Nasa's New Horizon probe will get its first glimpse of Pluto as it makes a historic fly-by, passing within 12,500 kilometres (7,767 miles) of the dwarf planet, and Google has marked the event with a Doodle on its homepage.
The craft is taking with it the ashes of the astronomer that discovered it, and is set to provide more information than ever before on the makeup of the icy planet.
The fly-past will take place at 12.49pm UK time and its main imaging camera will send back the first detailed close-up pictures of the surface of Pluto, showing features just 50 metres across.
The 700 million dollar (£451 million) probe, the size of a baby grand piano, has journeyed a distance of three billion miles and with a speed of more than 36,000 mph is the fastest craft ever to leave Earth orbit.
The mission marks the conclusion of the Nasa's quest to explore every planet in the solar system, starting with Venus in 1962.
Today's encounter with Pluto coincides with the 50th anniversary of the first ever fly-by of Mars by the Mariner 4 probe.
The Google Doodle, by Kevin Laughlin shows a short animation of the probe spinning around Pluto.Reuse content