The US scientist will be in a control room at Maryland's Johns Hopkins University, anxiously waiting to learn whether 26 years of work have been for nought.

Six billion kilometres away a robot explorer he helped build will be sweeping past Pluto. Until its recent demotion to "dwarf" status Pluto was the solar system's ninth planet, and the only one still unexplored.

The lead scientist on NASA's $US770 million ($1.167 billion) New Horizons mission, Dr Stern, who will give a free public talk this evening at the University of Sydney, began designing possible Pluto voyages in 1989.

New Horizons was finally hurled into space in January 2006 for its decade-long trip to the solar system's edge.

Aboard the probe are an array of mementoes, including a tiny urn holding some remains of Clyde Tombaugh, the astronomer who discovered Pluto in 1930. Concerned he would not live to see a mission to his planet, Tombaugh requested his ashes be flown. After his death in 1997, "they were sent to me by his family … in a breath-mint box", said Dr Stern.

The probe is also carrying two quarter-dollars, a CD with the names of 437,000 people from around the world, and a 29 cent 1990 US postage stamp featuring an artist's impression of Pluto above the words "not yet explored".

New Horizon's cameras should be able to snap features "as small as large buildings".

After skimming past the dwarf planet the probe will turn to listen to radio signals beamed up from Canberra's Tidbinbilla deep space tracking station.

So little is known about Pluto, said Dr Stern, everything New Horizons sees will be a discovery. "It will be like opening a Christmas present. Pluto is yet to be unwrapped".

To book for Dr Stern's 6.30pm talk, phone 9351 3472.