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back to article Mini-asteroid sneaks up on Earth

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. …

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Happy

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 ?

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WTF?

Errrr what!?!?

"stony asteroids under 25 meters in diameter would be expected to burn up in our atmosphere"

Blatant lie, so what's the deal with all the sub 25 meter meteorites that people find on the ground?

If that thing hit us it wouldn't be the apocalypse, but we'd certainly know about it.

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Boffin

There's this effect called "time."

The meteorites that reach the ground might well be smaller than 25m in diameter, AFTER they have passed the atmosphere.

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Flame

Er,

probably because they were a lot bigger before they hit Earth

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FAIL

I think...

...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.

Yawn!

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Headmaster

They start out

as super-25-meter asteroids, and burn up the difference on entry.

So, need any more blatantly obvious stuff pointed out?

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Flame

They were much bigger,

Before they hit the atmosphere, doofus.

Flames, you know why.

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Anonymous Coward

letters and/or digits

Presumably they were larger before the outer layers were toasted.

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Headmaster

sub 25 metre asteroids

I suspect that those sub 25 metre (not meter, as you say) started as >25 metre asteroids before our atmosphere subjected them to some extreme weight-loss

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Boffin

Think about it....

....for a minute.

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Stop

@Errrr what!?!?

My guess would be that they started out bigger than 25m and burned off some mass on the way down.

I'm sure that even bigger than 25m, they could not be as dense as you.

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25m

Presumably thay were greater then 25m before entering the atmosphere.

A bit scary that this asteridwas discovered only 3 days ago. Not much warning.

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Happy

ERRRRR

How about that the ones that make it through have a different compostion; or that they were bigger than 25meters before hitting the atmosphere and were burned down to less than 25meters?

It's not rocket surgery!

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Flame

Presumably...

...those asteroids were bigger than 25 meters when they first hit the atmosphere.

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FAIL

Start size

Perhaps they started bigger than that...

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@ Errrr what ?1? 13:07

What about all the sub 25 M ones on the ground ?

Who knows, im stumped.

Or maybe before they hit our atmosphere they were 26 metre ones that nearly burnt up.

Just a thought.

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Stop

Errrr, they started off bigger didn't they!?!?

Clearly!

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Alien

Atmospheric friction

The meteorites which are found on the ground begin their descent through the atmosphere as much larger rocks. What hits the ground is only what's left after the atmosphere has burned away large amounts of its original mass.

But I still think it's a Quagaaar escape pod.

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Oz
FAIL

Re: WTF

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)

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Meteorite sizes

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:

http://www.nytimes.com/1994/01/25/science/meteoroids-hit-atmosphere-in-atomic-size-blasts.html

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FAIL

What a bunch of pricks!

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.

Unbelievable.....

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Gold badge

Re: What a bunch of pricks!

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?

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Anonymous Coward

RE: Ken

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.

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FAIL

????? and here is my letter "A"

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.

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Boffin

no real grasp

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.

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Alien

Whoooooosh

Cor, that were close!

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Troll

Nice graphic

I'd never have been able to picture what was going on without that insightful diagram!

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Happy

Rendezvous with Rama?

Comes at a time when I'm re-reading this classic.

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Alien

They do it in threes

I haven't read that book in ages but IIRC according to the sequel the second Rama was missed because the Earth was in the grip of a huge financial crisis.

Cue theme from The Twilight Zone

:D

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Blatant lie?

Maybe the asteroids we find on the ground started much bigger than 25m wide?

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Meteorites do burn up in the atmosphere.

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.

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jai
Silver badge

expected to burn up in our atmosphere

of course, they _would_ tell us that, wouldn't they, regardless of if it's actually true

i would run for the hills, but that didn't save the dinosaurs did it?

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Coat

Only discovered 10th Jan?

Only discovered 10th Jan? Good job it's small then!!

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Joke

I'm hoping...

..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.

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There were different standards in Dinosaur days

The T-Rex has notoriously short arms. Therefore, when holding up a donut, I reckon all trexy would have said is Uh-Oh.

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Joke

What, no marshmallows?

I like marshmallows better

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Anonymous Coward

Please give us more notice next time.

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.

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Badgers

So has anyone calculated the new orbit?

Comming that close to earth has got to have changed it's orbit by a mesurable factor?

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Alien

Re: "since well before the Space Age began"

Doesn't mean it is not a booster stage. Perhaps the aliens who built the pyramids are finally returning to see what we (they?) have wrought.

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Pint

Bruce Willis? I thought it was supposed to be Clint Eastwood.

Or is this supposed to be the one where they team up?

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Clint

Yeah! all he gotta do is shoot the cigar out of the pesky asteroids mouth.

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Anonymous Coward

Advanced graphics

Good to see that computer graphics have advanced way beyond when I used to play Elite about 25 years ago.

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Alien

2010 ?

As its 2010, wouldnt this object be more likely to be a large black rectangular block?

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Boffin

Phew

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.

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What if...

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.

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Coat

I, for one, welcome

our tiny planetoid overlords.

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Grenade

Very quick.

If it's going to cross the orbit of the moon in 22 hours, that's about 5km per second (rough reckoning), which means it's going like sh*t off a shovel.

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25m

What's all this 25 meter tosh.

Surely you mean "the size of a LONDON BUS"

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Happy

Well what do you know...

I didn't realise that buses in London were different in size to the rest of the UK - you learn something new every day.

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Alien

Vogons

It's just the Vogons come to build an interstellar bypass.

They seem a day early however.

Have your towel at hand.

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