Title
Episodic bright and dark spots on Uranus
Date Issued
01 July 2012
Access level
open access
Resource Type
journal article
Author(s)
Sromovsky L.A.
Hammel H.B.
de Pater I.
Fry P.M.
Rages K.A.
Showalter M.R.
Merline W.J.
Tamblyn P.
Neyman C.
Margot J.L.
Fang J.
Dauvergne J.L.
Gómez-Forrellad J.M.
Hueso R.
Sánchez-Lavega A.
Stallard T.
Observatoire de Paris
Abstract
The northern mid-latitudes of Uranus produce greater episodes of bright cloud formation than any other region on the planet. Near 30°N, very bright cloud features were observed in 1999, 2004, and 2005, with lifetimes of the order of months. In October 2011, Gemini and HST observations revealed another unusually bright cloud feature near 23°N, which was subsequently identified in July 2011 observations and found to be increasing in brightness. Observations obtained at Keck in November 2011 revealed a second bright spot only 2°N of the first, but with a substantially different drift rate (-9.2°E/day vs -1.4°E/day), which we later determined would lead to a close approach on 25 December 2011. A Hubble Target of Opportunity proposal was activated to image the results of the interaction. We found that the original bright spot had faded dramatically before the HST observations had begun and the second bright spot was found to be a companion of a new dark spot on Uranus, only the second ever observed. Both spots exhibited variable drift rates during the nearly 5. months of tracking, and both varied in brightness, with BS1 reaching its observed peak on 26 October 2011, and BS2 on 11 November 2011. Altitude measurements based on near-IR imaging in H and Hcont filters showed that the deeper BS2 clouds were located near the methane condensation level (≈1.2. bars), while BS1 was generally ∼500. mb above that level (at lower pressures). Large morphological changes in the bright cloud features suggest that they are companion clouds of possibly orographic nature associated with vortex circulations, perhaps similar to companion clouds associated with the Great Dark Spot on Neptune, but in this case at a much smaller size scale, spanning only a few degrees of longitude at their greatest extents. © 2012 Elsevier Inc..
Start page
6
End page
22
Volume
220
Issue
1
Language
English
OCDE Knowledge area
Astronomía
Scopus EID
2-s2.0-84860877875
Source
Icarus
ISSN of the container
10902643
Sponsor(s)
We thank Michael Brown of Caltech for contributing his 19 September 2011 Keck images of Uranus to this investigation. This research was partly based on Hubble Space Telescope observations. We thank William Januszewski of STScI for help in setting up the Hubble TOO Program. We thank Thomas Gaballe of the Gemini Observatory for assistance with our Gemini-North observations. We thank Elie Rousset and Philippe Tosi who assisted with the observations of Uranus from Pic du Midi. We thank Team Keck (science staff at the W. M. Keck Observatory) for contribution of telescope time and for technical assistance with some of the observations. The Keck Observatory is made possible by the generous financial support of the W. M. Keck Foundation. We also thank two anonymous reviewers who made useful suggestions to improve the paper. L.A.S. and P.M.F. acknowledge support by Grants from the Space Telescope Science Institute and NASA’s Planetary Astronomy and Planetary Atmospheres Programs. I.D.P. acknowledges support by NASA Grant NNX07AK70G. R.H. and A.S.L. are supported by the Spanish MICIIN Project AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07. This work was partially supported by an RCUK Fellowship and an STFC Standard Grant for T.S. We thank those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality few of our groundbased observations would have been possible.
Sources of information: Directorio de Producción Científica Scopus