Surface geology from Viking landers on Mars: A second look

Abstract

Aside from reddish dust, products of martian weathering are not abundantly obvious on Viking lander images. Surface stones appear sound, spalls and disintegration fragments are largely lacking, pitting of stones is probably not due to differential weathering, and reddish stone colors more likely result from adhered dust than from patination. Judging from wind-scoured drifts, deflated ground, rippled bed forms, lee-side tails, basal scours, fretted rocks, and ubiquitous dust, wind is currently the most effective transportive and erosive agent. The dogma that martian eolian material is almost exclusively of 10–100 µ size is challenged by granule ripples and the possibility that wind-drifted deposits consist largely of sand-sized particles. Fretting is more common than faceting on martian ventifacts. Crusts on martian surface fines are more akin to case-hardened rinds than to true duricrust. Crusting, a possibly continuing process, may be the product of atmospheric breathing of the regolith. Pits on surfaces of many martian stones are probably vesicles modified by eolian erosion. Pits on nonvesicular rocks may be solely the product of wind blasting. Vesicular lava, dense lava, and breccias are the most likely rocks among surface stones around the landers. The “bedrock” outcrops near VL-1 may be large boulders embedded in a breccia substrate. Pyroclastics seem a likely constituent of surface deposits.