Asteroid near miss?

[kinetic (Steve)]

I thought you were supposed to be looking out for these buggers
for us Dennis?


http://www.newscientist.com/article/...f=online-news#

[DavidU (Dave)]

Thats a bit of a worry. 3 times bigger than the Hiroshima nuke

[Robh (Rob)]

It states such asteroids (here 10 metres across) hit Earth once per decade. Anyone know why would it have exploded at that height (15 to 20 kms)? Was that because its trajectory was more tangential than normal to the Earth's atmosphere on entry?

Rob

[jjjnettie (Jeanette)]

It sure scared those little kiddies.

[citivolus (Ric)]

My understanding is that velocity, entry angle, and composition all help determine if the object makes it to the ground.

Wish I could have seen it!

[renormalised (Carl)]

Originally Posted by Robh

It states such asteroids (here 10 metres across) hit Earth once per decade. Anyone know why would it have exploded at that height (15 to 20 kms)? Was that because its trajectory was more tangential than normal to the Earth's atmosphere on entry?

Rob

The height at which an asteroid or large object detonates in our atmosphere depends on several factors...

1. Air resistance
2. What the asteroid is made out of and
3. Structural integrity of the asteroid
4. Velocity of impacting object

An iron asteroid of the same size would've hit the ground, or come very close before it flash vapourised. A stony-iron or solid stony asteroid of 10m in size would do so at around the altitude given. The stresses caused by heating and drag as the asteroid entered the atmosphere would increase until it exceeded the structural integrity of the materials it was made out of. If it was full of cracks and cavities to begin with, or just a loosely held together rubble pile, it would fly apart at a much greater altitude...probably 30-50kms, or higher.

Anything larger than 30m in size that was iron or solid stone would hit the ground nearly intact, leaving a big crater (Meteor Crater in Arizona was formed from a 50m stony-iron asteroid that impacted at 25kms. The blast was the equivalent of a 20MT nuke). But an asteroid that was full of cavities and cracks, you'd be looking at an impactor having to be 100m or larger to survive.

[Robh (Rob)]

Originally Posted by renormalised

The height at which an asteroid or large object detonates in our atmosphere depends on several factors...

1. Air resistance
2. What the asteroid is made out of and
3. Structural integrity of the asteroid
4. Velocity of impacting object

An iron asteroid of the same size would've hit the ground, or come very close before it flash vapourised. A stony-iron or solid stony asteroid of 10m in size would do so at around the altitude given. The stresses caused by heating and drag as the asteroid entered the atmosphere would increase until it exceeded the structural integrity of the materials it was made out of. If it was full of cracks and cavities to begin with, or just a loosely held together rubble pile, it would fly apart at a much greater altitude...probably 30-50kms, or higher.

Anything larger than 30m in size that was iron or solid stone would hit the ground nearly intact, leaving a big crater (Meteor Crater in Arizona was formed from a 50m stony-iron asteroid that impacted at 25kms. The blast was the equivalent of a 20MT nuke). But an asteroid that was full of cavities and cracks, you'd be looking at an impactor having to be 100m or larger to survive.

Carl,

Thanks for taking the time to give such a complete picture.
(Typo. I assume that 25kms is the velocity of impact i.e. 25km/s).

Regards, Rob

[TrevorW]

When did the tsunami and eathquake happen in Indonesia wasn't this about the same time

[renormalised (Carl)]

Originally Posted by Robh

Carl,

Thanks for taking the time to give such a complete picture.
(Typo. I assume that 25kms is the velocity of impact i.e. 25km/s).

Regards, Rob

No problems

Yes, it's the velocity of impact

[Dennis]

Originally Posted by kinetic

I thought you were supposed to be looking out for these buggers
for us Dennis?


http://www.newscientist.com/article/...f=online-news#

Thanks for the link to the article Steve.

That one slipped through on my rostered night off…

Cheers

Dennis

[Jen]

Nice bit of info there Carl

[Astro78]

Originally Posted by Robh

Anyone know why would it have exploded at that height (15 to 20 kms)? Was that because its trajectory was more tangential than normal to the Earth's atmosphere on entry?
Rob

I've been wondering the same thing. Silicate content, I believe, would be a major factor. But found this from UNQ Physics dept:

"Earth orbital speed is 28.8km/s, orbital escape speed is the square root of two times this, 42.1km/s, and surface escape speed is 11.2km/s. The slowest meteor would be one that just catches up with the earth then "falls", 11.2 km/s. Don't expect anything less than 12km/s. But a retrograde body in parabolic orbit (the maximum speed for a body at a distance of 1AU that is a member of the solar system) might close with earth at a speed of 42.1+28.8=70.9km/s plus the 11.2 "fall" for a total of (total2=70.92+11.22) 72km/s. So we expect a range of 12-70km/s with the slower ones in the evening ("catch up" and prograde, no retrograde) and fast ones in the morning"

I'd bet the slower ones are most likely to explode higher. If you get a definitive answer, pls let me know.

Apologies Carl, missed your reply before I chimed in

[Jabba (Keenan)]

I was just reading about this in an article on the news.com.au website this morning... quite interesting and worrying at the same time.

Would an asteroid of that size (10 metres wide) have much of an affect when impacting Earth?

Also (***kind of off topic***), since when are asteroids of such small size? I always thought comets were small fragments of dust/rock and asteroids were mini planets... could anyone enlighten me please ? (I am a keen novice astronomer! hehe)

[Astro78]

I believe comets are icy and can come from anywhere, although possibly originating from the Oort cloud.

Asteroids are from the one 'Asteroid belt' (I believe) and are of similar composition because of this.

Not positive though

[Jabba (Keenan)]

I thought I read somewhere about asteroids, although 'most' of them are found in the asteroid belt... they are scattered all around

[renormalised (Carl)]

Originally Posted by Jabba

I was just reading about this in an article on the news.com.au website this morning... quite interesting and worrying at the same time.

Would an asteroid of that size (10 metres wide) have much of an affect when impacting Earth?

Also (***kind of off topic***), since when are asteroids of such small size? I always thought comets were small fragments of dust/rock and asteroids were mini planets... could anyone enlighten me please ? (I am a keen novice astronomer! hehe)

If the object landed at (nearly) the same velocity it entered the atmosphere at (usually around 25-40km/s for most impactors), at 10m it would leave a crater around 100-120m across. Which means you're looking at the equivalent of a couple of hundred tons of TNT in explosive energy.

Some impacting objects of this size would have been slowed down by air resistance to such an extent that they would only fall at the terminal velocity for an object of their size falling from height...several hundred miles an hour. At this speed, they'd leave a pretty big gouge in the ground and/or bury themselves in a deep hole. Some may even skip along the surface until they come to rest.

An asteroid, whilst it's in space, can be an object anywhere from a metre or more in size. It's a fuzzy region when you get down to objects of this size because they can be classed as meteorites as well. The Hoba Meteorite is one such example.

Comets are usually admixtures of rock and ices that are weakly held together by gravity...most are usually greater than 1km in size but you can get smaller cometary nucleii. Many sungrazers are less than 1km across and can be as small as 50-100metres in size.