Ancient Glaciation on Mars By J. Kargel, R. Strom presented by Megan Simpson

Could it have once looked like this? Glaciers? On Mars?

Introduction Glaciation has been used to explain certain features on Mars in the past This paper expands on several aspects –the distribution and characteristics of the esker –the chronology of glaciation

What is an esker? Long sinuous ridges are widely distributed on Mars These resemble terrestrial eskers which are elevated ridges of glaciofluvial sediment Peculiar because, unlike stream beds, they: –cross topographic divides –have very low and high tributary junction angles and rectilinear patterns –have discontinuities and variations in width and height –often reside within subglacially eroded tunnel valleys

Martian Ridges similar to Terrestrial Eskers Subhorizontal layering Ridge crests that are sharply crested, rounded, flat-topped or double-crested Individual ridges measure km long, km wide, m high which coincide with the upper end of the terrestrial esker scale

Evidence for Glaciation in Argyre Ancient impact basin on Mars, lat 51° S, long 42° Evidence includes: segmented esker systems, tunnel valleys, glacial outwash and glaciolacustrine plains, glacial erosion, rock glaciers, kettles, ice/meltwater sculptured hills, glacial grooves and ridges These landscapes suggest erosion and deposition by ice and meltwater

a. anastomosing sinuous ridge b. double-ridged, rounded, sharp-crested c. sharp crested ridge d. rock glaciers e. braided fluvial deposit f. massive ice disintegration g. kettle plains h. floor eroded by ice/meltwater i. uplands with esker, tunnel valley system Argyre

Evidence for Glaciation in Hellas Impact basin, lat 45°S, long 290° Deep erosional scouring Erosional lineations trend downslope Fluvial channels consistent with erosion by meltwater Terrain ends on the floor of Hellas with landforms that suggest glacial deposition and massive ice disintegration

Hellas

a. glacial scouring (~250 km wide) b. cuspate ridges interpreted as terminal moraines (~250 km wide) c. probable proglacial lake region (~ 270 km wide) More Hellas

More More Evidence South Polar Region Region near lat 78°S, long 40° Largest sinuous ridge system on the planet Glacial features include lineated terrain, etched pits, scouring by ice streams, radiating patterns resembling glacial finger lakes

Even More Evidence Northern Plains Arcuate, cuspate ridges - ‘thumbprint terrain’ Interpreted as ice-pushed ridges Concentrated in the region 30° - 50°N Scale of these ridges indicates deposition in fairly deep water

Global Distribution Many more probable glacial landscapes Concentrated south of 33°S and in Northern Plains Glaciation was NOT global Ice may have covered 18% of Mars

Surface Melting Favored Most glacial features resulted from stagnant or recessional glacial conditions requiring melting ice This would require a dense greenhouse effect These glacial landscapes similar to terrestrial landscapes that formed from a transition to temperate conditions

Source/Age/Duration Martian glacial landscapes required extensive water cycling Episodic northern oceans may have been the source Age of glaciation determined by use of cratering relations –indicates episodes occurred late in Martian history Duration uncertain, but small bit of geologic time (~ 2 million years)

Conclusion Mars landscapes similar to terrestrial landscapes formed by glaciation Glaciation has been important on Mars Landscapes occur south of ~33°S and in Northern Plains, suggesting huge ice sheets Many glacial landforms produced by meltwater, late in Martian history This may mean Mars had a warm, moist climate and dense atmosphere much later than previously believed Most landscapes have been preserved, suggesting a quick change from a warm, humid climate to cold, dry climate