<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.18999">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>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.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>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.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>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.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>- Gerry Quinn</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=jack.smith.1946@gmail.com
href="mailto:jack.smith.1946@gmail.com">Jack Smith</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=urth@lists.urth.net
href="mailto:urth@lists.urth.net">The Urth Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, February 09, 2011 11:04
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: (urth) grumble at wolfe
comment made attached to guardianarticle</DIV>
<DIV><BR></DIV>Thanks for the link to horseshoe orbits! This might work.
<DIV><BR><BR>
<DIV class=gmail_quote>On Wed, Feb 9, 2011 at 12:33 AM, Jeff Wilson <SPAN
dir=ltr><<A href="mailto:jwilson@io.com">jwilson@io.com</A>></SPAN>
wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV class=im>On 2/8/2011 9:36 PM, Gerry Quinn wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>I forgot about that.<BR>But one or both could have an
elliptical orbit.<BR>Again, I don't know whether precession would make
this unrealistic or<BR>not. And 35000 leagues is incredibly, dangerously
close for two<BR>Earth-sized planets.<BR>But in terms of basic mechanics,
a series of conjunctions should be<BR>possible (for story purposes, I
think it would probably be sufficient if<BR>the series lasted a few
centuries).<BR></BLOCKQUOTE><BR></DIV>They could be paired in a horseshoe
orbit:<BR><BR><A
href="http://curious.astro.cornell.edu/question.php?number=210"
target=_blank>http://curious.astro.cornell.edu/question.php?number=210</A><BR><FONT
color=#888888><BR></FONT></BLOCKQUOTE></DIV></DIV></BLOCKQUOTE></BODY></HTML>