15.06
Meteoritic Influx on the Outer Planets: Implications for Photochemistry
J. I. Moses (LPI)
The recent ISO detection of H 
O on Saturn, Uranus, and
Neptune, and CO on Saturn and Neptune (Feuchtgruber et al. 1996,
IAU Circular 6514) raises many intriguing possibilities concerning
sources of oxygen in outer-planetary atmospheres. One possibility
is that the oxygen is supplied from interplanetary dust
particles (IDP's) that are constantly raining down into all the
atmospheres of the solar system. A one-dimensional model of
photochemistry and vertical transport is used in conjunction
with a meteoroid ablation model to determine the effects of incoming
IDP's on photochemistry and aerosol formation in outer planetary
atmospheres; predictions regarding Jupiter and Saturn will be
emphasized.
Preliminary results suggest that IDP influx will have a
profound effect on atmospheric chemistry. Oxygen atoms supplied
to the stratosphere from the photolysis of ablated water molecules
can react with CH 
to form formaldehyde (H CO), which is
then photolyzed to form CO. The CO can then react with an OH radical
to form CO . The altitude profiles of H O, CO , and CO will
be very different if IDP's comprise the main source of the oxygen:
H O mixing ratios will peak high in the stratosphere, CO much
lower, and CO somewhere in between. Secondly, water photolysis
provides an abundant source of H atoms, which greatly speed up the
conversion of C H to C H 
in the lower stratospheres of
the outer planets; therefore, IDP influx causes a dramatic reduction
in the C H (and also C H 
) abundance on the outer planets.
Finally, water supplied from IDP's will condense in the stratospheres of
the outer planets and have a major effect on the production and
evolution of the stratospheric aerosol layers. Model predictions
will be compared with observations in order to provide constraints
on the flux of interplanetary debris in the outer solar system.