THE SOUTHWORTH PLANETARIUM
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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: LXVIII
"Made from the best stuff off Earth."

THE DAILY ASTRONOMER
Thursday, January 20, 2022
Earth Calling

Subscriber SH made our day by posting a question about radio communication
with Alpha Centauri, which, at a distance of 4.37 light years, is the
closest star system to the Sun. Wouldn't we be able to beam a radio message
to A Cen and then wait for their response, which should arrive about nine
years or so after our initial transmission?

We could. We know Alpha Centauri's location, we have the resources
available to direct such a transmission AND Proxima Centauri, the smallest
of the three stars comprising the system, has a known Earth-sized planet
within the star's habitable zone.* It seems as though we could send a
message, receive a reply and settle once and for all the preposterous
questions, "Are we alone?" The only problem is we don't know if that planet
even harbors life. Moreover, even if it is life-bearing, are the life-forms
on that world capable of receiving and transmitting radio waves? Based only
on our example, the probability is lamentably low.

Regard Earth's natural history. According to the most recent examination of
microscopic fossils, life started on Earth about 3.7 billion years ago.
Radio was invented in 1895. Throughout the vast majority of Earth's
history, the planet has been radio quiet. Then again, the Alpha Centauri
system is about 5.3 billion years old, nearly equal to the Sun's age:
plenty of time for whatever life exists to have advanced from the level of
the prokaryotic to that of the professional broadcaster.

The other issue: will they even be listening? If so, will they be listening
to the right frequencies? Imagine this scenario: you and a companion are
separately exploring a mountain range. You each have a powerful
walkie-talkie that can transmit along ten frequencies: A - J.
Unfortunately, before you separated, you didn't select your communication
frequency. So, you try to call your friend on A, but she has the WT set to
G. Or, she's trying to contact you on H, but you're listening and
transmitting on B. One can appreciate the difficulty with all these
possible combinations. Well, there are so many frequencies along the radio
band that the communication problem becomes exponentially greater.

Also, who knows if they've even developed radio technology or perhaps have
gone beyond it?

Also, the inverse square law tells us that any transmission beamed to Alpha
Centauri or one that is beamed from Alpha Centauri to us will be highly
attenuated.

We could transmit a signal to Alpha Centauri. In fact, we're transmitting
radio waves constantly throughout space. Such transmissions reach Alpha
Centauri about 4.4 years after they're first broadcast. However, we've
heard nothing yet and it might be in the cards that A Cen will remain
silent...or not.

On Monday, we'll draw this discussion out farther into space.



*The term habitable zone refers to a region in which the temperatures could
be conducive to life's formation, neither too hot nor too cool. (It is also
called the "Goldilocks Zone.") Unfortunately, a planet within this zone
won't necessarily have conditions favorable for life's development. Realize
that Venus (a Dantean blast furnace) and Mars (a dessicated and frigid
desert) are both in the Sun's habitable zone. Life might have existed on
Mars and could *possibly* exist in some form now. However, one will NOT
find life on Venus, unless a wayward Dalek is scurrying about there and
even it can't be considered indigenous.



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