Pluto’s solar wind interaction more like a planet’s

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Data from New Horizons has found that Pluto, in its interaction with the solar wind, behaves more like a planet than a comet.

Previously, most researchers thought that Pluto was characterized more like a comet, which has a large region of gentle slowing of the solar wind, as opposed to the abrupt diversion solar wind encounters at a planet like Mars or Venus. Instead, like a car that’s part gas- and part battery-powered, Pluto is a hybrid, the researchers say. “This is an intermediate interaction, a completely new type. It’s not comet-like, and it’s not planet-like. It’s in-between,” McComas said. “We’ve now visited all nine of the classical planets and examined all their solar wind interactions, and we’ve never seen anything like this.”

…Pluto continues to confound. Since it’s so far from the sun – an average of about 5.9 billion kilometers (3.7 billion miles) – and because it’s so small, scientists thought Pluto’s gravity would not be strong enough to hold heavy ions in its extended atmosphere. But, “Pluto’s gravity clearly is enough to keep material sufficiently confined,” McComas said. Further, the scientists found that very little of Pluto’s atmosphere is comprised of neutral particles converted to electrically charged ions and swept out into space.

As I’ve written previously, we simply don’t know enough yet about planets to come up with a reasonable definition. As far as I’m concerned, Pluto will remain a planet until we do.


  • Jim Jakoubek

    “As I’ve written previously, we simply don’t know enough yet about planets to come up with a reasonable definition. As far as I’m concerned, Pluto will remain a planet until we do.”

    Mr. Zimmerman, I agree that a more reasonable definition of what a planet is would be in order as until 2006 Pluto was one and now is not so much. As our knowledge increases, I would submit that Pluto and other Kuiper objects will not be considered so. Remnants from the forming of the Solar System that managed become spheres and have shown some aspects of our growing knowledge about such things does not make a planet IMHO.

  • Steve Earle

    I propose a rule that states that only bodies discovered prior to 1931 be considered for planetary status…. ;-)

    But seriously, I think some consideration should be given to history and tradition. Pluto has been thought of as a planet almost since the moment it was discovered.

    Not to mention that these other bodies took considerably more time and effort than Pluto to even locate in the first place. They may rival or even surpass Pluto in size, but IIRC they are much further away. Truly they are Kuiper belt objects, whereas Pluto is much more a part of our little Sol-system.

    Heck , Pluto even comes closer to the sun than Neptune during part of its orbit, yes?

  • ken anthony

    A planet doesn’t have to orbit a star. The defining quality of a planet is it’s big enough to be round. This means some moons could also be considered planets. Colonists everywhere will certainly consider their homes to be planets.

    The traditional planets are those that orbit a star. One day we may find a moon the size of the earth… would that not be a planet?

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