How would an alien observer see the solar system?
This is the question that inspired the study by researchers at Queen's University Belfast and the Max Planck Institute for Solar System Research in Germany published in the latest edition of the journal Monthly Notices of the Royal Astronomical Society. Lead author Robert Wells, a PhD student at Queen's University Belfast, says they started with the list of what is now thousands of planets that can be observed from Earth orbiting other stars. One reason they can be seen is that they make a dark spot when passing in front of their star and do it at intervals suggesting they're planets and not comets, giant space ships or Dyson spheres. It doesn't take a rocket scientist (or a PhD student at Queen's University Belfast) to flip that scenario around and figure out that if we can see them, they can probably see us. And, since we always assume that extraterrestrials are smarter than us, they can probably see more than we do.
However the more important factor is actually how close the planet is to its parent star - since the terrestrial planets are much closer to the sun than the gas giants, they'll be more likely to be seen in transit.
You can read the rest of the article at mysteriousuniverse.com
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