Posts Tagged planets

Mercurial Mercury

I went to school in the mid 80s to mid 90s.  At that time most of what there was to know about the general natures of the planets were known.  Mars was a lifeless rock.  Venus was a hellacious greenhouse.  The asteroids were chunks of rock that never became a planet, not a planet that blew apart.  We had gas giants.  We had Pluto.  And then there was the great unknown abyss.  Really, the further one got from the sun, the less was known.  There certainly had to be something out there, something a little farther than Pluto, but we weren’t taught about Oort Clouds and Kuiper Belts.

We were taught that the moon was tidally locked to the earth, which is why we always see the same face.

And we were taught that Mercury was tidally locked to the sun.

In looking around for outdated scientific theories, it never occurred to me that there was one residing firmly inside my own head.  Because in spite of what every science teacher who touched on astronomy taught me in school, Mercury is not tidally locked.  What’s more, this has been known by science since 1965.

1965.  As in for at least 20 years before the first time I was likely taught about what tidal locking was and what astronomical bodies it applied to.

I’m not sure exactly what to chalk that up to.  Certainly teachers who are covering general sciences and aren’t astronomy-specific aren’t going to keep up on every new development.  It’s probably just what they learned in school, what the textbooks still said, any number of possible excuses.  I’m not trying to point any fingers or assign any blame here.  Instead, I find it an interesting exercise in the speed at which new scientific knowledge proliferates.

We probably think of ourselves as living in a very connected age, one in which new bits of information can fly around the world.  We aren’t reliant on monthly scientific journals, weekly news magazines, daily news papers.  We have the internet, a constant source of the new, the updated, and the changing.  And yet, in this world, there is still obsolete scientific knowledge out there.

From a story telling perspective it means there are two Mercuries.

On Mercury classic we have a world where one side is exposed to all the heat and radiation spat out by the sun, shooting around in an orbit half as far as the earth, and one side impossibly cold, exposed only to the unfeeling harshness of space.  With no atmosphere, there’s no potential of the heat getting shared around the planet, so the dark side approaches absolute zero.  Here, stories can take place on the delimiter between the two, trying to constantly walk that tightrope between too hot and too cold.  Or under the surface.  Or in protective domes on either side.  It’s an interestingly static world.

And then we’ve got modern Mercury, spinning on its axis so slowly that a Mercurial day is two Mercurial years long.  The heat of the day and the cold of the night would be just as drastic as on the static planet, but now the delimiter moseys slowly around the planet, meaning that anyone looking to walk that tight rope has to be in constant, but slow, movement.  Considering the length of a day on Mercury and the diameter of the planet, some quick envelope math suggests the line between night and day is moving at just 2.25 miles per hour.  Compare that to the nearly 1000 mph that would be required to constantly stay on the day/night line on planet earth.  Life under the surface may not change, but settlements on the surface need to either prepare for that continual 2.25 mph trek, or be prepared to withstand both extremes that the planet offers.

Both planets present their unique challenges.

So I suppose this is in part an exploration of the natures of Mercury, old and new, and in part a warning about relying on what you are certain about when crafting a story.  Because I could have told you with certainty until yesterday that Mercury was tidally locked.  If you’re intentionally using old/bad science, that’s fine and dandy, but if you’re looking for realism, make sure the reality in your head matches the reality around us.

Mercury photo released by NASA to public domain.

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