Mercury has comet-like gas tail

Feb 6, 2008 10:14 GMT  ·  By

New observations on one of the most mysterious planets in the solar system suggest that Mercury has a comet-like tail. However, while the cometary Tails are relatively bright and often visible with the naked eye from the surface of the Earth, Mercury's tail is less visible in the visible spectrum. Previous observations conducted in the middle of 2006 showed that the smallest planet in the solar system presents a tail of sodium gas extending from the surface as much as 40,000 kilometers in space.

The new observations conducted by astronomers from Boston University, reveal that the sodium gas tail can reach more than 2.5 million kilometers into space. Similar surveys were previously made by a different group of astronomers, mapping a gaseous structure extending 15 times the radius of the planet.

Sodium gas is being routinely ejected from the surface of Mercury, but the weak gravity of the planet is not powerful enough to retain it from escaping into space, and establish a small atmosphere. The solar winds acting on Mercury also contribute in a large proportion to the formation of the comet-like tail, by pushing the ejected gas behind the planet. Similar to sodium gas florescent bulbs, sodium atoms within the tail of Mercury emit bright light in the visible spectrum, however not bright enough to be observed with the naked eye.

Gas escapes the surface, in a manner identical to the well known evaporation processes we experience regularly on Earth, meaning atoms and molecules receive enough energy so that they can suffer a transition to the vapor state. There are multiple actions which can provide with such energy inputs starting with surface-sputtering, solar winds and sunlight, or impacts determined by micrometeorites falling onto the surface of the planet.

Although not very abundant in the crust of Mercury, sodium gas is only one of the few that can be detected relatively easy by conducting observations from the surface of the Earth, and its presence may eventually put in evidence more abundant gases that are currently invisible to ground-based telescopes. Also, measurements on the length and width of the comet-like tail can be used to study different surface-sputtering processes that may determine them.

Back in 2006, Boston University astronomers using the U.S. Air Force 3.7 meter telescope, obtained the first image of Mercury's tail by concentrating the observations of regions of the planet's surface, that seemed to be the source of the gaseous emission. In order to accurately measure the length of the tail, Boston University astronomers had to use a series of smaller telescopes, scattered throughout the U.S.

The breakthrough came in the month of May 2007, when Jody Wilson and Carl Schmidt obtained a large field image showing the full extent of the sodium gas tail originating from the surface of Mercury.