Interpretation of some Martian features.

Abstract

The morphology of Martian maria, long neglected, is believed to contain important clues to their origin. (I) Most maria of the south tropical belt are elongated strips trending southeast. (2) All have tributary or terminal pointed bays on their north sides or northwest ends. (3) Bays that lie north of the equator hook back, barb- like, towards the northeast (Dawes' forked bay, Syrtis Major, Margaritifer Sinus). (4) Bays south of the equator do not hook back. (5) Some of the strongest canals of the northern hemisphere trend northeast (Cerberus, Thoth). Trends of maria and strong canals are those of the trade winds. They are interpreted as dust deposited by prevailing winds. The strongest winds will be those of the southern summer, near perihelion. These must show a monsoon effect, crossing the equator from north to south, being deflected to the left by the planet's rotation, to become northwest anti-trade winds. The Martian map shows a striking flow pattern agreeing with this expectation. Vertices of the bays are now recognizable as point sources of dark dust. Consideration of all geological processes points to only one possible explanation. These vertices are interpreted as sites of active volcanoes that erupt great amounts of ash. The green color of the maria, long attributed to vegetation, is regarded as due to weathering of ferromagnesian ash. On earth, with abundant oxygen, soils are colored red, yellow, and brown by iron oxide and hydroxide. On Mars, with no oxygen, reaction with water and carbon dioxide yields the green secondary minerals, chlorite and epidote, a process well-known in underground terrestrial weathering. The Observatory, University of Michigan, Ann Arbor, Mich.