Yesterday the internet was abuzz with talk about UFOs and the Roswell   
   incident, which took place 66 years ago this week.   
      
   Discovering life beyond Earth has always been considered by some to be the   
   holy grail of science. However, no little green men or even measly microbes   
   have been conclusively found. But this hasn’t dampened the enthusiasm among   
   astronomers who are still    
   searching the cosmos for signs of extra-terrestrial life.  The current leading   
   search method uses giant radio dishes to scan the stars, listening for   
   possible faint signals coming from distant civilizations.   
      
   National Geographic News caught up with SETI (Search for Extraterrestrial   
   Intelligence)  radio astronomer, Andrew Siemion, who is based at the   
   University of California at Berkeley, to chat about how astronomers listen for   
   aliens.   
      
       
      
   What kind of alien signals are scientists looking for?   
      
   There are intentional signals – much like a lighthouse or a beacon – [that]   
   can produce an emission intentionally designed to produce a signal so that   
   other intelligent life know they exist.   
      
   Then there is leakage signal — akin to our aircraft radar, and TV broadcasts.    
   A signal like this, however, would have to be very powerful for us to be able   
   to detect this right now from Earth.  For example, the farthest we could   
   detect signals like what    
   we are leaking right now with our current technology is probably at best only   
   1 light year out. [The nearest star to Earth is Proxima Centauri at 4.3 light   
   years.]   
      
   However if we allow extraterrestrial (ET) telescopes to get large – say a   
   radio telescope that has the diameter of the Earth – then they could detect   
   very weak signals.   
      
   Many in the SETI community believe that the first signals we may detect will   
   not be leakage signals but intentional ones designed to notify others of their   
   presence.   
      
   But new telescopes are coming online soon, like the Square Kilometer Array,   
   the largest radio telescope ever built in history. It will have 10 times the   
   collecting area of the Arecibo radio telescope in Puerto Rico, and will be   
   sensitive enough to ET    
   signal leakage from 5 to 10 stars of the nearest stars.   
      
       
      
   Any region of the sky that current searches find particularly exciting?   
      
   In just the last two years NASA’s Kepler planet-hunting mission has taught us   
   is that most stars have planets.  We are also learning that the habitable   
   zones are much broader than what we [previously] thought.  We know there are   
   lots of way to get the    
   heat needed to keep water in its liquid form.  What this means is that we are   
   really starting to expand our ideas about the kind of conditions that would be   
   necessary for life to emerge.   At SETI today, we not only do all-sky surveys,   
   but  more and more    
   targeted searches too – focusing on the nearest stars to the Earth.   
      
   Research is showing us that 10 to 15% of stars have a planet in the habitable   
   zone -where liquid water could exist on the surface.   
      
   Because our equipment is not that sensitive it’s best for us to look at stars   
   that are closest to Earth.   
      
   One of my proposed studies plans on focusing on just that – the 100 nearest   
   stars to the Earth.   
      
       
      
   What are the biggest advances since the start of SETI that allow us to focus   
   these searches?   
      
   Technologically we have gotten larger and larger telescopes and faster and   
   faster computers. And for radio SETI, the sensitivity of our experiments and   
   the amount of radio channels we can explore is directly related to how fast   
   our computers are. Because    
   we don’t know where ET might be broadcasting it’s a good idea to look at as   
   many channels as possible.  The first experiments decades ago could look at   
   only 10 channels, and now we can look at billions.   
      
   Looking into the future, in perhaps a decade time, we might be able to explore   
   the entire radio spectrum over the entire sky.   
      
   So what this means to me is that, if, after a couple of more decades of   
   searching we haven’t discovered a signal, we may have to fundamentally rethink   
   the way we conduct the search for ET.   
      
       
      
    What do you think are the chances of finding an ET signal?   
      
   Overall the SETI community is optimistic since we continue to learn more about   
   astrobiology, and that conditions suitable for life may be quite ubiquitous   
   and technology is getter faster and more sensitive.   
      
   But the bottom line is that we really don’t know since we are constantly   
   restricted by the fact that we only have a single example of life anywhere in   
   the universe.  That severely limits the amount of statistics we can apply.   
      
   If we could find just one more genesis of life- even if it was just a lonely   
   microbe – I could answer this question much more scientifically and   
   quantitatively.   
      
       
      
   Why do you think we haven’t stumbled across a signal yet?   
      
   The famous Fermi Paradox asks just that: if intelligent life is so common then   
   where are they? My personal opinion is that electrical engineers in the cosmos   
   are pretty rare.   
      
   I think life is pretty common and even intelligent life might be relatively   
   common but technological civilizations like our own may be relatively rare.   
      
   If every star had a planet with intelligent life just like our own, were long   
   lasting and survive their technological development, and was altruistic and   
   decided to signal its presence, we would have already detected something.   
      
   So clearly intelligent life is not that common.  But we need to explore much   
   more of the radio spectrum to really say something more profound about how   
   rare civilizations like our own might be.   
      
       
      
   What is the most likely form of a signal we might find a signal?   
      
   It might very well happen while an astronomer is conducting a new kind of   
   experiment, maybe something that looks at dark energy or dark matter,   
   something that is very sensitive and they encounter something in their   
   observational data they did not expect.   
      
   Perhaps after exhausting all possibilities they may come to the most amazing   
   conclusion about where that anomalous feature in their data is coming from.   
      
       
      
   What would be our response to a true detection?   
      
   Any potential signal will need to be confirmed if it is extraterrestrial in   
   origin. After conducting internal tests to confirm that it is indeed real, we   
   would ask other observatories to check out the candidate signal to look for   
   confirmation.   
      
      
   [continued in next message]   
      
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