Mauna Kea study
demystifies comets

HILO » Down deep, all comets might be the same, astronomers using telescopes on Mauna Kea now suspect, following the July 4 Deep Impact comet probe.

Scientists had believed that comets came from two distinct "family trees," based on vastly different orbits and apparently different compositions, said University of Minnesota astronomer Chick Woodward, who used the Gemini telescope to observe the Deep Impact experiment.

"Now we see that the difference may really be just superficial, only skin deep," Woodward said. "Under the surface, these comets may not be so different after all."

The conclusions of astronomers from the Keck, Subaru and Gemini observatories were reported yesterday in Science magazine.

Deep Impact sent a piano-size probe crashing into Comet Tempel 1, a type of celestial body called a periodic comet because it regularly comes close to the sun after spending time in more distant parts of the solar system.

Astronomers had believed that such comets were different from others that usually remain in the Oort Cloud, far out past the solar system's most distant planets.

Sometimes a stray from the Oort Cloud will make a one-time tour close to the sun, revealing its nature by releasing gas and dust under the influence of the sun's heat.

Now analysis of underlying dust blasted out from under Tempel 1's dusty skin shows that it is made of pretty much the same stuff that Oort Cloud comets are made of, astronomers said in the Science report.

The material knocked free by the probe included water, carbon-containing substances such as the gas ethane, and silicates such as olivine, a green mineral found in Hawaii in places like the Big Island's Green Sands beach.

The temperatures required to produce these chemicals suggest all comets originate in a not-too-frigid area of the solar system as it was born billions of years ago.

"It's now likely that these bodies formed between the orbits of Jupiter and Neptune in a common nursery," said Subaru astronomer Seiji Sugita, of the University of Tokyo.

Astronomers have also calculated how much dust the Deep Impact probe kicked up: about a thousand tons, enough to fill about 25 tractor-trailer trucks.