Seasons on Mercury?

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Will wonders never cease? Now it seems that our solar system's most sun-drenched planet may actually have seasons! Just like on Earth.

OK, maybe not exactly like Earth.

Mercury's atmosphere is what scientists call an "exosphere," and is made up of atoms kicked up from the surface. It is very tenuous and has a very low density, meaning atoms in the atmosphere rarely run into each other. It also has a tail that streams away from the planet in the opposite direction of the sun.

MESSENGER looked at differences in three atoms in the exosphere — sodium, calcium and magnesium — between the probe's three flybys. They detected much less sodium during the third flyby than they had during the second.

"While this is dramatic, it isn't totally unexpected," [mission scientist Ronald Vervack, Jr., of The Johns Hopkins University Applied Physics Laboratory] said. This is because radiation pressures from the sun change as Mercury moves through its orbit, which changes the amount of sodium liberated from the surface.

In essence, Mercury's atmosphere experiences seasonal effects during the planet's orbit.

(from Space.com)

Not quite like the changing leaves and cold fronts we are used to, but pretty interesting nonetheless.
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