Mercury has a tail of sodium atoms millions of kilometres long, similar to a comet's.
Why it is true
Sunlight and micrometeorite impacts knock sodium atoms off the surface, and the pressure of sunlight pushes them behind the planet. The tail is invisible to the naked eye but shows up in photos taken with filters that only let through the yellow light of sodium.
Source: NASA Science (missão MESSENGER)
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Related facts
All other planets of the solar system fit in the space between Earth and Moon.
Mercury has water ice at its poles despite being closest to the Sun.
Uranus was the first planet discovered with a telescope, in 1781.
Neptune was discovered in 1846 thanks to mathematical calculations, before anyone saw it through a telescope.
