Comets fire up interest of public, researchers

Two comets that are dimmer than Hale-Bopp will make their appearance next week and will be observed by Uwe Fink, a UA professor of lunar and planetary sciences.

The first comet joining Hale-Bopp in the night sky is Comet Wirtanen, which made its closest swing by the sun March 14 at a distance of 159 kilometers. Wirtanen makes a complete orbit around the sun every 5.46 years.

Comet Wild 2 will make its closest pass by the sun May 6, at a distance of 224 million kilometers. Wild 2 completes an orbit around the sun every 6.17 years.

"We're going to be studying the activity of the comets," Fink said.

Fink defined the activity of the comet as the amount of dust the comet evaporates off its nucleus. The more dust, the more active the comet is, he said.

Michael Hicks, a graduate student in planetary sciences who is observing the comets with Fink, said, "We look at the gas coming off the comet and analyze what it's made of."

Fink and his graduate students will use a spectrometer he designed to study the comets.

The group will observe the comets at the UA's 61-inch telescope on Mt. Bigelow this weekend as they fly sunward, he said. Mt. Bigelow is in the Santa Catalina Mountains.

Using spectroscopy, Fink said he can observe the comets' emission features which are not visible to the naked eye.

Spectroscopy uses a comet's light emissions to determine its makeup. Using a sample spectrum, scientists can identify elements such as water vapor, hydrogen cyanide, ammonia and sodium.

Hicks said the two dim comets are called "Jupiter comets." When these comets entered Earth's solar system, they passed too close to Jupiter, which altered their orbits.

The comets are now "trapped" in our solar system with fairly short-term orbits, he said.

Hicks said Hale-Bopp is a "long-term" comet because its orbit takes it outside our solar system. These comets are harder to observe because scientists don't know they exist until they enter Earth's solar system, which is once in a lifetime.

Short-term comets like Wirtanen and Wild 2 are predictable and allow scientists to plan for sample retrieving missions and observations, Hicks said.

Hicks said comets come from the Oort Cloud, which lies outside the Earth's solar system, a hundred times farther from the sun than Earth.

He said that because scientists can rely on the predictability of comets 500 times dimmer than Hale-Bopp, like Wirtanen and Wild 2, they can get a glimpse of preserved origins of our solar system.

"These (comets) are pristine chunks that have been unaltered from the beginning," Hicks said.

The samples will be retrieved by an unmanned NASA spacecraft, the Stardust mission, which will fly through the comet's tail and take samples of the particles, Hicks said.

In the case of Hale-Bopp, Hicks said the comet's tail is 50 times bigger than Earth, with a nucleus only 20 miles across in diameter.

"The tail is evaporating from the nucleus at a furious rate," he said.

Fink said he will be taking three groups of undergraduates from his Planetary Sciences 106 class to Mt. Bigelow on March 28, 29 and 31. The first group will leave early Friday morning.

Hale-Bopp made its closest pass by the Earth March 23 at a distance of 120 million miles. Hale-Bopp is visible in the northwest evening sky a few hours after sunset.

UA scientists say Hale-Bopp is at its brightest March 25 through April 12.

Flandrau Science Center will be offering bus trips to view the comet at its peak brightness Sunday and Tuesday. Groups will be taken to a dark location in Marana where large telescopes and giant binoculars will be set up. The bus trip will follow a planetarium presentation.

Tickets will be sold at the Flandrau door the night of each trip for $25.