A stringent upper limit to SO2 in the Martian atmosphere T. Encrenaz, T. K. Greathouse, M. J. Richter, J. H. Lacy, T. Fouchet, B. Bézard, F. Lefèvre, F. Forget and S. K. Atreya A&A, 530 (2011) A37 Published online: 04 May 2011 DOI: 10.1051/0004-6361/201116820