On 10 July, ESA's Rosetta spacecraft will fly past 21 Lutetia, the largest asteroid ever visited by a satellite. After weeks of manoeuvres and a challenging optical navigation campaign, Rosetta is perfectly lined up to skim by at 3162 km (2000 miles). This event will be live webcasted by ESA at 16:00 GMT (above).
Rosetta is expected to pass Lutetia at a relative speed of 54 000 km/hr, when both are located some 454 million km from Earth. As Lutetia is a major scientific target of Rosetta's mission, most of the orbiter and lander instruments will be on for flyby, studying the asteroid's surface, dust environment, exosphere, magnetic field, mass and density.
The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) camera system is expected to obtain visible-spectrum images before and at closest approach.
Rosetta launched in 2004, is on its way to a 2014 rendezvous with comet 67P/Churyumov-Gerasimenko.
For a complete time-line of events and more information can be found at ESA web page.