Fly Me to the Moon (A Habitable One, Please)

I mentioned in previous blogs the book, The Millennial Project: Colonizing the Galaxy in Eight Easy Steps.  It was a book written years ago by Marshall T. Savage where he listed the way he thought mankind should use toward interstellar colonization.  

One of my favorite steps in the book was the one he called, Avalon.  This was the step where, in his book, humans would colonize the moon by placing domes, filled with water to provide protection against radiation, over the craters and creating Earth-like habitats inside of them.  

When I read this section of Savage’s book, I found myself wanting to live in such a place.  The lesser moon gravity would make it possible for someone to strap on a pair of wings and fly.  You could even put a dome over a smaller crater and create a private villa for yourself.  

Living on a moon would be cool.  

Finding life on a moon would be cool, as well.  An article in Scientific American’s January, 2014 edition talked about the efforts of some scientists to locate habitable exo-moons, the satellites of the exo-planets we’ve been finding in recent years.  While some of the planets we’ve found are in the “goldilocks zone,” the volume around a star where water would remain a liquid, most of the exo-planets we’ve located are gas giants, which would not be hospitable places for life, at least as we know it, to exist.  Some scientists have speculated, though, that if these massive exo-planets had moons sufficiently large to support a breathable atmosphere, then those exo-moons could harbor life.  

The methods used to find exo-moons are similar to those finding exo-planets, looking for the wobble in the planet’s revolution that could be caused by a satellite’s gravity as they revolve around a shared center of gravity.  The problem is that such a wobble is several magnitudes smaller than the wobble the planet causes in the star it revolves around and would be much, much harder to detect.  There has been only one possible candidate for an exo-moon found so far, and it has not been validated yet.  It could be more of dual system, with a Neptune sized world revolving around a brown dwarf, both of which are traveling around their primary.  

One thing I got out of the article are the three ways moons can be formed.  

Way Number One is forming out of a disk.  Just as the Earth formed out of the dust and debris circling the Sun, the moons of a gas giant, such as Jupiter, would form out of the dust and ice circling that planet.  One problem for creating a habitable moon is that this method has an upper limit to the size of the moon that can form, and that limit is too small for the satellite to have enough gravity to hold a breathable atmosphere.  

Way Number Two: Massive Collision.  This is how scientists believe the Earth and Moon were formed, when a much larger “Earth” was struck by another body, about the size of Mars.  The collision tore a huge chunk of material out of the Earth.  Eventually this chunk grouped together to form our Moon.  This method can produce satellites of any size, even to the point of creating a dual planetary system where both bodies could support life.  Dual planetary systems have been used as settings in a number of science fiction stories, most notably in Ursula K. Le Guin’s, The Dispossessed.  

Way Number Three is almost literally a cheat: Planetary Capture.  A satellite in space, created by one of the two other methods, comes close enough to a gas giant that it is captured and brought into orbit around the planet.  They believe this is how Neptune acquired its moon, Triton.  If it came from a dual planetary system described in Way Number Two, then the gas giant would still the partner away while flinging the other satellite off into space.  If the satellite were big enough, and the gas giant in the star’s habitable zone, then it could be habitable.  

I’ve always like habitable moons as settings for stories.  The most famous examples I can think of are from the Star Wars universe.  Yavin was the exo-moon where the Rebel Alliance base was hidden in the original Star Wars movie, which later was identified as Chapter IV, A New Hope.  Endor was the exo-moon where the Empire hid the second Death Star and where the Ewoks lived.  

You notice how both Yavin and Endor had trees everywhere?  Wonder where Lucas got the concept “moon=forest”?  

It does seem to me that, as settings, moons are regarded like islands where the planets are more like continents.  Hidden places that you really have to search for hard to find, or which you find by stumbling over accidentally.  

One of my favorite exo-moon settings came from a role-playing game, Traveller 2300 (later known as 2300 AD).  One of the first adventure modules in the game takes place on a world called Aurore, which is actually a moon orbiting a gas giant in the planet.  The gas giant is actually outside the habitable zone of the star it circles but provides enough thermal energy in the form of infrared light to make it warm enough to have liquid water.  The Aurore is tidally locked to its gas giant primary, one side always faces the gas giant.  This creates two habitable zones where the humans have planted their colonies, a “Hot Zone,” which faces the gas giant where its too hot to live, and a “Cold Zone,” the size that perpetually faces away from the gas giant and is constantly covered in ice.  

I really liked the description of Aurore, with the gas giant always on the horizon, bulging up like the setting sun, but never rising or going down.  An exo-moon circling a gas giant in the habitable zone of its star might see a different sight if tidally locked.  At “Noon,” when the gas giant is overhead, blocking the star, the inhabitants would look up and see a massive black disk or hole in the sky, with the stars visible around it.  At “Midnight,” when the star would be behind the moon, the light reflecting from the star would reflect off the gas giant, revealing it in all its glory.  In between, you’d see the gas giant go through phases as the star rose up at dawn, only to plunge the world into night as it vanished behind the gas giant.  Moon-dawn, and Gas Giant-Dawn would be two points in the “day” when light would return. 

That would be such a cool thing to see.