Astronauts have tramped upon the moon, and planetary probes - our robotic surrogates - have now either touched upon or flown by every planet in the solar system but one, Pluto.

The probe had been flying since before I was born, but that had been its first message since leaving the solar system.

As the probe flew it began to take on a crystalline appearance.

Three probes launched by the United States National Aeronautics and Space Administration (NASA) had already flown by Saturn in the 1970's and 1980's.

The probe would fly within 120,000 miles of Mars on June 19.

Twice at least, probes flew through the middle of her scattered ship.

Under an extended mission, the probe would fly on to meet a dying comet known as Wilson-Harrington in January 2001, and then continue on for a September swing by the comet Borrelly, one of the most active to visit the inner solar system regularly.

In contrast, exploration of the planets evolved haphazardly over the decades as American probes flew to Mercury, Venus, Mars, Jupiter, Saturn and beyond.

During these extended missions, the probe flew by Io three times in late 1999 and early 2000 and three times in late 2001 and early 2002.

The probe then flew by the Comet Grigg-Skjellerup in 10 July 1992 which it approached to a distance of about 200 km.