The world needs to sharpen up its asteroid alerting capabilities, say
scientists, following the massive asteroid airburst over the Yukon in northern
Canada earlier this year
(www.space.com/scienceastronomy/astronomy/classified_impacts_000502. html).
The blast, which took place 16
kilometres above the Earth, was equivalent to a four-thousand-tonne bomb going
off and was bright enough to turn street lights off.
Just as earthquakes have the Richter scale, there鈥檚 a scale that measures
the severity of asteroid impacts. Called the Torino scale, it ranges from 0 for
a near miss to 10 for a global climate catastrophe
(http://impact.arc.nasa.gov/torino/index.html).
Reassuringly, the greater the destruction of an impact,
the less frequently it occurs: there鈥檚 been a 10 roughly every 100 000 years.
For a fascinating examination of the threats鈥攁nd many proposed
countermeasures鈥攍ook up the proceedings of the 1995 Planetary Defense
Workshop at www.llnl. gov/planetary, to which the late, great comet hunter
Eugene Shoemaker made many contributions.
Just for fun, you can simulate your very own catastrophic strike at
http://janus.astro.umd.edu/astro/impact.html. Choose the size, velocity and
type of meteorite or asteroid, select a planetary target and hit the 鈥渒aboom鈥�
button. The site then calculates how much damage your strike caused, the size of
the crater, its depth, and the scale of the ensuing earthquake. Having
discovered the damage an asteroid can do, you鈥檒l want to take out some insurance
from www.ufo2001.com/asteroid.htm. 鈥淒on鈥檛 get hit without it,鈥� runs the ad.
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If you鈥檙e still unconvinced of the threat, check out
http://gdcinfo.agg.emr.ca/toc.html?/crater/world_craters. html
for an idea of the number of large
meteorites that have actually hit this planet. You can tour the world and zoom
in on impact structures to learn how they were formed. Me? I鈥檓 off to buy a
meteor-proof baseball hat . . .
