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David A. Aguilar / CfA
If an alien civilization builds brightly lit cities like those shown in this artist's conception, future generations of telescopes might allow us to detect them.
Astronomers suggest that artificial illumination creates a signature that could point to the existence of civilizations on other worlds — and they say we should get started on a survey of the edges of our own solar system, just in case.
The suggestion comes from Harvard's Abraham Loeb and Princeton's Edwin Turner, in a research paper submitted to the journal Astrobiology. A version of the paper appears on the arXiv.org preprint server and sparked a write-up today on Technology Review's Physics arXiv Blog.
Loeb, who chairs Harvard's astronomy department and is affiliated with the Harvard-Smithsonian Center for Astrophysics, acknowledged that detecting aliens by looking for the glow of their cities would be a long shot. But he pointed out that the cost of the exercise would be low.
"We say that we can piggyback on existing surveys that people are doing anyway. There's no need to use extra resources. ... My philosophy is simple: If we can do it, why not do it and check? Why put blinders on ourselves?" Loeb told me today.
Here's how the idea could work: An object's brightness varies with distance, but the relationship between those two factors will depend on whether the brightness is due to reflected sunlight or due to illumination from the object itself. For a self-illuminated object, the brightness varies by a factor of 1 over the distance squared, but "if you have an object that reflects light from another source ... the flux dies out like 1 over the distance to the fourth power," Loeb said.
Monitoring the changes in the brightness of an object on the edge of our solar system, in a broad disk of icy material known as the Kuiper Belt, could provide a "very simple test" to determine whether extraterrestrials have turned on the lights, Loeb said.
"We conclude that existing telescopes and surveys could detect the artificial light from a reasonably brightly illuminated region, roughly the size of a terrestrial city," on a Kuiper Belt object, Loeb and Turner write.
NASA
The lights of Cairo, Alexandria and the Nile shine through the night on Oct. 28, 2010, as seen from the International Space Station. Astronomers say such illumination could serve as a tip-off in the search for civilizations on other worlds.
How likely is it that E.T. would be found on the edges of our own solar system? Not that likely, but Loeb and Turner speculate that it could happen. "Artificially lit KBOs [Kuiper Belt objects] might have originated from civilizations near other stars," they write. "In particular, some small bodies may have traveled to the Kuiper Belt through interstellar space after being ejected dynamically from other planetary systems."
In addition to the E.T. search, Loeb said the Kuiper Belt survey would also be useful for studying how Kuiper Belt objects reflect light at different points in their orbits. "Even if the answer is, 'No, there is nothing peculiar,' we can still learn something from doing that," he told me. "And if there's something out there worth finding, that could change our perception of our place in the universe."
The technique could conceivably be extended to other stars once next-generation telescopes such as the James Webb Space Telescope and the Giant Magellan Telescope come online, over the next decade or so. There's been a lot of debate over whether the traditional search for radio signals from alien civilizations might be fruitless if E.T. moved beyond analog radio transmissions — and the search for artificial illumination could be worth checking out as a new frontier.
Someone could even try looking for the spectral signature of artificial light. (Do aliens use incandescent bulbs, compact fluorescent or LEDs?) But that particular kind of search would not be easy.
"For this signature to be detectable, the night side needs to have an artificial brightness comparable to the natural illumination of the day side," Loeb and Turner write. And when you consider that Earth's day side is about 600,000 times brighter than the night side, that means E.T. would have to cope with one heck of an electric bill.
What do you think about the search for E.T.'s city lights? Feel free to add your comment below.
More about the search for extraterrestrial intelligence:
- Donations revive the SETI quest
- Gallery: Four decades of SETI
- Alien-hunters add super-Earths to their list
- A new idea in the search for E.T.'s footprints
- More from Cosmic Log about aliens ... and about SETI
Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.
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Obama has certainly wasted taxpayer money on more ridiculous programs. I say go for it.
My first thought when I started reading the article was "Oh! Duh." The idea seems so obvious, but as the article points out, it would take some really good telescopes to detect such lights.
I just have to say "@!$%#ing brilliantly simple"!
The US's budget for NASA is less than 1% of the feds yearly budget........they spend that in a couple weeks normally. For all the things the gov. is doing wrong and wastefull, you think this is a problem?! Are you ****ing kidding me? Don't call your congressman call a doctor that specializes in dealing with dumb people
hey you up there please pull down the window shade. lol
What if they can see in the dark? What if they go to bed early? So many questions to be answered by science.
and the winning doppler shift frequency is? they are at least hammering out the right steps, coupled with planetshine and perhaps choosing a couple of gas spectra, say methane and co2.....hmmm....I say they gotta sit at the drawing board just a bit more before they come out with a new space telescope proposal for spotting et's home...meanwhile, back at the ranch, an offshoot of this may well be an alogarithm or two and some cool optics that would help see those ncc=1792 beacons at a parsec or more, best if they work at detecting navigation lights that are moving at warp speed....warp speed or not, a us made 100 year starship would do well to gear up with a couple of different types of long range sensors......this being one of them...I suggest a scale model of this 100 year space ship that starts out with us constructing platforms that we keep sending out to the kupier belt AND back, tweaking and adding to the experiments continually..(from a MOON BASE, kids)..thats where a new space telescope belongs, on something that we send out to the edge of our realm and back....maybe it would prove critical in relaying data from the voyagers as they blaze forward......if after a few years from now our government is not moving on this, due to naysayers brimstone sayers or whatever, perhaps it would be best to open source it and make it a world wide project, that'll make it even harder for the gop to capitolize on yet another public project...let alone the other side of the fence that if they did not cut it would surely get their noses down into the trough like all the rest, lets all seven billion of us do something that makes the entire race proud and just friggin ADVANCE a little.....still, supposing something else needs light as we know it is another proverbial shot in the dark (pun intended_
If intelligent life evolved on a Kuiper Belt Object, the ocular systems assuming they have, if any, would have developed in a light-deficient environment. I doubt if they would have a need for artificial light as we do with our extreme differences between day and night.
Yeah, and if you ordered a cheeseburger that came burned, you'd segue into "And Obama burned the voters too!"
The above was a reply to comment #25 but it ended up here. Go figure.
One can assume that there is life out there. The odds are against anyone who assumes otherwise. In the length of time it would take for the light to reach earth, any other civilization would likely be extinct in the present. Because if they are at all like us, the have destroyed their planet and killed each other already long long ago.
Looking for life out there is a waste of time, even if it is there. In fact I don't much like the idea of finding a new group of beings to spend tax money on. If by some odd chance I discover life out there, I'm keeping quiet about it.
You're silly.
So this is why it costs so much to send our children to college. Paying the salary of professors who spend time writing research papers about city lights from distant worlds.
Amen, Danno! University expenses go up 8, 12, 16% per year while the economy is faltering everywhere else. University professors have a sense of entitlement that doesn't admit of making sacrifices like everyone else is making. At least we can expect them to do meaningful research. If I were running a university, I would deny tenure to any professor who dabbles in this nonsense on the university's dime.
One does not need to understand the method of technology in creating a light source to be able to see the illumination that results from said technology. Not a real bright statement there.
and the gammus when connected to the frain can ramistand the colingroce to the 7th triton when compared to the folengrotten which is then produced by the dandercomon!
We have been through this before. Last time it was radio waves. Other beings and places may not be as stupid as we are. They may have developed better sensors and do not need light to see. Good god they may have even figured out Albert E. did not know very much. Mean while, back at the ranch, what have we done to provide a life for 7 billion people?
If it's not "light," then it's not "seeing."
For communicating your existence to other civilizations, it's hard to beat a method that 1) can carry information at high bandwidth 2) can be transmitted in a wide range of directions at the same time 3) carries information at the speed of light. What is it? Why, light (or, more generally, EM radiation, only one tiny spectral region of which we call light). Remember, other civilizations are constrained by the same physics and universal constants that we are.
To answer your question "what have we done to provide a life for 7 billion people?", the answer is "exactly what we've done." A large part of that activity has been to release energy by burning substances deposited on and within the Earth - substances whose stored energy came, by one way or another, from the Sun.
One way of looking at it is that long before humans ever existed, the Sun's energy and physical processes converted materials into other materials (some of which were swimming, slithering, or walking around, or growing up out of the ground at some point in the process) and some of those materials, when burned, release some of that energy back out and become other materials. We're doing that burning and releasing that energy far, far, faster than it was being stored (over timescales of decades versus hundreds of millions of years).
Why do we always keep making the assumption that "because we did it, everybody has to do it that way". Other life forms may not need to use radio and light - they could have other ways we have not imagined for communicating and sensing their surroundings.
it's hard to beat a method that 1) can carry information at high bandwidth 2) can be transmitted in a wide range of directions at the same time 3) carries information at the speed of light. What is it? Why, light (or, more generally, EM radiation, only one tiny spectral region of which we call light).
Life on the edge of the Kuyper Belt? I think you're talking out of Uranus.
The scientific community has established that there are billions of stars and trillions of planets - in our own Milky Way galaxy. Multiply that by billions of other galaxies and there is a 100% that there are 21,000 planets with life out there.
The question isn't whether there is life on other planets. The question is where is it? And yes, those with higher intelligence will not need any type of lighting to land on Earth. If they can travel throught he universe, I am confident that you need some guy holding two orange flashlights instructing them how to land!
Perhaps some of our ignorant people pointed that out. I did the research and math that they didn't - or couldn't. It would indeed take a solar complex of a few acres. About 640,000 acres - bigger than Hong Kong; smaller than Rhode Island. But that number would only be relevant if the complex were in direct overhead sunlight 24/7/365; you would need an array perhaps ten to twenty times that large plus the ability to store most of the power being generated at any given time.
Good lord, I'm not sure I'd want our local power provider, National Grid (National Greed) to get wind of this as they'd probably raise their rates again!
Someday, we will deploy a very long baseline space interferometer (possibly at the 5 Lagrangian points) which will have resolution equivalent to a conventional telescope of many millions kilometers diameter. This should provide us the ability to directly visualize extrasolar landscapes.
It might also allow us to visualize our own distant past if we are able to locate a suitable reflection (i.e. gravitational mirror). That is, admittedly, a far-fetched proposition. But, it is theoretically possible.
That is the problem with much of this discussion. We confuse what is theoretically possible with reality. Yes, it is theoretically possible that advanced civilizations are out there just waiting to be found. But the reality is we've been looking since Schiaparelli thought he saw canals on Mars, and we haven't found a thing. We don't find them because they don't exist--not, at least, within a range that would have any meaning for us. We are alone within our corner of the universe; our existence is precious for its uniqueness; and we'd better start acting like what we have here REALLY matters.
Joyce-4263422
Obama has certainly wasted taxpayer money on more ridiculous programs. I say go for it.
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America's elder statesman of finance, Alan Greenspan, has shaken the White House by declaring that the prime motive for the war in Iraq was oil.
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Bush gives new reason for Iraq war
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I can't believe the ridiculous comments I'm reading here. All of a sudden everyone is an EXPERT on astronomy & physics & alien technology & behavior? Give me a BREAK! Do you REALLY THINK these people are stupid? Do you think they don't understand the practical considerations AT LEAST as well as all of us? Did you read the part where they said it wouldn't require anything that isn't already going to be in use, & all it would require is for someone to take the time to do it? Or the part about how even if we don't find any "alien cities," it would still be helpful in other ways?
Or maybe you just think this entire space travel & exploration isn't important? We shouldn't be "wasting money" on something so impractical? Anybody have ANY IDEA how many of our modern comforts are a product, directly or indirectly, of the space programs? Or how much we actually SPEND on it, particularly in comparison to some of the REALLY EXPENSIVE & USELESS things we fund? Unbelievable. This subject, and the debate around it, really displays both the BEST and WORST of humanity.
What if ET is out there and is avoiding us? Maybe ET doesnt want us to know they are there? With all the TV and radio signals not to mention all the light we spew into the sky on a daily (and nightly) basis you would think somebody(or thing ) would have noticed by now. Just sayin.
to junicons comments... life tends to fill nitches. it will fill each and every knitch it can. look how many life forms our own planet has spawned...and still it tries new variables. i guess what i am saying is that a world will try many differing life forms and the chances are better then one would think that creatures such as our selves would exist.
also things such as eyes,hearing,touch and so forth would or should hold true even on other worlds. (vibration scenceing as well) we have millions of different life forms here on earth. but smell,touch,sight and sound are rules that apply to most of them. think this would still hold true on other worlds as well. i am not saying a world could not have blind cold blooded creatures. just that as a mathmatical guess most worlds with life would follow closer to ours then not.
Then why is a banana shaped to fit perfectly in our hand?
You can't explain that?
/We'll do it live!!!
Anyway. I think that sensory organs form based on the surroundings. Not EVERYTHING has eyes, ears, olfactory senses, etc.
Many of the most successful creatures on this planet have a permeable membrane and scoot around forming tiny pseudopods.
In general, if we find intelligent life somewhere else, even locally in our galaxy, they could be vastly different in appearance and function than humans. Heck, we humans are actually pretty lucky to be the most technologically advanced organism on our planet, most creatures have more than 2 legs, and quite a number of the most intelligent ones are either equipped for swimming in the oceans or are 7-10 feet tall with long noses and huge tusks.
...perhaps the key to our success started with our opposable thumbs and our need to adapt where our bodies could not naturally do so.
Long-story-short, who knows how environments on other worlds may have played favorites with a different type of life form to become intelligent and technologically advanced. Intelligent life on Earth also could have looked a lot different if we didn't have cyclical ice ages and disease and a large meteorite didn't wipe out the Dinosaurs...not to mention the other extinction events in Earth's recent natural history.
I think we as a spiecies have a limited amount of resources to travel to other planets. the distances are vast and even at great speeds would take lifetimes. if we do not use our resources wisely we will some day loose the ability to travel to other worlds. it is much harder then we would like to think it is. MUCH MUCH harder. if ever our world starts to die or we are faced with a catacylismic event, as of now we would die. to explore space is the next great frontier, think of things we would find.... minerals, chemicals,life forms,vistas and images, space to live. I also think that most "living" planets would be on a scale of 2 to 3 times ours in size so the life forms would be larger as well. (james camoron i think got that correct on avitar) look at the creatures our own little planet spawned...t-rex, mammoths, huge huge creatures. now make our world 3 times the size...to me its fun to think about space and other worlds, i would veture to say our own imaginations could not come close to the reality of what is in our universe.