Monday, December 30, 2013

How Many Extraterrestrials Are There?

Yesterday’s post discussed the highly advanced Saturnian gas creatures and their battle with interstellar foes in Donald Wandrei’s Something From Above (1930).  Both species wanted to control the supply of Seggglyn, an invisible metal with anti-gravity powers.  In a later story,Wandrei’s Raiders of the Universes, (1932), the evil Xlarbtians threaten to unleash the power of their ‘Dark Planet’—an enormous spherical warship—to destroy Earth unless they receive all the radium on the planet. 

Both stories exemplify the cosmicist view of earth as a puny, inconsequential world at the mercy of vast extraterrestrial empires.  Space aliens seem especially interested in natural resources and real estate.  They are always running out of these items.

Just how many space aliens are out there?  Should we be concerned?  Fortunately, there is a mathematic formula to calculate their probable numbers.  It is called the Drake Equation, after Frank Drake, who presented it at the very first SETI* meeting, back in 1961.  For future reference, here is a modified and simplified version of the equation:

N = R x P x E x L x I x C x T

N stands for the number of alien civilizations in our galaxy that may have developed communication via radio waves, (as opposed to telepathy, which is more typical in pulp science fiction).  R is the average rate at which stars form in our galaxy.  P is the number of those stars that have planets orbiting them.  (As of this writing, 1056 “exoplanets” have been discovered so far, circling 802 stars, and of these planetary systems, 175 have multiple planets.)

The number of planets that are likely to support life is represented by E.  These would lie in the habitable orbital zone of a star—defined as at a sufficient distance from the star to allow liquid water to exist on the planet.  To date, some scientists have identified at least nine exoplanets that meet this criterion, and possibly 30 planetary moons.

L is the number of planets that could actually evolve a form of life.  I is the proportion of these planets that could develop intelligent life.  The number of inhabited planets capable of inventing technology that can be detected from space is represented by C.  Finally, and perhaps most critically, T stands for the amount of time that an extraterrestrial civilization has been producing detectable radio signals.

The Drake Equation yields a ‘guestimate’ of the number of different alien civilizations in our galaxy.  It was intended to spur discussion and support for the SETI project, not provide a hard figure.  Obviously many of the variables themselves are completely unknown and involve considerable speculation.  In 1961, scientists estimated were that the Milky Way contained between 1000 to 100,000,000 extraterrestrial civilizations.  This was thought to be a conservative estimate.

The recent identification of over a thousand exo-planets circling other stars and the tantalizing findings of the Mars rover missions lends some credence to SETI’s grand project.  While we wait for that telltale radio signal from beyond, it may fall to us to discover life that we can bring with us to other planets, in particular, Mars. 

Robert Zubrin, among others, (see his excellent book The Case for Mars) advocates terra-forming the planet, first by creating a green house effect in the atmosphere, and then by introducing hardy microorganisms from Earth.  This would facilitate human colonization over a period of a few decades. Given that the gas creatures of Saturn and the evil Xlarbtians already have a head start on us, we should hurry to get this done.


*Search for Extraterrestrial Intelligence (SETI), see SETI Institute

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