NASA / Reuters

Astrophysicists suggest looking for the shimmering light of cities on far off planets

The nighttime light of cities could be a new target in the search for extra-terrestrial life. A recent paper by Avi Loeb of the Harvard-Smithsonian Center for Astrophysics and Edwin Turner of Princeton University suggests that we should be scouring faraway planets for urban metropolises.

It’s an idea that relies on a lot of assumptions being true, but the basic premise is that if there are planets with human-like intelligent life, they'll likely have invented their way out of the dark nights caused by revolving around a sun. In other words, cities full of lights shining out, waiting to be seen.

But if there are alien mega-cities – and we can only hope that there are – this approach might offer a way to track them down and identify places in the universe where other intelligent life has evolved. Loeb and Turner suggest that the lights of big cities would be a relatively easy tell. The Harvard-Smithsonian Center for Astrophysics explains:

As the planet orbits, it goes through phases similar to those of the Moon. When it's in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the day side. So the total flux from a planet with city lighting will vary in a way that is measurably different from a planet that has no artificial lights.

This sort of observation of far-off planets isn’t possible yet, but telescopes are improving. The researchers note that through their method, telescopes today would be able to observe a Tokyo-sized city as far away as Pluto. Once the hardware is improved, astronomers and scientists might consider pointing their telescopes to the 1,235 Earth-sized planets NASA’s Kepler mission has so far identified.

Loeb concedes that finding an alien city is a long-shot, but that no extra resources would be needed to look. And as our own planet becomes increasingly urbanized, maybe it will be us that gets discovered.

About the Author

Nate Berg

Nate Berg is a freelance reporter and a former staff writer for CityLab. He lives in Los Angeles.

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