On the Subject of Asteroid Impacts - Do we have numbers?

Factual Questions
1

I think the idea/discussion of asteroid to Earth impacts are pretty fascinating. What I have a hard time discerning from the net are the estimated results of various sizes of asteroids.

For example, the Meteor Crater is Arizona is just under a mile across and was estimated to have been created from an asteroid that was approximately 50m across. What I do not know is what radius of impact/damage this would cause today.

Would a 50M nickel and iron asteroid wipe out an entire state or just a city? How far would the immediate effects be felt?

What size asteroid would be required to annihilate an entire country or region like our United States or Europe?

What size asteroid would destroy life as we know it on the planet?

I know there are lots of variables, like composition and where it lands (my understanding is an ocean impact is potentially more deadly) but generally speaking do we have some guidelines or estimates of size to damage?

Any sites or links one could recommend?

2

The Near Earth Object Program has some details that include the Risk Table which includes size and threat levels for each known object.

3

Ooooh…just found this…Impact: Earth!

4

At the top there is a link to “famous craters”, which provides a list of several craters and the parameters of the asteroid that created them, ready to run in the simulator (just click on calculate impact effects and put a distance in).

Oddly though, if I try to enter the parameters for the Russian meteor (assuming dense rock), and using the higher end estimates that I have seen for it (20 meters in diameter, moving at 30 km/s), the airburst produces a shock wave traveling at only 9 mph and 0.24 psi of pressure - hardly enough to break windows like what actually occurred (that is for 1 km away and a 90 degree angle of entry, which didn’t actually occur; 45 degrees produces 4 mph and 0.12 psi). Although the results are quite a bit more impressive if you select iron; 500+ mph airblast. but still no cratering impact (note that the Meteor Crater was created by an iron meteor, and the Russian meteor was about 10% iron from analysis of collected fragments).

Also, they list the Chicxulub impactor as 17.5 km in diameter while Wikipedia says 10 km, which is quite a significant difference (over 5 times the volume/mass and impact energy).

5

Thanks for the link, that site is great to play the “what if” game.

For those that have not played with the sim itself, here is one example simulation I ran:

Asteroid of Nickel and Iron
Approximately 1 mile across
Traveling at 25km/s
Lands off the coast of California in 1000m of water
Enters at a 60 degree angle

Results to someone a full 300 miles away:

Energy before atmospheric entry: 4.42 x 10^24 Joules = 1.06 x 10^9 MegaTons TNT

Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 13.8 milliseconds.

The crater opened in the water has a diameter of 245 km ( = 152 miles ).
For the crater formed in the seafloor:
Transient Crater Diameter: 149 km ( = 92.6 miles )
Transient Crater Depth: 52.7 km ( = 32.7 miles )
Final Crater Diameter: 287 km ( = 178 miles )
Final Crater Depth: 1.63 km ( = 1.01 miles )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 33200 km^3 ( = 7960 miles^3 )
Roughly half the melt remains in the crater, where its average thickness is 1.9 km ( = 1.18 miles ).

Time for maximum radiation: 13.1 seconds after impact
Visible fireball radius: 310 km ( = 192 miles )
The fireball appears 146 times larger than the sun
Thermal Exposure: 8.4 x 10^9 Joules/m^2
Duration of Irradiation: 1.18 hours
Radiant flux (relative to the sun): 1970
Effects of Thermal Radiation:
Clothing ignites.
Much of the body suffers third degree burns.
Newspaper ignites.
Plywood flames.
Deciduous trees ignite.
Grass ignites.

The major seismic shaking will arrive approximately 1.61 minutes after impact.
Richter Scale Magnitude: 10.6 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at a distance of 483 km:

General panic. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters.

Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.
The air blast will arrive approximately 24.4 minutes after impact.
Peak Overpressure: 3730000 Pa = 37.3 bars = 530 psi
Max wind velocity: 1530 m/s = 3430 mph
Sound Intensity: 131 dB (Dangerously Loud)

Damage Description:
Multistory wall-bearing buildings will collapse.
Wood frame buildings will almost completely collapse.
Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.
Highway truss bridges will collapse.
Highway girder bridges will collapse.
Glass windows will shatter.
Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
And my favorite part

The impact-generated tsunami wave arrives approximately 1.36 hours after impact.

Tsunami wave amplitude is between: 254 meters ( = 833 feet) and 508 meters ( = 1670 feet).

image an 833 foot wave 300 miles away… all from a 1 mile wide iron asteroid.

6

Of interest: http://www.arm.ac.uk/neos/anim.html

http://www.arm.ac.uk/neos/1980-2010/

This one needs to be nuked: Center for NEO Studies

7

I looked up the number for that one and apparently, it isn’t an asteroid but part of the rocket from Apollo 12.

8

Of possible interest: the ranking system used to assess impact hazards is the Torino Scale.

9

That is a very interesting piece of information, thanks for sharing.

10

How about a near Earth object worth a cool 20 trillion dollars!?

Meet 3554 Amun Google, Microsoft and James Cameron hope to. :smiley:

11

Up until recently, the only historical impact known to have caused damage was the one in Siberia (now two in Siberia, I guess). Then about 10 years aog, Scientific American mentioned a fairly large meteor had been seen breaking up over the Amazon jungle in the late 1930’s. Remoteness and other current affairs apparently caused the news to be forgotten. (Plus there was some major event in the 1980’s in the sea off South Africa, leading to speculation that the SA government had tested an atomic bomb, but may have been a meteor.

So 3 or 4 major hits in 100 years… and a few documented near misses; about 1 every 50 years or so. Does not bode well for future risks.

12

There were 4 close approaches by asteroids just this week. All were only discovered a few days or weeks in advance.

FOX 5 DC | Local News, Weather, and Live Streams | WTTG

If you want more to worry about, the Close Approaches tab on the NEO page shows you a schedule of near approaches.

http://neo.jpl.nasa.gov/ca/

These are just the ones that we have detected in advance.

13

Well, it is hard to say, exactly, from that data. Based on what we do know from direct observation od Near Earth Objects and can infer from meteor craters and debris, the distribution of hazardous objects with respect to size and speed is roughly log-normal. (Some studies suggest that object sizes follow a power law scaling but skewed by the unobservability of small objects. Since small objects pose a negligible threat to Earth and are less likely to be intercepted, I think a log-normal fit to relative mpmentum is a better fit to represent probability of threat.) So, three or four significant impacts in a century may or may not represent the scale of the threat. Given what we currently know about the distribution of objects we should experience intercepts like the recent on somewhere between once every 30 to 150 years. So…either our model is right on target (and the prediction that impact by a >150m diameter object has about a 1% probability of occurring this century) or we’ve happened to get a slightly richer number of impacts than the overall distribution and ws should scale back the model proportionally…or, there is some as-yet unseen long period Oort object that is independent of the NEO distribution model waiting to smack into Earth next Thursday. (Probably not, unless it is really outside the plane of the ecliptic, in which case we probably wouldn’t see it unless a random astronomer happens to notice a moving star.)

In short, we cannot infer anything absolutely from the current data, except that there is certainly a non-negligible chance of injurous impact by an unseen hazard, and that the odds are good that the threat is worse than a once-per-century impact in a remote location.

Stranger