Mercury's Sodium Tail

Image Credit: Center for Space Physics / Boston University.

Original caption:
Mercury’s tail of sodium gas captured by a wide-angle telescope showing an enormous extent of the atoms escaping from the planet’s surface. The insert shows the source regions of the tail gases imaged at a different time using a very narrow field of view telescope. The source regions occur at high latitudes, probably related to solar wind access to Mercury’s surface along specific magnetic field lines. The impacts of the solar wind ions and electrons result in sputtering sodium from the surface. Since Mercury is close to the Sun, the sputtered atoms are pushed away by the pressure of light, with this photon radiation pressure leading to the long tail. The brightness of the source regions is about 1 million times greater than the faintest part of the distant tail. The sizes of the source regions span about ¼ of the planet’s radius, while the tail extends to about 1500 times the radius of the planet, about 1.5 million miles.

(Boston University Astronomers Map Full Extent of Mercury's Comet-Like Tail) http://www.bu.edu/phpbin/news/releases/display.php?id=1511
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