Summary of Atmospheric Chemistry Working Group- Keith Noll, group leader

I. What is really known?

Several significant uncertainties limit the ability to accurately 
predict the possible changes in atmospheric composition that might 
be observed after the impacts of the the SL9 fragments.  The mass of 
the fragments, the depth of penetration before disruption, the 
volume of atmosphere promptly affected by the impact, the amount of 
tropospheric material heated and transported into the stratosphere, 
the composition of the comet, and the chemical processing of shocked 
and heated material are all crucial unknowns that will determine the 
outcome of this event.  Some theoretical predictions about the 
impact have been made, but the predictions vary considerably 
depending on the model and assumptions used.  

In view of these large uncertainties, the consensus of the working
group was that a wide range of observations covering many possible
scenarios should be made. 


II. What are the key and diagnostic observations to be made? 

A very long list containing all the observed molecules in Jupiter's
atmosphere and some that have not been observed can be constructed.
Because of the difficulty in making predictions about this event, it
is tempting to consider each as a potentially useful observation.
However, given the fairly severe constraints on observing time with
spectrometers on large telescopes, some prioritization is clearly
necessary.  In the following list molecules are grouped by element
with brief comments about each group. 

    A. Search for the following molecules.
	1. Hydrogen: H3+, H3O+
		diagnostic of processes in the ionosphere
		the introduction of heavy nuclei into the 
		ionosphere (i.e. C and O) may cause catalytic
		destruction of H3+.  H3+ is best observed near
		3.5 um.
	
	2. Helium:
		Helium emission may be observable in the extreme 
		UV (He at 504 A, He+ at 304 A).  Could indicate the
		degree of heating of the upper atmosphere.

	3. Carbon: CH4, CH3D, hydrocarbons, CH, CH3+
		The 7.8 um CH4 band may yield the best measure of
		temperature changes in the stratosphere.  Its 
		abundance should be unaffected by the impact.
		C2H6 and C2H4 may serve the same purpose, although
		their abundances may be temperature dependent.

	4. Oxygen: H2O, CO, H2CO, OH, CH3OH
		Oxygen is essentialy absent from Jupiter's stratosphere.
		Reaction network calculations suggest that most of
		the oxygen should eventually end up in CO, although 
		the time scale for this is uncertain (days - months).
		H2O and CO can come both from the comet and Jupiter's
		deep atmosphere.  Both are best observed near 5 um.


	5. Nitrogen: NH3, HCN, NH
		Ammonia abundances in the stratosphere may increase 
		dramatically if warmed parcels of gas are transported
		into the stratosphere.  The NH3 spectrum could dominate 
		8 um spectrum.  It could also be observed at 5 um, and 	
		at cm-radio wavelengths.

	6. Sulfur: H2S
		As a possible precursor to both Jupiter's lower cloud
		and to the coloring-agent in Jupiter's clouds, H2S
		is one of the most sought-after molecules in Jupiter.
		The impacts may provide a unique window of opportunity
		to observe this molecule by transporting significant
		quantities to observable levels of the atmosphere.	
		The best prospects seem to be to observe lines of the 
		8 um band that will be interspersed with the strong
		NH3 spectrum.

	7. Phosphorous/Germanium/Arsenic: PH3, P4, GeH4, AsH3
		These three elements are all normally depleted above
		the cloudtops by photodissociation.  The impacts
		may temporarily increase the abundances of phosphine,
		germane, and arsine in the stratosphere.  Observations
		of local abundance increases would provide a measure 
		of the mass of tropospheric gas mixed above the 
		cloudtops similar to the case for ammonia.

	8. Silicon: SiH4, SiO
		Silicon in Jupiter's atmosphere is located far
		below any reasonably conceivable penetration by the 
		fragments.  Therefore, the measure of either molecule
		would provide constraints on the comet mass and the
		volume of atmosphere over which the material was
		spread.  Laboratory experiments indicate that SiO
		should be the preferred product, although the 
		experiments were not specifically designed to 
		simulate jovian conditions.  SiH4 is observable 
		near 5 um, SiO can be observed at 8 um and in the
		UV near 2300 A.


    B. Observational/Spectral coverage

                Continuous spectral coverage from 1600A-20 microns
		Assuming good observing conditions from groundbased
		sites, the Jupiter spectrum will be observed over
		the complete spectral range from ~1250 Angstroms to
		20 microns with gaps only in the terrestrial 
		absorption bands.  There will also be some 
		spectroscopic observations in the far-UV and in the 
		radio.  The planned observations will be 
		heterogeneous in time, aperture, and technique, and
		will most likely require a large effort to 
		synthesize into a coherent data set.  The effort may
		be comparable to that needed after the International
		Halley Watch observations.

	
III.  What areas are not being addressed?
	The main deficiencies appear to be temporal coverage at UV
	and mid-IR wavelengths (2.5-20 um).  There is probably 
	little that can be done to address this due to the lack of 
	mid-IR spectrometers, especially from 8-20 um, and the 
	limited time available on HST (IUE spatial resolution is 
	probably insufficient).