AAO Press Releases

14 January 1998

Comet Hale Bopp's Elegant Neckline

Comet Hale-Bopp, which provided sensational viewing in the northern hemisphere last year, is again attracting attention as it recedes from the inner Solar System.
In early January 1998, the Earth passed through the plane of the comet's orbit (the flat slice of space in which Hale-Bopp moves). Dust particles ejected from the comet during its passage around the Sun accumulate in this plane, suggesting that a thin, flat dust-cloud might be seen faintly by scattered sunlight as the Earth passes through it.
A group of Italian astronomers, led by Marco Fulle (Trieste) and Gabriele Cremonese (Padua), predicted the appearance of a bright line, or spike (Neck-Line) in addition to Hale-Bopp's normal tail. Observations of the Neck-Line will provide important data on the comet\rquote s structure and activity.
The Italian astronomers requested the Anglo-Australian Observatory to photograph the event using its UK Schmidt Telescope near Coonabarabran in New South Wales. In making their request, they pointed out that this was the only instrument in the world capable of producing the deep, wide-field images required.
During the first week in January, three wide-angle photographs of comet Hale-Bopp were obtained. At the time, the comet's distance was almost 600 million kilometres. All three photographs show a well-developed Neck-Line structure, and one of them, taken on the night of January 2/3, is shown here.
The slender Neck-Line, in reality composed of dust and small stones, seems to pierce the heart of the comet and its tail---although most of the material visible in the Neck-Line actually lies between Earth and the comet.
The three photographs will be sent to Italy for analysis, and it is expected that they will reveal much about dust ejection and dust/gas interaction in Comet Hale-Bopp.

These observations have significant implications for our understanding of comets in general. Images may be viewed at http://www.aao.gov.au/local/www/qap/work/HB2.jpg