|Probing the atmospheres of Uranus, Neptune and Titan with CH4 lines
|Methane is a key species in the Outer Planets. It is the third most abundant molecule in all four Giant Planets, with an abundance of about 2 % in Uranus and Neptune, and reaching 5% (of N2) at the surface of Titan. Because of its large abundance, methane plays a dominant role in governing the atmospheric chemistry of all these planets. Indeed, the photolysis of methane by solar photons initiates a complex chemistry, giving rise to a wealth of hydrocarbons. In the case of Titan, the photochemistry of methane is even more complex, because of the coupled CH4-N2 chemistry taking place in Titan.s upper atmosphere. Initial observations of Neptune and Titan, performed in the framework of the GT-KP ..Water and related chemistry in the Solar System. (PI: P. Hartogh) have allowed the detection of CH4 emission at 119.6 micron and in several other lines, but with a low spectral resolution. These measurements have constrained the stratospheric abundance of CH4. In the case of Uranus, the PACS measurements of the CH4 line at 159 microns shows only tropospheric absorption, and with a low signal-to-noise ratio. The goal of this proposal is to use the high spectral resolution of HIFI in order to resolve the 1882 GHz methane lines on Neptune and Titan. These optically thick lines will allow to constrain the vertical temperature profiles in their stratospheres, and in Neptune.s case, the vertical distribution of methane. For Uranus, we propose to observe again the methane line at 159 micron with PACS, but with a gain of a factor 3 in sensitivity, in order to confirm the detection and better constrain its abundance.
|New constraints on the CH4 vertical profile in Uranus and Neptune from Herschel observations . Lellouch E. et al. . Astronomy & Astrophysics, Volume 579, id.A121, 5 pp. . 579 . 10.1051/0004-6361/201526518 . 2015A&A...579A.121L ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2012, OT1_rmoreno_2, SPG v14.2.0. https://doi.org/10.5270/esa-84d9adp