City lights may aid in search for extraterrestrial life


November 7, 2011

The Earth's lights from space (Image: NASA)

The Earth's lights from space (Image: NASA)

Image Gallery (5 images)

It's difficult to look at the night sky and not wonder whether intelligent life exists out there. Indeed, the odds are very much in favor of there being countless civilizations scattered throughout the heavens, but the challenge remains in proving it. Recently, two scientists hit upon the novel but common-sense idea of searching for city lights on the dark side of distant worlds - a task advanced next-gen earth and space-based telescopes will likely be able to tackle in the not-too-distant future.

We've all seen the beautiful images of Earth's nighttime tapestry and, indeed, science fiction abounds with the imagery of developed planets glowing at night. Still, Harvard astrophysicist Abraham Loeb and Princeton astronomer Edwin Turner hadn't considered the possibilities lit-up alien cities might offer until they attended a meeting with their colleagues in the Middle East.

"Both Ed and I were attending a conference in Abu Dhabi about novel ways to detect life, and we had a tour guide on a trip to the nearby emirate of Dubai who bragged that it was so bright at night that you could see it easily from space -- that's what gave us the idea," Loeb told Astrobiology Magazine .

To test their concept, Loeb and Turner made calculations based on a non-existent planet in the Kuiper Belt, a region in space that contains billions of comets and extends from about 30 to 50 astronomical units (AU). One AU is the distance from the Earth to the sun, almost 93 million miles.

They found that with existing telescopes, a city roughly the size of Tokyo, approximately 30 miles (50 km) wide, would be readily discernible on a Kuiper Belt object at about 50 AUs distant. With the powerful Hubble orbiting telescope brought to bear, that same city could be visible up to 1000 AUs away, out in the Oort Cloud (another comet-laden region) well beyond our solar system.

"The closest star is 100 times farther than that," Loeb said, pointing out that the day side of our planet is about 600,000 times brighter than the night side. "To see nighttime city lights as bright as Earth's on a world in the habitable zone of the closest star, you would need a telescope with optics at least 100 times wider in diameter than the Hubble Space Telescope's."

The artificial lighting we use on Earth falls into two categories: thermal (from incandescent bulbs, for instance) and quantum (from fluorescent lights and LEDs). Both forms have color spectra that are readily distinguishable from sunlight and could indicate the presence of something other than natural illumination.

It's rather ironic to note that Loeb and Turner's proposed approach to detecting extraterrestrials uses what is essentially light pollution, the very phenomenon which renders ground-based astronomy unfeasible on so much of the Earth today. Hopefully, any aliens that zero in on our lights will turn out to be the friendly sort!

Source: Harvard

Check out the NASA video below for a look at the Earth's bright lights (Credit: Don Pettit (production); Don Pettit and others (photography))

About the Author
Randolph Jonsson A native San Franciscan, Randolph attended the U.S. Naval Academy at Annapolis, Maryland before finding his way to the film business. Eventually, he landed a job at George Lucas' Industrial Light + Magic, where he worked on many top-grossing films in both the camera and computer graphics departments. A proud member of MENSA, he's passionate about technology, optimal health, photography, marine biology, writing, world travel and the occasional, well-crafted gin and tonic! All articles by Randolph Jonsson

Radiowaves and now lighting... why not look for motion too? Transportation could show life forms.

Carlos Grados

The whole theory assumes that other civilisations are as wasteful as we are? I doubt any species that is more advanced than we are will be wasting as much energy in the form of light as we do.

David Anderton

And if they dont need light to see or have no eyes?

Philippe Heeren

Good point by Philippe .... it may be life, \"but not as we know it!\" (credits to Spock).


It is equally likely that they will light the dark side of their planet brighter than we do.


David Anderton: Well, lighting doesn\'t really use that much energy. Lighting currently represents only a smallish fraction of total electricity consumption globally (and electricity consumption as a whole is itself only a part of overall energy consumption).

When more advanced technologies such as LEDs and such become more widespread, the share of lighting energy of the total can be reduced by an order of magnitude or two without reducing the amount of artificial light.

Also, a considerably more advanced civilization would probably have more energy available (via fusion, large-scale renewables or something else).


Agreed with David Anderton, lol Intelligent life is not wasteful..

Look at all the plants and animals that Inhabit our planet... and you will surely understand what I mean.

Philippe H -- true that they are most likely telepathic

Arman Irani

David, why are you assuming they\'d be more advanced than us?


SETI has been around for over 30 years... they\'re searching for radiowaves and such. I could be wrong but I would think that any civilization the was advanced enough to produce artificial light would also be emitting radiowaves of some sort. If a civilization is producing artificial light but not emitting radiowaves then chances are this civilization is many, many years ahead of us technologically and if that is not the case then we could be dealing with a civilization that may not be breathing oxygen.

Dana Lawton

re; Dana Lawton

1. Without the genus of Nikola Tesla radio may not have been invented until much later. While Guglielmo Marconi may have invented radio independent of Tesla\'s previous invention he did so using several of Tesla\'s patented inventions.

2. Depending on the planets ionosphere it is possible that they use radio communications intensively without noticeable signal escaping.

3. Edison inc. was not the first to invent the incandescent light bulb it is just history and technology conspired to make his the one you don\'t need to be a historian to remember. and even so there is still other light sources such as limelight, and gas mantle lamps that can light the night sky effectively if the locals are willing to pay the price.


More advanced != less \"wasteful\" (whatever that means)

We produce more light now than we did 100 years ago. Are we more or less advanced now?

As time goes on, we light more and more things up as our ability to create and consume energy increases. A sufficiently advanced race might never have natural darkness in their cities, or they may indeed see in a different spectrum or not \"see\" like us at all and thus have no or very little visible light.

I\'m just hoping more advanced aliens don\'t have people posting comments without first analysing what they are saying.


I forgot.

4. An alien species, as a whole may see no value in a dark sky, preferring an endless twilight.


The theory assumes two things: 1) That alien life is land based, and 2) That the land based life lives above ground.


Stupid, insulting, contra-progressive, and ridiculous. If ET is smart enough to get to us. Then they are smart enough to detect a \'Cinderella Solar System\' from thousands of light years away. Take their Ph.D.\'s away from them. We are trying to reduce/eliminate Light Pollution, beside to view the stars, it\'s bad for the animals, people physiologically and psychologically. This is the exact thing the National Park Service/Night Sky Team is fighting against. Stupid.

Tom Teters

The idea that... after 5 billion years, intelligent alien life would be right around our level of progress scientifically is insane.

Dana Lawton
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