grumble at wolfe comment made attached to guardianarticle

Gerry Quinn · 09 Feb 2011, 12:26 · from 2011-February.txt.gz

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From: gerryq at indigo.ie (Gerry Quinn)
Date: Wed, 9 Feb 2011 12:26:55 -0000
Subject: (urth) grumble at wolfe comment made attached to guardianarticle
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	<4D52272C.3010600 at io.com>
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Message-ID: <1D44D6669EA441B78E6880BA3C756D6F@jill>

I think horseshoes are a bit problematic.  If you look at Cruithne's orbit, its actual distance from Earth varies on a short scale with a period of one year.  Over a longer term, the average distance varies.  Since Cruithne's orbital period is one year, there's no room for meaningful six-year conjunctions.

Hence I'm inclined to prefer the simpler concept: Blue has a circular orbit similar to the Earth's, while Green has an elliptical orbit with a period 6/7 that of Blue.  Ignoring precession, this can give a conjunction every six years, while they are far apart the rest of the time.

As another possibility, we could imagine that there are dark stars of some kind (black holes or dense dark matter objects, for example) present in the system - these might induce interesting orbital motions in the hadronic planets.

- Gerry Quinn

  ----- Original Message ----- 
  From: Jack Smith 
  To: The Urth Mailing List 
  Sent: Wednesday, February 09, 2011 11:04 AM
  Subject: Re: (urth) grumble at wolfe comment made attached to guardianarticle

  Thanks for the link to horseshoe orbits!  This might work.

  On Wed, Feb 9, 2011 at 12:33 AM, Jeff Wilson <jwilson at io.com> wrote:

    On 2/8/2011 9:36 PM, Gerry Quinn wrote:

      I forgot about that.
      But one or both could have an elliptical orbit.
      Again, I don't know whether precession would make this unrealistic or
      not. And 35000 leagues is incredibly, dangerously close for two
      Earth-sized planets.
      But in terms of basic mechanics, a series of conjunctions should be
      possible (for story purposes, I think it would probably be sufficient if
      the series lasted a few centuries).

    They could be paired in a horseshoe orbit:

    http://curious.astro.cornell.edu/question.php?number=210

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