Mr Brian Geoffrey Marsden

NOT everyone would be pleased to be dubbed a "cheery herald of fear" by the media, but Brian Marsden did not mind.

He was used to occasional barbs from the fourth estate every time he or one of his colleagues blithely predicted that the end was nigh, care of some new comet or asteroid that appeared to be on a collision course with Earth.

His brush with infamy, when The New York Times labelled him a "herald of fear", came in 1998 when he sparked worldwide headlines after announcing that comet 1997 XF11, a monstrous 2km wide blob of ancient rock and ice, might possibly slam straight into Earth in the year 2028.

His later calculations thankfully ruled out a catastrophic crossing of paths any time soon, a brighter forecast that attracted almost as many headlines.

The incident led him to persuade other astronomers that it might be a good idea if, in future, bold predictions were avoided until precise calculations could be made about a comet's trajectory.

Still, the brouhaha gave a credibility boost to the Hollywood films Deep Impact and Armageddon.

Dr Marsden recently attracted headlines after his push to have Pluto busted down from planet to planetoid. This also made him quite unpopular.

However, after he demonstrated that there were other rocky objects in roughly the same orbit as Pluto, and of roughly the same size, the International Astronomical Union decided in 2006 that Pluto be demoted to a minor or dwarf planet.

Dr Marsden was a veteran director of the Harvard-Smithsonian Centre's Minor Planet Centre, which records new comets and asteroids, and served as its director emeritus from 2006 until his death.

He was also director, from 1968 to 1999, of the Central Bureau for Astronomical Telegrams, which reports on new supernovas and objects likely to pass close to Earth.

He was credited with discovering his own asteroid, 37556 Svyaztie, in 1982 with colleague N.S. Chernykh, and his life's work was recognised with the naming of another celestial object in his honour - asteroid 1877 Marsden.

As well as tracking asteroids and comets, often using minimal observations, Dr Marsden spent much time re-discovering "lost" ones.

Because their orbits are wobbly and difficult to calculate even when tracked for some time, countless such objects have been spotted in the past, never to be seen again.

One of Dr Marsden's specialties was using complex equations to work out where they have ended up, confirming his calculations with direct observations.

He was also able to "backtrack" orbits and thereby show when comets and asteroids were first discovered, and who found them.

One of his most famous such re-discoveries involved comet Swift-Tuttle. It had not been seen since the 1800s but Dr Marsden correctly predicted it would reappear in 1992.

His unusual career choice was influenced by his father Thomas, a mathematician, and in particular by his mother Eileen whom he saw watching a solar eclipse one day when he was a child.

Apparently what impressed him was not so much the sight of the eclipse, but his mother informing him that astronomers had predicted when it would happen.

By the time he was 11 he was calculating the position of planets, and by the end of

high school he was already a junior member of the Royal Astronomical Society.

Such was his progress in his field that he was already an international name among colleagues by the time he finished university.

One of the pivotal moments in his career came after he moved from Yale University in the US to the Smithsonian Astrophysical Observatory in Massachusetts in 1965.

At the time its director was Fred Whipple, the first to realise comets were "dirty snowballs" made of ice and rubble. Whipple's discovery that ice shot off comets in powerful jets of gas enabled Dr Marsden to more accurately work out their finer movements through space.

Dr Marsden is survived by Nancy Lou Zissell, their daughter Cynthia and son Jonathan, as well as three grandchildren.