Mercurys Sodium Tail

APOD: 2022 May 3 - Mercurys Sodium Tail

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 May 3
The featured image shows the planet Mercury below the star
cluster Pleiades. Mercury, oddly, looks like a comet as it is sporting
a long ion tail made of sodium. The image was acquired last week. 
Please see the explanation for more detailed information.

Mercury's Sodium Tail
Image Credit & Copyright: Sebastian Voltmer

Explanation: That's no comet. Below the Pleiades star cluster is actually a planet: Mercury. Long exposures of our Solar System's innermost planet may reveal something unexpected: a tail. Mercury's thin atmosphere contains small amounts of sodium that glow when excited by light from the Sun. Sunlight also liberates these atoms from Mercury's surface and pushes them away. The yellow glow from sodium, in particular, is relatively bright. Pictured, Mercury and its sodium tail are visible in a deep image taken last week from La Palma, Spain through a filter that primarily transmits yellow light emitted by sodium. First predicted in the 1980s, Mercury's tail was first discovered in 2001. Many tail details were revealed in multiple observations by NASA's robotic MESSENGER spacecraft that orbited Mercury between 2011 and 2015. Tails, of course, are usually associated with comets.

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