---

Since it’s launch in 2009 NASA’s Kepler spacecraft has identified more than 1,000 exoplanets, but we may not be the only ones looking for intragalactic neighbors. Recently, McMaster’s Ralph Pudritz and his former post-doc René Heller have proposed a new strategy to find alien civilizations which may have already identified Earth as a habitable planet.

Since exoplanets are too far away to observe directly, the Kepler spacecraft identifies exoplanets by looking for a tell-tale dimming of the signal from potential host stars indicating that a planet or moon is transiting the star, passing between the star and our observation point within our solar system. This method has given Earth astronomers a wealth of information about planets outside our own cosmic backyard such as surface temperature and stellar illumination information to identify the potential for a planet to host life. Understanding that strategies similar to our own would likely be used by distant astronomers, Ralph and René have taken a unique new approach by asking: What if extraterrestrial observers detect Earth as it is transiting our sun from their perspective?

In a paper to be published in the journal Astrobiology, Ralph and René suggest that our search for evidence of extraterrestrial civilizations should be focused within Earth’s “transit zone” – the slice of the galaxy from which an observers could see Earth passing between their vantage point and our home star. This allows us to narrow our search for extraterrestrial life to the zone where extraterrestrials could “discover” Earth and would be likely to attempt to initiate communications or send a signal. The transit zone offers approximately 100,000 potential host stars for planetary systems observable using our current radiotelescope technologies, including some as close as 4 parsecs away. Astronomers worldwide have already launched a comprehensive search for signals sent by intelligent life from other parts of the galaxy. Ralph and René propose that the Breakthrough Listen Initiative, an important part of this search, can maximize the chance of receiving such a signal by concentrating their search within Earth’s transit zone where it is most likely that we have already been identified as a habitable or life-bearing planet.

Their strategy has recently been highlighted inNature, covered by theCBCand reported in the McMasterDaily News.