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Mercury, November/December 2005 Table of Contents

Courtesy of E. DeVore.

by Dennis Schatz

There were five of them, all nicely lined up on the edge of the workbench in our garage. Colin and I had labored the past hour, trying to find the perfect combination of water, dry ice, and dirt, so that our model comet would look like a dirty snowball -- the classic description for a comet. Was it better to use hot water, cold water, or ice cubes mixed in water? Should the dry ice be crushed or in little chunks? These were the major scientific questions we pursued.

It was 1985, and the world was getting ready for the return of Halley’s Comet. As a museum educator and father, I was excited: not because the view of the comet was going to be spectacular like in 1910, but because my two sons (Colin aged ten and Evan aged seven) could be among the lucky few to see it twice. Colin was happy just to be mixing water, dry ice, and dirt together to see what we got.

The results of the experiment were clear. Equal amounts of cold water and crushed dry ice worked the best. Add a couple of scoops of dirt, plus a smidgen of ammonia and corn syrup, and you have the closest thing to an astronomical object that you can create on Earth.

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