THE first space mission to Pluto contains an unusual piece of cargo: ashes from the cremated remains of Clyde Tombaugh, the astronomer who discovered the outermost planet in 1930.

After two days of delays, the New Horizons spacecraft blasted off from Cape Canaveral on Thursday, on a nine-year, 4.8 billion-kilometre journey to the edge of the solar system.

New Horizons is the fastest craft ever built by NASA, designed to reach a top speed of nearly 76,000kmh next year by using Jupiter's gravity to slingshot itself into the outer solar system. It is expected to reach Pluto in July 2015.