David Nightingale: Goldilocks Zones
Someone said to me a while ago 'all your essays are about science', and I read between the lines that they were consequently of little interest. But what about Borodin, Queen Zenobia, Dorothy Parker, Pickpockets, Granny D, Robin Williams, Selfridge, Adirondack murders, Robert Frost, Julius Caesar, Emperor Aurelius....? ... and it brings to mind the irate Archbishop who once accused the author of Principia Mathematica of only ever writing about sex.
But of general concern to humanity surely, without writing about science, is where future generations are to live, assuming we even do survive? One talks of things mushrooming, thinking perhaps of expanding mushroom clouds, and world population figures have indeed been mushrooming [ref1] : in 1800 (1 billion), 1900 (nearly 2 billion), 2000 (6 billion), 2050 (10 billion) ... and, before any dreaded catastrophe, there's a long-term ever-increasing motivation to spread out.
Not long ago, the only other planets of our mother sun that people even considered moving to were our nearest neighbors Venus and Mars -- hopelessly unpleasant each, too hot and too cold respectively. But in the last 25 years we have discovered 1000s of exo-planets! Nothing was confirmed before 1990, and now suddenly there's a plethora.
These other planets have to have a mother star of course -- that is, something massive and hot to orbit around, like moths around a light bulb. This is where Goldilocks comes in. The old folk tale has the pretty little girl coming through the forest, entering the cabin of the three bears, and trying their 3 bowls of porridge -- which for some reason had been left on the table. "This porridge is too hot", she says, and then, trying another one "this porridge is too cold" -- and finally eating the 3rd one she says "Ah! This porridge is just right" .....
We are looking for suitable planets to expand to in our galaxy. They mustn't be either too hot or too cold, and, like earth, must be just right, in the habitable zone -- the Goldilocks zone.
Now, without any science or math, let's comment on what humanity has done so far. We used to look for star wobbles, but since then a better way has been to look for stars that seem to dim sometimes. If a star dims rhythmically that's a good sign that something may be passing in front of it -- such as a steadily orbiting planet perhaps.
Well, we have candidates. Of the 1000s of exoplanets discovered by the (2009) Kepler telescope a nice earth-sized one is Kepler 186f, discovered in 2014. Yet another is Kepler 452b discovered in 2015. The Subaru telescope (Subaru is the Japanese word for the Pleiades) on Hawaii's Mauna Kea has also discovered many -- for example the huge 'pink' planet GJ504b, which is way too large and nearly 600 light years away.
All of these recently discovered planets are hopelessly too distant. If we could travel at the speed of light it would still take hundreds of years, and generations to reach them!
Our nearest star to the sun is Alpha Centauri, and this journey would take only about 4.3 years (at the speed of light.) Alpha Centauri is actually three stars -- if you are able to look closely, as through a telescope. Two of those three are similar to our sun, and slowly rotate around each other every 79 years -- although this is irrelevant. What is relevant is that each of those 2 widely-separated sun-like stars seems to have local planets, like our solar system. Well, we can't travel at the speed of light, so this seems hopeless too. But, out of the billions and billions of stars [ref 2] in our galaxy it has been estimated that 5% may have habitable planets -- i.e. there may be about 10 billion Goldilocks ones, where the porridge will be 'just right'.
1. Readers Digest Atlas; also, www.census.gov; also, wikipedia.
2. Estimated to be ~200 billion stars in the Milky Way.
Dr. David Nightingale is Professor Emeritus of Physics at the State University of New York at New Paltz and is the co-author of the text, A Short Course in General Relativity.
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