The first one was made by the Viking Orbiter 1 spacecraft in 1980 (Duxbury and Ocampo, 1988) and brought a negative result, setting the upper limit of the normal optical depth of the putative tori to τ ≲ 3 × 10 − 5 {\displaystyle \tau \lesssim 3\times 10^{-5}} .
2006 August, Alexander V. Krivov, Artem G. Feofilov, Valeri V. Dikarev, “Search for the putative dust belts of Mars: The late 2007 opportunity”, in Planetary and Space Science, volume 54, numbers 9–10, page 871