A&A 430, L37-L40 (2005)
A dual origin for Neptune's carbon monoxide?E. Lellouch1, R. Moreno1 and G. Paubert 2
1 Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, 92195 Meudon, France
2 Institut de Radio-Astronomie Millimétrique, 18080 Granada, Spain
(Received 5 November 2004 / Accepted 14 December 2004)
Heterodyne observations of Neptune have provided a measurement of the CO(2-1) line profile with a total bandpass of almost 8 GHz and a resolution of 4 MHz. The lineshape indicates that the CO mole fraction in Neptune's atmosphere is not uniform, but increases by a factor of ~2 from the troposphere/lower stratosphere (0.5 ppm at p>20 mbar) to the upper stratosphere (1 ppm at p<20 mbar). This indicates the existence of both external and internal sources of CO. The equivalent flux associated with the external source is ~ cm -2 s -1. We propose that the stratospheric CO results from a large (2 km) cometary impact that occurred ~200 years ago, although there remains problems with this hypothesis.
Key words: planets and satellites: Neptune -- radio-lines: solar system
© ESO 2005