On July 4, 2005, NASA's Deep Impact probe completed its scientific mission by colliding with comet Tempel 1 at a speed of more than 23,000 miles per hour. The Jet Propulsion Laboratory in Pasadena, California reported: "Deep Impact scientists theorize the 820-pound impactor vaporized deep below the comet's surface when the two collided." Scientists want to know more about the nature of comets.