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 seem 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."
[caption id="attachment_94949" align="aligncenter" width="640"] Diagram of a planet transiting in front of its star. Left: The lower black curve shows the brightness of the star noticeably dimming during transit when the planet is blocking some of its light. Right: Observer on green exoplanet is in the transit zone and can see transits of the Earth. (Credit: R. Wells)
These zones of transit are called ‘transit zones’ (astronomers haven’t been able to come up with clever names since the ancient Greeks) and, as Wells points out, planets that are solid and close to their star – like Mercury, Venus, Earth and Mars in our solar system – are more likely to be seen in the transit zones than larger gas balls like Jupiter, Saturn, Uranus, Neptune and (fill in your favorite political figure here). Based on that, they determined that at most three planets could be seen crossing in front of the Sun at any one time.
Seen by whom? Looking at (and imagining looking from) the thousands of known exoplanets, they determined that an observer on 68 of them could see at least one planet on our transit zone and nine of those would be in the ideal position to see the Earth. If you’re planning to put up a lead umbrella in their direction, those Peeping ET planets are HATS-11b, 1RXS 1609b, LKCA 15b, WASP-47b, c, d, e, WASP-68b, and WD 1145+017b. You can find their stars and location in the The Extrasolar Planets Encyclopaedia.
Should nudists and the paranoid be concerned about being observed? The good news is, none of these exoplanets are in so-called habitable zones that could support life – at least life as we know it that has at least one eye to press against a telescope. The bad news is, exoplanet detection projects like SuperWASP and Kepler are bound to find more and – statistics being what they are – will certainly find one or more that could sustain peeping life.
Put some clothes on.