At the same time, professional and amateur astronomers at large and small telescopes on Earth will observe the impact and its aftermath, and results will be broadcast over the Internet. The comet will not be disturbed from its normal path around the Sun, because the impact will not be forceful enough to change the comet's direction. Comet Tempel 1 Comet Tempel 1 was discovered in 1867. Orbiting the sun every 5.5 years, it has made many passages through the inner solar system. This makes it a good target to study evolutionary change in the mantle, or upper crust, of the comet.
Comets are visible for two reasons.
First, dust driven from a comet's nucleus reflects sunlight as it travels through space. Second, certain gases in the comet's coma, stimulated by the Sun, give off light like a fluorescent bulb. Over time, a comet may become less active or even dormant. Scientists are eager to learn whether comets exhaust their supply of gas and dust to space or seal it into their interiors. They would also like to learn how a comet's interior is different from its surface.