Curiosity, the largest and most advanced spacecraft ever sent to another planet, stuck its extraordinary landing Sunday night without a hitch and is poised to begin its pioneering two-year hunt for the building blocks of life — signs that Earth's creatures may not be alone in the universe. Applause erupted across the campus of the Jet Propulsion Laboratory in La Cañada Flintridge and engineers inside mission control could be seen hugging and weeping with joy.