Carbon Monoxide on Jupiter: Evidence for Both Internal and External Sources
✍ Scribed by Bruno Bézard; Emmanuel Lellouch; Darrell Strobel; Jean-Pierre Maillard; Pierre Drossart
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 548 KB
- Volume
- 159
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
Thirteen lines of the CO band near 4.7 µm have been observed on a jovian hot spot at a resolution of 0.045 cm -1 . The measured line profiles indicate that the CO mole fraction is 1.0 ± 0.2 ppb around the 6-bar level and is larger in the upper troposphere and/or stratosphere. An external source of CO providing an abundance of 4 +3 -2 × 10 16 molecules cm -2 is implied by the observations in addition to the amount deposited at high altitude by the Shoemaker-Levy 9 collision. From a simple diffusion model, we estimate that the CO production rate is (1.5-10) × 10 6 molecules cm -2 s -1 assuming an eddy diffusion coefficient around the tropopause between 300 and 1500 cm 2 s -1 . Precipitation of oxygen atoms from the jovian magnetosphere or photochemistry of water vapor from meteoroidal material can only provide a negligible contribution to this amount. A significant fraction of the CO in Jupiter's upper atmosphere may be formed by shock chemistry due to the infall of kilometer-to subkilometer-size Jupiter family comets. Using the impact rate from Levison et al. (2000, Icarus 143, 415-420) rescaled by Bottke et al. (2002, Icarus 156, 399-433), this source can provide the observed stratospheric CO only if the eddy diffusion coefficient around the tropopause is 100-300 cm 2 s -1 . Higher values, ∼700 cm 2 s -1 , would require an impact rate larger by a factor of 5-10, which cannot be excluded considering uncertainties in the distribution of Jupiter family comets. Such a large rate is indeed consistent with the observed cratering record of the Galilean satellites (Zahnle et al.