Evolution of a Dark Vortex on Neptune with Transient Secondary Features

Dark spots on Neptune observed by Voyager and the Hubble Space Telescope are
thought to be anticyclones with lifetimes of a few years, in contrast with very long-lived
anticyclones in Jupiter and Saturn. The full life cycle of any Neptune dark spot has not
been captured due to limited temporal coverage, but our Hubble observations of a recent
feature, NDS-2018, provide the most complete long-term observational history of any
dark vortex on Neptune. Past observations suggest some dark spots meet their demise by fading and dissipating without migrating meridionally. On the other hand, simulations
predict a second pathway with equatorward migration and disruption. Our HST
observations suggest NDS-2018 is following the second pathway.