The Hardest to find thing in the Universe?

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What is rarer than a shooting star?

Rarer than a diamond?

Rarer than any metal, any mineral, so rare that if you scan the entire earth, all six million billion billion kilos or 13,000,000,000,000,000,000,000,000 pounds of our planet, you would find only one ounce of it?

What is so rare it has never been seen directly, because if you could get enough of it together, it would self-vaporize from its own radioactive heat?

Gallery: What we think Martians look like

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We’ve been conjecturing about life on Mars for centuries. In popular culture, the concept of intelligent life on Mars was championed by astronomer Percival Lowell in the late 1800s and his theories on the Martian canals. Science fiction writers — always game for some reckless conjecture — took up the banner from there. –GALLERY