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Session 71 - Comets & Asteroids.
Display session, Friday, January 09
Exhibit Hall,

[71.08] The Mystery of the H20 Cometary Masers

A. P. Graham (U. Virginia), V. Strelnitski (Maria Mitchell Observatory)

It has been shown that the H_20 1.35 cm line is undetectable in comets unless it is amplified by the maser mechanism. Although the possibility of detectable masing seems likely in many bright comets, the 1.35 cm line has been reliably observed only one time in the past quarter of a century, in Comet Bradfield (1974b). We postulate that the low rate of detection of water masers in comets is due to the highly specific requirements for observation. It can be shown that the most favorable, and perhaps, only possible case for observing an H_20 maser occurs when an observer looks along a jet of nuclear emission. We estimate the probability for this case to occur in a random search by considering at random the position of the jet's origin on the nucleus and the orientation of the comet's axis of rotation. The probability we find is less than 0.01, which explains the low rate of detection. We suggest that pre-observational studies of the nuclear rotation and jet structure of a target comet could facilitate a greater probability of maser detection.

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