A mission to land the first space probe on a comet reaches a major milestone when the unmanned Rosetta spacecraft finally catches up with its quarry on Wednesday.
It's a hotly anticipated rendezvous: Rosetta flew into space more than a decade ago and had to perform a series of complex maneuvers to gain enough speed to chase down comet 67P/Churyumov-Gerasimenko on its orbit around the sun.
The European Space Agency says Rosetta will spend about two years traveling alongside 67P and closely observing the comet. If all goes according to plan the probe will also drop a small landing craft onto the comet's icy surface in November.
Scientists hope the mission will reveal more about the origins of comets and other celestial bodies.