F*#$^@*in' comets, how do they work?

Phil Plait of Bad Astronomy can help you understand this miracle of the cosmos. His post on 10 Things You Didn't Know About Comets does include some things I already knew—the whole "comets are basically dirty snowballs" bit—but there's plenty of wonderful new-to-me-anyway knowledge to make up for it.

For instance, that circled dot in the image up there? That's Halley's Comet, as photographed in 1982, while it was out on the far side of Saturn. Notice how there's just a dot, and no big, long tail? That's not a misleading trick of space photography. When they're far enough away from the sun, comets lose their snowball slushiness and freeze down into tiny, solid balls.

Comets tend to have long, elliptical orbits. The farther they are from the Sun, the slower they travel, so really they might spend 99.9% of their lives far, far from the heat of our nearest star. That in turn means that all that volatile stuff in the nucleus is frozen, and actually it gets so cold that even the water freezes into ice harder than rocks on Earth.

Bad Astronomy: 10 Things You Don't Know About Comets

For more about this Halley pic, visit the Smithsonian Air and Space Museum.

• [Terry]

  What we do know is that every time we get to check out one of these “facts” by actually examining a comet, it turns out not to be true.

  “Examining a comet”? Did I miss something? Did we actually catch a comet? When? Which one?

  • [Brainspore]

    You don’t need to catch a comet to < http://en.wikipedia.org/wiki/List_of_Solar_System_probes#Comet_probes>examine one.

    • [Felton]

      How else are we going to tag them? ;-)

• [nanuq]

  “comets loose their snowball slushiness”

  Er, lose actually. Sorry, pet peeve of mine.

  • [kevinsky]

    When I read “comets loose their snowball slushiness” I immediately thought of Calvin and Hobbes loosing a volley of slushy snowballs at Susie Derkins.

  • [Anonymous]

    with a monarch’s voice
    Cry “Havoc!” and let slip the dogs of war;
    That this foul deed shall smell above the earth

• [ncm]

  What you don’t know about comets is about the same as what Phil Plait doesn’t know about comets. Most of what Phil Plait thinks he knows about comets started out as honest speculation that was then taught to him as if it were fact. What we do know is that every time we get to check out one of these “facts” by actually examining a comet, it turns out not to be true.

  Which is worse: not knowing something, or insisting you know something that isn’t actually true?

  You get a better picture of what we actually know about comets by thinking of them as nothing but asteroids with eccentric orbits. Where does the tail come from? Nobody knows, including Phil.

  • [thanatomaton]

    Such as what specifically? Is there any particular point you feel was incorrectly addressed, or do you just generally agree? Specifically.

• [ab5tract]

  The dirty snowball theory comes from the same tradition that was convinced that the moon’s surface was smooth as glass. That is, the “I think it makes sense, I have more institutional authority than you, therefore your theory loses” tradition. Which is fine, because that means it is only a matter of time until the ridiculousness of the claim is revealed.

  Give a look to astronomy that actually incorporates the revelations of plasma physics. As far as sensible explanations go, comets as electrical entities makes the only kind of sense to me.

  http://www.thunderbolts.info/thunderblogs/archives/special_edition/100313_se_teu5.htm

  In 2003, as comet NEAT raced through the extended solar atmosphere, a large coronal mass ejection (CME) exploded from the Sun and appeared to strike the comet, causing a ‘kink’ to propagate down the comet’s tail (see lower left). Of course, for solar physicists, the timing of the mass ejection could have no connection to the approach of the comet. However, SOHO has recorded several instances of comets plunging into the solar corona in ‘coincidental’ association with CMEs.

  But how would an electric Sun respond to the approach of a relatively small but strongly charged object? In electrical terms, the influence of the comet could be far more significant than its trivial mass in relation to the Sun. Alfvén considered CMEs to be caused by a breakdown or breach of the Sun’s double layer—an event that provokes an explosive exchange between the insulating plasma cell of the Sun and that of the comet. Hence, it not unreasonable at all to ask if a collision of a comet’s sheath with that of the Sun would cause a ‘short-circuit’ that could trigger such an explosion.

  • [Anonymous]

    @ Ab5tract#9:
    “The dirty snowball theory comes from the same tradition that was convinced that the moon’s surface was smooth as glass. That is, the “I think it makes sense, I have more institutional authority than you, therefore your theory loses” tradition. Which is fine, because that means it is only a matter of time until the ridiculousness of the claim is revealed.”

    Huh? We’ve sent spacecraft to visit comets. We even blew a 100-meter crater in one to see what it looked like beyond the surface !

    You can say that other models make ‘more sense’ to you – but we are basing our models on real data and observations.

    So why would you describe the model based on real data and observation as ‘ridiculous claims’ ?