Meteoritic Influx on the Outer Planets: Implications for Photochemistry

J. I. Moses (LPI)

The recent ISO detection of H tex2html_wrap_inline11 O on Saturn, Uranus, and Neptune, and CO tex2html_wrap_inline11 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 tex2html_wrap_inline15 to form formaldehyde (H tex2html_wrap_inline11 CO), which is then photolyzed to form CO. The CO can then react with an OH radical to form CO tex2html_wrap_inline11 . The altitude profiles of H tex2html_wrap_inline11 O, CO tex2html_wrap_inline11 , and CO will be very different if IDP's comprise the main source of the oxygen: H tex2html_wrap_inline11 O mixing ratios will peak high in the stratosphere, CO tex2html_wrap_inline11 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 tex2html_wrap_inline11 H tex2html_wrap_inline11 to C tex2html_wrap_inline11 H tex2html_wrap_inline35 in the lower stratospheres of the outer planets; therefore, IDP influx causes a dramatic reduction in the C tex2html_wrap_inline11 H tex2html_wrap_inline11 (and also C tex2html_wrap_inline11 H tex2html_wrap_inline43 ) 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.