git ssb

title: "Planet X-3: Pluto Still Isn't a Planet, Neither Are 2003 UB313 and 2003 EL61" date: 2005-07-30 13:59 status: published tags: Pluto, Planet X, astronomy, the Solar System

links:

• url: /weblog012 title: "Pluto Isn't a Planet" rel: related type: text/html
• url: /weblog020 title: "Planet X" rel: related type: text/html
• url: /weblog021 title: "Planet X-2" rel: related type: text/html

<p>
They finally found it - again - <a href="http://www.gps.caltech.edu/~mbrown/planetlila/" title="from Mike Brown's pages at Caltech">another tenth planet, this time unnamed but temporarily designated 2003 UB313</a>. It was also announced yesterday that <a href="http://www.gps.caltech.edu/~mbrown/2003EL61/" title="again from Mike Brown's pages at Caltech">2003 EL61</a> may be roughly 70% Pluto's size. </p>
<p>
UB313 however, is definitely larger than Pluto, although perhaps only slightly. <a href="http://www.washingtonpost.com/wp-dyn/content/article/2005/07/30/AR2005073000403.html">According to the Washington Post, Mike Brown has labelled the object the tenth planet</a>; they acknowledge that there are astronomers who disagree with this label, but don't mention that Mike is actually one of them. <a href="/weblog021" title="Planet X-2">As I wrote about last year</a>, he doesn't consider Pluto to be a planet, and argues that if Pluto is considered a planet, many other objects (<a href="http://www.gps.caltech.edu/~mbrown/sedna/#planets" title="Mike Brown's Sedna page">including Sedna</a>) must logically also be considered planets. </p>
<p>
So UB313 must logically be classified as a planet as long as Pluto is. I'd be willing to bet that by this time next year there'll be another object found to be larger than Pluto, if not several; then, the International Astronomical Union will have to reconsider their definition of what constitutes a planet (or come up with one). For now, if you're asked how many planets there are in the solar system, it's <em>definitely</em> wrong to say “nine”. </p>
<p>
<a href="http://www.discover.com/">Discover Magazine</a> <a href="http://www.discover.com/issues/nov-04/cover" title="Beyond Pluto">discusses the outer solar system in more depth</a> in <a href="http://www.discover.com/issues/nov-04/">their November 2004 issue</a>; you'll have to log in to read past the first page of the article, which usually entails using <a href="http://www.bugmenot.com/">BugMeNot</a>. </p>