Is Pluto still a planet?I'm confused by all the news that's been going back and forth in the world of astronomy: is my favorite planet, Pluto, still considered a planet and part of our solar system, or not? Much to my surprise, the International Astronomical Union has indeed voted on a resolution that defines exactly what a planet is and Pluto no longer qualifies. This means that Pluto is indeed not a planet any more and that our solar system no longer has the nine planets I learned about as a kid, but only eight! Don't worry, though, Pluto is now to be known as a dwarf planet, so it's not been completely ejected from our solar system, just relabeled. The eight planets in our solar system are now, in order from the Sun outwards, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. As The Planetary Society explains, "a "planet" is now defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit." "A dwarf planet, according to the new definition, is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite." Got it? There are now three dwarf planets in our solar system, so Pluto isn't alone. It's joined by the asteroids Ceres and Xena (aka UB313), though more than a dozen are on the IAU's dwarf planet watch list, if you can believe it. One key reason that Pluto has been given the boot is because its orbit is not in the same ecliptic plane as the rest of the planets and isn't circular as are the planets, but is rather "eccentric". Indeed, at certain points in its orbit, Pluto is actually closer to the sun than Neptune. You can see some of this shown here:  A wee bit of data about Pluto too: Discovered in 1930 by Clyde Tombaugh, Pluto has an orbital period of 90,613 days (what we on Earth would consider 248 years) and is only 18% the size of Earth with a surface area of far less than 1% of our own planet. Gravity is far less than our planet's gravity too, at 0.58 m/s2 (about 0.06 Earth Gee). Sound like somewhere worth visiting? Maybe not. The average surface temperature is a chilly 44K which converts to -380F. Pluto also has three moons, Charon, about 35% the size of Earth's moon, and two much smaller moons provisionally called Nix and Hydra. Additional reading:
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Never miss another useful Q&A article again! Subscribe to AskDaveTaylor with Google Reader. DAVE TAYLOR, THANK YOU. ...for clearing that up so in such a timely manner for us, now i know what to tell my younger sister. and can spend my time painting:) Posted by: ming at August 25, 2006 1:28 AMThank you for clearing this, I am using it for a essay in school that is a huge chunk of my grade Posted by: Jenny at September 25, 2006 2:08 PMThanks so much, this is really helpful. Posted by: Sam at December 6, 2006 2:55 PMThanks sooooooooooooooooooooooo much man!!! Posted by: Edward at December 6, 2006 3:09 PMwhat's new about the planet why did they move the pluto out of the nine planet Posted by: andie at February 27, 2007 4:57 AMi'd like start by saying thanks. ur short,but still clear and interesting, summery of pluto helped me finish my project and now i know wat to say on display day. it s also a huge part of my grade. second i'de like to say that i m mad that they would do that to pluto. its been a planet for......ever! watever, i'll still say mercury,v,e,m,j,s,u,neptune,PLUTO! Posted by: pluto lover at April 8, 2007 9:59 AMHey!! thanks for that. it helped me understand some stuff and prove some people wrong :) Shivania Posted by: shivania at May 1, 2007 8:15 PMIs pluto still a planet???? don't write so much i get so confused Posted by: <3 at May 4, 2007 10:09 AMThanks for the info. I can't believe this. How the heck are the kids going to learn all of the planets now that they can't sing the song I learned them to that goes "My (Mars) very (Venus) educated (Earth) mother (Mars) just (Jupiter) served (Saturn) us (Uranus) nine (Neptune) pizza pies (Pluto)." Posted by: Jennifer at May 28, 2007 12:17 AMAccording to this link, pluto will retain as a planet... http://science.slashdot.org/article.pl?sid=06/08/10/1645259&from=rss Posted by: Rico at May 31, 2007 12:29 AMThere is also more than 1 dwarf planet. I think one is called Ceres, and one is called UB131 2007? Or something like that - unfortunately I forgot the exact name of the last one, but it's nickname is Eris. I think =/ Thanks for the info though! It's pretty handy! Posted by: Stacey at August 14, 2007 11:59 AMthen if pluto is not still a planet waht is it now???? Posted by: arvin mercado at November 28, 2008 8:54 PMArvin, it's now called a "dwarf planet". My opinion? It's kind of silly... Posted by: Dave Taylor at November 28, 2008 9:15 PMthen it is still a planet is'nt it?? Posted by: Arvin Mercado at December 1, 2008 4:41 AMLOL! A swarf! Well, it's always been a little small! Good show! Now let's work on reclassifying earth. Posted by: Stephen at April 21, 2009 1:54 PMUgh...Pluto is a planet - These yo-yo's can't find the bathroom without a map. And now that I've actually READ their idiot-definition, I am even MORE convinced that I'm right. How about this: Cessna's Law of Planetary Description A 'planet' is defined as any celestial body that meets ALL of the following: a) It generates its own gravity Anything not conforming to the above is a 'rogue' planet, a 'planetoid', an asteroid, a meteor, or a comet.
*Pluto is a planet, but Ceres is not. So by the new standards, would not Neptune also fail the criteria seeing as it has also not cleared its own orbit, passing outside the orbit of Pluto? I'm sure they probably thought of some great excuse to get Neptune off the hook! Posted by: John at April 21, 2009 4:23 PMFor me Pluto is a Plutoplanet! Posted by: Pio Yap at April 21, 2009 5:10 PMIf Pluto is called a dwarf planet, can Jupiter be called an "obese planet"? Posted by: Wibawa at April 21, 2009 6:54 PMWow. I can't believe that They've revoked Pluto's planetary status. I was taught that there were nine! My Very Educated Mother Just Served Us Nine Pizzas. Now what'll it be? Did she serve us noodles? Young children rarely like noodles unless they're covered in spaghetti sauce and have meatballs with them. I just wonder if these people actually thought their decision through completely before passing it. Posted by: Daphne at April 21, 2009 9:16 PMthank you very much for clearing things for me Posted by: arnet at April 21, 2009 9:25 PMhello my school is researching this now in class why was it called 2003 ub313 i know why it had 2003 but why ub313? Posted by: indy at June 17, 2009 6:46 PMIndy, apparently Pluto isn't called 2003 UB313: that's actually a Kuiper Belt Object "Eris" that's been called the potential tenth planet in our solar system. It's actually bigger than Pluto, as it happens. The way these names work is that the first part is the year of initial discovery, then the next letter defines when during the year the discovery was made (A = first half of January, B = second half of January, etc). So "U" = the second half of October. The B313 is just a numeric sequence as far as I can tell, and it means that during the last two weeks of October, 2003, this was the 313th object to be identified and registered. Pluto itself? It's considered minor planet 134340. Why that big a number? I have no clue. :-) Posted by: Dave Taylor at June 18, 2009 9:37 AMI have a lot to say, but ...
I do have a comment, now that you mention it!
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