Slashdot Mirror
Introducing Asteroid 2004 MN4
Numerous readers wrote in with bits about a potential asteroid collision: "The recently discovered asteroid 2004 MN4 is currently listed as having a 1/233 chance of hitting the Earth. It is 420 m across and if it strikes the Earth it will release an energy of 1,900 Megatons of TNT (the largest nuclear weapon ever detonated, Tsar Bomba had a yield of only 50 Megatons). It is also the only asteroid that currently has a Torino scale value of 2." So, in summary, there's a 1-in-233 chance of the worst disaster in recorded history happening on April 13, 2029, and a 232-in-233 chance of nothing happening. Have a nice day! Update: 12/24 22:14 GMT by M : The rock is now rated a 4 on the Torino scale, or a 1-in-62 chance of impact.
Oh thats great fun. I calculated the results for a 1320m asteriod made of dense rock arriving at 17m/s on a 45 degree angle and impacting on land for someone standing 100km (62.5 miles) away:
----
Your Inputs:
Distance from Impact: 100.00 km = 62.10 miles
Projectile Diameter: 1320.00 m = 4329.60 ft = 0.82 miles
Projectile Density: 3000 kg/m3
Impact Velocity: 17.00 km/s = 10.56 miles/s
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 5.22 x 1020 Joules = 1.25 x 105 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 9.2 x 105years
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?
Transient Crater Diameter: 13.1 km = 8.12 miles
Transient Crater Depth: 4.63 km = 2.87 miles
Final Crater Diameter: 18.4 km = 11.4 miles
Final Crater Depth: 0.711 km = 0.441 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 3.22 km3 = 0.772 miles3
Roughly half the melt remains in the crater , where its average thickness is 24 meters = 78.6 feet
Thermal Radiation:
What does this mean?
Time for maximum radiation: 0.95 seconds after impact
Visible fireball radius: 15.2 km = 9.45 miles
The fireball appears 34.6 times larger than the sun
Thermal Exposure: 2.29 x 106 Joules/m2
Duration of Irradiation: 20.8 seconds
Radiant flux (relative to the sun): 110
Effects of Thermal Radiation:
Much of the body suffers second degree burns
Deciduous trees ignite
Seismic Effects:
What does this mean?
The major seismic shaking will arrive at approximately 20 seconds.
Richter Scale Magnitude: 8.0
Mercalli Scale Intensity at a distance of 100 km:
VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
Ejecta:
What does this mean?
The ejecta will arrive approximately 144 seconds after the impact.
Average Ejecta Thickness: 26.1 cm = 10.3 inches
Mean Fragment Diameter: 11.8 cm = 4.65 inches
Air Blast:
What does this mean?
The air blast will arrive at approximately 303 seconds.
Peak Overpressure: 157000 Pa = 1.57 bars = 22.3 psi
Max wind velocity: 242 m/s = 540 mph
Sound Intensity: 104 dB (May cause ear pain)
Damage Description:
Multistory wall-bearing buildings will collapse.
Wood frame buildings will almost completely collapse.
Highway truss bridges will collapse.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
"The first time I got drunk, I got married. The second time I bought a chimpanzee, after that I stayed sober" Arian Seid
Am I seeing this right?
It looks like it's up to a 4, now.
I guess I'd just like to see the math on how they come up with these numbers.
Nobody's stopping you; it's not a secret. Go get it.
But get ready for some heavy lifting; as you dig into it you'll very quickly realize why they didn't try to put any in a popular news article.
I'm not too up on it myself but you can start with phase spaces, I think, though that hardly touches the real fun, which is the probabilistic aspect of determining the path of an object through all of the influences of the solar system... while I'm not up on the details I do know they don't use naive formulations of that problem, they've got some powerful and brain-bending tricks to prevent the estimate from diffusing too quickly.
So what's the bottleneck here? Poor imaging?
Yes. The image on the telescope is not a theoretical point, but has a certain diameter depending on the telescope diameter, atmospheric distortion, ccd resolution, etc. So you cannot pinpoint the asteroid position precisely, but only give a bounding box.
Combining multiple observations will give you more data, and you can start narrowing down the estimate. Right now the error on the position, projected to year 2029, is about 200 times bigger than the diameter of Earth, so we say that there's a 1/200 probability of impact. A planet is a very tiny target.
When the precision is sufficient to say that, for example, the asteroid will pass by the left side, it will suddenly drop to zero. If it is actually going to impact the Earth, the probability will slowly going up until it will reach 1.
Not so fast!
The number 4 in Japanese is "shi" (U+56DB), but "shi" also means death (U+6B7B)!
It's just as unlucky as 13 in western culture, and more specific about our fate.