Let me ask you a question. What would you do if you knew the world was coming to an end? Not just your world, your life, but the entire planet. I’ll even give you a time-frame to work with, ninety days. What would you do with those last three months of your life?
The question isn’t as silly or far-fetched as you might imagine. While it is unlikely that anything man-made could wipe out all life (it’s just barely possible, but not likely,) the universe isn’t quite so limited. We now have the ability, as a race, to see some of the larger and more dangerous objects in space that might be headed our way, if we know where to look and when. In 1994 the fragments from the comet Shoemaker–Levy 9 collided with Jupiter (it had been ripped to pieces by Jupiter’s tidal forces in 1992.) Pieces larger than a mile impacted the planet at cometary speeds of 134,000 miles per hour (37.22 miles per second.) And, there were several of them. According to the Earth Impact Effects Program, a quarter mile asteroid striking the earth would release the energy of 3,300 megatons of TNT. That’s roughly equivalent to 60% of the world’s remaining nuclear weapons detonated at the same time, in the same place. The crater would be about twice the width of Manhattan. Now, multiply that by four and within a very short time almost all life on earth would be threatened (a worldwide ice age would ensue no matter where it hit.) Putting in the information I have for a one mile asteroid or rocky comet, I was curious what the effect would be two thousand miles away if Apollo asteroid (53319) 1999 JM8 were to hit us as it is considered the most potentially dangerous Near-Earth Object in our system.
Your Inputs:
Distance from Impact: 3220.00 km ( = 2000.00 miles )
Projectile diameter: 7.00 km ( = 4.35 miles )
Projectile Density: 8000 kg/m3 (this is a high-end estimate)
Impact Velocity: 25.00 km per second ( = 15.50 miles per second, averaged estimate )
Impact Angle: 60 degrees (randomly picked)
Target Density: 2750 kg/m3 (I chose a land strike here)
Target Type: Crystalline Rock
Energy:
Energy before atmospheric entry: 4.49 x 1023 Joules = 1.07 x 108 megatons TNT (this is pretty low)
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.7 x 108years
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 tilt of Earth's axis (< 5 hundredths of a degree).
Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 1.4 milliseconds.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
Transient Crater Diameter: 82.2 km ( = 51 miles )
Transient Crater Depth: 29.1 km ( = 18.1 miles )
Final Crater Diameter: 147 km ( = 91.1 miles )
Final Crater Depth: 1.33 km ( = 0.825 miles )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 3460 km3 = 830 miles3
Roughly half the melt remains in the crater, where its average thickness is 652 meters ( = 2140 feet ).
Thermal Radiation:
The fireball is below the horizon. There is no direct thermal radiation.
Seismic Effects:
The major seismic shaking will arrive approximately 10.7 minutes after impact.
Richter Scale Magnitude: 10.0 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at a distance of 3220 km:
Ejecta:
The ejecta will arrive approximately 18 minutes after the impact.
At your position there is a fine dusting of ejecta with occasional larger fragments
Average Ejecta Thickness: 1.22 cm ( = 0.481 inches )
Mean Fragment Diameter: 101 microns ( = 3.99 thousandths of an inch )
Air Blast:
The air blast will arrive approximately 2.71 hours after impact.
Peak Overpressure: 16000 Pa = 0.16 bars = 2.27 psi
Max wind velocity: 35.4 m/s = 79.1 mph (TWO THOUSAND MILES AWAY!)
Sound Intensity: 84 dB (Loud as heavy traffic)
Damage Description:
Glass windows may shatter.
Glass windows will shatter.
So, what happens a thousand miles away if the object is moving at cometary speeds and hits water at a 45-degree angle?
Your Inputs:
Distance from Impact: 1610.00 km ( = 1000.00 miles )
Projectile diameter: 7.00 km ( = 4.35 miles )
Projectile Density: 8000 kg/m3
Impact Velocity: 55.00 km per second ( = 34.20 miles per second )
Impact Angle: 45 degrees
Target Density: 1000 kg/m3
Target Type: Liquid water of depth 152.0 meters ( = 500.0 feet ), over crystalline rock.
Energy:
Energy before atmospheric entry: 2.17 x 1024 Joules = 5.19 x 108 megatons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 5.7 x 108years
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 tilt of Earth's axis (< 5 hundredths of a degree).
Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 4.36 milliseconds.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
The crater opened in the water has a diameter of 179 km ( = 111 miles ).
For the crater formed in the seafloor:
Transient Crater Diameter: 109 km ( = 67.8 miles )
Transient Crater Depth: 38.6 km ( = 24 miles )
Final Crater Diameter: 202 km ( = 125 miles )
Final Crater Depth: 1.46 km ( = 0.908 miles )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 13500 km3 = 3250 miles3
Roughly half the melt remains in the crater, where its average thickness is 1.45 km ( = 0.899 miles ).
Thermal Radiation:
Time for maximum radiation: 4.71 seconds after impact
Visible fireball radius: 56.6 km ( = 35.2 miles )
The fireball appears 8 times larger than the sun
Thermal Exposure: 4.75 x 107 Joules/m2
Duration of Irradiation: 56.1 minutes
Radiant flux (relative to the sun): 14.1
Effects of Thermal Radiation:
Clothing ignites
Much of the body suffers third degree burns
Newspaper ignites
Plywood flames
Deciduous trees ignite
Grass ignites
Seismic Effects:
The major seismic shaking will arrive approximately 5.37 minutes after impact.
Richter Scale Magnitude: 10.4 (This is greater than any earthquake in recorded history)
Ejecta:
The ejecta will arrive approximately 11 minutes after the impact.
At your position there is a fine dusting of ejecta with occasional larger fragments
Average Ejecta Thickness: 30.3 cm ( = 11.9 inches )
Mean Fragment Diameter: 884 microns ( = 34.8 thousandths of an inch )
Air Blast:
The air blast will arrive approximately 1.36 hours after impact.
Peak Overpressure: 159000 Pa = 1.59 bars = 22.6 psi
Max wind velocity: 244 m/s = 545 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 may shatter.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
Tsunami Wave:
The impact-generated tsunami wave arrives approximately 11.6 hours after impact.
Tsunami wave amplitude is between 8.5 meters ( = 27.8 feet) and 16.9 meters ( = 55.6 feet).
And don’t think you’ve escaped anything if you are on the other side of the planet. With an ejecta between half an inch and twelve inches, the sun would be cut off for years, possibly decades, and current crops would be buried worldwide. This doesn’t even presuppose the fact that such a collision would trigger an earthquake on every fault line and activate the entire ‘ring-of-fire’ volcano system.
We don’t have anywhere near the capability to stop asteroids or comets of this size. But asteroids and comets aren’t the only threat.
A massive gamma ray burst anywhere relatively close to our solar system could devastate the planet. Scientists have calculated that gamma-ray radiation from a relatively nearby star explosion hitting the Earth for only ten seconds could deplete up to half of the atmosphere's protective ozone layer. But it is much more likely to last longer than ten seconds. Gamma ray ‘flashes’ can also come from rapidly spinning neutron stars or pulsars. Right now, the closest pulsar to earth is PSR J0108-1431 which is about 280 light years away. But wait, there’s more…
A truly massive solar event could easily sterilize portions of the planet. Huge solar flares and ejecta have been known to happen. Should a solar flare of sufficient intensity strike the earth, anything and everything beneath it for the time it lasted would be vaporized. The shockwave would spread out from that point and travel possibly thousands of miles. At the same time, it’s more than likely the ozone layer would completely disappear.
None of this is ‘speculation,’ it’s all science.
Public interest in space research is mediocre at best which means that we are and will remain at risk until something catastrophic happens and people demand better. Until then, there is nothing you can do about the situation except pray.
So, I ask you again, if you knew you only had three months before the world ended, what would you do?
KM
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