Monday, January 30, 2017

What are the odds aliens exist?

Recently the star KIC 8462852 (aka Tabby’s Star) has made news again because of its strange behavior. Possible explanations for its varying brightness (such as comets) don’t seem to fit the observational data, which has some speculating that the star’s behavior could be explained by the presence of an alien civilization.

By Brian Koberlein from EarthSky

While many astronomers admit that is a possibility, they don’t think aliens are the likely cause. For one, mysterious behavior is not enough to conclude the cause is aliens. For another, the likelihood that an alien civilization actually exists is still a matter of some debate.

The odds of an alien civilization coexisting with humans is often calculated by the Drake equation. It was first proposed by Frank Drake in 1961. Simply take the rate at which stars form in our galaxy and multiply it by the fraction of stars with planets, the average number of planets per star that could support life, the fraction of those that actually develop life, the fraction of life bearing planets that develop civilization, the fraction of civilizations that have detectable signals, and finally the length of time a civilization might last. Crunch the numbers and you have the number of civilizations in our galaxy capable of communicating with us.

When Drake first proposed the equation, the values for each term were largely unknown, but we now have good estimates for many of them. We know that most stars have planets, and the odds of a potentially habitable planet is actually quite high, possibly as high as 100 billion in our galaxy alone.

Unfortunately the really important factors of the Drake equation are still completely unknown. On how many potentially habitable planets does life actually arise? How many of those give rise to civilizations? How long does a typical civilization last? No idea. Depending on the answer to those questions the number of civilizations in our galaxy could range from hundreds of thousands to only one.

The equation was never intended to give an absolute number, though it is often used that way. There are also alternatives such as the Sara Seager’s equation, which focuses on our ability to detect civilizations indirectly rather than requiring active communication. Just because an alien civilization is quiet, that doesn’t mean we can’t see evidence for them. Seager’s approach is to focus on stable red dwarf stars with known potentially habitable worlds. Since red dwarf stars are by far the most common, the odds that we’d find alien life near such a star is higher. She then focuses on planets that transit their home star from our vantage point and are near enough that we have a chance of observing the effects of the planet’s atmosphere on the star’s light. She estimates that there might be two inhabited worlds might be detectable in the next ten years.

Of course this presumes that life forms readily on a habitable planet and survives billions of years, which might not be the case.

Click here to read more.

Source: EarthSky

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