<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>On Jan 25, 2016, at 10:31 AM, John Clark <<a href="mailto:johnkclark@gmail.com">johnkclark@gmail.com</a>> wrote:</div><blockquote type="cite"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,sans-serif">On Mon, Jan 25, 2016 at 11:47 AM, Dan TheBookMan </span><span dir="ltr" style="font-family:arial,sans-serif"><<a href="mailto:danust2012@gmail.com" target="_blank">danust2012@gmail.com</a>></span><span style="font-family:arial,sans-serif"> wrote:</span><br></div><div class="gmail_extra"><div class="gmail_quote"><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline">> </div>I don't see why the decision couldn't have been along the lines of:</div><div>There are three types of planets we now know of:</div><div>1. Rocky ones like Earth and Mars,</div><div>2. Gassy ones like Jupiter and Neptun, and</div><div>3. Icy ones like Pluto.</div><div>I don't see why 1 plus 2 alone must be planets, must be where Nature made the joints, while 3 is not.</div></div></blockquote><div> </div><font size="4">The dividing line between planet and non-planet is always going to be somewhat arbitrary. I think astronomers were worried that if we included #3 as telescopes get bigger (no thanks<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>to<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>religious Hawaiians) we could end up with hundreds or even thousands of planets. And that's too many for third graders to learn.<br></font></div></div></div></blockquote><div><br></div>That, sadly, does appear to have been the initial motivation.<div><br></div><div>And I agree that it seems arbitrary, though many distinctions are more taking a fuzzy boundary and setting a threshold. I've no problem with that, though, in this case, it seems like the threshold was gerrymandered to keep Pluto-like objects off any final tally of planets.<br><br><div><div style="line-height: normal;"><span style="line-height: 20px; background-color: rgba(255, 255, 255, 0);">Regards,</span></div><div style="line-height: normal;"><span style="line-height: 20px; background-color: rgba(255, 255, 255, 0);"><br></span></div><div><div style="line-height: normal;"><span style="line-height: 20px; background-color: rgba(255, 255, 255, 0);">Dan</span></div><div style="line-height: normal;"><span style="background-color: rgba(255, 255, 255, 0);"> Sample my Kindle books via:</span></div><div style="line-height: normal;"><a href="http://author.to/DanUst" style="background-color: rgba(255, 255, 255, 0);"><font color="#000000">http://author.to/DanUst</font></a></div></div></div></div></body></html>