EDP Sciences
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Volume 430, Number 2, February I 2005
Page(s) L37 - L40
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200400127

A&A 430, L37-L40 (2005)
DOI: 10.1051/0004-6361:200400127


A dual origin for Neptune's carbon monoxide?

E. Lellouch1, R. Moreno1 and G. Paubert


1  Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, 92195 Meudon, France
    e-mail: emmanuel.lellouch@obspm.fr
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 ~ $1\times10^8$ 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