Deep Impact - Bullseye!
The Deep Impact spacecraft hit its mark on July 4, 2006, and the result was spectacular.
After a journey measured in the hundreds of millions of miles, Deep Impact's copper-loaded "smart bullet" slammed into comet 9P/Tempe1 1, penetrating deep beneath the comet's surface before vaporizing and blasting out a cone of debris. The flash from the 23,000-mile-per-hour impact was visible from Earth-based telescopes, and light reflecting off the spreading debris cone was improving the comet's visibility.
Within a couple of hours after impact, observers reported the comet had brightened from about magnitude 10.6 to about magnitude 8. This is still too dim to be seen with the unaided eye. A modest telescope will be required to view the comet in areas with dark skies. Tempel 1 is continuing its transit of Virgo in the night sky and remains in the vicinity of Spica, Virgo's brightest star, as well as of Jupiter, a few degrees to the right of Spica and a few degrees above the southwest horizon.
The impact was providing scientists with plenty of data and some surprises. Few had expected a blast as great as the one apparently achieved. Indications are the Deep Impact probe passed through a fluffy surface to get at more solid material underneath. A crater that's perhaps as large as a football field is believed to have resulted. However, scientists won't know for sure till they're able to see the crater itself - currently obscured by the debris cloud.
Instruments have so far confirmed chemical signatures of water ice in Tempel 1's debris field. Comets like Tempel 1 are believed to be debris left over from the formation of the Solar System, some 4.5 billion years ago. It's been theorized that they "seeded" Earth with the water and organic compounds needed to permit life.
And that, of course, is one big reason scientists have been eager to get beneath a comet's surface. They've wanted to sample the early material to determine its composition. In the process, they'll see if it truly could contain the building blocks of life.
Data from the mission is expected to keep scientists busy for years. One, leading scientist, in fact, said he expects to be analyzing data until his retirement.
The Deep Impact mission is a joint project of NASA, the Jet Propulsion Laboratory/CalTech and the University of Maryland.