Jupiter's Great Red Spot Is Not Disintegrating by Flaking Apart

In May and June 2019, a worldwide network of amateur astronomers imaged Jupiter as the Great Red Spot (GRS) experienced unusual morphological changes. Red, high-altitude haze/cloud material extended outside the confines of the normal elliptical boundary of the GRS. The red material extended in patches referred to as "flakes" or "blades," which rotated counterclockwise around the GRS, primarily from its western side to its southeastern side. By examining the velocity field of the GRS, we determine that the flakes represent a superficial advection of red haze material in the upper troposphere, rather than an actual disruption or fragmentation of the GRS vortex, as has been suggested in some sensational media reports. The flaking events are thus similar to blowing some foam off the top of a full glass of beer, rather than spilling some of the beer itself out of the glass.

Two sets of 10-hour separated Hubble Space Telescope (HST) imaging data were used to measure the GRS velocity field. HST/WFC3 observations were taken on 9-10 April 2019 (before the flaking events in May/June 2019), and on 26 June 2019 after the events. Maximum and average wind speeds were the same (to within uncertainties) in April and June. The most significant velocity field change we found is an increase in the dynamical width of the GRS, from 10.1 deg to 11.6 deg longitude (with an uncertainty of 0.4 deg), as measured by the east-west distance between peak northward and southward winds. This preliminary result indicates an increase of about 1800 km, but more work is needed to constrain the general short-timescale variability in the GRS dynamical size and shape. If the red flakes were a sign of the disintegration of the GRS vortex, then its size and/or wind speeds would be expected to become smaller rather than larger.

Acknowledgement: This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute. These observations are associated with programs 13937, 14661, and 15665, with support provided by NASA through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.