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Nearby Star May Have More Planets Than Our Solar System

Posted by Unknown on from the told-you-space-lizards-were-real dept.

The Bad Astronomer writes "HD 10180 is a near-twin of the Sun about 130 light years away. It's known to have at least six planets orbiting it, but a new analysis of the data shows clear indications of three more, for a total of nine! This means HD 10180 has more planets than our solar system. And whether you think Pluto is a planet or not, all nine of these aliens worlds have masses larger than Earth's, putting them firmly in the 'planet' category."

1 of 102 comments (clear)

  1. Re:mass? by Anonymous Coward · · Score: 5, Informative

    The current IAU definition is (c/o Wikipedia)

    The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
    (1) A "planet"[1] 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, and (c) has cleared the neighbourhood around its orbit.
    (2) A "dwarf planet" 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[2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
    (3) All other objects[3], except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
    Footnotes:
    1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
    2 An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
    3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
    The IAU further resolves:
    Pluto is a "dwarf planet" by the above definition and is recognised as the prototype of a new category of trans-Neptunian objects.

    Pluto fails because it hasn't cleared its orbit.

    Many people don't like the definition for many reasons. Among them, that what constitutes a "clear" orbit is not specified and is arbitrary (no planet has an orbit 100% free of other objects), that the point of 'hydrostatic equilibrium' is also unspecified and arbitrary, and that it only applies to the Solar System ("The Sun" is in there).