Geology of Mars

Prathamesh S. PawarM.Sc. (I) Geology,Dept. of Geology,

S. P. Pune University

Mars - Introduction

• Red Planet; named Mars by Romans after their god of war

• 4th Planet; distance from sun 230 million km• Oblate spheroid, bulged at equator• Radius 3400 km, almost the size of Earth’s core• Very thin atmosphere, dominated by CO2

• Polar ice caps containing dry ice and water ice• Almost no active geology

Exploration

Why Mars?

• Life?• WATER???• Studying geology- minerals/rocks which need

presence of water to form e.g. clays, and sedimentary rocks

• Habitability, colonization?

Gravity

• Very less• 0.375 times Earth’s gravity• Because of lesser mass and lesser

Magnetism

• Currently almost no magnetism.• Suggests solidified core .• Older rocks, especially from southern

hemisphere show magnetism.• Might had ability to generate magnetic field

during the initial 0.5 to 1 billion years of its formation.

Interior of Mars• Crust

– Average thickness is 60-70 km; Thicker than earth’s crust; thinner in northern hemisphere and thicker in southern

– Composition wise similar to Earth’s crust; not divided in plates Mantle– Average thickness 1500 km– Silicate composition; richer in Fe content than Earth– No convection, probably little convection happened in primordial

mantle giving rise to bulges Core– Composed of Fe and S; might be richer in S– Most probably solidified, no liquid, as suggested by absence of

magnetism– Although Older rocks on mars do show some magnetic properties

indicating that early martian core had a molten part which induced magnetism

Mineralogy and Petrology

• Currently we know only the surface mineralogy and petrology which is dominated by Silicates

• Primary – basic igneous rocks (basalts & andesites), volcanic ash

• Secondary – sedimentary rocks (sandstones and conglomerates), secondary minerals (clays, hematite) and soils/regolith

• No spacecraft or rover have encountered a metamorphic rock on the surface

Sojourner rover analyzing a rock

Primary Minerals & Rocks

• Igneous planet - Basalts widespread - olivine, pyroxenes (both opx & cpx), plagioclases

• Cpx present in younger volcanics while opx in older ones, indicating that older melts had higher temperature than younger ones

• Some areas show presence of andesitic lavas• Intermediate and such more fractionated

igneous rocks are very rare

Secondary Minerals

• Products of weathering – Clays like smectite, hematite, goethite

• Products of hydrothermal origin and alteration - iron sulphates, opaline silica, gypsum

• Soils are similar to basaltic soils found on the Earth

Hematite spherules

• Most conspicuous of all minerals seen on Mars

• Seen by the Opportunity rover

• Debated origin – most probably formed in shallow, agitated waters (like oolites)

Sedimentary Rocks

• Lithified as well as unconsolidated sediments are common in interiors of canyons, large craters and in northern lowlands

• Identified sediments are of aeolian and fluvial in origin

• Sandstones & conglomerates are common; carbonates & evaporites are relatively rare

• Sandstones show primary structures like horizontal and cross bedding

Global Physiography

• Crustal dichotomy• Northern hemisphere dominated by huge,

continuous lowland (thought to be a giant impact feature) – average crustal thickness 30 km

• Southern hemisphere dominated by rugged, old highlands – average crustal thickness 60 km

• Topography dominated by impact craters, volcanoes, lava plains, huge canyons and valleys

Common Landforms

• Volcanoes• Lava flows and plains• Gullies• Fans and cones• Valley networks• Chaos terrains and outflow channels• Mesas and buttes• Dunes• Impact craters

Volcanoes• Huge volcanoes sitting on

massive crustal bulges• Two main regions- Tharsis

and Elysium• Giant shield volcanoes,

comparable to those of Hawaii but very larger - hundreds of km across and tens of km high

• Multiple and overlapping calderas

• Large size is representative of no tectonic movements

Olympus Mons

• Largest volcano in the solar system

• Giant shield volcano in Tharsis region

• Nearly 22 km high – 3 times higher than Mt. Everest

• 600 km wide• Estimated age varies

from 2 My to 350 My

Lava Flows and volcanic plains

• Widespread around Tharsis and Elysium volcanic provinces

• Two types – sheet flows and channel flows

• Channel flows are comparatively rare

Gullies• Erosional features• Common on crater rims, older volcanoes, hills and

valley margins• Origin debated, but probably due to seasonal freeze

& thaw of CO2

Fans

• Closely resemble terrestrial alluvial fans

• Liquid water suspected in formation

• Aged between 3-4 By

Valley Networks

• Branching networks of valleys closely resembling river drainage patterns on Earth

• Prominent in southern highlands, extend upto hundreds of km

• Important in deciphering the role of liquid water in Martian history

Chaos terrains• Very peculiar features; consists of irregular groups

of large blocks, some tens of km across and a hundred or more meters high

• These blocks might show show shapes resembling mesas and buttes

• Thought to be formed because of sudden release of huge quantities of liquid water, most probably due to sudden melting of ground-ice

Outflow channels• These are wide, deep

channels created by large amounts of flowing water which was released through chaos terrains

• Originate from a chaos terrain and end in vast plains

• Show streamlined island like erosional features

Dunes• Typical aeolian landforms• Common in northern plains• Show typical types like longitudinal,

barchans and many complex types

Impact craters• The most widespread & prominent landform• A variety of sizes and types observed• Vary from few cm to tens of km deep and thousands of km across• Oldest known craters are nearly 4 By old while new ones are still

being formed

Thank You…