Death of Brian Marsden

Astronomer Brian Marsden made waves in 1998 when he said that Earth was possibly on a collision course with an asteroid and again years later when he led a campaign to unseat Pluto as a major planet.

Mr. Marsden, who died Thursday at age 73 after a prolonged illness, was among the best-placed of scientists to make the asteroid prediction. As head of the International Astronomical Union’s Minor Planet Center, he was responsible for keeping track of the identity and track of nearly everything in the solar system.

“He was a cross between an archivist, a giver of credit for discoveries, and a preliminary orbit calculator,” said Donald Yeomans, manager of the Near-Earth Object Program Office at the National Aeronautics and Space Administration. “He was one of the very few who paid any attention to the possibility that these near-earth objects could be a problem.”

In the case of the “1997 XF11″ asteroid, later observations showed the asteroid’s orbit wouldn’t intersect with Earth, and Mr. Marsden retracted his warning within 24 hours. Astronomers and others lobbed a barrage of criticism, but Mr. Marsden was unbowed.

“Much as the incident was bad for my reputation, we needed a scare like that to bring attention to this problem,” he told Scientific American magazine in 2003.

Most of Mr. Marsden’s work was the less dire but still epochal job of identifying, naming and alerting the scientific community to new asteroids. He also headed the Central Bureau for Astronomical Telegrams, responsible for monitoring comets. Mr. Marsden in 1994 alerted the media that Comet Shoemaker-Levy 9 was on a collision course with Jupiter. This time his prediction proved accurate, and the comet broke up upon impact, creating a vivid light display.

Calculating orbits had been his specialty since he was an adolescent. Mr. Marsden grew up in Cambridge, England, the son of a mathematician. He said his mother sparked his interest in astronomy when she showed him a solar eclipse, viewed through smoked glass. What impressed him, he said, was not the image, “but the fact that it had been predicted in advance.”

A prodigy of calculation, Mr. Marsden joined the Royal Astronomical Society while in high school and published predictions on the movements of Jupiter’s moons. He studied mathematics at the University of Oxford and went to graduate school at Yale starting in 1959, where for the first time he had access to a computer.

When he joined the Smithsonian Astrophysical Observatory in Cambridge, Mass., asteroids weren’t in fashion. They were notoriously “vermin of the sky,” creating streaks on the photographic plates of astronomers studying stars much farther away.

During Mr. Marsden’s tenure, interest grew and by the 1990s the Minor Planet Center was awash in data supplied by professional and amateur astronomers. Thousands of new asteroids were added to the records each month.

“If it moves or it’s fuzzy, it goes through us,” he told Astronomy magazine in 1998.

Mr. Marsden refined the way comet orbits were calculated, and he succeed in predicting the return in 1992 of Swift-Tuttle, the comet with the longest known orbital period. Mr. Marsden made the re-identification of “lost comets” and “lost asteroids”—typically spotted once but without a known orbit—a specialty.

In addition to his notoriety for raising alarms about an asteroid impact, Mr. Marsden won enmity with a segment of the public as a leader of the campaign to downgrade Pluto. Partly at his urging, the International Astronomical Union voted at a meeting in Prague in 2006 to designate Pluto and three asteroids “dwarf planets.” At the end of his career, Mr. Marsden noted that Pluto was retired as a planet on the same day that he retired as an astronomer.

Wall Street Journal by STEPHEN MILLER

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