New Photos Reveal Great Comet's Spiraling Jets

Astronomers have made rare images of the heart of a popular comet and revealed jets of gas spiraling thousands of miles into space.

Comet McNaught has been called the Great Comet of 2007 for the show it put on first in the Northern Hemisphere and then south of the equator. The ball of ice and dirt hung frustratingly close to the Sun, however, so many skywatchers never got a good look.

The New Technology Telescope (NTT) at the European Southern Observatory in Chile was used to make detailed observations that were released yesterday. Scientists found sodium in the comet's emissions, something rare in a comet, they said.

"We had previously pointed the NTT very low to observe the planet Mercury, which is very close to the Sun and is therefore only visible low in the sky just after sunset," said ESO astronomer Colin Snodgrass. "I realized that we could take advantage of the same low pointing limit to observe the comet while it was near the Sun."

The images reveal three jets of gas that spiral away from the comet's rotating nucleus.

"These jets are produced when sunlight heats ices on the surface of the comet, causing them to evaporate into space and create 'geyser' like jets of gas and small dust particles, which stretch over 13,000 km into space-greater than the diameter of the Earth-despite the fact that the nucleus of the comet is probably less than 25 kilometers [15 miles] in diameter," Snodgrass explained.

The comet releases dust, too. But the dust follows a different path from the gas jets, the observations revealed. The dust is tossed off the side of the comet facing the Sun, creating a bright fan of material that's blown back by the pressure of solar radiation.

Snodgrass and his colleagues hope to determine the comet's rotation rate by comparing images taken over time.

Separate observations called spectroscopy, which split light into its various wavelengths to reveal the comet's elemental composition, shows signs of cyanide, carbon, and ammonia-all expected.

"Measurements showed this sodium emission to be extending over more than 100,000 kilometers [62,000 miles] in the tail direction and fading rapidly with time," said ESO scientist Emmanuel Jehin.

Narrow sodium tails have been detected in only a handful of great comets-those that come close to the Sun and therefore are the most active.

"The dust grains are vaporized under the intense heat and start releasing sodium atoms which then react to the solar radiation and emit light-at the very same yellow-orange wavelength of the lamps on our streets," Jehin said.

Sodium has also been observed around Mercury and the Moon forming very tenuous atmospheres.

Comet McNaught was named for Robert McNaught, who discovered the object last year. At its peak, it was the brightest comet in four decades and was even glimpsed in broad daylight by some observers.

Separate observations called spectroscopy, which split light into its various wavelengths to reveal the comet's elemental composition, shows signs of cyanide, carbon, and ammonia-all expected. The researchers were surprised to discover sodium, however. "Measurements showed this sodium emission to be extending over more than 100,000 kilometers [62,000 miles] in the tail direction and fading rapidly with time," said ESO scientist Emmanuel Jehin. Narrow sodium tails have been detected in only a handful of great comets-those that come close to the Sun and therefore are the most active... Sodium has also been observed around Mercury and the Moon forming very tenuous atmospheres.

I suppose some people will take this news with a grain of, uh, never mind...


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Moon Has A Sodium Tail
Boston University
Center for Space Physics
and American Geophysical Union
1 June 1999
Boston University astronomers announced today the discovery of an enormous tail of sodium gas stretching to great distances from the moon. The observations were made at the McDonald Observatory in Fort Davis, Texas, on nights following the Leonid meteor shower of November 1998. The tail of sodium gas was seen to distances of at least 500,000 miles from the moon, changing its appearance over three consecutive nights... Ten years ago, groundbased telescopes revealed that sodium gas (Na) was in the lunar atmosphere, an element that can be used to trace the shape and behavior of such a thin atmosphere... The BU team considered several theories that could explain these unusual features, ruling out a comet, the impact of Leonid meteors upon dust in the solar system, and even possible instrumentation problems... [T]he August observations without meteors and the November observations with meteors imply that the daily flux of micrometeors that strikes the moon's surface creates an extended tail at all times; it was just so enhanced during the strong Leonid storm that it was observed rather easily.
Bulletin of Physics News
Number 36 (Story #5), May 31, 1991
by Phillip F. Schewe
and Ben Stein
The Moon has a comet-like coma and tail. Michael Mendillo of Boston University, reporting at this week's meeting of American Geophysical Union in Baltimore, showed that the moon has a tail, consisting of sodium gas, extending at least 15,000 miles away from the lunar surface. The sodium, Mendillo believes, is released from lunar rocks by meteorite impacts and is later dissipated into space where it is formed into a tail by the force of solar radiation.
Sodium Nebula Around Jupiter
Phillip F. Schew
November 27, 1990
Physics News
A sodium nebula around Jupiter may be the largest object ever recorded on film. A group of astronomers at Boston University, working at the McDonald Observatory in Texas, have detected a neutral cloud of sodium out to distances beyond 400 Jovian radii. The Boston astronomers believe that the shape of the nebula will provide information about Jupiter's magnetosphere and that their technique of measuring non-spherical neutral clouds may be applicable to the study of other planetary magnetospheres.
Sodium Cloud Around Io
Physics News
Phillip F. Schewe and Ben Stein
November 9, 1999
Astronomers have previously known of a sodium cloud which precedes the moon Io in its orbit around Jupiter. The cloud is believed to arise from slow escape of sodium from Io. Now the Galileo spacecraft is providing details of another sodium feature at Io, more of a fast-escaping spray or jet, thought to come about when Io plows through Jupiter's potent magnetic field, a process which induces mega-amp currents through Io's atmosphere... New pictures, reported by scientists at the University of Colorado... and Boston University (Jody Wilson), localize the source of the sodium to a region smaller than Io's diameter, suggesting that Io's atmosphere might not be global; that is, the atmosphere might be patchy and not extend all the way to the poles.
Sodium Tail
On 1997 April 16, astronomers at the La Palma Observatory used a dedicated comet camera, CoCAM, to discover a previously unobserved type of cometary tail, the sodium tail, visible here as the straight line from bottom right to top left, consisting of neutral atoms.
Sodium Gas Tail of Hale-Bopp Comet
Update 4/20/97
Astronomers say the have found a third tail trailing behind the Hale-Bopp comet - a thin straight jet of sodium gas unlike any other seen before, The Boston Globe reported yesterday. The discovery was made Friday by a team of astronomers at the Isaac Newton Group of telescopes in the Canary Islands. The scientists were at a loss to explain how the sodium tail was created. The astronomers used a filter over a telescope that allowed them to detect the light given off by sodium gas, the same yellow glow seen in ordinary sodium-vapor street lamps. Astronomers have long known that comets have two types of tails - one made of dust and the other of electrically charged gas called plasma. They have also known that comets contain sodium, but had never seen it before in the form of a tail.

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