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Dr. Comet, 95, still hunting space ice boulders

Fred Whipple coined the term "dirty snowball."  

By Richard Stenger

(CNN) -- Fred Whipple knows comets, having spent more than five decades pursuing the strange ice boulders. Now the man who first described them as "dirty snowballs" will have a chance to see them up close.

Whipple, 95, is a member of the Comet Nucleus Tour (Contour) science team, which just sent an unmanned spacecraft on its way to close encounters with two or more comets.

The oldest scientist ever to take part in a NASA space mission, the man known as "Doctor Comet" has provided considerable inspiration to his colleagues, some of whom were his students.

"Fred is the most venerable cometary scientist in the world," Contour lead scientist Joseph Veverka said when Whipple joined the project.

"There isn't a scientist working in this field who is unaware of Whipple's work in the study of comets."

A former director of the Smithsonian Astrophysical Observatory, Whipple first proposed that comets resembled dirty snowballs.

In 1950, he suggested comets were solid chunks of ice mixed with rocks and dust particles, rather than loose collections of rocks and dust.

More than three decades later, his theory was confirmed when the European Space Agency probe Giotto flew near Halley's Comet.

"Comets have long been an unexplored wasteland. Today we know that they are black and cold, consisting of ices and dust that coalesced from an interstellar cloud as it collapsed to form the solar system," Whipple wrote to comet-studying colleagues several years ago.

Interactive comet tour 
Contour, a closer look 

His path into the field of cometary science was a circuitous one. Numbers were much more to his liking as a student at Occidental College in California.

Working as a store clerk, he walked around with customers and added up their purchases in his head. Whipple eventually majored in math at the University of California, Los Angeles.

Then his interests turned to the sky. He received a doctoral degree in astronomy from the University of California, Berkeley. He took a job at Harvard University where he inspected photographic plates of sky surveys to make sure the telescope camera worked properly.

To kill time, Whipple hunted for comets in the photo negatives. He discovered six.

In March 1950, Whipple shook up the astronomy field with his report on comet nuclei in the Astrophysical Journal. He reasoned that gases streaming from comets as they travel near the sun come from an icy cometary nucleus.

The sun heats the water ice and releases the water as vapor. The gas venting accounts for the long, picturesque comet tails that delight Earth observers.

Whipple originated the term "dirty snowballs" to describe the combination of water ice and debris that make up comets.

Drawing of Contour approaching the rocky, icy core of a comet  

In 1955, he took the helm at the Smithsonian Astrophysical Observatory, now part of the Harvard-Smithsonian Center for Astrophysics. The center's observatory in Amado, Arizona, bears Whipple's name.

Through the years, Whipple crossed paths with other notable astronomers. He brought then young Carl Sagan to the faculty of Harvard University.

Who was Whipple's last graduate student at Harvard? None other than Joe Veverka, Whipple's new "boss" with the $160 million Contour project.

The Contour spacecraft is slated to take photos and collect data as it passes within 62 miles (100 kilometers) of two comets in 2003 and 2006. After then, the probe might visit another comet as well.


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