Aliens surveilling Earth
You've put up blackout curtains, duct-taped the doors and plugged the chimney. You've disconnected the cable, gotten rid of all room monitors and spent a fortune on a secure phone. And yet ... you still feel like you're being watched. Perhaps your Peeping Tom is more of a Pepping ET. Scientists imagining what Earth looks like from other stars have identified nine exoplanets with a clear view of our planet as it passes in front of the Sun. That means civilizations on those planets can see the Earth. What else can they see? Do they know what you're wearing ... or not?

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.
Transiting planets
© R. Wells

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