THE SOUTHWORTH PLANETARIUM

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2021-2022: LXX

"We humans have lost the wisdom of genuinely resting and relaxing. We worry too much. We don't allow our bodies to heal, and we don't allow our minds and hearts to heal." -Thich Nhat Nanh

THE DAILY ASTRONOMER

Monday, January 24, 2022

Celestial Connections

We know of only one life-bearing world in the Universe. We're living on its surface. Despite our continued ignorance of other speciated planets, we suspect -or at least hope- that life not only exists but abounds in the Universe. We predicate that optimistic statement on both simple statistics and observations of Earth life. Most of the 125 known galaxies in the Universe contain billions of stars, most of which likely harbor more than one planet. Plenty of places exist where life could develop. We also know that Earth life has proven to be fiercely resilient through the withering assaults and widespread extinction events the planet has experienced throughout its history. When life starts, life sticks...if Earth is any example.

So, how can we discover these other beings and connect with them? Unfortunately, both detection and connection will likely prove challenging both by virtue of the separation distance between stars and our uncertainty as to where to institute the search. We'll begin with a process of elimination:

First, we needn't bother seeking life signals from other galaxies. The chance of detecting such a signal even from a relatively nearby galaxy such as Andromeda would be exceedingly low, about equal to the chance of having someone in Barrow, Alaska slam their kitchen window down in response to someone else yodeling in Portland, Maine. The distance separating galaxies is so vast any radio wave would be so highly attenuated as to be imperceptible here. While one acknowledges that more sophisticated means of communication might have been developed by other species, even technology can't counteract that pesky inverse square law, which causes any signal to diminish with the square of the distance.

We should also ignore the highly massive and luminous stars because they don't last long. As an example, regard Betelgeuse, the red supergiant star defining Orion's eastern shoulder. Though it has only reached the tender age of 9 million years, it will soon explode as a supernova. ("Soon" meaning sometime between now and one million years from now.) The highly massive stars expend their core fuel reserves so rapidly that they won't exist nearly long enough to allow life to evolve. In fact, any attendant planets around these behemoth stars probably won't have cooled sufficiently to even create a crust or substantial water bodies. As such highly massive stars represent a miniscule fraction of the galaxy's stellar population, we still have an abundance of targets.

It is sensible to focus first on those stars known to harbor exoplanets. As of today, astronomers have confirmed the discovery of 4946 such worlds. Further, the focus should narrow to those stars who possess Earth-like planets revolving within the "habitable zone," a region in which temperatures would allow water to exist as liquid, solid and gas. This requirement is based on the assumption that water is essential for life elsewhere as it is for life on Earth. It also presupposes that life forms need a solid surface on which to develop, as opposed to the turbulent "clouds" within gas giants. These immense worlds most likely consist of material unsuitable for life, such as liquid metallic hydrogen and ammonia.

As of now, astronomers have found approximately sixty such planets, located around both nearby stars (those within a 50 light years radius) and farther flung stars more than 1000 light years away. While it is highly probable that astronomers will eventually find thousands more, for now, these sixty are the only "promising planets" known.

Determining if life actually exists on any of these planets doesn't involve listening for radio communication, which, as we learned last week, is quite problematic.* Instead, it involves analysis of any atmospheres surrounding those planets. Astronomers can determine the chemical composition of these atmospheres by studying the starlight that passes through it. Chemicals within the gaseous envelope will absorb light at specific wavelengths. Think of each chemical having its own "barcode." Scientists would hope to find evidence of water vapor, methane, molecular oxygen and other substances associated with metabolic activity. While such detections won't provide conclusive proof of life's existence, it would provide us with strong evidence that perhaps living beings are thriving on that world.

The surest way to be certain that we're not alone in this cosmos is to witness the arrival of extraterrestrials who hopefully won't be carrying copies of "To Serve Man" under their arms. Or, discovery of some sort of craft or object that was obviously designed by another race. Barring such an encounter, detection of other life will remain frustratingly indirect. All the same, the drive to know that we are not unique will induce us to continue the search, even if the outer reaches remain stubbornly silent.

Tomorrow, humanity's first truly interstellar probe?

*The problem being that life could well exist on a planet but would likely lack the means by which to transmit radio waves. After all, Earth life persisted for billions of years before Tesla and Marconi showed up.

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