"Our observations had been made in March at the McDonald Observatory in Fort Davis, Texas," says Jody Wilson, post-doctoral research associate, Boston University's Center for Space Physics (CSP). "We were in the process of analyzing our data in early April when reports came from the Canary Islands about the new tail. It then took just a day's work to get our results."
The telescopes used to capture such tail structures are very modest in size, according to Jeffrey Baumgardner, senior research associate, CSP. "The goal is to photograph a large portion of the sky, not the fine detail that would come from a large telescope," he says, noting that the team's instrument's main lens is only four inches in diameter. "The technological sophistication lies in the detector system at the end of the telescope. The light signal from sodium gas is very faint and not visible to the naked eye, but easily detected with our camera," adds Baumgardner.
Sodium gas has been detected in previous comets, like Haley's comet in 1986.
"The point is that the position of this sodium tail and its pattern of brightness away from the nucleus are very different from the normal comet tails," says Michael Mendillo, professor of astronomy, Boston University. "This implies that the source of sodium is not necessarily on the nucleus, but extended from it."
The ion tail, composed of electrically charged gas, is pulled out from the comet in a direction away from the sun by magnetic fields in the solar wind, Wilson explains. "But the fan-shaped dust tail is pushed outward by solar radiation pressure," he says. "We don't know the exact mechanism that produces the sodium tail. Sodium gas is continuously produced and lost from other solar system bodies, for example, from surfaces of Mercury and our Moon."
Wilson, an expert on the extended sodium atmosphere produced by volcanoes on Jupiter's moon Io, plans to use his models of sodium flowing from a tiny body to explore possible sources of Hale-Bopp's sodium tail.
The Center for Space Physics, established in 1988, provides a link between research groups in astronomy, physics, and engineering with a focus on the study of upper atmospheres and space environments of the earth, sun, and other planetary bodies. The Center is active in various NASA and other spacecraft missions and is preparing to launch its own satellite, TERRIERS, in early 1998.
Images of comet Hale-Bopp with the three tails can be found on the World Wide Web at:
Color: http://vega.bu.edu/cometc.gif
Black/White: http://vega.bu.edu/cometbw.gif
Color Figure Caption: This image represents the sum of three separate pictures taken through filters that capture light emission from water ions (at a wavelength of 6198 A), dust (at 6050 A), and sodium gas (at 5893 A). The brightest portions of each of these emissions are shown using red, blue and yellow colors, respectively. (The sodium tail has been artificially enhanced to make it more visible in the photo)
Photo credit: J. Wilson, J. Baumgardner, M. Mendillo (Boston University)
To find this image on the web go to: http://vega.bu.edu/cometc.gif
Black/White Figure Caption: This image represents the sum of the separate pictures taken through filters that capture light emission from water ions (at a wavelength of 6198 A), dust (at 6050 A), and sodium gas (at 5893 A). The brightest portions of each of these emissions are shown here. (The sodium tail has been artificially enhanced to make it more visible in the photo)
Photo credit: J. Wilson, J. Baumgardner, M. Mendillo (Boston University)
To find this image on the World Wide Web: http://vega.bu.edu/cometbw.gif
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