Surprises Found in Comet Recipe

The recipe for Tempel 1: (In the back from left to right) a cup of ice and a cup of dry ice; (in measuring cups in the middle row from left to right) olivine, smectite clay, polycyclic aromatic hydrocarbons, spinel, metallic iron; (in the front row from left to right) the silicate enstatite, the carbonate dolomite, and the iron sulfide marcasite. Materials courtesy Caltech researcher George Rossman. CREDIT:

Newly analyzed data from NASA's Spitzer Space Telescope details the recipe for comets based on observations of Tempel 1, the object smacked in early July by the Deep Impact probe.

"We are assembling a list of comet ingredients that will be used by other scientists for years to come," said Carey Lisse of Johns Hopkins  University's Applied Physics Laboratory.

Spitzer used its infrared cameras to monitor material kicked up by the Deep Impact probe. Earlier this week, other Tempel 1 observations from dozens of telescopes around the world and in space were announced. The upshot: Tempel one is a fluff ball, with more than 50 percent of its contents being grains of water ice. The Spitzer findings expanded on that basic result.

Lisse's team found standard comet components, such as silicate. The astronomers likened the silicate grains to crushed gems, saying they were smaller than typical sand grains.

There were surprises, too, such as clay and carbonates -- the stuff of seashells. These were unexpected because they are thought to require liquid water to form.

"How did clay and carbonates form in frozen comets?" Lisse said in a NASA statement released today. "We don't know,  but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body."

Scientists hope now to begin using this new recipe to make better computer models for how the solar system formed. Comet innards - what Spitzer saw - are thought to be pristine leftovers from the formation of the Sun and planets around 4.5 billion years ago.

"Now, we can stop guessing at what's inside comets," said Mike A'Hearn, principal investigator for the Deep Impact mission and an astronomer at the University of Maryland. "This information is invaluable for piecing together how our own planets as well as other  distant worlds may have formed."

Lisse presented the findings this week at the 37th annual meeting of the Division of Planetary Sciences in Cambridge, England.

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