Tuesday Linkses, My Precioussss

On that note, we don’t have a good name for planet-like objects that aren’t currently orbiting a star — even though these objects are now known to be very common. Ironically, “planet” is derived from the Greek word for “wanderer”, since they wander across the field of stars in the geocentric model. Now astronomers have found objects that really fit the definition of a wanderer, but calling them “planets” seems inappropriate, since orbiting a star (not just the Sun) is a common requirement in modern definitions for planets. So, what do we call these objects? “Planet-like object” is too clunky; “planetoid” is already in use. Any suggestions?

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4 Responses to “Tuesday Linkses, My Precioussss”


  1. 1 Laurel Kornfeld September 20, 2011 at 12:08

    The term generally used for planets not orbiting any star is “rogue planets.” That makes sense, as compositionally, they still are planets and what they are hasn’t changed. This may be one of many new categories we have to create with an adjective in front of the word “planet.” Chances are these bodies at one time orbited a star only to somehow be ejected from that orbit. A good precedent is the classification of brown dwarfs on the lowest end of the stellar category. If an object ever conducted hydrogen fusion, even if it is not doing so now, it is considered a type of star.

  2. 2 Robert L. Oldershaw September 20, 2011 at 12:52

    These objects discovered by Sumi et al (MOA group) are not necessarily planets at all. Rather they are unbound planetary-mass objects.

    A good and more accurate acronym might be:

    UPMOs

    Unbound Planetary-Mass Objects.

    Or USOs, for Unbound Substellar Objects.

    They could be primordial black holes. All we currently know is their approximate mass range, and that is only a “ballpark figure”.

    RLO
    Discrete Fractal Cosmology

  3. 3 Matthew R. Francis September 20, 2011 at 15:47

    Caleb Scharf puts in a vote for “vagabond” for planets not orbiting any star. I like that idea: it’s a one-word name (like exoplanet), and very descriptive. (Source: http://bit.ly/oKmlae)


  1. 1 Galactic Vagabonds « Galileo's Pendulum Trackback on September 20, 2011 at 20:54
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