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Kuiper Airborne Observatory Comet Crash Observing Plans


Kuiper Airborne Observatory Comet Crash Observing Plans

15 April, 1994
		E. W. Dunham	KAO Project Scientist
		G. L. Bjoraker	NASA Goddard Spaceflight Center
		D. M. Hunten	University of Arizona/LPL
		P. G. Wannier	JPL

The Kuiper Airborne Observatory (KAO) will be carrying out three investigations of the comet impact on Jupiter. All of these observations make use of the KAO's ability to climb above most of the water vapor in the Earth's atmosphere. All of the scheduled instruments are spectrometers, two grating spectrometers and one heterodyne instrument. A synopsis of the three investigations follows:

Bjoraker Observations:

G. Bjoraker (NASA GSFC) and T. Herter, G. Gull, & S. Stolovy (Cornell) will be observing Jupiter from the KAO using KEGS (Kuiper Echelle Grating Spectrometer). Its Si:As BIB array is used with 20 spatial and 128 spectral elements at a spatial resolution of 5x10 arcsec. The objectives are to search for H2O emission lines at 23.87 mu and to measure the stratospheric temperature using CH4 emission lines at 7.68 mu. Jupiter's doppler shift of +26 km/sec will be exploited to separate jovian emission lines from residual telluric lines. If the impact takes place below the water cloud (P>6 bars) large amounts of H2O (2000 ppm) may be transported in a warm bubble to the stratosphere. If the impact takes place above the water cloud then H2O in the comet itself may result in ~100 ppm in the stratosphere in a column above the 1 millibar level, depending on the size of the impactor. The minimum detectable size of the impactor is on the order of 500 meters.

Hunten Observations:

D. Hunten, A. Sprague, F. Witteborn, R. Kozlowski, M. Marley, G. Bjoraker, D. Wooden, K. Wells, W. Hoffmann, L. Deutsch, G. Fazio, J. Hora, K. Shivanandan, and M. Sykes will use HIFOGS (High-efficiency Infrared Faint-Object Grating Spectrograph), a proven instrument with a 120-element linear Si:Bi detector array (and another array for longer wavelengths, not used for this experiment) to observe the comet impact. The primary purpose is to reveal any new chemical compounds, as well as to monitor changes in known emissions after the impacts. The 13 - 17 mu band will be sensitive to ethane, acetylene, and molecular hydrogen, as well as other simple hydrocarbons and nitriles. The 5 - 7.8 mu band is sensitive to ammonia, water vapor, and methane. The methane spectra will be complementary to imaging carried out at 7.8 mu at the IRTF. Ammonia and water vapor will trace the rise and further evolution of the bubbles from the impact sites. After the KAO observations are over, HIFOGS will be moved to the Arizona-NASA 60-inch telescope for further studies of the evolution of the exotic compounds.

Wannier Observations:

P. Wannier (JPL) and J. Zmuidzinas (Caltech) will lead an effort to use a heterodyne radio receiver on the KAO to detect water vapor in the upper stratosphere of Jupiter following the comet encounter. The receiver uses a superconducting tunnel junction and will operate at the 547 GHz ground-state transition of 18-oxygen water. The upper Jovian atmosphere is normally extremely dry, but its humidity is expected to be raised by water from the comet (sublimation of cometary ices) or from Jupiter (stirring up water normally present in the deeper atmosphere). The heterodyne technique enables spectra of very high resolution to be obtained. Such a high-resolution line profile contains information on both the depth of the observed water (from pressure-broadening) and on the longitude distribution (from observed Doppler shifts).

KAO Deployment Plans:

The KAO will be deployed to Australia to maximize the number of times the immediate aftermath of an impact can be observed. The available integration time on each flight will be typically 4-5 hours, from impact time to substantially after the central meridian crossing of the impact point. The KAO will leave NASA Ames on 12 July, and will return on 6 August. The last part of the deployment will be devoted to observations of southern hemisphere objects as part of the regular airborne astronomy program. The flight schedule for the comet impact observations in Australia is:

17 July		Bjoraker	(c/d)		5-36 um 	T. Herter
18 July		Bjoraker	(G)		R = 9000
19 July		Bjoraker	(K)		
20 July		** Instrument change **
21 July		Hunten		(R)		5-17 um		F. Witteborn
22 July		Hunten		(V/W)		R ~ 200-1000
23 July		** Instrument change **
24 July		Wannier		(Post-		548 GHz		Zmuidzinas
25 July		Wannier		impact)		R = 1.8x10^5