Chromophores from photolyzed ammonia reacting with acetylene: Application to Jupiter's Great Red Spot

Colour and tropospheric cloud structure of Jupiter from MUSE/VLT: Retrieving a universal chromophore

“…• As we were able to fit the shape of the shortwave spectral feature of both the belts and the GRS well using the same chromophore compound, we cannot rule out the possibility of a universal chromophore as proposed by Sromovsky et al (2017). However, in order to fit the most recent observations of the GRS following its recent intensification in colour, we found that this chromophore compound required steeper blue-absorption than could be provided by the tabulated optical constants of Carlson et al (2016) in order to be in keeping with previous constraints on the opacity of the main cloud layer. This is nonetheless in keeping with a chromophore production mechanism involving photolysed ammonia reacting with acetylene as proposed by Ishikawa (1987, 1988), although the issue with the predicted relative absence of acetylene that would be required to produce chromophore in the troposphere according to this mechanism remains to be resolved.…”

“…Fit -observed Figure 7: Spectral fit to the NEB at five different viewing geometries, comparing the fit to the observed spectra (in black, with uncertainties shaded in grey) using six different chromophore models. In red is the fit using the Crï¿oeme Brï¿oelï¿oee model (Sromovsky et al, 2017;Baines et al, 2019) with the chromophore optical constants of Carlson et al (2016) (χ 2 /n = 3.22). We can see that this fails to fit the blue-absorption gradient of the spectrum of the NEB, underestimating the slope at the shortest wavelengths at low viewing angles while overestimating the slope at green wavelengths at high viewing angles.…”

“…Given our lack of knowledge of the uncertainty in the PSF, we have avoided performing retrievals close to Jupiter's terminator where the surrounding sky would have provided a non-negligible contribution to the observed spectrum. On top of these MUSE data, we also make use of a single ready-calibrated Cassini/VIMS spectrum of the GRS obtained in 2000, as provided in the supplementary material of Carlson et al (2016), to provide broader context to temporal changes in spectra of the GRS. We do not describe the calibration procedure of this latter observation here, instead we refer the reader to Baines et al (2019) for a more detailed explanation.…”

“…In all cases, we require a spectral slope between 476 nm and 600-650 nm that is greater than can be provided by the chromophore of Carlson et al (2016), as shown in Figure 9 and Table 3. Usually, our model does this by raising the imaginary refractive index at the shortest wavelengths, and decreasing it at longer wavelengths relative to Carlson et al (2016). We also retrieved a secondary absorption peak around 850 nm, although this could be a result of uncertainties in methane band absorption data as opposed to a genuine chromophore absorption feature.…”

“…We also retrieved a secondary absorption peak around 850 nm, although this could be a result of uncertainties in methane band absorption data as opposed to a genuine chromophore absorption feature. How-ever, we should clarify that the experimental uncertainties on the optical constants of the chromophore of Carlson et al (2016) were not published, and so it is possible that the uncertainty in the thickness of the chromophore film produced in the laboratory, or some other factor, may affect the value of the imaginary refractive index spectrum they derive. We therefore cannot rule out the possibility of red colour on Jupiter forming in a manner similar to that of the chromophore of Carlson et al (2016).…”