Evidence that the Dark Areas on Mars are Elevated Mountain Ranges

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IN the communication under the above title1, Dr. Wells makes a good point in reference to Lowell's conclusion regarding Martian topography. It agrees in part with the phenomena I have often observed, namely, that the migration of portions of some maria and gradual shading off of some low-cloud or frost areas implies very gradual slopes2. But even in the case of abrupt topographic differences, I think Lowell was over-optimistic in his value of 2,500 ft. It must be remembered that the maximum phase occurs at about twice the oppositional distance. At that time the terrain slopes away from the observer at about 45°. Furthermore, the colour contrasts of both maria and deserts show a marked drop at about half the radius from the centre of the planet's disk, apparently from the Martian atmosphere. There is also the troublesome factor of irradiation. Mars has some twilight effects, further lessening the contrast. The total of these effects and the limitation of detail under the best ‘seeing conditions’ makes an abrupt topographic difference of 20,000 ft. or less impossible to detect.

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  1. 1

    Wells, R. A., Nature, 207, 735 (1965).

  2. 2

    Tombaugh, C. W., Provisional Topographic Maps of Mars—Mariner 4 Region, Publ. New Mexico State Univ. Obs. TN-701-66-8, NASA (1965).

  3. 3

    Tombaugh, C. W., The Absence of an Aqueous Morphology on Mars and some Geologic Consequences, Publ. New Mexico State Univ. Obs. TN-557-65-6, NASA (1960).

  4. 4

    Tombaugh, C. W., Astro. J., 55 (1950).

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TOMBAUGH, C. Evidence that the Dark Areas on Mars are Elevated Mountain Ranges. Nature 209, 1338 (1966) doi:10.1038/2091338a0

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