Dramatic Change in Jupiter's Great Red Spot From Spacecraft Observations

Abstract

Jupiter's Great Red Spot (GRS) is one of its most distinct and enduring features. Since the advent of modern telescopes, keen observers have noted its appearance and documented a change in shape from very oblong to oval, confirmed in measurements from spacecraft data. It currently spans the smallest latitude and longitude size ever recorded. Here we show that this change has been accompanied by an increase in cloud/haze reflectance as sensed in methane gas absorption bands, increased absorption at wavelengths shorter than 500 nm, and increased spectral slope between 500 and 630 nm. These changes occurred between 2012 and 2014, without a significant change in internal tangential wind speeds; the decreased size results in a 3.2 day horizontal cloud circulation period, shorter than previously observed. As the GRS has narrowed in latitude, it interacts less with the jets flanking its north and south edges, perhaps allowing for less cloud mixing and longer UV irradiation of cloud and aerosol particles. Given its long life and observational record, we expect that future modeling of the GRS's changes, in concert with laboratory flow experiments, will drive our understanding of vortex evolution and stability in a confined flow field crucial for comparison with other planetary atmospheres.

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

“…(left) in 2000, as obtained by Cassini/VIMS and provided in the supplementary data of Carlson et al (2016); (second from left) the same spectrum, but normalised to an I/F value of 0.83 at 673 nm as suggested by Carlson et al (2016) in order to be in line with contemporaneous observations of the GRS (although Sromovsky et al (2017) suggest an intermediate scaling factor of 1.12 times the spectrum on the far left, based on comparisons of disc-averaged spectra of Jupiter); (second from right) in 2014, as obtained by VLT/MUSE before the simultaneous shrinking and reddening events described in Simon et al (2014Simon et al ( , 2018; and (right) in 2018, as obtained by VLT/MUSE after the shrinking and reddening of the GRS. In the case of the GRS (2000) spectra, we smoothed the methane k-tables and solar spectra to 7 nm resolution to be in keeping the VIMS-V spectral sampling before performing our retrievals.…”

“…The fit of this optimal chromophore solution to spectra of the GRS before and after the reddening events reported by Simon et al (2014Simon et al ( , 2018 2018, as we also show clearly in figure 10. Nonetheless, we should also note that the general fit to the Cassini/VIMS spectrum of the GRS from 2000, as calibrated and supplied by Carlson et al (2016), is poorer than to the MUSE spectra from 2014 and 2018, regardless of the model used.…”

“…However, elements of Jupiter's appearance have changed considerably since the Cassini flyby. We note in particular the dramatic reddening of the Great Red Spot (GRS) that has accompanied its progressive shrinking in size (Simon et al, 2014(Simon et al, , 2018, as well as progressive cycles of colour changes in the southern North Temperate Belt (NTB) as reviewed by Rogers (1995) and Fletcher (2017). These provide additional opportunities for constraint of the origin and altitude of chromophores in Jupiter's atmosphere that were not previously available.…”

Jupiter cloud morphology and zonal winds from ground‐based observations before and during Juno's first perijove

“…The difference could be due to different measuring methods (we define the size of the GRS as the apparent size of the dark oval in blue wavelength images; our measurements for the GRS size over HST images in 2015 are 13.9 ± 0.2° and 10.2 ± 0.2°; see supporting information Figure S9). Amateur and PlanetCam images over December 2015 to July 2016 show a constant size within an uncertainty of 0.2° implying that the diminishing size of the GRS over the last decades [ Simon et al , ] may have reached a stable configuration. Oval BA [ Sánchez‐Lavega et al , ] did not experience major changes over 2016.…”

Spectral comparison and stability of red regions on Jupiter

“…However, it is known that the GRS color can change quite dramatically from time to time [ Peek , ], unfortunately, no data were obtained when it was in its very palest state, such as in 2012; its most dramatic red state was captured in the 2014 data and is further discussed in Simon et al . []. Over the time range shown in Figure , the GRS core shows more variability at shorter wavelengths than the reddest spots of the NEB.…”