From NASA’s Spaceweather.com
INDONESIAN ASTEROID: Picture this: A 10-meter wide asteroid hits Earth and explodes in the atmosphere with the energy of a small atomic bomb. Frightened by thunderous sounds and shaking walls, people rush out of their homes, thinking that an earthquake is in progress. All they see is a twisting trail of debris in the mid-day sky:
This really happened on Oct. 8th around 11 am local time in the coastal town of Bone, Indonesia. The Earth-shaking blast received remarkably little coverage in Western press, but meteor scientists have given it their full attention. “The explosion triggered infrasound sensors of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) more than 10,000 km away,” report researchers Elizabeth Silber and Peter Brown of the Univ. of Western Ontario in an Oct. 19th press release. Their analysis of the infrasound data revealed an explosion at coordinates 4.5S, 120E (close to Bone) with a yield of about 50 kton of TNT. That’s two to three times more powerful than World War II-era atomic bombs.
The asteroid that caused the blast was not known before it hit and took astronomers completely by surprise. According to statistical studies of the near-Earth asteroid population, such objects are expected to collide with Earth on average every 2 to 12 years. “Follow-on observations from other instruments or ground recovery efforts would be very valuable in further refining this unique event,” say Silber and Brown.
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I worry about asteroid events more than I do climate change. Here’s why, Spaceweather.com has this summary:
A bunch of that “stimulus” money would be better spent for humanity if we worked on building an asteroid detection and defense system.
Very impressive!
Such near earth objects may be dangerous, but more often just incredibly fascinating to observe. There are many more such objects than most people are aware of.
On December 7 and 8, 2004, a small PHA (PHA=Potentially HAzardous) object called 2004 RZ164 passed close to the Earth (< 0.2 AU), and I was able to make a couple of videos of it, from series of telescopic long exposure webcam images. That was a thrill!
My image and videos of 2004 RZ164 as seen through an 8 inch amateur telescope.
http://arnholm.org/astro/deepsky/a2004_rz164/
Here is the 2004 RZ164 orbit in 3D in the JPL small body browser
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2004%20RZ164;orb=1
I experienced something similar 30 years ago when I was living in Sweden.
It was in late May and I was watching the TV news.
Suddenly there was a bright flash. Despite a clear blue sky I then automatically assumed that a front was coming with thunder and rain from the south.
A while later, for how long I don’t know, I heard a huge bang. It felt as if a military artillery gun was firing right outside my window or as if someone had thrown a hand grenade next to the house.
At first I didn’t connect the dots.
It was only a few minutes later, when someone else asked me to come outside the house and look that I connected the dots.
The epicenter of the explosion happened 20 km east of where I was living 30000 feet in the air.
The space rock, whatever it was, was never found and probably all of it disintegrated in the air.
The pictures in that video is very similar to what the cloud looked like that I saw at time.
“Do they even have a view?” Jimmy Haigh
I imagine they are opposed to carbonaceous asteroids.
@AnonyMoose. Stop it. Coffee out the nose at 7am ain’t a good way to start the day.
I am baffled as to how a hot, fast moving rock the size of a small house can explode with the force of an atomic bomb. Sure, I realize that there is a lot of kinetic and thermal energy there, but c’mon, rock is hardly an energetic material, its not like it was 50 kilotons of TNT or anything.
Could someone please enlighten this poor benighted soul?
I believe that many asteroids are not very dense, and are loose agglomerations of rocks and ice. If one of these hits an atmosphere, it will break up quite quickly.
There is a theory with some observational evidence that quite large but diffuse ‘snowball’ objects are hitting the atmosphere frequently, and just dissipating at a very high altitude, adding to the planet’s supply of water. But there’s no money to carry out a search for them….
There are a few nickel-iron asteroids, which, presumably, are quite dense. If a small one of these – say, 40m diameter, were to impact the atmosphere I suspect it would survive to hit the ground. And if this were in a city like Bombay, the most populous city in the world….
I always believe we were very fortunate that one of these explosions didn’t trigger a crisis during the cold war.
Imagine an asteroid explosion over one of our major cities during the Cuban Missile Crisis. Would we have struck back at the Soviets before we determined it was a natural event? The Soviets might very well have done so if it happened to them.
BTW: A large comet or asteroid impact can cause immediate climate change on a world-wide scale!
Someone (perhaps a Socialogist or Economist – anyway somone with impecable credentials) should generate a computer simulation to absolutely “prove” that NEO’s are the biggest cause of global warming and the horrific rise we have witnessed in CO2 levels since the end of the Little Ice Age bar none. The closer they get to earth the more they bleed thir putrid chemicals into our pristine atmosphere. AND, that “Cap and Trade” legislation must be passed immideately to offset the tremendous expense to the advanced nations of fighting this terrible menace for mankind and civilization. This is something Al Gore should pick up and run with immediately. Why hasn’t he done so? What is he waiting for?
It would be during the break up phase you have all that kinetic energy converted to heat very rapidly. While the object is in one piece it is heating a long column of atmosphere as it burns up. If at some point the object suddenly comes apart into thousands of smaller pieces, the frontal area of all those objects is much larger than the frontal area of the original piece. As a result the rate energy is deposited in the atmosphere goes up very rapidly, so instead of converting the kinetic energy into heat over a period of time, almost all the kinetic energy is converted to heat in a very short period of time.
It is just a time rate of energy release situation. That raises a very large volume of the atmosphere to very high temperatures in a very short period of time. It is the expansion of that ball (pancake) of super heated air that causes the explosive effect.
Larry
It came close a couple of times, the satellites designed to look for the flash signatures or nuclear weapons bursts and the exhaust heat plumes of rocket launches witnessed some of these high altitude explosions and were for a time investigated as possible surreptitious nuclear tests. That was when science began to realize how common such energetic atmospheric impacts were, and that many of them occur over oceans or uninhabited parts of the earth during day light and are never noticed by the public at large.
It is only the large fire ball /bolides that hit in populated areas during the dark of night that usually get noticed. When you realize how small a fraction of the earths surface high density human occupation covers compared to the open oceans and barren desert/mountain areas, these are a lot more frequent than many people suspect.
Larry
“Could someone please enlighten this poor benighted soul?”
E = MV^2
I suppose a carbonaceous asteroid could produce a fuel-air bomb in addition to its kinetic energy. Double ouch!
Was it positively identified as an asteroid?, did some astronomical observatory see it before or during its entrance in the atmosphere?
To facilitate an understanding of the magnitude of the kinetic energy, consider this notional example:
The volume of a 10-meter diameter object (spherical) is 523.6 cubic meters. If the material is similar to rock (~specific gravity of 2), the total mass will be slightly over 1 million kilograms.
If the object is traveling relative to the Earth at 30 km/sec (a low to middling speed for meteors), the kinetic energy (found from 1/2 mv^2) is 4.7 x 10^14 joules. The energy equivalent of 1 kT TNT is 4.184 x 10^12 joules, which places the kinetic energy of the meteor at 112.6 kT equivalent.
This is high relative to the news item, but in the ballpark. I have been in the business of designing kinetic energy weapons. At a sufficient speed, pure mass is far more energetic upon collision than TNT is upon explosion.
At least a massive meteor will produce no radiation or radioactivity!
As Michael J pointed out, the key is in the speed. My question though is this:
A very small object will be attenuated very sharply by the earth’s atmosphere, so will strike the ground with a low velocity. As the mass increases less speed will be lost. Does anyone have a ballpark figure for the kind of mass necessary to allow impact speeds to be close to the original speed?
correction:
e = 1/2 m v^2
Sorry. Thanks, Michael J Dunn
“At least a massive meteor will produce no radiation or radioactivity!” Michael
What about one from outside the Solar System? How fast would it have to go?
Layne Blanchard (20:00:27) : “I had the opportunity as a young boy to observe a large object pass over the Lake Tahoe area.”
I saw one in the late ’50s while visiting the ancestral family farm in Iowa. Just after dark, seemingly close overhead, but silent with no visible trail. Probably skimmed the atmosphere and left.
In daylight I assume it would have looked a lot like this:
To Vincent’s question:
“A very small object will be attenuated very sharply by the earth’s atmosphere, so will strike the ground with a low velocity. As the mass increases less speed will be lost. Does anyone have a ballpark figure for the kind of mass necessary to allow impact speeds to be close to the original speed?”
Actually, it doesn’t turn out that way. The key parameter determining deceleration is the ballistic coefficient, which is related to the mass per unit area of the approaching object (and also to the drag coefficient, but we will take that as a constant across all spheroidal objects). For a constant density, mass increases with the cube of the diameter but frontal area increases with the square of the diameter. This means that larger objects will have larger ballistic coefficients and will decelerate less. And faster objects (say 70 km/sec) will have so much kinetic energy, that the relative deceleration may be minor. But you have to work out the numbers.
An excellent scale example is the Barringer Meteor Crater in Arizona (http://en.wikipedia.org/wiki/Meteor_crater) which was characterized as being comprable to a 5-10 megaton nuclear surface detonation. The impact object is estimated to have been 50 meters in diameter.
To Back2Bat’s question:
“What about one from outside the Solar System? How fast would it have to go?” [to produce radiation/radioactivity?]
I don’t know what you are asking exactly, but (a) asteroids are solar system objects, not interstellar objects, (b) any interstellar object would arrive in our vicinity at or above the local solar system escape velocity (about 617.5 km/sec; it would take 20 seconds to transit the Earth’s diameter), and (c) there’s nothing in this that results in nuclear physics (unless the impact temperature is high enough to enable thermonuclear reactions).
Layne, Fluffy, what you saw were touch-and-go incidents, much like the effect of skipping a stone across water. If the impact angle is sufficiently oblique, the NEO will indeed return to space without impact or explosion. It’s common enough to have been photographed on several occasions. And, for the curious, the “skipper” need not be flat, as the Brits demonstrated with their dam-busters during WWII.
“(c) there’s nothing in this that results in nuclear physics (unless the impact temperature is high enough to enable thermonuclear reactions).” Michael J Dunn
Thanks for the info. Yes, that was my question; how fast would an object have to impact to cause thermonuclear reactions? I have a morbid curiosity about explosions, I guess.
BTW, Vincent said what you said but with less precision. He deserves partial credit, don’t you think?
As CuriousGeorge has already posted above ( Curiousgeorge (18:53:56) : ), check out the interactive calculator at . http://www.lpl.arizona.edu/impacteffects/
This calculator answers some of those questions in the body of the web page.
It also includes a PDF that is interesting reading of more detailed information about impactors.
http://www.lpl.arizona.edu/impacteffects/CollinsEtAl2005.pdf
In that paper on page 4 (numbered 820 in the pdf) it explains that the important parameter is the ratio between the mass of the object and the mass of atmosphere it will displace during entry. When the bodies mass is much greater than the displaced atmosphere you can largely ignore the atmospheric braking process.
The full PDF is worth reading!
Larry
Apologies to Vincent; I misread what he wrote. Either too much or too little coffee today. Sorry.
As for thermonuclear temperatures, we can estimate by calculating the specific kinetic energy of ~600 km/sec as being 1.8 x 10^11 joules/kg. If the asteroid is composed of (e.g.) iron (atomic weight = 56 grams/mole), this gives us about 1.67 x 10^-14 joules/molecule. This can be equated to thermal energy as 3/2 kT, where Boltzmann’s constant (k) is 1.38 x 10^-23 joules/kelvin, giving a temperature T = 1.2 billion degrees. This is in the ballpark for some fusion reactions (e.g., deuterium-deuterium)…but there is no possibility of any fusion occurring for anything made of iron, or other “heavy” elements (meaning heavier than the isotopes of hydrogen).
Consider the craters of the Moon and thank God we are not afflicted with such events.
Might be interesting to investigate whether periodic massive changes in climate are synchronized with recurrent, massive meteor bombardment events.
Michael J. Dunn (09:00:58) :
To facilitate an understanding of the magnitude of the kinetic energy, consider this notional example:
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Outstanding answers and discussion, gentlemen! All of you that weighed in are appreciated. The prize, if there was one, would have to go to Mr. Dunn.
Honorable mentions to Hotrod and Backtobat.
Thank you!
As for thermonuclear temperatures, we can estimate by calculating the specific kinetic energy of ~600 km/sec as being 1.8 x 10^11 joules/kg. Michael J Dunn
Thanks for those calcs. I really wish I had paid more attention in physics.
I guess there is little danger of Jupiter blowing up from an extra-solar system meteor strike?