What is a dead comet?

  • How is a Dead Comet different from the normal comet?

    How are they formed?

    And why is the Halloween asteroid 2015 TB145 called a dead comet?.

    I suppose it is a bit of a pun because of Halloween. But with a dead comet I would understand one which has lost its volatiles and no longer forms a coma or tails as it approaches the Sun.

    @LocalFluff Quite right, just a Halowe'en pun, it's good for science to engage with the Zeitgeist. Obviously, having a dead comet which looks like a skull on the 31st of October is a great way of promoting astronomy.

    Also, comet is from the latin _coma_ "Hair of the head". So it's even more punny.

    @TonyEnnis So this was a bald dead comet, a coin with head but no tail. :-)

    If it has a tail,it might be even more freakish,more like a gastly from pokemon ;)

  • user1991

    user1991 Correct answer

    7 years ago

    A comet is usually characterized by its tail. A dead comet has lost all its ices and gases (responsible for producing this tail), leaving just a rocky core.

    The Halloween comet is such a dead comet, in that it has no tail, but furthermore it resembles a skull, making it particularly relevant for Halloween.

    It's the first time it's been detected.So why don't we call it asteroid?.

    Asteroids formed closer to the Sun, and have never really developed a tail or coma - they have never been comets. A dead comet, on the other hand, while similar in morphology now has quite a different history (and formed further out in the solar system).

    How did we come to know about the history of this comet that once it had a tail or coma?

    Let me emphasize that in a way this discussion is mere semantics. A comet develops its tail when it is relatively close to the Sun. Therefore, it has to have a rather eccentric orbit. The eccentricity of the orbit can be constrained observationally. In addition (from what I gather from the NASA press release), the albedo (reflectiveness) is reminiscent of values typical of comets.

    So it's the first time dead comet is used then?

    I am not an expert on comets, but it is not the first time this term is used, no. So it was not invented just for Halloween, if you were wondering. I've done a quick literature search, and the first mention I found was in a paper from 1984. And that is just by a title search, the term was quite probably used before that as well.

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