I've spent half a century (yikes) writing for radio and print—mostly print. I hope to be still tapping the keys as I take my last breath.
If an asteroid the size of a school bus gets through Earth’s atmosphere without breaking up into dust, it’s going to do some serious harm to wherever it lands.
For example, Barringer Crater (sometimes referred to as Meteor Crater) was the landing pad for an asteroid about 40 m across. It excavated a hole in Northern Arizona 1.2 km in diameter and 170 m deep.
That impact happened about 50,000 years ago, the blink of an eye on a geological scale, and scientists have calculated the energy released was the equivalent of 20 million tonnes of TNT. That’s about half the strength of the atomic bomb that killed 140,000 people in Hiroshima.
Calculator Lets People Forecast Neighbourhood Impacts
Scientists at Purdue University and Imperial College, London have developed a web-based program that allows people to figure out the damage likely to result from pieces of space rock of varying sizes.
As BBC News science correspondent Jonathan Amos points out “It will also tell you how far away you need to be to avoid being buried by all the material thrown out by the blast, or set on fire.”
The software is a development of an earlier program, the impact effects calculator, which was first released in 2004. The device is called Impact Earth.
Calculate Local Destruction
Users can dial in a number of parameters, such as the size of a hypothetical asteroid, the angle of approach, speed, and distance from impact.
Suppose a chunk of space rock the size of a refrigerator pounds into the sidewalk at the corner of Maple and King, Impact Earth will tell users how far away they need to scuttle to be safe.
And, should the interested party be lounging on a beach and want to ruin a perfectly good holiday, the calculator will also generate a tsunami wave height should the asteroid splashdown in the ocean.
An Impact Simulation
Suppose a 15-kilometre wide (9.3 miles) space rock smashes into San Francisco. You know that’s not going to be good for the Bay Area; the crater will be 181 kilometres (113 miles) across.
An earthquake of about 10.2 magnitude (that’s bigger than any recorded earthquake) will be triggered, not that this will be significant in San Francisco because there’ll be nothing left to knock down. However, Los Angeles will shake like jelly, and many buildings will come tumbling down to add to the misery caused by the fireball that arrived a couple of minutes earlier.
We know all of this because of the work of Jay Melosh who studies impact craters at the University of Arizona.
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In addition, the folks in Denver will see about 30 centimetres (one foot) of earth and rock thrown out of the crater, called ejecta, land on their fair city. About 13 minutes after the impact, windows and doors will rattle in New York City and Fifth Avenue will be covered in half an inch of ejecta.
But, here’s the good news provided by the Earth Impact Effects Program (Purdue University and Imperial College, London):
- “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).
- “The impact does not shift the Earth’s orbit noticeably.”
Phew! That’s a relief.
Many Asteroids Pose Potential Danger
There are millions of bits of rock whizzing about the asteroid belt, and almost all of them remain safely glued in orbit far away from our planet.
The National Aeronautics and Space Administration (NASA) has so far counted more than 10,000 asteroids, comets, and meteorites that have developed minds of their own and escaped to become what astronomers call Near Earth Objects. However, “near” to a space scientist is measured in Astronomical Units (AU); one AU is equal to about 150 million kilometres.
NASA keeps tabs on all the known problem rocks and says collisions on the scale of the one that dug out the Barringer Crater “occur once or twice every 1,000 years.”
Low Probability of Collision
So, the advice is not to lose sleep over something with a very low probability of happening, although there are occasional surprises.
In March 2009, an asteroid called DD45 came within 63,000 kilometres of Earth and was only spotted three days before its fly-by.
An impact from this 60-metre rock would have been devastating; the Tunguska Asteroid that walloped Siberia in 1908 was smaller, and it demolished 60 million trees.
In April 2017, an asteroid the size of the rock of Gibraltar flew by at a distance of 1.8 million kilometres. Scientists say this rock is between 650 metres and 1.4 kilometres in length. A collision with an asteroid of this size would unleash a blow about 1,000 times bigger than the Hiroshima bomb. The Telegraph notes “The blast would completely destroy a city the size of London or New York and cause extensive damage for hundreds of miles.”
In February 2013, a super-bright meteor, called a bolide, exploded above Chelyabinsk, Russia. The meteor packed a wallop equivalent to 30 Hiroshima bombs and occurred 12 miles (20 kilometres) above the city. About 1,500 people were injured mostly by flying glass. Scientists are still puzzled about where the meteor came from, although they suspect it might have been the result of collision between two deep space bodies about 10 million years ago..
Scientists have been experimenting with a simulation of a cosmic demolition derby. The idea is that if a medium-sized asteroid is heading for a crash landing on Earth, a large battering ram on a rocket could be launched to meet it. The resulting impact would nudge the asteroid onto a different path that would take it safely away from our planet. You only have to watch a NASCAR race to see how two colliding vehicles change their course.
Another approach is to change the speed of the asteroid. Again, an intercepting spacecraft would be used to either slow down or speed up the rock. Technology.org explains that this would mean that the “Earth has either passed by or is yet to arrive when the asteroid reaches the hypothetical point of collision.”
All of this clever stuff is being researched by the European-funded project NEOShield.
- Mark your calendars. Asteroid 1999 AN10 is going to make a close encounter in 2027. It is half a mile wide and will pass about 236,000 miles (380,000 km) from Earth. That’s a little bit less than the distance to the Moon.
- The asteroid that probably wiped out the dinosaurs 65 million years ago was about 10 kilometres (6.2 miles) across. It smashed into what is today the Gulf of Mexico and left a crater 170 kilometres (106 miles) across.
- According to the Discovery Channel “The Earth was born as a result of repeated asteroid collisions, the Moon was created by a single giant impact.”
- “Impact Catastrophe Calculator Updated.” Jonathan Amos, BBC, November 3, 2010.
- “Asteroid the Size of Gibraltar Rock Passes by Very Close to Earth.” Reuters and Helena Horton, The Telegraph, April 19, 2017.
- “Intercepting Asteroids to Avoid Armageddon.” Science Daily, October 23, 2013.
- “Intercepting Asteroids to Avoid Armageddon.” Technology.org, May 2, 2014.
- “Asteroid Has Minor Chance of Hitting Earth in Century.” Robert Roy Britt, Space.com, March 1, 2006.
- Earth Impact Effect Program.
© 2017 Rupert Taylor