HST/WFC3 observations of Uranus’ 2014 storm clouds and comparison with VLT/SINFONI and IRTF/Spex observations

摘要

Highlights ? Major storm event on Uranus probed with HST/WFC3 filter imaging in November 2014. ? Observations compared with lower spatial resolution H-band VLT/SINFONI observations. ? Main cloud resolved to have two components at different pressure levels. ? Spectra (and IRTF/SpeX spectrum) fitted with simple 3-layer model using NEMESIS. ? Cloud model determined that simultaneously matches observations from 0.467 ? 1.8 μ m. Abstract In November 2014 Uranus was observed with the Wide Field Camera 3 (WFC3) instrument of the Hubble Space Telescope as part of the Hubble 2020: Outer Planet Atmospheres Legacy program, OPAL. OPAL annually maps Jupiter, Uranus and Neptune (and will also map Saturn from 2018) in several visible/near-infrared wavelength filters. The Uranus 2014 OPAL observations were made on the 8/9th November at a time when a huge cloud complex, first observed by de Pater et?al. (2015) and subsequently tracked by professional and amateur astronomers (Sayanagi et?al., 2016), was present at 30–40°N. We imaged the entire visible atmosphere, including the storm system, in seven filters spanning 467–924? nm, capturing variations in the coloration of Uranus’ clouds and also vertical distribution due to wavelength dependent changes in Rayleigh scattering and methane absorption optical depth. Here we analyse these new HST observations with the NEMESIS radiative-transfer and retrieval code in multiple-scattering mode to determine the vertical cloud structure in and around the storm cloud system. The same storm system was also observed in the H-band (1.4–1.8?μm) with the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope (VLT) on 31st October and 11th November, reported by Irwin et?al. (20