Pluto’s Anniversary

pluto

Seventy nine years ago today, on March 18, 1930, Kansan Clyde Tombaugh discovered the “dwarf planet” Pluto.

Pluto compared with Earth

Pluto compared with Earth

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Published in: on March 18, 2009 at 4:30 pm  Comments (14)  

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  1. It’s actually 79 years ago. And Pluto is still a planet, in spite of the controversial demotion by four percent of the IAU, most of whom are not planetary scientists, who nonsensically voted that dwarf planets are not planets at all. Their decision was immediately opposed by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto.

    • I am certainly in accord with you on this question, as the quotation marks around the phrase “dwarf planet” were intended to imply. The “demotion” was ill-advised, poorly timed and insufficiently justified.

      Those interested in learning more about NASA’s New Horizons mission should visit the New Horizons website. Along with a great deal of interesting information, the site includes this fascinating locator for the current position of the New Horizons probe, updated hourly.

    • pluto has to be a planet because it doesn’t circle around any planet and just the sun.

  2. Here’s another recent take on the question of Pluto’s status.

  3. Isaac Asimov, in his book “The Relativity of Wrong” (chapter 9, The Incredible Shrinking Planet) gave a most interesting history of the search for Planet X and the history of Pluto. Being a history, it matters little that it was written in 1988.

  4. […] our earlier brief comment on this topic see our post of March 18th on the 79th anniversary of Pluto’s discovery by Kansas native astronomer Clyde […]

  5. Within this past Year The State of Illinois officially declared Pluto A planet despite the IAU. Shouldn’t we all follow suit with them?

  6. i think pluto is a planet

  7. I LOVE PLUTO AND I THINK IT SHUD BE A PLANET!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  8. […] for more on Pluto, you can visit our earlier posts Is Earth a Planet? and Pluto’s Anniversary. Published […]

  9. What are the three major things needed for a planet to be a planet again?

    • I think you’re probably asking about the International Astronomical Union’s 2006 resolution, which said, in essence, that a planet is a celestial body that 1) is in orbit around the sun; 2) has enough mass for its own gravity to allow it to assume a round or nearly round shape; and 3) has cleared the neighborhood around its orbit. (I’m paraphrasing of course; the actual definition is a bit more technical, but this is the sense of the definition.)

      • That third criterion is very much still in dispute. Until four percent of the IAU, in violation of the group’s own bylaws, came up with this provision, there never was a requirement that an object “clear its orbit” to be considered a planet. In fact, the term is so vague that it could preclude all objects in the solar system from being considered planets, as have asteroids in their orbital fields, and Neptune does not clear its orbit of Pluto. This criterion is also biased against objects further from their parent star, as the further an object is, the bigger an orbit it has to clear. If Earth were in Pluto’s orbit, it would not clear that orbit either. Plus, several exoplanet systems have been discovered in which two giant planets cross one another’s orbit. This definition would preclude either one of them from being considered planets. These problems are the reason many astronomers reject this third criterion and stick with only the first two: a planet must orbit a star and be large enough for its gravity to pull it into a round shape.

      • Of the three, I certainly think you’re right that “clearing the neighborhood” is by far the weakest. But even hydrostatic equilibrium (roundedness) has its problems.

        I’m particularly glad you mention the case of exoplanets, which will increasingly impact this arena. They’re likely, however, to make things murkier in the short run, inducing clarity only later.


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