Uranus's Northern Polar Cap in 2014. Issue 11 (14th June 2018)

• Record Type: Journal Article
• Authors: Toledo, Daniel; Irwin, Patrick G. J.; Teanby, Nicholas A.; Simon, Amy A.; Wong, Michael H.; Orton, Glenn S.
• Is Part Of: Geophysical research letters. Volume 45:Issue 11(2018)
• Page Start: 5329
• Page End: 5335
• Publication Date: 2018-06-14
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL077654
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: In October and November 2014, spectra covering the 1.436 to 1.863‐μm wavelength range from the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope showed the presence of a vast bright north polar cap on Uranus, extending northward from about 40°N and at all longitudes observed. The feature, first detected in August 2014 from Keck telescope images, has a morphology very similar to the southern polar cap that was seen to fade before the 2007 equinox. At strong methane‐absorbing wavelengths (for which only the high troposphere or stratosphere is sampled) the feature is not visible, indicating that it is not a stratospheric phenomenon. We show that the observed northern bright polar cap results mainly from a decrease in the tropospheric methane mixing ratio, rather than from a possible latitudinal variation of the optical properties or abundance of aerosol, implying an increase in polar downwelling near the tropopause level. Plain Language Summary: In this paper we show that Uranus's northern polar cap in 2014 results from a hole‐like depletion of methane rather than a formation or accumulation of aerosols as was previously thought. In this regard, our results provide key insights on the Uranus postequinox circulation as well as on the formation and nature of the different bright features observed before and after 2007 equinox in both hemispheres. Key Points: The polar cap observed in 2014 results from a decrease in the tropospheric methane mixing ratio Very similar haze and cloud scattering properties are observed at latitudes within and far away from the polar cap