SETI.org
The Allen Telescope Array looks out for signs of extraterrestrial intelligence in space.
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updated 10/28/2011 12:17:40 PM ET 2011-10-28T16:17:40

Any intelligent extraterrestrial life that exists probably won't announce itself by blowing up the White House, or win over the hearts of children as a lovable alien with a glowing finger. Many scientists simply hope to find evidence of them by scanning the skies for a radio signal from a distant star's alien civilization. But such efforts may also risk overlooking clues of past alien activity right here on Earth.

If aliens did leave their mark on Earth by some wild chance, we could search for the possible "footprints" of alien technology or even analyze the DNA of terrestrial organisms for signs of intelligent messages or tinkering. Such a CSI-style forensics search could complement, rather than replace, the outward-looking search for extraterrestrial intelligence, said Paul Davies, a physicist and cosmologist at Arizona State University in Tempe.

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"My proposals aim to spread the burden from a small band of heroic radio astronomers to the entire scientific community," Davies said. "Projects like genomic SETI are an attempt to complement radio SETI, not undermine it."

Davies wants scientists to broaden their thinking about how aliens could have left behind their mark. Having worked with SETI for three decades, he has written about his ideas in a book, "The Eerie Silence" (Houghton Mifflin Harcourt, 2010) and articles such as one that appeared in the online August edition of the journal Acta Astronautica.

But Davies does not think such intelligent alien life must necessarily exist. And his many years of supporting SETI have not stopped him from describing the needle-in-a-haystack search as "a search without any clue as to whether there is a needle there at all, or how large the haystack may be."

Alien signposts
To their credit, SETI astronomers have not ignored the possibilities beyond extraterrestrials deliberately beaming a message straight at Earth. Suggestions over the past 50 years include extraterrestrial radio traffic that happens to pass by, or a powerful radio or optical beacon that sweeps the Milky Way galaxy like a lighthouse.

A very advanced alien civilization might have built huge astro-engineering projects called Dyson spheres to directly tap the power of stars. By putting a shell of material around a host star, aliens would not only trap much of the star's heat, but also create a unique infrared signature that Earth astronomers could detect.

Just as Earth sends out robotic explorers, an alien civilization could have left behind dormant probes at strategic locations such as in the asteroid belt. Earth astronomers could try searching for such probes or even beaming "hello" radio messages to suspected locations in an attempt to "wake up" the probes.

Left behind
There's also a chance that past visits to Earth by intelligent aliens left signs much closer to home. But probability and the length of the universe's age suggest that any such alien visit would have taken place before humans ever emerged on Earth, Davies said.

That means any traces of an alien visitation would have had to survive for hundreds of millions or billions of years for humans to still find them today.

Darryl Leja , NHGRI
This illustration of a mouse's tail that transforms into a strand of DNA depicts the fascinating possibility of aliens using bioengineering to leave behind unintentional or intentional traces or messages in the  DNA of life on Earth.

"If there is another form of life on Earth, we could find it within 20 years, if we take the trouble to look," Davies told Astrobiology Magazine. "Of course, it may not be there, but searching our own planet is far easier than searching another one."

Non-human deposits of nuclear waste consisting of plutonium would point to artificial origins, because natural deposits would have long since decayed, Davies said. Scars of mining or quarrying could remain buried beneath the Earth or on its moon.

Alien "messages in a bottle" or artifacts similar to the monoliths of "2001: A Space Odyssey" would seem less likely to survive for hundreds of millions of years on Earth because of geological and weather forces.

Shadow life
Perhaps the most fascinating possibility is if aliens used bioengineering to leave behind unintentional or intentional traces or messages in the DNA of life on Earth. The self-perpetuating nature of life forms could help ensure survival of any such biologically embedded messages.

Citizen scientists and school students could pitch in to run genomic versions of SETI programs to find any such traces, Davies said. Data-mining software programs could do much of the heavy lifting as just a small part of the usual genomic analyses going on in everyday research.

Alien bioengineering might have also created a "shadow biosphere" of life built upon biochemistry separate from that of Earth life forms. Examples would be life forms that don’t use DNA or proteins, or incorporate different elements in their biochemistry than all other known life forms on Earth do.  Scientists have already begun major efforts to find shadow biospheres, but of natural  rather than artificial origins.

If scientists find "weird" shadow organisms that arose separately from the Earth life forms we know, that won't necessarily suggest intelligent alien involvement. But such a find could give more credibility to the idea that life has a good chance of arising when given the right circumstances, rather than simply being a one-time freak accident, Davies said. And that might make everyone feel a little less alone.

This story was provided by Astrobiology Magazine, a web-based publication sponsored by the NASA astrobiology program.

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Interactive: Calculate the chances of finding E.T.

Explainer: SETI: 50 years of searching for E.T.

  • Somewhere out there, alien civilizations might be communicating with each other. They might even be trying to contact us. In 1960, this reasoning compelled astronomer Frank Drake to point a radio telescope at the stars and listen for chatter. He didn't hear E.T. calling us, calling home, or calling anywhere else during his four-month-long experiment at the National Radio Astronomy Observatory in Green Bank, W.Va., but the effort officially kicked off what is known as SETI, the search for extraterrestrial intelligence. Click the "Next" label to check out highlights from the first 50 years of the search.

    — By John Roach, msnbc.com contributor

  • 1974: Earthlings send message to aliens

    By 1974, Drake and his colleagues still hadn't heard anything from ET, but they hadn't given up hope. Instead, they sent a message out to the aliens with the Arecibo radio telescope in Puerto Rico, the first deliberate message sent from Earth out to the stars. The message contained information about life-giving chemicals, DNA, a simple drawing of our solar system, and pictures of human beings and the Arecibo telescope. The string of 1's and 0's was sent to a group of about 300,000 stars in called the Great Cluster in Hercules, Messier 13, about 25,000 light years away.

  • 1977: The Wow Signal

    Courtesy of Jerry Ehman / Bigear

    Did E.T. make a prank call to Earth on Aug. 15, 1977? We may never know for sure, but astronomer Jerry Ehman was struck enough by a string of letters and numbers on a printout of radio data from the Big Ear Radio Observatory at Ohio State University to scribble "Wow!" in the margin. The extraordinary signal might have been E.T., or something else. Whatever it was, astronomers have been unable to find it again despite dozens of searches, leaving open the possibility that E.T. called but hung up after the first ring.

  • 1992-1993: NASA's brief search

    U.S. Senate Historical Office

    Exactly 500 years after Christopher Columbus arrived in the New World, NASA officially launched its SETI program, the High Resolution Microwave Survey. Experts called it the most ambitious and technologically advanced alien-search effort ever conducted, but after just a year of operation the program was squashed. Sen. Richard Bryan, D-Nev., shown here, led the effort to kill the program, telling the Senate that "millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval."

  • 1995: Project Phoenix rises from ashes

    Image: Paraffin candles
    Seth Shostak / SETI Institute

    When NASA funding for alien searches ran dry, private enterprise picked up the pieces - including some of NASA's equipment - and launched Project Phoenix. The targeted search focused on about 1,000 stars thought most likely to harbor alien civilizations and was conducted at various radio astronomy observatories around the world. In this image, SETI Institute astronomer Seth Shostak looks for E.T.'s call on a computer bank at the Arecibo observatory in Puerto Rico.

  • 1999: SETI for the masses

    SETI @ Home / UC-Berkeley
    Five million Internet users have contributed more than 3 million years of processing time to the search for signals from extraterrestrial civilizations through the SETI @ Home screensaver program, shown here.

    Hundreds, then thousands, and ultimately millions of computer users around the world got in on the search for E.T. with the 1999 launch of SETI@home, a distributed computing project run at the University of California at Berkeley. The program enlists personal computers to sort through the mountains of SETI data, one chunk at a time, collected by the Arecibo radio telescope. The combined power of all the computers running the program essentially acts like a super duper supercomputer, but at a fraction of the cost.

  • 2007: Telescope array turned on

    For most of the past 50 years, SETI projects have required astronomers to wait in line for time on giant radio telescopes around the world. That changed in 2007 with the opening of the Allen Telescope Array, a constellation of 42 radio telescopes with 20-foot-wide dishes in the scrublands about 300 miles northeast of San Francisco. The array, privately financed by software billionaire Paul Allen and others, puts the search for E.T. front and center. The project is jointly run by the SETI Institute and the University of California at Berkley. In the coming decades the array may grow to 350 antennas, making it one of the most powerful radio telescopes in the world.

  • The future of SETI

    NASA
    An artist's interpretation of the Kepler observatory in space. Credit: NASA

    As of this writing, extraterrestrials remain elusive, assuming that they exist at all. Given that the search is only 50 years old, many astronomers see little reason to despair - things are just getting going. NASA recently lent a new hand to the search with its Kepler mission, a space telescope that is looking for Earthlike, habitable planets around thousands of stars in our Milky Way galaxy. Detection of these planets will help SETI scientists focus their efforts.

    Other ideas include a push to expand the search beyond just radio signals. Paul Davies, a physicist at Arizona State University and author of several popular science books, argues that messages from E.T. might even be floating around in the junk DNA of terrestrial organisms and that we should start searching decoded genomes for the biotech equivalent of a message in a bottle.

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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