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The Question
(Submitted November 24, 1997)
I am a freshman at the University of Arizona. I am writing a paper on solar
flares for astronomy and was wondering if there in any chance that a solar
flare could be large enough to wipe out all communication and bring mass
destruction to our planet. Thanks.
The Answer
Dear freshman at the U. of Arizona
You can sleep soundly tonight--all we know about solar flares
suggests they can never pose a life hazard at the Earth's surface*. And as
far as I know, no one ever suggested that one of them caused the demise of
dinosaurs. Asteroid impacts, giant volcanoes--yes; flares--no.
Very few flares produce charged particles, and the energies involved
are generally too low to penetrate the entire atmosphere, which is
equivalent to about 10 feet of concrete. In such a thick layer, both
ions and electrons dissipate their energy among a growing number of
secondary fragments, whose number grows but the energy of each one drops,
until it is so low that other processes stop them.
The Earth's magnetic field also helps deflect particles, especially near
the equator. I don't remember numbers, but I would guess that in the last
40 years, the most flare particles did was double for a few hours the
cosmic ray intensity to which all life is exposed continually, day in and
day out.
For your project on flares, you may want to look up on the web:
http://www.phy6.org/Education/wsun.html
http://www.phy6.org/Education/wsolpart.html
and other files reachable from those.
Dr. David P. Stern
for 'Ask an Astrophysicist'
*note added:
However, you may be interested that in August 72 (between the missions of
Apollo 16 and 17) there was a solar flare intense enough to have delivered
a fatal radiation dose to any crew caught in an Apollo capsule in
Earth-moon transit!
Dr. Paul Butterworth
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