"Death comes to all, but great achievements build a monument which shall endure until the sun grows cold." -Ralph Waldo Emerson
In the great cosmic ocean, there's only one planet that we know -- for certain -- has the right conditions and history to result in intelligent life: our own.
Image credit: NASA, from the Space Shuttle, for Sun-Earth Day 2008.
Life -- or even intelligent life -- may be possible in environments vastly different than our own: around different classes of stars, at different temperatures, and even with different molecules and/or chemical elements.
But we know for…
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