Not sure I see ...
.. the man-made global warming angle on this one? Surely the Met Office, CRU at East Anglia or the IPCC must have a quotable link to global warming ?
A diminutive asteroid will today pass within 76,000 miles (122,000 km) of Earth at 12:46 GMT, although NASA has confirmed Bruce Willis's services will not be required. Path of asteroid 2010 AL30. Graphic: NASA/JPL The body - dubbed 2010 AL30 - was discovered by the LINEAR survey of MIT's Lincoln Laboratories on 10 January …
...what they meant to teach you is that sub 25 meter stony asteroids would, at worst, break up whilst passing through our atmosphere if not, at best, be completely disintegrated by it and leaving no discernible trace for us plebs whatsoever. If it just breaks up then any surviving fragments would, by nature, be smaller than 25 meters.
That's how I interpreted things in relation to your comment anyway.
Meteorites that a larger than the suggested 25 metres will not burn up in entirety. Therefore you will be left with a rock mass in the lower atmosphere and landing on the surface. Small meteorites on the ground suggest that the original incoming meteor would have been just a bit bigger than 25 metres. (OK, that's ignoring density and angle of flight, for starters, but the principle is correct)
Very small particles decelerate rapidly when hitting the atmosphere and are structurally robust enough that they just filter down through the air as meteoritic dust. Really big objects - think house size and above, are so massive in comparison to their surface area that they hardly decelerate at all and hit with their original velocity.
For objects between these sizes all sorts of things can happen. generally, the smaller and denser the object the more likely it is to reach the surface; however, relatively large (several metres across) stony meteorites (or the bizarre carbonaceous chondrites) tend to disintegrate through deceleration in the upper atmosphere and very little survives to hit the ground, or what lands is a shower of fragments.T =he vast majority of meteorites are made from stone, however, almost all the largest meteorites are made from structurally resilient iron/nickel.
There's been quite a lot of excitement recently caused by the release of classified data showing that relatively large objects are ploughing into the upper atmosphere and exploding on a quite regular basis. And when I say exploding - I mean think multi kiloton explosions:
I'm gob smacked by the amount of commentard idiocy going on here, the quote said UNDER 25m, UNDER as in LESS THAN not MORE THAN, duh
Meteorites that burn up in the atmosphere are commonly known as Shooting Stars and are no bigger than grains of sand.
Anything even remotely near 25m in size is not going to "burn up" in the atmosphere in a million years, even something a couple of cm in diameter is likely to reach the surface of the earth.
A stony asteroid of up to 25m is likely to break into bits on the way down because of the forces acting on it as it decelerates. These smaller bits would cause much less damage than one big one but would cause havoc if over a populated area.
So the statement "stony asteroids under 25 meters in diameter would be expected to burn up in our atmosphere" is completely off the mark.
Yes, the quote said "under", which is why so many people tried to explain why objects *over* 25m across might not be completely reduced to smoke before they reach the ground. I don't find that idiotic, though I confess I was rather amused at the *number* of such replies.
Your assertion that "even something a couple of cm in diameter is likely to reach the surface of the earth" conflicts with the received wisdom (NASA guy) and the more widespread knowledge that even something as slow-moving as an orbiting spacecraft (typically smaller than 25m and travelling at only around 15-25000 mph) require *very* careful design to avoid burning up. Care to substantiate it?
No problem, the care and design that goes into an orbiting spacecraft is to ensure that upon re-entry, the occupants remain alive and not spread over a large area. Not really a concern for an asteroid.
If you really believe that any asteroid entering the atmosphere which is less than 25 meters in diameter burns up before reaching the surface, then to be honest you have no real grasp of what we are talking about so I can see why you perceive the utterings of some NASA PR drone to be wisdom.
So you have no real clue. I am fine with that.
For the record - it will really depend on material type (rock vs. snow), material structure (solid vs agglomeration vs fractured). Further different solid rocks will have different burns rates depending angle of attack and shape...
So the 25 m is a rough scale size below which one typically does not worry.
OK, start with the drag equation for high Reynolds number (http://en.wikipedia.org/wiki/Drag_equation) and plug in the numbers for a 25m lump of rock entering the atmosphere at 10km/s. If it doesn't slow down before it reaches the lower atmosphere, where the density is about 1 kg/m3, it will be met with about 10^10N of drag, which will do work at 10^14 Nm/s, or 100 terawatts.
Since I *do* have a clue, I know that a better calculation would be to integrate along a vertical trajectory through a model atmosphere. You can try that if you are feeling energetic, but it won't affect the basic conclusion which is that the atmosphere can be fairly approximated by a fucking brick wall for larger objects.
Meteors do burn up in the atmosphere, mostly. The meteorite is the little bit that's left over.
Also, today's one is likely, if it does ever hit at a later time, to graze the atmosphere obliquely. Plenty of burning up time before it could reach the ground.
Pictures? Will need to look out for The Sky at Night.
Posted in Space, 13th January 2010 12:27 GMT
A diminutive asteroid will today pass within 76,000 miles (122,000 km) of Earth at 12:46 GMT
I'm afraid 19 minutes' warning meant I missed its arrival. It was obviously a giant ball of cotton wool and has hit something, judging by the millions of bits falling all over the place.
..that the lead-time is inversely proportional to the reciprocal of the square of the distance of the object as viewed from arms length in comparison to the size of a hole in a polo mint...or some such formula.
i.e. bigger = more time (I would hope)
PS. The polo-mint inverse square reciprocal law does yield an SI unit (the 'Polo') but was rejected due to trademark infringement.
Todays meteor would have a value of 0.02 Polos (at a guess), with a value of >0.5 polos being one to worry about :-)
Larger meteors being measured in 'Donuts', where 1 donut = 375.2 polos (due to the squaring rule and the variance in sugar coating).
I believe the dinosaurs were wiped out by a donut-meteor.
It feels like Monday to me....sorry.
NASA publishes a list of what's (known to be) coming our way (or at least, the ones they don't mind us knowing about) at http://neo.jpl.nasa.gov/neo/close.html. Only yesterday a 1.6km lump (which would make quite a mess of this planet) came pretty damn close, in astronomical terms. How we've managed to survive this long, god alone knows.
the composition of the asteroid is not stony, but metallic (andyman has a valid point here)? A sub 20 metre metallic asteroid (actually it would become a meteorite wouldn't it?) would still pack a wallop... provided that subsequent gravitational tugs on it's path by sun, earth, etc would put it on a collision course with Earth at some later stage.
Indeed, I am enamoured of Vogon poetry even if it is the second worst poetry in the known universe.
Of the 5 books in the trilogy & whilst six times none doesn't equal 42 even in base thirteen, there is some semblance of utter nonsense that assumes utter genius, the insane type.
I think therefore um... George Bush
First off, clearly an asteroid this size burning up in the atmosphere would not only heat the Earth through that direct method, but would also release copious (yes, I said copious!) amounts of CO2 into the upper atmosphere, thus trapping not only that heat, but a significantly larger portion of the sun's deadly radiation which the holes in the ozone layer has precisely focused on London and Washington.
So much for the lack of global warming angles, eh?
Next up, we need to know on which side of the Earth did this asteroid pass? Will its gravitational effects cause the length of the day to increase or decrease? What of the year? Passing inside the lunar orbit means it may have changed the length of the month.
Where are the facts and figures with which we might determine the answers to these questions? Was the time of its passing given in original or modified GMT?
One hopes that all minds have boggled appropriately.
and touch screens clearly don't go well together !
Rumour has it that the NASA kit is capable of detecting an object like this much further out.
Unfortunately a small piece of donut stuck to the screen prevented it from being spotted earlier as it obscured the view. Apparently the culprit is nearly as large as the metorite.
The shuttle and other spacecraft returning to Earth from orbit re-enter at a very shallow angle to slowly lose kinetic energy. A meteorite may come in vertically, in which case it has 100km of atmosphere to slow it down, which isn't much when compared to the 40000km the shuttle takes. The kinetic energy dissipation on impact may cause it and surrounding material to melt and splash large droplets of molten rock everywhere. Perhaps one of the reasons why you don't have large bits left behind ? Or maybe it's the souvenir hunters who got there first chipping pieces off ?
More beer please !
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