Why NASA should build an even bigger telescope

Former International Space Station Commander Terry Virtz spent seven months in space. He recently told me his most memorable moments involved staring at the nightside of Earth and noticing how city lights delineate the boundaries of continents and signal politics through the level of illumination that various populated regions exhibit.

Can astronomers follow Virtz’s insights and study city lights on other planets?

Our best chance for imaging city lights outside the solar system is around the nearest star to the Sun, Proxima Centauri, a red dwarf located 4.25 light years away. This star is nearly 600 times fainter than the Sun, and so a planet needs to be 20 times closer to Proxima’s furnace than the Earth is from the Sun, in order for it to support life based on liquid water. In August 2016, astronomers  discovered  a planet weighing 1.3 Earth masses in this habitable zone. Because of its proximity to the star, this planet — Proxima b — is thought to be tidally locked, showing the same side to the star at all times, just like the Moon does relative to Earth. Proxima b has a permanent dayside and a permanent nightside.

If the event Proxima b is already inhabited by a technological civilization, its dayside may be coated with photovoltaic cells to generate electricity that would illuminate and warm the nightside, which is otherwise be too cold and dark for comfortable life.

In a recent scientific paper, my research team showed that NASA’s recently launched James Webb Space Telescope could potentially detect city lights on the permanent nightside of Proxima b. Even if the artificial illumination is as faint as our civilization currently utilizes on the nightside of Earth, Webb could detect it as long as it was limited to a frequency band that is a thousand times narrower than the starlight. Future space telescopes, like NASA’s proposed Large Ultraviolet Optical Infrared Surveyor, will be sensitive to even fainter levels of artificial illumination on the nightside of Proxima b. In another paper, we showed that a substantial coverage of Proxima b’s dayside with solar panels is detectable on its own, based on its characteristic spectral edge in reflecting starlight.

Proxima b orbits its star every 11.2 days, making birthday celebrations 30 times more frequent than on Earth. The high demand for bright lights during birthday parties on the nightside of Proxima b would be a reason for us to celebrate as well, if the signal would be noticed by our future telescopes.

Obviously, we could also search for bright artificial lights on spaceships moving through space.

But how far away could our deepest image of the universe detect a single city? I, and a colleague, calculated that the Hubble Ultra Deep Field could notice a city like Tokyo on a spaceship that is 30 to 50 times farther than the Earth-Sun separation. 

But most importantly, if Webb will discover city lights on Proxima b, NASA should consider building a bigger telescope that will trace these faint lights to learn about the continents and politics on this distant planet.

Avi Loeb is head of Harvard’s Galileo Project, a systematic scientific search for evidence of extraterrestrial technological artifacts. Loeb is the founding director of Harvard’s Black Hole Initiative, the director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and he chairs the advisory board for the Breakthrough Starshot project. He is the author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.”