Mercury’s sodium exosphere streams into a faint comet-like tail
Mercury has almost no bound atmosphere, yet sunlight and micrometeoroid impacts knock sodium atoms off the surface into a tenuous exosphere that the solar wind and radiation pressure push into a long, glowing tail.
Telescopes on Earth and spacecraft have imaged that yellow-orange sodium plume stretching millions of kilometers anti-sunward — a planetary “comet” made of sputtered rock, not ice.
Even airless worlds leak. Mercury’s sodium tail shows how a bare crust can feed space with atoms, linking surface geology to a visible stream across the inner solar system.
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