Triton, Neptune

Are we alone in the universe? If you consider how vast space is, such a possibility seems extremely unlikely. In the Milky Way alone, there are billions of star systems similar to ours, up to half of which could have an Earth-like planet, according to one model. 

If life exists outside of Earth, it’s been awfully quiet. That’s what physicist Enrico Fermi famously pointed out when he blurted out “Where is everybody?” during a discussion of intelligent alien life. But the so-called Fermi paradox hasn’t stopped scientists from scouring space for signs of life — from residues of microbial life to advanced alien technology. 

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