Brian G. Marsden, famed astronomer and tracker of comets and asteroids, passed away on Nov. 18 due to prolonged illness. At Harvard, Marsden served as supervisory astronomer at the Smithsonian Astrophysical Observatory and as director emeritus of the Minor Planet Center.

Marsden was renowned for his proficiency in computational astronomy, calculating the positions and orbits of comets and asteroids using observational information, critical for monitoring potentially threatening objects bound for Earth. “He had an unusual facility with numbers. He could do ‘party tricks,’ like he would ask you for your birthday and he could tell you what day of the week you were born,” said Astronomy Professor Robert P. Kirshner ’70.

Among his many accomplishments, Marsden was most proud of correctly predicting the 1992 return of Comet Swift-Tuttle, the comet associated with the Perseid Meteor shower every August. Marsden became the subject of controversy in 1998, when he indicated that an object named 1997 XF11 could collide with Earth. Data from 1990 clearly proved that a collision was highly unlikely but Marsden said he did this to encourage the collection of more routine observations.

Marsden also identified a group of comets that closely passed by the Sun, now known as the “Marsden group.” However, most people recognize Marsden as the individual responsible for the demotion of Pluto to dwarf planet status. “It was hard to get an accurate mass of Pluto,” said Gareth V. Williams, Marsden’s son-in-law and director of the Minor Planet Center. “Every year the measured mass got smaller. Brian graphed the date and estimated mass of Pluto and it was a straight line downwards. The running joke was that it would disappear entirely.”

Growing up in Cambridge, England, Marsden’s mother introduced him to astronomy in 1942 as they watched a solar eclipse. Marsden however, was fascinated not by the eclipse itself but by the fact that it had been predicted in advance.

Marsden began calculating astronomical positions at age 11. He became a junior member of the Royal Astronomical Society in high school. He went on to attend New College, Oxford, where he developed an international reputation for computing orbitals of comets. After graduating, Marsden enrolled in Yale University as a graduate student, writing his Ph.D. degree thesis titled “The Motions of the Galilean Satellites of Jupiter.” He served as Director of the Central Bureau of Astronomical Telegrams from 1968 to 2000.

“He was very important because he was the guy who knew things second,” said Kirshner. “If people found something, they reported it to Brian, who would then follow up and disseminate the information around the world for other scientists.” In 1978, Marsden also assumed directorship of the Minor Planet Center, the official organization attending to the discovery of asteroids, a position he held until 2006. He joined the Harvard-Smithsonian Center for Astrophysics in 1987.

“I took pretty much the same route; I was interested in computation rather than observing,” said Williams. “Brian’s name became known to me early on as this guy who would make these pronouncements. I was 14 and I wanted to know how he did it.” Williams eventually wrote his final undergraduate paper about the identification of asteroids. “No one at the university [in England] had experience in asteroids so my advisor suggested I send my write-up to Brian,” Williams said. Marsden later took Williams under his wing, offering him the position of Minor Planet Center Director and introducing him to his daughter, whom Williams married.

“I’m very grateful to Brian for a lot of things, even before I knew him,” Williams said. “For increasing my interest in computational astronomy and then for taking a risk in inviting me over to the us to work with him, for giving me my charming wife.”

“He’s left a void that will be very hard to fill,” said Williams. “We’ve lost one of the greatest astronomers of all time.”