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Samuel Glasstone, in The Book of Mars (NASA, 1968, p. 109), wrote

"In 1934, the German-born astronomer Rupert Wildt suggested that the bright areas on Mars were composed 'of strongly oxidized sandy formations, with iron almost completely in the form of the oxide Fe2O3 [ferric oxide].'"

Does someone know the original paper by Wildt? Or an earlier sugestion that the red hue of the dust is due to iron oxides?

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Rupert Wildt, "Ozon und Sauerstoff in den Planetenatmosphären." Veröffentlichungen der Universitäts-Sternwarte zu Göttingen 3 (1933): 151-159 (scan online)

Will man die Annahme gelten lassen, daß die Zufuhr juvenilen Kohlendioxyds in der Entstehungsgeschichte des Mars von der gleichen Größenordnung wie bei Erde und Venus war, so folgt aus dem heutigen spärlichen Vorkommen von freiem Sauerstoff, daß in der Vergangenheit das Kohlendioxyd sehr vollständig zur Photosynthese verbraucht und der abgespaltene Sauerstoff wieder fossil geworden ist. Im Einklang damit würde die Beobachtung stehen, daß ausgedehnte Teile der Marsoberfläche eine stark rötliche Tönung aufweisen; diese lassen sich am einfachsten als stark oxydierte Sandsteinformationen, deren Eisen fast nur als Fe2O3 vorläge, deuten. Bemerkenswert ist in diesem Zusammenhang, daß die Venusoberfläche keine Farbtönung aufweist;

My translation: "If one accepts the assumption that the supply of juvenile carbon dioxide during the formation history of Mars was on the same order of magnitude as on Earth and Venus, the conclusion to be drawn from the rarity of free oxygen at present is that the carbon dioxide was completely used up by photosynthesis in the past and that the oxygen generated from it has become fossil again. Consistent with that would be the observation that extensive parts of Mars' surface show a strong reddish hue; the most straightforward interpretation is that these are formations of highly oxidized sandstone, in which iron occurs almost exclusively as Fe2O3. In this context it is noteworthy that the surface of Venus does not show any color hues;"

Above I cited Wildt's publication as it is currently being cited by Google Scholar. His notice is dated December 23, 1933, but it was presented in a meeting on January 12, 1934. Various publications citing Wildt use the following style:

Rupert Wildt, "Ozon und Sauerstoff in den Planetenatmosphären." Veröffentlichungen der Universitäts-Sternwarte zu Göttingen, No. 38 (1934)

Best I could determine from a quick review of the literature, Wildt was the first to suggest that the reddish color of Mars could be due to iron oxide in sandstone by analogy with terrestrial varieties of sandstone of a reddish color.

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  • $\begingroup$ Thanks a lot! I came accross the paper but the title didn't suggest martian surface as topic. $\endgroup$
    – Leos Ondra
    Mar 14 '21 at 21:17

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