After a decadelong journey chasing its target, the European Space Agency's (ESA) Rosetta has today become the first spacecraft to rendezvous with a comet, opening a new chapter in solar system exploration. Comet 67P/Churyumov-Gerasimenko and Rosetta now lie 252 million miles (405 million kilometers) from Earth, about halfway between the orbits of Jupiter and Mars, rushing toward the inner solar system at nearly 34,000 mph (55,000 km/h). The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany it for over a year as they swing around the Sun and back out toward Jupiter again. Comets are considered to be primitive building blocks of the solar system and may have helped "seed" Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through a comprehensive, in-situ study of the comet, Rosetta aims to unlock the secrets within.