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2021-2022: LXVIII

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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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