For centuries, Earthlings have gazed at the heavens and wondered about life among the stars. But as humans hunted for little green men, the extraterrestrials might have been watching us back.
In new research, astronomers have drawn up a shortlist of nearby star systems where any inquisitive inhabitants on orbiting planets would be well placed to spot life on Earth.
The scientists identified 1,715 star systems in our cosmic neighbourhood where alien observers could have discovered Earth in the past 5,000 years by watching it “transit” across the face of the sun.
Among those in the right position to observe an Earth transit, 46 star systems are close enough for their planets to intercept a clear signal of human existence – the radio and TV broadcasts which started about 100 years ago.
The researchers estimate that 29 potentially habitable planets are well positioned to witness an Earth transit, and eavesdrop on human radio and television transmissions, allowing any observers to infer perhaps a modicum of intelligence. Whether the broadcasts would compel an advanced civilisation to make contact is a moot point.
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