Chelyabinsk-Sized Asteroid Impacts May Be More Common Than We Thought 50
The Bad Astronomer writes "Using data from the Feb. 15, 2013 asteroid impact over Russia, scientists have determined that we may be hit by objects in this size range (10 — 50 meters across) more often than we previously thought, something like once every 20 years (abstract). They also found the Chelyabinsk asteroid was likely a single rock about 19 meters (60 feet) across, had a mass of 12,000 tons, and was criss-crossed with internal fractures which aided in its breakup as it rammed through the Earth's atmosphere."
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Well, it's less than half the density of water [wolframalpha.com].
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You know what, that's 4 times too big, used diameter for radius. I accept any shame heaped upon me.
Re:quite dense (Score:5, Informative)
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You know, I just default in my head to nice little 2d pictures.
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You know, the entire planet of Saturn would float if there were an ocean big enough to put it in ;-)
But yea, he's wrong anyway.
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Bedevere: "Wait. Wait ... tell me, what also floats on water?"
Villagers: "Bread? No, no, no. Apples .... gravy ... very small rocks ..."
Arthur: "A duck."
Bevedere: "Exactly. So... logically ..."
Villager: "If it ... weighs the same as a duck ... it's made of wood."
Bevedere: "And therefore?"
Villagers: "A witch! ..."
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Yeah, I realized that too. Can I have partial credit for showing my work?
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Wikipedia tells me [wikipedia.org] that iron has a density of 7.874 g/cm^3. A 60-foot-diameter asteroid has a volume of 4/3*pi*30^3 cubic feet, or about 113100 ft^3. So, units tells me that an iron sphere that size would be about 27,800 tons. So it's not as dense as a solid iron asteroid would be.
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I have a small piece of Chelyabinsk in my meteorite collection, It's a stony, not an iron, although it does have enough iron-nickel chondrules in it to be attracted by a magnet.
Yeah, density of about 3.4 gm/cm^3 is about right. (My piece, at just over 10gms, is about 3 cc.)
A 60-foot diameter iron is about what carved out the mile-wide Barringer (aka Meteor) Crater in Arizona. Irons tend not to airburst, or if they do, do it lower down in the atmosphere. It may also have been travelling faster.
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At least somebody got it right...
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If you did the sums you'd land up with about 1.75 tonnes per cubic metre, or not quite twice as dense as water. Even less if they're colonial short measure tons.
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I am this AC, and I stand corrected. Good thing I'm not in the asteroid-density-measuring department, or I would not do too well.
Friction versus increasing pressure (Score:5, Insightful)
It's nice to see that the author didn't buy into the myth that it's friction which causes the increase in temperature as a fast moving body move through the atmosphere.
"As this main mass plummeted through our atmosphere at a speed of 20 kilometers per second â" dozens of times faster than a rifle bullet â" the huge pressure it generated compressed the air in front of it, heating it up."
That kind of journalistic competency it worth noting.
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Phil Plait is a well-known astronomer. I'd say he's probably an astronomer first, a writer second. So one shouldn't be too surprised by his accuracy.
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Well the reason there is a pressure wave in front of the asteroid at all is due to friction. If it were frictionless it would simply pass through the atmosphere without disturbing it. This is more semantics with the english language than making any scientific point.
Re:Friction versus increasing pressure (Score:5, Informative)
No and no. Even if it were frictionless, the air molecules would still have to get out of the way. The object is moving at Mach 25 or more, 25 times faster than the air molecules can get out of the way (ie, the speed of sound) easily. Therefore the air compresses. Hypersonic fluid dynamics is completely unlike subsonic fluid dynamics.
Friction doesn't (well, hardly) enter into it.
Neither does semantics. You're wrong, and so are the dummies who up-moderated you.
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The thing that really brought that home to me is hypersonic nozzles. Subsonic nozzles go in (like a hose nozzle), hypersonic nozzles go out (like one of the Saturn V main engines).
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It's not merely semantic. There's far more depth of information in the article's description, and hence far more accuracy.
It's the difference between saying that someone was killed by a gallon of water versus saying that the person drowned. The former is factually correct, but not nearly as accurate.
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It's negligible. That's a fact, not friction.
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You've just described one way that friction works, not that it doesn't apply.
Since the Earth's surface (Score:2)
is 71% water, such impacts should be around 2.45x as frequent as observed. Then add in the ones that impact in the Sahara and Australian Outback...
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Using our best estimate for the Chelyabinsk airburst energy, of about 500 kt, we have estimated the bolide flux at the Earth over the period from 1994 to mid-2013. This estimate is based on 20 years of total global coverage by the US government or infrasound sensors, more than doubling the earlier time coverage.
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And Antarctica, Greenland...
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I just spotted a meteor literally just there. (Score:1)
I had just posted above me spotting a meteor above my town there, lasted around 3.3 seconds. Longest I have seen, most I have seen were 1.3s at best.
And it was a bright one too, none of these crappy weak streaks that vanish in to nothing, it was brighter than a typical helicopters search light in the distance, brighter than 3 planes worth of lights.
They have been increasing in frequency I've noticed over the years. And that sudden 3.3s meteor at that brightness, especially after that crap that happened in
Missed a paper reference (Score:5, Informative)
The Slate article mentions there were two Nature papers, but the article summary above only gives a link to one. The papers are:
This one came up with 20 year frequency for these sized events: A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors [nature.com]
This one looked a bunch of YouTube videos and analyzed how it broke up as it went through the atmosphere:The trajectory, structure and origin of the Chelyabinsk asteroidal impactor [nature.com]
Has MSNBC blames global warming yet? (Score:1)
Or have the just blame the Republicans?
I have an idea (Score:2)