Detecting extraterrestrial cities on exoplanets becomes possible

May 15, 2012
By Michael Salla, Ph.D.

An artist's concept of 55 Cancri e, a hot "super-Earth" that orbits its sun every 18 hours. Credit: NASA

For the first time, NASA has been able to detect infrared light from a rocky “super-earth” variety of exoplanets. The Spitzer Space Telescope detected infrared light from the exoplanet “55 Cancri e” which has a rocky core and is nearly twice the Earth’s diameter, and eight times its mass. While 55 Cancri e is much too close to its sun – 55 Cancri A – to sustain life as we know it, the detection is a historic first for NASA. The detection of infrared light on the super-earth category of exoplanets, prime candidates for finding extraterrestrial life, makes possible the discovery of alien cities in distant solar systems. On May 8 NASA announced: “NASA’s Spitzer Space Telescope has detected light emanating from a “super-Earth” beyond our solar system for the first time. While the planet is not habitable, the detection is a historic step toward the eventual search for signs of life on other planets.”  According to Dario Borghino from  Gizmag: “This marks the first time that light has been detected from a planet of such a small size, and the find is telling astrophysicists where to look in their search for signs of life on planets beyond our own.”

The plot shows how the infrared light from the 55 Cancri system, both the star and planet, changed as the planet passed behind its star. Credit NASA.

The Spitzer Space Telescope was launched by NASA in 2003 and studies the universe in infrared light. In contrast to the Kepler Space Telescope that studies how distant stars dim as exoplanets cross in front of them, Spitzer analyzes infrared light directly from the exoplanet itself. Basically, as the exoplanet goes behind the sun, the total infrared light from the sun and exoplanet dims. In the NASA statement announcing the finding, the infrared light coming from both “55 Cancri e”  and its sun were analyzed in the attached table (on right).  As 55 Cancri e” dropped behind its sun, the total thermal emission dropped, and increased when the exoplanet appeared again in its orbit. This raises the question, could Spitzer detect a large extraterrestrial metropolis giving off heat in a distant world? We can look for an answer from Dr. William Danchi, Spitzer program scientist who states:
The radiation that is measured is in the infrared, which is sensitive to the composition as well as temperature of the atmosphere of the planet. Spitzer was able to measure such a small diameter planet because it was hot, and hot objects emit exponentially more photons that cool objects. It would be much harder to detect a small, cool planet.
An earth like planet in a distant solar system orbiting the habitable region of its solar system, would be much cooler than 55 Cancri e which is much closer to its sun, but what if the habitable exoplanet was covered by very large extraterrestrial cities generating vast amounts of heat? Could the thermal infrared signature of an alien New York City be seen using the detection method pioneered by the Spitzer telescope?

Infrared satellite image of New York City, USA.

While Spitzer may lack the detection sophistication to measure the thermal signature of large alien metropolises, its replacement, the James Webb Space Telescope is being promoted as having such a capacity. According to NASA: “The [Spitzer] spacecraft is pioneering the study of atmospheres of distant planets and paving the way for NASA’s upcoming James Webb Space Telescope to apply a similar technique on potentially habitable planets.” The James Webb telescope launches in 2018, until then, we will have to rely on the Spitzer telescope which officially retires in 2014, to find an alien New York City.
© Copyright 2012. Michael E. Salla. Permission is granted to include extracts of this article on websites and email lists with a link to the original. This article is copyright © and should not be added in its entirety on other websites or email lists without author’s permission. Further Reading



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