Volume 579, July 2015
|Number of page(s)||5|
|Section||Planets and planetary systems|
|Published online||15 July 2015|
New constraints on the CH4 vertical profile in Uranus and Neptune from Herschel observations⋆
LESIA, Observatoire de Paris,
5 place Jules Janssen,
2 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive Pasadena, CA 91109, USA
3 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
4 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
5 Space Science Institute, 4750 Walnut St., Suite 205, Boulder, CO 80301, USA
6 Faculty of Science, Kyoto Sangyo University. Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555, Japan
Received: 12 May 2015
Accepted: 12 June 2015
Dedicated line observations of CH4 rotational lines performed with Herschel/PACS and HIFI in 2009–2011 provide new inferences of the mean methane profile in the upper tropospheres and stratospheres of Uranus and Neptune. At Uranus, CH4 is found to be near saturation, with a ~9 × 10-4 tropopause/lower stratosphere mole fraction. This is nominally six times larger than inferred from Spitzer in 2007, although reconciliation may be possible if the CH4 abundance decreases sharply from ~100 to 2 mbar. This unexpected situation might reflect heterogeneous conditions in Uranus’ stratosphere, with local CH4 depletions and heating associated with downwelling motions. Higher CH4 abundances compared to values inferred under solstitial conditions by Voyager in 1989 suggest that atmospheric mixing is effectively subdued at high latitudes and/or is time-variable. At Neptune, the mid-stratosphere CH4 abundance is (1.15 ± 0.10) × 10-3, in agreement with earlier determinations and indicative of either leakage through a warmer polar region or upwelling at low or middle latitudes. On both planets, spatially resolved observations of temperature and methane in the stratosphere are needed to further identify the physical processes at work.
Key words: planetary systems / planets and satellites: gaseous planets / planets and satellites: individual: Uranus / planets and satellites: individual: Neptune
© ESO, 2015
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.