A flare for pondering Halley's outburst.Two astronomers speculate that shock waves shock wave, wave formed of a zone of extremely high pressure within a fluid, especially the atmosphere, that propagates through the fluid at a speed in excess of the speed of sound. A shock wave is caused by the sudden, violent disturbance of a fluid, such as that created by a powerful explosion or by the supersonic flow of the fluid over a solid object. from solar flares may have triggered Comet Halley's brief and unexpected outburst, first observed last February (SN: 3/2/91, p.133). The comet, normally a quiescent body of ice and dust as it exists the solar spotlight, suddenly appeared 300 times as bright as predicted some 2 million kilometers from the sun. The researchers suggest that heightened solar activity just before and during the outburst may account fo Halley's brightening. A shock wave generated by a solar flare may have damaged the comet's fluffy ice crust, and the kick from a second may have cracked open part of the crust, releasing a pocket of gas from within the comet. The expelled gas could have dragged out enough dust -- which reflects sunlight well -- to account for the brightening. Devrie S. Intriligator of the Carmel Research Center in Santa Monica, Calif., and Murray Dryer of the National Oceanic and Atmospheric Administration in Boulder, Colo., present their proposal in the Oct. 3 NATURE. |
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