The Solar System

Is Pluto a planet?
Answered by Dr. Jeff Hall
  • Dr. Jeff Hall

    Dr. Jeff Hall

  1. Dr. Jeff Hall Astronomer, Director, Lowell Observatory


    It was quite the set of telephone conversations in 2006 after the, quote, "demotion" of Pluto. A couple of us spent, I think, three solid days on the phone fielding inquiries from the press around the world about this. One of our astronomers, Dr. Will Grundy, is a member of the science team of New Horizons spacecraft, which is currently on its way to Pluto and reaches its closest encounter -- I believe it's Bastille Day in 2015. It will go zooming by Pluto and give us our first images of this distant world.

    Now what Will will tell you is, whatever you call it, we don't know what we're going to find when we get to Pluto, but it's guaranteed to surprise us, as almost every other planetary mission has. Think back to the old Voyager missions to Jupiter and Saturn and our first close-up look at the planets and their satellites. They're all very strange, and surprises turned up at every juncture. I expect Pluto will do the same thing.

    When we begin to develop a more complete picture of the outer solar system, the whole classification business may well come back up. There are a lot of objects out there that are fairly large. Pluto itself is fairly large by the standards of outer solar system objects. We are really trying to focus on the science of Pluto, what it can tell us about the history of the early solar system, and not spend so much time arguing about what you call it.

    More answers from Dr. Jeff Hall »

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