Benzene on the Giant Planets

Abstract

We report the detection of benzene ( c-C ₆H ₆) in the upper atmospheres of Jupiter at midlatitudes and Saturn (disk average). Observations with the Short-Wavelength Spectrometer of the Infrared Space Observatory reveal emission from the Q-branch of benzene around 14.84 μm on these two planets but not on Uranus and Neptune. Column densities have been derived through radiative transfer calculations assuming various mixing ratio profiles. The inferred abundances are 9 ^+4.5_-7.5×10 ¹⁴ molecules cm ^-2 above the 50-mbar level on Jupiter and 4.7 ^+2.1_-1.1×10 ¹³ molecules cm ^-2 above the 10-mbar level on Saturn. Upper limits have been derived for Uranus and Neptune. Results are compared with existing chemical models.