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posted by on Wednesday February 22 2017, @01:02PM   Printer-friendly
from the i-can-be-a-planet-too! dept.

Scientists against the demotion of objects like Pluto, Eris, Sedna, etc. to "dwarf planet" status have crafted a new definition:

It's no secret that Alan Stern and other scientists who led the New Horizons mission were extremely displeased by Pluto's demotion from planet status in 2006 during a general assembly of the International Astronomical Union. They felt the IAU decision undermined the scientific and public value of their dramatic flyby mission to the former ninth planet of the Solar System.

But now the positively peeved Pluto people have a plan. Stern and several colleagues have proposed a new definition for planethood. In technical terms, the proposal redefines planethood by saying, "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters." More simply, the definition can be stated as, "round objects in space that are smaller than stars."

From the proposal:

The eight planets recognized by the IAU are often modified by the adjectives "terrestrial," "giant," and "ice giant," yet no one would state that a giant planet is not a planet. Yet, the IAU does not consider dwarf planets to be planets. We eschew this inconsistency. Thus, dwarf planets and moon planets such as Ceres, Pluto, Charon, and Earth's Moon are "fullfledged" planets. This seems especially true in light of these planets' complex geology and geophysics. While the degree of internal differentiation of a given world is geologically interesting, we do not use it as a criterion for planethood in the spirit of having an expansive rather than a narrow definition.

Here's another article about the significance of the New Horizons mission. New Horizons will fly by 2014 MU69 on January 1, 2019.


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  • (Score: 2) by TheRaven on Wednesday February 22 2017, @02:03PM

    by TheRaven (270) on Wednesday February 22 2017, @02:03PM (#470155) Journal
    The problem with counting Pluto is that there are a bunch of other objects that have to be classified as planets if Pluto is (unless, as another poster suggested, you grandfather Pluto in as an exemption, but that's not a great way of defining a taxonomy) and some, like Eris, are a lot bigger than Pluto. You end up with the solar system being Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Ceres, Pluto, Haumea, Makemake, and Eris now, which isn't too bad, but there are an estimated 200 objects with similar characteristics to Pluto, and no one is going to remember that list.
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  • (Score: 2) by VLM on Wednesday February 22 2017, @02:45PM

    by VLM (445) Subscriber Badge on Wednesday February 22 2017, @02:45PM (#470182)

    Of course when I was a kid there were nine planets. I don't predate Pluto. Now there are thousands of exoplanets, so we don't expect kids to memorize all 2000 or so known exoplanets. Most don't even have names and more are discovered every week.

    I'd compare it to constellations. We kinda expect kids to learn the constellations in their hemisphere... kinda... sorta, well at least we'd like to even if the kids don't learn or forget five minutes later. And that constellation list is a large number. So as long as we keep the number of planets to less than a hemisphere's worth of constellations we're not being too unreasonable.

    One way to describe a planet under these criteria is "here's something big enough to someday be economically useful". If there's "too many", well, "too bad".

  • (Score: 3, Insightful) by khallow on Wednesday February 22 2017, @04:19PM

    by khallow (3766) Subscriber Badge on Wednesday February 22 2017, @04:19PM (#470246) Journal

    You end up with the solar system being Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Ceres, Pluto, Haumea, Makemake, and Eris now, which isn't too bad, but there are an estimated 200 objects with similar characteristics to Pluto, and no one is going to remember that list.

    Why is that supposed to matter? The real problem here is that the current definition only works for the Solar System. In other star systems, you may have either lack of information to determine the "clearing of orbit" of a body or weird orbital dynamics that prevents us from even defining "clearing the orbit" (such as in a binary star system where multiple large exoplanets have the same resonance dynamics with respect to the smaller star as Pluto and the other current trans-Neptunian dwarf planets have with respect to Neptune, alternately hang out in the L4/L5 positions of the binary system, or orbiting inside a ring of material like Saturn's "shepherd moons").

    It's hard to determine orbital dynamics and what other bodies may be precluding the potential planet from being a planet, but fairly easy to determine mass.

  • (Score: 1) by toddestan on Sunday February 26 2017, @06:45AM

    by toddestan (4982) on Sunday February 26 2017, @06:45AM (#471754)

    And if that's what happens, what is the problem with there being some many planets? Used to be that Jupiter had 4 moons. Now it has dozens of moons, some of which I'm pretty sure don't even have proper names. Yet I don't see everyone redefining what a moon is just because no one can remember all of Jupiter's moons.