Whoa.
Either those circles are just from center-pivot irrigation, or the aliens have arrived en masse.
Actually, these strange circles on Google Maps are exactly that: the result of circle irrigation, a method some farmers use to water crops. You know, by rotating sprinking equipment in a big circle. Better coverage that way, I guess.
The above images are from the Google Maps view of Earth, Texas, by the way, and you can check it out yourself here.
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