Mercury Found to Have Super Long, Glowing Tail

Feb. 28, 2008 -- The first rock from the sun has a glowing dragon tail of sodium atoms that is more than seven times longer than ever suspected.

New measurements of Mercury's yellow-orange tail, which streams in the solar wind like the long tail of a kite, put it at more than 100 times the radius of the planet itself.

The neutral sodium atoms that make up the 1.6-million-mile-long streamer are thought to be blasted off the surface by the sun and micro-meteor impacts. These impart enough energy to launch the atoms into space.

Other elements are also in the tail, but it's the sodium which lights up and can be detected.

"This (sodium) ion is the 'little atom that could,'" said Mercury researcher Ann Sprague of the Lunar and Planetary Laboratory at the University of Arizona in Tucson. It scatters photons like crazy, making it a great clue to various processes at work on and around the planet.

Mercury's tail had been spotted before, but its great length was missed because previous attempts were looking at too small a piece of the sky, said researcher Jeffrey Baumgardner of Boston University. Baumgardner is the lead author of a report on Mercury's sodium tail in the current issue of Geophysical Research Letters.

"Our forte was wide-angle imaging," Baumgardner told Discovery News.

The 8 degree-wide image his team created using a telescope at McDonald Observatory in Texas is about 16 full-moons wide. The actual 2 degree sodium tail is as long as four full moons. In their image Mercury is blocked out because its brightness outshines the sodium tail. If Mercury were shown to scale in the image, it would be less than a pixel in diameter.