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Aliens? Really?!

Following what I started yesterday, let's get look at another topic that makes the rounds in popular astronomy, Aliens. Now, personally, I believe in probability. So, I'm interested in the drake equation, a probabilistic look at alien life. The drake equation takes into account a total of 7 factors, of which we'll look at the fraction of that planets per star could support life. After studying a star, astronomers can define a circumstellar habitable zone or more commonly known as the Goldilocks zone, as a region around the star where a planet can support liquid water. Too close and the planet's water will evaporate and too far and it's water will condense into ice. And this zone is at different distances for different stars given that the brightness of stars varies from one to another. Why is the presence of liquid water essential for life? Are there life forms that are supported by other compounds? These are valid questions to which I don't currently have answers. Maybe you can give me an answer if you do.

Moving on, how can we detect alien life on extra-solar planets? Astronomers are currently studying the atmospheres of extra-solar planets they observe and by studying it's spectrum, they can infer what the atmospheric composition of the planet is. We can then look for compounds that support life on earth to search for life on the extra-solar planet. This is not a conclusive proof but it's a beginning. Maybe aliens will discover humans before we discover them, based the radio waves we're sending out into space, as illustrated in this comic by abstruse goose. Search for hypothetical Dyson spheres are another way of searching for (advanced) alien life. You could also look at the work at Search for Extra-Terrestrial Intelligence Institute or SETI Institute.

You could also read what Randall Munroe, of the webcomic xkcd, has to say about this.

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