July 21, 2006 — Scientists weren't sure what to expect when a bullet the size of a trash can smashed into the body of a comet last year. But learning that the ancient ball of ice and dust contained particles forged in the hottest of fires was a complete shock.
"It was a huge surprise," said Carey Lisse, a researcher at the Johns Hopkins University Applied Research Laboratory in Laurel, Md. "We saw structures and materials that had to be cooked at more than 1,000 degrees Kelvin (1,340 degrees Fahrenheit). To get that hot, you'd have to get closer to the sun than Mercury."
He and his team used the Spitzer space infrared telescope to study the shower of particles streaming from Comet Tempel 1 after it was rammed by an 850-pound projectile on July 4, 2005, as part of NASA's Deep Impact mission.
The findings, which are published in last week's online issue of Science, buttress similar conclusions recently announced by a team analyzing bits of comet particles returned to Earth as part of the Stardust mission.
The discoveries are forcing researchers to rethink theories about the solar system's formation to account for the existence of super-heated materials such as crystalline silicates mixing with volatile gases, such as methane, that stabilize only when temperatures are below about 100 degrees Kelvin (minus 280 degrees Fahrenheit).
The Deep Impact scientists also found chemical fingerprints of clays and carbonates in the comet. These are materials that typically form in the presence of liquid water. The inner solar system has liquid water, but it is believed to be too cold in the outer reaches of the solar system where comets formed for it to exist.
"The most likely possibility is that the whole solar system was churning," Lisse said in an interview with Discovery News.
Nearly all of the material coalesced to form the sun, the largest body in the solar system. The other matter formed a disc, from which the planets took shape. The gas giants — Jupiter, Saturn, Uranus and Nepture — formed first and stabilized the system, Lisse said.
Comets and other small icy bodies were trapped in the cold, outer reaches of the solar system, beyond Neptune's orbit.
"What Deep Impact gave us was like a Rosetta stone of the composition of small bodies in our solar system," Lisse said.
