git ssb

title: "Planet X-2" date: 2004-03-15 19:52 modified: 2004-04-27 17:40 status: published tags: Planet X, Sedna, astronomy, the Solar System

<p>
The press release is now online, as is Mike Brown's Sedna page, at <a href="http://www.spitzer.caltech.edu/Media/releases/ssc2004-05/">http://www.spitzer.caltech.edu/Media/releases/ssc2004-05/</a> and <a href="http://www.gps.caltech.edu/~mbrown/sedna/">http://www.gps.caltech.edu/~mbrown/sedna/</a> respectively. Right then - Sedna isn't a planet - it's not even a Kuiper Belt Object. According to Mike Brown, the Kuiper Belt has a fairly sharp edge at 50AU (1 Astronomical Unit is the distance from Earth to the Sun, 150 Gm); Sedna comes no closer than 70AU. The appropriate term for Sedna is “Inner Oort Cloud Object” (and I'd like to take this opportunity to lay claim to the acronym “IOCO”). </p>
<p>
The Oort Cloud was theorised by a bloke named Oort, hence the name. It's a cloud (duh) of small icy bodies which inhabits the outer reaches of the solar system; Oort inferred the cloud's existence to explain the origins of dirty snowballs (comets). The Oort cloud is thought to lie much further out than this; it seems there is also an Inner Oort Cloud, apparently created when a passing star... passed. </p>
<p>
Mike Brown also gives a very interesting suggestion of how to define a planet. He says a planet is any body whose mass is greater than the total of all other masses in similar orbits. By this definition, Pluto isn't a planet... but we knew that already. </p>