We could see the light from Alien cities in the Kuiper Belt!

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 lam posts 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, back scattering,
surface shadowing, out gassing, 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.”
More information: Read Loeb and Turner’s
paper: Detection Technique for Artificially-
Illuminated Objects in the Outer Solar System and
Beyond.

Source: Universe Today