AOH :: SHOCKWAV.TXT| Collisionless Shock Waves in interstellar
matter, from Scientific By: Roald Z. Sagdeev Charles F. Kennel
Reprinted without permission from Scientific American, April
1991 Collisionless Shock Waves Shock waves resonate through the
solar system, much like the reverberating boom from a supersonic
jet. In the latter case, the disturbance is caused by an
aerodynamic shock, an abrupt change in gas properties that
propagates faster than the speed of sound. It had long been
recognized that in a neutral gas, such as the earth's
atmosphere, particles must collide if shocks are to form.
Beginning in the 1950s, we and our colleagues theorized that,
contrary to the expectations of many scientists, similar shock
waves could form even in the near vacuum of outer space, where
particle collisions are extremely rare. If so, shocks could play
a significant role in shaping space environments.
"Collisionless" shocks cannot occur naturally on the earth,
because nearly all matter here consists of electrically n