Kuiper Airborne Observatory Observing Plans

June 30, 1994

MOUNTAIN VIEW, Calif. -- NASA's Kuiper Airborne Observatory (KAO) from Ames Research Center will observe the giant planet Jupiter as seven of the fragments of Comet Shoemaker-Levy 9 plunge into its massive atmosphere July 17-22.

Scientists on board will also study effects of the entire comet's collision with Jupiter during post-impact flights July 24- 25. The flights will depart from the Melbourne International Airport, Melbourne, Australia.

"All of our investigations make use of the KAO's ability to climb above most of the water vapor in the Earth's atmosphere," Dr. Edward Dunham said. The KAO is a modified C-141 jet transport aircraft fitted with a 36-inch reflecting telescope. Dunham is KAO project scientist at Ames.

Flying at 41,000 feet where most of Earth's atmospheric water vapor is frozen out, the KAO can observe water vapor on Jupiter with minimal contamination by Earth's atmosphere.

Three advanced spectrometers attached to the telescope will search -- at infrared wavelengths -- for signs of water and new elements or compounds rising in Jupiter's atmosphere from the comet's explosion.

Jupiter, a giant whirling mass of clouds with a highly compressed hydrogen core, is 300 times the Earth's mass and 10 times Earth's diameter. Because Jupiter rotates on its axis in less than 10 hours, scientists will be able to view the impact sites only 10 to 15 minutes after the collisions on Jupiter's night side.

The impact sites -- possibly continent-sized remnants heated hundreds of degrees by the erupting fireballs -- will be visible from Earth for about five hours.

Jupiter's "air" is made mostly of hydrogen and helium, in ratios similar to the sun. Jupiter's highest visible clouds are ice crystal clouds -- like Earth's wispy cirrus clouds -- but made of ammonia ice. Beneath the ammonia cirrus clouds are water cirrus clouds and then, lower still, are clouds of water droplets like Earth's puffy cumulus and gray nimbus clouds.

If a comet nucleus explodes below Jupiter's cloud deck, chemical compounds normally hidden from view may rise above the clouds as they are heated by the fireball from the explosion.

Investigations on July 17-19 will look for water in Jupiter's tropospheric (lower atmosphere) clouds brought up by the comet impact and for water from the comet, if it breaks up above Jupiter's tropopause. The tropopause is the boundary between an atmosphere's lower and middle regions.

Dr. Gordon Bjoraker, Goddard Space Flight Center, Greenbelt, Md., is leading this investigation. He will use a high resolution spectrometer developed by Dr. Terry Herter, Cornell University, to observe Jupiter during the July 17 impacts small fragments c and d and the July 18-19 impacts of large fragments G and K.

This instrument, the Kuiper Echelle Grating Spectrometer (KEGS), can detect an impactor around 1/4 mile (500 meters) diameter or larger.

On July 21-22, Drs. Donald Hunten and Ann Sprague, University of Arizona, will search Jupiter's cloud tops for trace elements and new compounds excavated from Jupiter's depths. Their new team of observers will use the High-Efficiency Infrared Faint-Object Grating Spectrograph (HIFOGS) to observe Jupiter after the impacts of large fragments R, P and V.

"We're looking for new hydrocarbons made from the mixing of acetylene -- known to be in the jovian atmosphere -- with other elements," Sprague said. HIFOGS is sensitive to methane, ethane, acetylene, molecular hydrogen, water vapor, ammonia and other simple hydrocarbons and nitriles.

The Hunten-Sprague experiment will also look for increases in and heating of ammonia and other compounds. Changes in the ammonia and water vapor clouds will trace the rise and evolution of heated "bubbles" from the impact sites. (Water vapor clouds were discovered in Jupiter's atmosphere in 1975 by a KAO team.)

Following the KAO observations, HIFOGS, designed by Dr. Fred Witteborn of Ames, will be attached to a telescope in Arizona to further study the evolution of the exotic compounds.

Post-impact observations on July 24-25 will be made by Dr. P. G. Wannier, Jet Propulsion Laboratory, Pasadena, Calif. Wannier will try to detect water vapor in Jupiter's stratosphere following the comet impacts. The humidity of Jupiter's upper atmosphere, which is normally extremely dry, is expected to increase from the sublimation of cometary ices or from the stirring up of deeper atmospheric water.

Wannier will use a far-infrared heterodyne spectrometer (a very high frequency radio receiver) developed by Dr. Jonas Zmuidzinas, California Institute of Technology.

Flights are approximately 9 1/2 hours to allow observations from about the time of impact to four-five hours after impact. The aircraft will generally head west from Melbourne for about five hours to attain the optimal observing location. Observations will be made as the aircraft returns to Melbourne, Dunham said.

The schedule of seven maximum length flights in nine days -- with two instrument changes -- is the most ambitious schedule attempted in the history of KAO observation flights. The KAO will conduct three additional investigations of the southern hemisphere, following the comet investigations, before returning to Ames on Aug. 6.

The Kuiper Airborne Observatory, based at NASA Ames Research Center, Moffett Field, Calif. is managed by the Science and Applications Aircraft Division.

Contact: Diane Farrar (415) 604-9000