Fred Whipple
The Harvard astronomer who described comets as dirty snowballs and pioneered measuring meteor orbits from photographs.
Key facts
- Born
- 1906
- Died
- 2004
- Nationality
- American
- Field
- Astronomer
Fred Lawrence Whipple spent his long career at Harvard and the Smithsonian Astrophysical Observatory, which he directed from 1955 to 1973. He was fascinated by the small bodies of the Solar System.
In the 1930s and 1940s Whipple developed ways to photograph meteors from two stations at once, with rotating shutters that chopped each trail into short pieces so its speed could be measured. From these pictures his team calculated the orbits of hundreds of meteors. They showed that nearly all ordinary meteors are bits of comets and asteroids orbiting the Sun, not visitors from interstellar space.
In 1950 Whipple proposed that a comet's nucleus is a solid lump of ice mixed with dust and rock, a dirty snowball. As it nears the Sun, the ice turns to gas and releases the dust, which makes the comet's tail and spreads along its orbit to form the streams behind meteor showers. Spacecraft visits since 1986 have confirmed the essential idea, though comets are dustier than he imagined. He also linked the Taurid meteors to Comet Encke.
Whipple also invented the Whipple shield, a thin outer layer that breaks up tiny high-speed particles before they hit a spacecraft. Versions of it protect the International Space Station today.