Session 7E - Space and Basic.
ORAL session, Thursday morning, November 14
Majestic Ballroom, Adam's Mark
Observations of X-ray emission from comet Hyakutake (Science 272,194, 1996) appear to have been a surprise to most comet researchers. This was the first time that an x-ray image of a comet has been obtained. Existing plasma data suggests that this observation should not have been a surprise. Data obtained from the encounter with comet Halley by spacecraft (Nature 321, 1986; GRL 13, 1986) showed strong plasma wave turbulence and energetic electrons in the region of comet Halley which corresponds closely to the region where the X-rays were observed from comet Hyakutake. Plasma wave turbulence observed was close to the lower-hybrid frequency range where waves are very effective in energizing electrons to the required energies. We show that the interaction of the commentary plasma and the solar wind produce waves in the lower-hybrid frequency range which produce super thermal electrons with energies in the range of 100eV to 1000eV. These produce bremsstrahlung and excite k shell electrons of oxygen, carbon and heavy elements to produce the observed X-rays. The X-ray production is of the order of 10^7 watts, which is of order of that observed. X-ray brightness changed with time; probably reflecting variations in solar wind speed and density. Observations of this type show changing solar wind conditions o the comet.