Comets

[Dannyalcatraz]

I know we have some people on these boards who know their comets...

I was wondering (for purposes of a campaign I'm designing):

What would be the likely effects on an earth-like planet's climate if its orbit regularly intersected that of an extremely large comet (but without a collision)?

I'm envisioning a periodic "near miss" in which the planet passes through the comet's tail. The comet itself would largely be of the icy variety, so my guess would be a wettish world with a fairly cool climate...but I realize that something like this could also affect the planet's albedo, or even contribute to a greenhouse effect.

So, any educated guesses?

 

[trancejeremy]

I really doubt it would have a noticeable effect on climate. A tail simply isn't dense enough to do anything to a planet.

And comets are comets because they aren't that big (ie, not as big as planets). Otherwise they wouldn't get perturbed in the first place and sent on the wacky orbits, nor would they have tails (since the atmosphere would stick around, thanks to gravity).

That said, it doesn't have to be a comet, comet. It would be something like say, that novel Black Cloud by Hoyle, where the Earth is enveloped by a mysterious cloud, which turns out to be a life form. It could be something like that, but one that appears like a comet because it has a schedule it likes to keep.

http://en.wikipedia.org/wiki/The_Black_Cloud

Or the make up of the dust of the comet would be wacky, like the thread from the Pern novels by McCaffey, or some sort of nano-gizmo that is meant to affect the climate of the planet (sort of a terraforming device by aliens, or instellar seeding program)

 

[Dannyalcatraz]

To give you an idea of what's running through my mind:

1) The planet, not the comet, has its orbit perturbed- end result of a divine war started (covertly) by Illithids trying to hasten their ascendance to power (see Lords of Madness).

2) Given what happened with Shoemaker-Levy, I was hoping that the tail of the comet would contain chunks large enough to cause something like a ELE meteor shower.

3) The comet is not a mundane comet. Its made of a material that radiates the force that is behind arcane magic...call it mana, if you like. Thus, when material from the comet hits the planet's atmosphere, you not only get solid and/or icy material, its also "arcanoactively" charged material. That "arcanoactivity" accelerates the planet's magical mutation rate, resulting in more abberations, etc., thus hastening the rise of the Illithids...

Does it sound remotely plausible? Or would a particulate cloud or some other celestial feature make more sense?

Whatever I use, I need something that is "natural" but also big enough to wipe out most of the surface civilizations... Think of Asimov's Nightfall.

 

[paradox42]

IMO trancejeremy is right- a tail alone is too diffuse to provide the effect you're looking for. In Shoemaker-Levy's case, it wasn't a tail that struck Jupiter, it was pieces of the comet itself that had broken up due to tidal forces on approach to the planet. The tail of a comet is made up of tiny chunks of dust and ice spread out over millions of km; it looks like thick smoke or mist in full sunlight, but it's really a lot more sparse than any cloud that shows up in the atmosphere on Earth.

An ELE would probably require that the "near miss" be near enough that part of the comet breaks off, and thus that part would fall as the comet itself was passing- it wouldn't be out behind it very far or stick around as part of the tail. If there was a significant delay before the final chunkfall, the most likely scenario would be that the chunk gets into an unstable orbit for a while as a sort of tiny moon. In that case it could fall any time, though another near miss by the original comet could certainly provide the orbit perturbation necessary to cause it to finally impact.

On the note of the effects of an event like this on a fantasy world, have you checked out Malhavoc Press's When the Sky Falls? It's an Event book specifically designed to detail the impact of a meteorite or comet on a standard D&D world. It even includes the possibility of a magically-reactive impactor and what that might do to the world, not to mention suggesting where such an impactor might have come from and why it came to be. It's by Bruce Cordell, and compares favorably with his other stuff, so that gives you some idea of the quality of ideas and presentation contained therein.

 

[Dannyalcatraz]

I've perused it in a store and I have it on order from Amazon.*

Ok, so perhaps a comet, despite its lovely imagery, is not going to work...

What about passage through an asteroid belt, like what causes the Perseiid or Leonid meteor showers, but worse (and more spread out)?








*(For those of you who know my stance on online purchases, the store sold out before I decided to buy it.)

 

[cildarith]

We pass through cometary orbits all the time. That's where meteor showers come from. The month of August is famous for the Perseid Meteor shower. Perhaps you've heard of it. Maybe you've witnessed this annual event. All of the meteors (shooting stars) are fragments of Comet Swift-Tuttle. We are able to see them because the orbit of the comet and the orbit of Earth intersect.

Halley's Comet spawns two meteor showers because Earth's orbit intersects that of the comet twice. The Orionids in late October and the Eta Aquarids in May both feature showers of fragments from Halley's Comet.

/astronomy lesson

Hope that helps.