U.S. scientists have used sodium atoms to determine Mercury's comet-like tail is much longer than had been thought.
Mercury's gravity is too weak to hold a permanent atmosphere, so when atoms are evaporated from the planet's surface by solar photons or other processes, some of the atoms form a tail that points away from the sun.
Jeffrey Baumgardner and colleagues at Boston University's Center for Space Physics studied the bright yellow-orange light emitted by the sodium atoms in Mercury's tail and discovered the tail, previously detected to 15 times the radius of Mercury, actually extends more than 100 times that distance, or 1.6 million miles from the planet.
The physicists also discovered the time it takes for the sodium atoms to leave Mercury's surface and reach the tail's maximum length is approximately 15 hours.
The research by Baumgarder, Jody Wilson and Michael Mendillo appears in the journal Geophysical Research Letters.
Copyright 2008 by United Press International
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