Friday, June 15, 2012

Asteroid 2012 LZ1

What if it hit the earth?

An asteroid the size of a city block flew by Earth today, June 13, 2012, “Flag Day.” The near-Earth asteroid named 2012 LZ1, which astronomers think is about 500 meters wide, will come within 5,381,600 kilometers (14 lunar distances) of Earth this evening; far enough away not to worry. We left the flag out and enjoyed a balmy evening.
Asteroids have collided with the earth in the past. Some scientists believe it was an asteroid impacting the earth that led to the last mass extinction event; the one 65 million years ago (the K-T extinction event) that wiped out the dinosaurs, along with most other land and marine life. That asteroid was estimated to be 15 kilometers wide; 30 times larger than 2012 LZ1. It slammed into the earth with a force one billion times more powerful than the atomic bomb that leveled Hiroshima. Proportionally, if an asteroid the size of 2012 LZ1 did hit the earth, it would only hit with a force about 16 or 17 million times that of the Hiroshima atomic bomb.

A relatively large meteorite (40 meters in diameter) hit the earth in what is now Arizona about 50,000 years ago during the late Pleistocene era. It is estimated that the meteorite had the density of iron (7870 kg/m3), weighed about 300,000 tons, and was traveling with a velocity of 12 to 20 km/s (27,000 to 45,000 mph).

The Arizona landscape was cooler and wetter than it is today. The plain around it was covered with a forest, where mammoths, mastodons and giant ground sloths grazed. The force of the impact would have leveled the forest for miles around, hurling the mammoths across the plain and killing or severely injuring any animals nearby. Global effects were negligible.

I calculated the potential effects of the much larger 2012 LZ1 asteroid impacting the earth by using Purdue University’s  Impact Earth on-line tool. I used the following parameters:
  • Diameter: 502.3 m
  • Density: 3000kg/m3 (dense rock)
  • Angle of impact: 60 deg
  • Velocity: 17 km/s (38,000 mph)
  • Target: Sedimentary Rock
  • Distance: 65 km (40 miles)
S. Nelson, Tulane U., 11/16/11
I have the projectile impacting in an area between and approximately equidistant (40 miles) from Richland, Ellensburg, and Moses Lake, Washington. According to the Impact Earth calculations and my parameters, 2012 LZ1 strikes the earth with an impact equivalent to 6,700 megatons of TNT. It creates a crater 5.25 miles in diameter and 1850 ft deep. In Richland, Ellensburg, and Moses Lake, thermal radiation from the blast will arrive in mere milliseconds after impact. The fireball will be visible for almost 4 miles and appear 20 times larger than the sun. Thermal exposure is equivalent to thousands of degrees Fahrenheit.

People in this zone will suffer third degree burns over much of their body. The ejecta from the impact will arrive in less than 2 minutes, the blast wave in 3.25 minutes. Wind velocity will reach 237 mph. The sound intensity will be 95 dB. Multistory wall-bearing buildings will collapse. Wood frame buildings will be destroyed. Glass windows will shatter. Up to 90% of trees will be burned and/or blown down and the remainder will be stripped of leaves and branches. In Seattle and Portland, some 400 miles away, the impact will feel like a 7.2 magnitude earthquake. A fine dusting of particles and some larger fragments will fall on the cities.

The impact would put large quantities of dust into the atmosphere, blocking incoming solar radiation. Wildfires would be widespread, putting more dust, as well as smoke into the air. The dust could take months to settle back to the surface.  Meanwhile, the region would be overcast and dark, and temperatures would drop. This would result in a drop in temperatures.

Blockage of solar radiation would also diminish the ability of plants to photosynthesize, seriously disrupting agriculture, which might take years to recover. If the asteroid impacted in the Columbia River, the consequences would be even more catastrophic (for the purposes of this essay, I am not addressing the remote possibility of the asteroid impacting in the Hanford Nuclear Reservation, the consequences of which would be dire, but essentially unknowable).
On a global scale, the earth would not be strongly disturbed by the impact and would lose negligible mass. The impact would not make a noticeable change in the tilt of earth’s axis, nor would it shift the earth’s orbit noticeably. Climate consequences would most likely be regional or continental, rather than global.

1 comment:

Richard Badalamente said...

Asteroid 2012 LZ1 is now thought to be about twice as large as originally estimated, and had it impacted the earth it would have had serious global consequences. Originally the 2012 LZ1 Near Earth Object was estimated to be fairly large, at 502 meters (1,650 feet), but astronomers using the planetary radar system at Arecibo Observatory have found it to be about twice as large, about 1 kilometer (0.6 miles) wide. Scientists consider a kilometer-wide asteroid is at the size threshold that could set off an extinction-level event if it were to hit Earth.

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