Brian G. Marsden - Life

Life

Marsden specialized in celestial mechanics and astrometry, collecting data on the positions of asteroids and comets and computing their orbits, often from minimal observational information and providing their future positions on International Astronomical Union (IAU) circulars. In addition to serving as MPC director since 1978, he served as the director of the Central Bureau for Astronomical Telegrams (CBAT) from 1968 to 1999. He was president of Commission 6, and Commission 20 the IAU.

Marsden helped recover once lost asteroids and lost comets. Some asteroid and comet discoveries of previous decades were "lost" because not enough observational data had been obtained at the time to determine a reliable enough orbit to know where to look for re-observation at future dates. Occasionally, a newly discovered object turns out to be a rediscovery of a previously lost object, which can be determined by calculating its orbit backwards into the past and matching calculated positions with the previously recorded positions of the lost object. In the case of comets this is especially tricky because of nongravitational forces that can affect their orbits (one of which is emission of jets of gas from the comet nucleus), but Marsden has specialized in calculating such nongravitational forces. Notably, he successfully predicted the 1992 return of the once-lost Comet Swift-Tuttle.

In 1998, he calculated that an asteroid, (35396) 1997 XF11 might strike the Earth in 2028. Marsden chose to issue a press release, which Robert Roy Britt called a false alarm.

• "... astronomers created a media storm by announcing that an asteroid could collide with Earth in 2028, only to revise the estimates hours later." --Gretchen Vogel, Science, 20 March 1998

Other asteroid researchers called it a "mistake" and Marsden himself admitted the announcement was a strategy which needed "rethinking", and NASA asked astronomers not to sound a public alarm like that again but to communicate with each other. He took some criticism for publicizing this prediction right when movie companies were publicizing films like "Deep Impact" (see also Science by press conference). However, Marsden justified his actions with the argument that the problem of detecting asteroids needs more attention:

• "Much as the incident was bad for my reputation, we needed a scare like that to bring attention to this problem." (Scientific American magazine, 2003)

Follow-up work determined that an impact would be unlikely.

He once proposed that Pluto should be cross-listed as both a planet and a minor planet and assigned the asteroid number 10000; however, this proposal was not accepted. A similar proposal was, however, finally accepted in 2006 when Pluto was designated minor planet 134340 and also declared a dwarf planet.

• 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.”