From: University of Arizona
Posted: Tuesday, September 25, 2001
When the first U.S. spacecraft to carry a camera close to a comet successfully flew by comet Borrelly Saturday afternoon, Tucson astronomers supported the scientific milestone with observations from Kitt Peak.
University of Arizona astronomers using the university's 90-inch Bok telescope collaborated with National Optical Astronomy Observatory (NOAO) astronomers using the NOAO 84-inch telescope.
"We had excellent weather every night for observing this comet," said Humberto Campins, a senior research scientist at the UA Lunar and Planetary Lab and a program officer at the Tucson-based Research Corp.
"We are looking at the extended structure of the comet's dust coma and tail to help the NASA mission science team interpret their close-up images," said Beatrice Mueller, a research associate with NOAO and leader of the NOAO comet observations. Mueller also observed the comet several months ago to obtain information about its rotation in space to help NASA plan the flyby encounter.
Campins and UA Steward Observatory astronomer Donald McCarthy Jr. used PISCES, a broad-field infrared camera that McCarthy built, to photograph comet Borrelly before dawn last Thursday, Friday and Saturday. They took infrared images 12 hours before and 12 hours after NASA's Deep Space 1 spacecraft passed within about 1,250 miles of the comet on Sept.22.
The UA and NOAO teams are part of a NASA-funded network of observers in Arizona, Hawaii, California and elsewhere helping gather a detailed picture of the comet. While the Deep Space 1 spacecraft took up-close snapshots of comet Borrelly, ground-based astronomers took wide-view photographs of the whole comet before, during and after flyby.
NASA will release Deep Space 1 images of comet Borrelly tomorrow at a 1 p.m. EDT (10 a.m. MST) news conference from the Jet Propulsion Laboratory in Pasadena, Calif. The news conference will be carried on NASA television and it will be available on the internet at http://www.jpl.nasa.gov/webcast/ds1_webcast.html
"The spacecraft flew by the comet around 3:30 p.m. Tucson time on Saturday," Campins said. "The comet is visible for us between 3:30 a.m. and 5:30 a.m., after the comet has risen on the horizon and before the sky gets too bright at dawn."
Comet Borrelly cannot be seen with the naked eye, he added, but small telescopes may pick it up.
"The fact that Nalin Samarasinha of NOAO was simultaneously observing at visible light wavelengths on the 84-inch telescope was a godsend," Campins added.
Samarasinha was not scheduled to observe the comet with the NOAO Kitt Peak telescope at this time. But disrupted national air travel forced a change in the observing plans of a colleague, who swapped telescope time with Samarasinha and Mueller.
"It is a important to work in tandem in both wavelengths because the structure of these objects can change on short time scales. They can be completely unpredictable. Having simultaneous observations helps us determine what is happening with the comet at that moment. Both views give us a better look at the actual distribution of dust around the comet through time," Campins said.
"We could check with each on whether 'seeing' was poor or whether something needed adjusting on our telescopes," he added. "Simultaneous observations allowed us to make a number of decisions that allowed us to make much more efficient use of our time."
Launched in October 1998, Deep Space 1 completed its primary mission of flight-testing an ion engine and other advanced technologies two years ago. It was not designed for a comet flyby. Despite comet Borrelly's dense dust, the spacecraft took more than two dozen comet images that JPL finished downloading yesterday.
Observations of and from the encounter are important in planetary science and also will help researchers assess the hazards to future spacecraft during comet flybys, Campins said.
Until now, "The only detailed spacecraft picture of a comet we have is a 1986 picture of comet Halley from the European Space Agency's Giotto mission," he said. The Russians and French used the Vega 1 and 2 spacecraft to get less detailed, but still helpful, pictures of comet Halley that same year, he added.
"The Europeans and Russians deserve a lot of credit. If it weren't for them, we wouldn't know half as much about comets as we do now."
NOAO will release a black-and-white image of comet Borrelly taken with the 84-inch telescope tomorrow, Sept. 25, at its website, http://www.noao.edu/news/. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation.
Beatrice Mueller, Nalin Samarasinha
C/o Doug Isbell, NOAO Public Information
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