PARIS, 12 July 2006 - A British woman who baptised the newly-discovered Pluto 75 years ago has been honoured in a U.S. mission heading for the Solar System's enigmatic ninth planet, astronomers said last Thursday.

Venetia Phair, now aged 87 and living in Epsom, southern England, thought of the name of Pluto, the Roman god of the underworld, after the planet was discovered by American skywatcher Clyde Tombaugh in 1930.

An instrument aboard NASA's New Horizons spacecraft heading to Pluto has now been named in tribute to her, according to a newsletter of the Johns Hopkins University of Baltimore, Maryland, whose staff and students designed and built the device.

The gadget has been formally called the Venetia Burney Student Dust Counter (VBSDC), or "Venetia" for short. "It's ... a great honour to recognize Mrs. Phair for her historic, early role in the saga of the ninth planet," said New Horizons scientist Alan Stern of the Southwest Research Institute in Boulder, Colorado.

The role of "Venetia" is to count and measure dust particle impacts as the spacecraft speeds towards Pluto.

The grains give an indicator of the population of comets, which shed dust as they loop around the Sun, and of asteroids, which lose debris when they collide.

As the dust is too fine to be detected with telescopes, the Johns Hopkins team have placed a small screen about the size of a shoebox lid on the outside of the spacecraft.

When dust hits this detector, data is sent to an electronics box on the inside the craft which then calculates the dust's speed and mass.

New Horizons launched from Cape Canaveral on January 19. It is due to arrive at Pluto in July 2015.

Phair, whose maiden name is Burney, was 11 years old when Pluto was discovered.

Her grandfather, a retired librarian at the University of Oxford, spotted a newspaper article about the discovery and read it to the young child, whose interest in classical mythology allowed her to come up with the name of Pluto.

The grandfather was so taken with the name that he mentioned it to a friend who was a professor of astronomy at Oxford and, who in turn, campaigned vociferously for Pluto to become the official name.

For decades, though, the myth has endured that the planet was named after the Walt Disney dog of the same name. In fact, the Disney dog was named in celebration of the new planet.

Pluto is the ninth and outermost acknowledged planet of the Solar System, although this status may be scrapped at a meeting in Prague in August of the International Astronomical Union (IAU), which vets claims of new celestial sightings and approves names proposed for them.

Some astronomers believe Pluto is so small and its orbit so unusual that it should be downgraded to the status of a rock, rather than a planet. The issue is discussed in Issue 9 of Cosmos.

And if it is a planet, its role as the farthest planet from the Sun could be supplanted by another object which was spotted in July 2005.

The so-called Planet X has been provisionally named Xena by its discoverers, who are fans of TV's warrior princess. If the IAU accepts their claim that it is a 10th planet, Xena is likely to adopt a classical name.