Aliens Hanging Out in the Kuiper Belt? We Could See the Light from their Cities


When it comes to searching for ET, current efforts have been almost exclusively placed in picking up a radio signal – just a small portion of the electromagnetic spectrum. Consider for a moment just how much lighting we here on Earth produce and how our “night side” might appear as viewed from a telescope on another planet. If we can assume that alternate civilizations would evolve enjoying their natural lighting, wouldn’t it be plausible to also assume they might develop artificial lighting sources as well?

Is it possible for us to peer into space and spot artificially illuminated objects “out there?” According to a new study done by Abraham Loeb (Harvard), Edwin L. Turner (Princeton), the answer is yes.

For gathering light, the array of Earthly telescopes now at science’s disposal are able to confidently observe a light source comparable in overall brightness to a large city — up to a certain distance. Right now astronomers are able to measure the orbital parameters of Kuiper belt objects (KBOs) with the greatest of precision by their observed flux and computing their changing orbital distances.

However, is it possible to see light if it were to occur on the dark side? Loeb and Turner say that current optical telescopes and surveys would have the ability to see this amount of light at the edge of our Solar System and observations with large telescopes can measure a KBOs spectra to determine if they are illuminated by artificial lighting using a logarithmic slope (sunlit object would exhibit alpha=(dlogF/dlogD) = -4, whereas artificially-illuminated objects should exhibit alpha = -2.)

“Our civilization uses two basic classes of illumination: thermal (incandescent light bulbs) and quantum (light emitting diodes [LEDs] and fluorescent lamps)” Loeb and Turn write in their paper. “Such artificial light sources have different spectral properties than sunlight. The spectra of artificial lights on distant objects would likely distinguish them from natural illumination sources, since such emission would be exceptionally rare in the natural thermodynamic conditions present on the surface of relatively cold objects. Therefore, artificial illumination may serve as a lamppost which signals the existence of extraterrestrial technologies and thus civilizations.”

Spotting this illumination difference in the optical band would be tricky but by calculating the observed flux from solar illumination on Kuiper Belt Objects with a typical albedo, the team is confident that existing telescopes and surveys could detect the artificial light from a reasonably brightly illuminated region, roughly the size of a terrestrial city, located on a KBO. Even though the light signature would be weaker, it would still carry the dead give-away – the spectral signature.

However, we currently don’t expect there to be any civilizations thriving at the edge of our solar system, as it is dark and cold out there.

But Loeb has posed that possibly planets ejected from other parent stars in our galaxy may have traveled to the edge of our Solar System and ended up residing there. Whether a civilization would survive an ejection event from their parent system, and then put up lamposts is up for debate, however.

The team isn’t suggesting that any random light source detected where there should be darkness might be considered a sign of life, though. There are many factors which could contribute to illumination, such as viewing angle, backscattering, surface shadowing, outgassing, rotation, surface albedo variations and more. this is just a new suggestion and a new way of looking at things, as well as suggested exercises for future telescopes and studying exoplanets.

“City lights would be easier to detect on a planet which was left in the dark of a formerly-habitable zone after its host star turned into a faint white dwarf,” Loeb and Turner say. “The related civilization will need to survive the intermediate red giant phase of its star. If it does, separating its artificial light from the natural light of a white dwarf, would be much easier than for the original star, both spectroscopically and in total brightness.”

The next generation of optical and space-based telescopes could help to refine the search process when observing extra-solar planets and preliminary broad-band photometric detection could be improved through the use of narrow-band filters which are tuned to the spectral features of artificial light sources such as light emitting diodes. While such a scenario on a distant world would need to involve far more “light pollution” than even we produce – why rule it out?

“This method opens a new window in the search for extraterrestrial civilizations,” Loeb and Turner write. “The search can be extended beyond the Solar System with next generation telescopes on the ground and in space, which would be capable of detecting phase modulation due to very strong artificial illumination on the night-side of planets as they orbit their parent stars.”

Read Loeb and Turner’s paper: Detection Technique for Artificially-Illuminated Objects in the Outer Solar System and Beyond.

This article was inspired by a discussion on Google+.

Nancy Atkinson also contributed to this article.

12 Replies to “Aliens Hanging Out in the Kuiper Belt? We Could See the Light from their Cities”

  1. A civilization, even a very advanced one, surviving their being ejected from its parent star then traveling the billion year journey to our Kuiper belt or having their star die and become a white dwarf seems a little far-fetched to me… although this type of research will be very interesting when we have telescopes powerful enough to get this kind of spectral data from Keplar style planets.

    1. Well, you know… those are just human life scales (not calling it life as we know it). But, a billion years for a ‘living’ crystals might be a totally different scale (not sure what would they need artificial light for though ;D).

      And also you have to consider that even though “it is dark and cold out there.” (Canada?) there still might be something slowly replicating information.

    2. The narrative is extremely unlikely of course. It is a bit of a stretch to think that some ETI could wrangle their planet away from a dying star. It would require some mighty large rocket motors to do that. Secondly, even if they did that they would not remain on the surface, but rather burrow into the deep lithosphere or crust to seek the geo-center’s warmth and energy supply.


      1. @Clay, it’s Kepler. Not Keplar. 😀

        @Martin, I see that the last article with silicon-based life had its effect. 😀 Who cares about living crystals? Americans and Superman. :DD

        @lc, why do you need motors when you get ejected? There was an article on UT about shitloads of planets being ejected from their systems. But, I don’t know, I guess any aliens should have a chance to develop themselves and protect themselves against such horrible things. They should jump to other planet in a system or whatever…

        But, yeah, having an ejected planet with aliens near KBOs seems unlikely especially in our lifetime.

        Also, jumping from KBOs to exoplanets seems like a stretch. Maybe, some example would be great. What could they achieve and when.

      2. While it is true that planets get ejected from stellar systems this is due to some strong orbital resonance with another body. A small terrestrial planet which is in a 2 to 1 orbital resonance with a gas giant could be ejected. However, the orbit was not likely to ever be stable enough for the planet to foster the evolution of life. So if we use Earth as an example, in order to use Jupiter as the “ejector” Earth would have to be moved out beyond the orbit of Mars in order to accomplish this. This requires a considerable amount of planetary engineering and a lot of energy to adjust the orbits of planets.


  2. Every planet that transits its star is showing us a night side . . . So . . . . perhaps by examining the spectra, if we could be sensitive enough, we might find within the overall spectra the evidence that when the transit occurs the tell tale spectra of artificial lights shows up in the data?

  3. OK, this sounds too easy. Technically the instruments need to be sensitive but . . . . every transiting planet such as the thousands that Kepler is finding, has night side pointed right at us. So spectral analysis even though the host star is bright, within that spectra perhaps we could find the evidence of the unique lines of artificial light that would only be there if there was a technological civilization. I mean, if we can build instruments that can analyze the atmosphere of planets like this by spectral analysis, it doesn’t seem to big a stretch to look for the “street lights” does it?

  4. This is an interesting theoretical exercise, but the practical side stinks.

    I wouldn’t preclude the existence of some rare artificial or astronomical object that could be observable under the scenario. (Compare w/ astrophysical masers.) But in general civilizations wouldn’t be expected to put out much light pollution. They would mostly stabilize their population (as we will with next generation) and work towards greater efficiency and less pollution (as we do).

    The main observational efforts will surely be directed elsewhere.

  5. I would posit that the period of time that a civilization or species might broadcast artificial illumination into space on the order of magnitude illustrated in the ISS photo of Eqypt might be, geologically, extremely short, rather like the broadcast of AM radio signals from Earth (being replaced by digital radio noise now). Both mounting scientific evidence and common sense show that this level of waste of resources and environmental disruption are not sustainable. A technological species which hangs around long enough to have reasonable odds of being detected will have had to figure out how to provide artificial illumination (in whatever wavelengths it is sensitive to) in something other than the barbaric “bomb blast” method we see in looking down at Earth today.

  6. When the planet gets ejected from its star system and travels for a long time, get no heat. Life would simply sieze to exist……

  7. When the planet gets ejected from its star system and travels for a long time, get no heat. Life would simply sieze to exist……

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