• October 13, 2005

    Episode 5: Celestial fireworks on July 4th!

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    NASA's Deep Impact mission has given us our closest look at a comet nucleus, and achieved our first contact with one. The Deep Impact spacecraft ejected a robotic probe that collided with Comet Tempel 1 on July 4, 2005, causing a huge explosion. The impact smashed free a cloud of material that the nearby spacecraft observed. Scientists are now analyzing the data to determine the makeup of the comet. The old idea of comets being "dirty snowballs" may be changing to "snowy dirtballs," since Tempel 1 seems to contain more dust than ice. In fact, the comet may be "mostly empty," in the words of the mission's chief scientist, Dr. Michael A'Hearn from the University of Maryland. Scientists are also surprised by the number of craters on Comet Tempel 1's surface. Neither of the two comets spacecraft previously observed up close appeared to have any craters. Why would comets be so different? Comets are of great interest to scientists because the ice and other materials deep inside are likely pristine and unchanged from early days of solar system.