THE SOUTHWORTH PLANETARIUM
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Founded January 1970
Julian Date: 2458878.16
2019-2020:  XCV
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THE DAILY ASTRONOMER
Thursday, January 30, 2020
Another Look at the Drake Equation


The what?
The Drake Equation!   Let's have a look:

[image: unnamed.jpg]

If you were bracing yourself for an assault of differential calculus, you
may breathe again.  Crafted by SETI (Search for Extraterrestrial
Intelligence) pioneer Dr. Frank Drake, the Drake Equation is a partially
factual/largely speculative estimate as to the number of civilizations that
exist in our galaxy.       As of now, we know of only one civilized world
and we're living on it, allegedly.

Now that astronomers have found more than 4,000 exoplanets (4,173 as of
now), we're developing a slightly better estimate.  Of course, as many
terms in the above equation are more based on science fiction than science,
we cannot rely on any value we might derive from plugging in numbers.

*Ns* the number of stars in the Milky Way Galaxy, is approximately 300
billion.  This census varies considerably over time.  One problem pertains
to the "zone of avoidance," the large swath of the Milky Way concealed
behind the dust laden plane between our solar system and the galactic
center. By examining other barred spirals of comparable size, however,
astronomers are able to determine the Milky Way's stellar population with
far greater precision.

Fp   the fraction of stars with habitable planets. Although this value
remains speculative, astronomers believe that our galaxy could contain 40
billion potentially habitable planets.  This statement means that 40
billion planets might be terrestrial in nature and revolve within the
"habitable zone," the belt around stars where temperatures could be
conducive to life's development.    A "terrestrial" planet is small, rocky
and enshrouded in a thin atmosphere. Earth, Venus and Mars all match this
description.    Although Earth and Mars both orbit within the Sun's
habitable zone, Earth harbors life.  Mars doesn't.     Merely revolving
within the habitable zone doesn't inevitably result in life's development.

[image:
ipgjpd9vkgakl1pfy2grsbubntau1bvidb3fzmypm6kktohr0uu44hm2hm2x10nr.jpg]
While Earth and Mars both move within the Sun's habitable zone, only
Earth harbors life.    In some models, Venus, too, orbits with this zone.
Being 900 degrees hot from pole to pole, Venus is devoid of life, as well.

*Fl    *The fraction of habitable planets with life.  Now we're in "haven't
the faintest idea" territory. If we base the fraction on our own solar
system,one could say that one half or one third of planets of potentially
habitable planets have life.  The latter value refers to some models that
place Venus within the Sun's habitable zone. Using the Sun's family as a
representation of other solar systems isn't always the best idea.

*Fi    *Here again we find ourselves in a real bind.    We know of only one
life bearing world: Earth.  On that world, life evolved from the simplest
prokaryotic cells to advanced beings that can now binge watch Hee Haw
reruns.    If we base this value only on our own example, we could smugly
say that when life takes hold on a world, it will evolve slowly but
inexorably toward levels of increasing complexity.   Granted, we homo
sapiens have benefitted richly from asteroid induced mass extinctions that
devastated  -but didn't destroy- the reptiles while permitting mammals to
ascend to a position of dominance.  Take solace in this statement next time
you come to cross purposes with a Komodo Dragon.

*Lc  *Well, now we can't even use ourselves as an example because we're
still here!   Despite a history replete with doomsday predictions crafted
by prophets who knew how to make a fast buck, our civilization continues to
churn and spin and evolve with exponential abandon.   Don't believe it?
Just refer to the following image.

[image: Hong-Kong-.jpg]
*Portland*

We know that geologically civilization started about three hours ago around
the Tigris and Euphrates. Now, we have developed the capability of nuclear
annihilation.   If we somehow turned our atomic arsenal inwards, we could
destroy ourselves.  Mind you, the planet would still persist and some
tenacious species could evolve to higher states in our absence.

We hope that intelligent life proves intelligent enough to sustain itself
despite its inborne self-destructive instincts.

So, we invite you to offer your own estimates about life in the galaxy.
Nobody will be able to prove you wrong.  Well, not in this century



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