It's *cold* in Phoenix
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I was considering only things that are present in the Earth's atmosphere in sufficient quantity that they might conceivably form rain at that temperature. Yes, ethane and a bunch of other stuff are liquid at that temperature, but they are not present in the atmosphere in any significant quantity.
With the exception of CO<sub>2</sub>, I also only considered normal atmospheric pressure.
In other words, I only considered what sort of rain might actually be falling in Phoenix.
But if it was raining liquid ethane, I think you'd agree you would have a problem...
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I think you'd agree you would have a problem...
every problem is an opportunity!
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But if it was raining liquid ethane, I think you'd agree you would have a problem.
Definitely. If it's raining liquid anything other than water, you have a problem.
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In other words, I only considered what sort of rain might actually be falling in Phoenix.
Considering stuff that might actually happen in Phoenix is not what this thread is about.
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With the exception of CO2, I also only considered normal atmospheric pressure.
In other words, I only considered what sort of rain might actually be falling in Phoenix.
If the temperature is at -196 F in Phoenix, all bets are off.
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now you're getting it!
I haven't been getting it since about two years before my divorce.
OnT: It's cold in Phoenix, but not as cold as my ex-wife toward me.
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I haven't been getting it since about two years before my divorce.
That's not what she said.
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I only considered what sort of rain might actually be falling in Phoenix.
The whole "at -196 degrees" bit kind of messes with that, though.
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The whole "at -196 degrees" bit kind of messes with that, though.
Might be falling, given the actual composition of the Earth's atmosphere, supposing a temperature of -196 were possible in Phoenix or anywhere else on the surface of the Earth1. Satisfied????
1Location doesn't really affect either the probability of that occurring (it's pretty damned hypothetical, regardless of location) or the substance that might hypothetically fall as liquid rain at that temperature.
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1Location doesn't really affect either the probability of that occurring
If a really big snowball (comet, etc) grazed the earth on a course that was essentially tangential to the surface, it's remotely possible the temperature could get that low there.
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If a really big snowball (comet, etc) grazed the earth
I'd say that's a really big hypothetical. Further, I'd say that that is hypothetically equally (im)probable at any point on the Earth, so that Phoenix vs. !Phoenix is still irrelevant, until such time as the location of this hypothetical event is known, or at least predictable with some confidence level. I would even hypothesize that this hypothetical event might introduce into the atmosphere organic chemicals (comets are rather dirty snowballs) not normally present to rain at -196°F. However, at that point the entire biosphere of the Earth would have bigger problems to worry about than what liquid might hypothetically be raining at that temperature.
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If a really big snowball (comet, etc) grazed the earth on a course that was essentially tangential to the surface, it's remotely possible the temperature could get that low there.
Except, wouldn't the friction of the near collision counter the cold of said object?
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Except, wouldn't the friction of the near collision counter the cold of said object?
I think it actually doesn't. I remember watching a clip of something recently that said meteorites can be cold when they land--something about ablation, probably.
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I think it actually doesn't. I remember watching a clip of something recently that said meteorites can be cold when they land--something about ablation, probably.
That's true, but it only applies to the core of the object undergoing reentry. So the core of the almost-colliding object would not be heated. But the object's interaction with our atmosphere would cause the area around the near collision to experience an increase in temperature.
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But the object's interaction with our atmosphere would cause the area around the near collision to experience an increase in temperature.
Fine, imagine that it splits in half just at ground level, and the two pieces land next to each other, leaving a space in the middle affected by the cold of space.
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something about ablation
I remember reading that recently, too, but I don't remember where. Yeah, ablation is the reason. ... I still don't remember where I read it, but it was something about meteorites made of diamond.
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Fine, imagine that it splits in half just at ground level, and the two pieces land next to each other, leaving a space in the middle affected by the cold of space.
No, it doesn't need to split in half. Anything left when it lands will be nice and cool. All the heated material will have ablated off. My contention is that you initially suggested a near miss, not an actual collision. A near miss would generate heat as the object interacted with the atmosphere, but wouldn't allow the object to exert any cooling influence.
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A near miss would generate heat as the object interacted with the atmosphere, but wouldn't allow the object to exert any cooling influence.
Well, my initial idea for "near miss" was "grazing the roofs of single-family houses."
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Found the article I remember reading about diamond meteorites (but it's not the one that talks about ablation). It has some numbers that suggest the cooling effects of a really big snowball hitting (or grazing) the Earth are likely to be negligible (at least from the cold material of the snowball itself; depending on the size of the meteorite — which it would be if it actually hit — the dust kicked into the air could have a significant — but probably not -196°F — effect on global climate).
The first couple of sections are the most relevant:
If we drop the meteor from the edge of space, 100 kilometers up, it’ll punch through the atmosphere without slowing down too much and hit the ground moving about Mach 3—over a kilometer a second.
As it falls, it compresses the air in front of it. When the air is compressed, it heats it up. (This is the same thing that heats up spacecraft and meteors—actual air friction has little to do with that.) By the time it reaches the ground, the lower surface will have heated to over 500℃, which is enough to glow visibly.
If we set the diamond in space a little ways away from the Earth, and let it fall toward us, it will hit at about 11 kilometers per second. This is Earth’s escape velocity, and anything that hits the Earth from space will—thanks to gravity—be going at least that fast.
At 11 kilometers per second, the brief descent would be visible as a fireball. The energy of the impact would be comparable to a small atomic bomb, and the crater it would create would be a kilometer across—a little smaller than Meteor Crater in Arizona.
That air compression, and the resulting heat, will happen whether it hits or just grazes, and that's going to be doing a significant amount of damage, even if it just grazes. (That's even more true at higher speeds.)
The thought experiment of that article was for a diamond 100 feet in diameter, which would have a mass of about 5.2E+7 kg. This is rather small compared to a comet; even the very small, probably extinct P/2007 R5 is 3.1E+8 kg, or more1. Larger comets are on the order of 1E+13 kg; Halley's Comet is 3E+14. The larger mass of a comet would have correspondingly more kinetic energy. Such an impact would be very unlikely to leave enough of the comet intact to cool the impact area.
1That was calculated using the minimum estimated diameter and assuming the typical density of 0.6g/cm3, but if it is extinct, all that is left is rock and dust with a much higher density, and thus higher mass.
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the dust kicked into the air could have a significant — but probably not -196°F — effect on global climate
For the purposes I brought the idea up, I wasn't concerned with a global climate change, just dropping Phoenix to -196 briefly enough to get weird stuff come down in non-liquid form, or whatever we were talking about.
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I was showing that dropping a big snowball from space was unlikely to produce local cooling (more like setting off an atomic bomb, which has the opposite effect), and that, although you didn't mention it, the probable widespread, long-term cooling effect would also not produce the desired degree of cooling.
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I was showing that dropping a big snowball from space was unlikely to produce local cooling
Well, I talked about a grazing shot so that you might not get the big explosion, first off. Kind of like stepping out of an elevator in a cartoon just before you hit the ground, so you have no velocity. The idea is that it just lands hard enough to break in half, neatly, with the two halves close together. Then, you might wind up with radiated cold[1] in between them for a while.
[1] actually the opposite or whatever, you know what I meant. Probably.
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you know what I meant
Yeah, I know what you meant. It wouldn't work like that, but I get what you were trying to say.
Remember, anything coming from outside Earth's orbit is going to be moving at least 11 km/sec, plus whatever starting velocity it had. There would be more aerobraking in the case of something relatively less dense, like a comet, compared to something compact and dense like that What-If, but there's still no way it's making a gentle landing, no matter the angle of incidence.
With that, I think we've about pedanted this topic to death — cooling by comet, that is; feel free to continue discussing any other aspect of being cold in Phoenix, if you want to.
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Yeah, I know what you meant. It wouldn't work like that, but I get what you were trying to say.
I was aiming at humor, not scientific accuracy.
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In that case, carry on.
Filed under: Humor is a barrier to pedantry, and vice versa.
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AND YET NO FLAGGING!
:( is neither a frown nor sad.
Edit: And B*****m the stupid toaster.
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Well, my initial idea for "near miss" was "grazing the roofs of single-family houses."
Which would actually lead to a collision. No way an object would escape from an encounter that close.
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Now way an object would escape from an encounter that close.
I'm not entirely sure about that. It's probably just fantastically unlikely.
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I'm not entirely sure about that. It's probably just fantastically unlikely.
It would have to be going incredibly fast. So fast, in fact, that such a close encounter would likely devastate the earth's atmosphere, and likely decapitate a few mountains. It would also have a good chance of disrupting the earth's orbit. In fact, I'd consider such an encounter a belgium glancing blow (hopefully glancing off Belgium), not a damn near miss.
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The trajectory needs to be (locally) horizontal at the point of closest approach, or near as damnit. I think it might be possible, but I wouldn't want to be anywhere close if it happened; the shockwave would be epic at minimum. With that sort of thing, expect much heat.
That's also why working out the trajectory is non-trivial, as you're going to have to simultaneously take into account the interaction with the atmosphere and possibly the relativistic effects of Earth's frame dragging. That's not normally a combination that you worry about!
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simultaneously take into account the interaction with the atmosphere and possibly the relativistic effects of Earth's frame dragging
Unless it's coming from interstellar space at a good clip, the fastest it could be moving would be about 0.00025c. That's mighty B*****ming fast, but not really into the realm where relativistic effects are large; if you're trying to calculate a path that is exactly tangential, it probably matters to the extent of (WAG) only a few cm. The faster it's moving, the less effect aerodynamic forces would have (it would go through the entire atmosphere in only a little over a second); I'd guess at that speed, the effect would be the same order of magnitude as the relativistic effects.
I wouldn't want to be anywhere close if it happened; the shockwave would be epic at minimum. With that sort of thing, expect much heat.
This. Very much this.
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Well, don't keep us in suspense. Have they let you on the plane yet?
Only half an hour late. Got to enjoy a Green Flash Double Stout while waiting.
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Also, I do regret being too lazy to see if this was still an issue...
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Also forgot to mention that the rental
carSUV has a CVT, took me by surprise when I first started driving it.
to 
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