling within the Goldilocks Zone as well if you're talking planets with a chance of developing life that close to a star - there's not going to be much else other than Crispy Critters without one or else your looking at a completely sub-terrestrial ecosystem.
     

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