They begin life as notions, as questions or hypotheses. In time they turn into elaborate sculptures of metal, epoxy and silicon. In sudden eruptions of fire and billowing smoke they are tossed up and out of the atmosphere, out into the cold void between worlds. Streaking like bullets across the immense expanses of the solar system, they carry armadas of instruments to catalog and analyze all that they pass — chattering away back to their human parents with tiny electronic voices across hundreds of millions of miles.