Variable features on Mars, 2, Mariner 9 global results

Abstract

Systematic Mariner 9 monitoring of the space and time distribution of Martian bright and dark markings, the streaks and splotches, indicates a range of global correlations. The time variable classical dark markings owe their configurations and variability to their constituent streaks and splotches, produced by windblown dust. Streaks and splotches are consistent wind direction indicators. Correlation of global streak patterns with general circulation models shows that velocities ∼50 to 90 m/sec above the boundary layer are necessary to initiate grain motion on the surface and to produce streaks and splotches. Detailed examples of changes in Syrtis Major, Lunae Palus, and Promethei Sinus are generally consistent with removal of bright sand and dust and uncovering of darker underlying material as the active agent in such changes, although dark mobile material probably also exists on Mars. The generation of streaks and the progressive albedo changes observed require only threshold velocities of about 2 m/sec for about 1 day at the grain surface. We propose that the dark collar observed following the north polar cap in its retreat is produced by the scouring of bright overlying dust from the polar peripheral ground by winds driven by the temperature differences between frosted and unfrosted terrain. The stability of bright streaks and the variability of dark streaks and splotches, as well as their contrast, can be the result of size differences of the constituent particles.

Wind streaks: geological and botanical effects on surface albedo contrast

“…Flow of dust-laden wind past a topographic obstacle such as a hill or a crater produces a dead zone in its lee in which dust deposition is increased. Because the albedo of dust-sized particles is generally much higher than the material from which the dust is derived, the resulting depositional streak is brighter than its surroundings Pollack and Sagan, 1969;Sagan et al, 1973). An entirely different situation arises when the atmosphere is not laden with dust.…”

“…1); they have been used to assess regional and global wind circulation patterns on both planets (Arvidson, 1974;Thomas and Veverka, 1979;Thomas et al, 1981;Veverka et al, 1981;Ward et al, 1985;Wells and Zimbelman, 1989;Saunders et al, 1990;Greeley et al, 1992). Some martian wind streaks were observed to have changed between Viking observations (Sagan et al, 1973;Thomas and Veverka, 19791, proving that some sort of surface process was presently operating, with the wind being the only reasonable candidate. Most recently, Magellan radar observations of the venusian surface have revealed albedo features that are almost certainly a result of aeolian activity (Saunders et al, 1990;Greeley and Arvidson, 1990;Greeley et al, 1992).…”

New views of Mars eolian activity, materials, and surface properties: Three vignettes from the Mars Global Surveyor Mars Orbiter Camera

“…As spacecraft began to explore the planet, a geological interpretation emerged that invoked eolian erosion and deposition of bright dust to explain the albedo patterns and observed changes [Rea, 1964;Sagan and Pollack, 1969]. The arrival of Mariner 9 during a major global dust obscuration event in November 1971, followed by the gradual clearing of the atmosphere and observation of rapid changes in surface albedo patterns [Sagan et al, 1972[Sagan et al, , 1973 …”

Surface features on Mars: Ground-based albedo and radar compared with Mariner 9 topography

“…Transport of bright, fine particles onto or off underlying dark regions can also explain the observed albedo effects; seasonal winds and longer-term climatic changes account for the deposition and removal of the dust (Sagan and Pollack, 1969;Sagan, et al, 1971: Sagan, et al, 1972 -3 - Sagan, et al, 1973). The advantage to this model is that it is subject to test; biological models are ad hoc, as differences in the unknown life forms from their terrestrial counterparts can be invoked to explain minor discrepancies between theory and observation.…”

“…Sagan, et al(1973Sagan, et al( , 1972, find that strong seasonal and secular albedo variations on Mars can be understood in terms of the production and destruction of crater wind tails. Bright streaks in the lee of craters probably result from the deposition of bright fines; dark tails may be the scouring of fines off darker subsurface material, or, in some cases, may be the deposition of dark material (Sagan, et al, 1972, Figure 27).…”