Geology of the Terrestrial

Planets: Moon, Mercury, Venus,

and Mars: An Introduction

Rosaly Lopes

JPL

Why do the terrestrial

planets and moons look so

different from each other?

The faces of the solid planets and

moons are a mix of the four major

processes in geology:

• Volcanism (volcanoes, lava flows)

• Impact cratering (craters)

• Erosion (by water, wind)

• Tectonism (mountains, faults)

The Moon:

Impact craters

and volcanoes

Earth’s Moon:

“seas” of lava

Lava flows in Mare Imbrium Marius Hills:

cones and domes

Hadley Rille

Lava channel

Lava channels

and tubes: Kilauea,

Hawaii

Euler Crater, Moon

28 km diameter, ~ 2.5 km

~18 mi, 1.5 mi)

Meteor Crater, Arizona, USA

1.2 km wide, ~200 m deep

(0.75 mi wide)

Age: ~ 49,000 years

Impact Craters

Impact craters on Earth

Tenoumer

The Araguainha Crater or Araguainha

Dome is an impact crater on the border of

Mato Grosso and Goias. Diameter = 40 km,

it is the second largest known impact crater

in South America, and possibly the oldest.

Serra da Cangalha Araguainha Crater

Serra da Cangalha is an impact crater in

the State of Tocantins, near the border of

Maranhão State, in northeastern Brazil.

The crater is between 12 and 13 km in

diameter, making it the second-largest

known crater in Brazil. Its age is estimated

to be about 220 million years (Triassic).

Vargeão Dome

The crater is an almost perfectly circular

depression with steep walls, 12 km in

diameter and up to 225 m deep relative to

its rim. Its age is estimated to be less than

70 million years

Other structures: Colônia, Vista Alegre

crater

Landsat/ETM+ image showing the central

uplift of Araguainha (a). Digital elevation

models of some Brazilian impact craters,

based on the Shuttle Radar Topography

Mission: (b) Serra da Cangalha; (c)

Riachão; (d) Vargeão. (Romano and Crosta,

2004)

Enhanced Color Map of Mercury

Raden Saleh Crater: ejecta rays

(crater ~23 km diameter)

Mickiewicz crater:

central peak

Oblique view of a 280 km long scarp. The color scale represents elevation in which

red is high and blue is low. This scarp is interpreted to be a surface-breaking thrust

fault. Thrust faults are surface manifestations of the shrinkage of the planet resulting

from the cooling of its interior. Notice that the terrain on the left side of the scarp

stands about 2 km higher than that of the right side of the scarp. The state of Delaware

has been superposed on the figure for scale.

Caloris basin, the

largest young impact

crater on Mercury,

dominates the scene.

With an east-west

diameter of 1,640

km, Caloris hosts a

wide variety of

tectonic features,

including graben,

ridges, and the

Pantheon Fossae.

Mercury: volcano

(~30 km diameter)

The role of volcanism in Mercury’s

history had been previously debated, but

MESSENGER’s discovery of the first

identified volcanoes on Mercury’s

surface shows that volcanism was active

in the distant past.

Venus: planet volcano!

Venus: recent volcanism

Sif Mons shield (2 km high)

Serova Patera (caldera)

• Surface covered with volcanic plains and a

variety of volcanic features

• Mostly effusive activity - 90 bar atmospheric

pressure and lack of water inhibits explosive

activity

• Lavas most likely basalts

• Thousands of caldera-like features (>1km

across)

• Calderas on Venus described as “circular to

elongate depressions not associated with a

well-defined edifice and are characterized

mainly by concentric patterns of enveloping

fractures” (Head et al., 1992, JGR 97)

• Typical dimensions ~40-80 km across, depths

500m-1.5 km. Sizes imply large magma

reservoirs. Calderas relatively shallow

(~500m, up to 1.5 km)

100 km

Venus: widespread volcanism

Sif Mons: shield volcano, long

lava flows (2 km high, 350 km

diameter

Flat-topped domes, up to

50 km diameter

Michael Carroll’s view of pancake domes on Venus

From: Lopes and Carroll, Alien Volcanoes, Johns Hopkins, 2008

Lassen Peak: lava dome

Last erupted in

1914-21.

Domes are formed

by high viscosity

lavas that are low in

gas content

Mars geology:

craters,

mountains,

canyons,

river valleys,

dunes….

and giant volcanoes!

Mars: giant volcanoes

• 6.1_MOLA_global_la

beled2.JPG

Topographic map of Mars, warm colors are high

elevations. Data from MOLA (Mars Global Surveyor)

Tectonism on Mars:

No plate tectonics,

but…

Valles Marineris,

a giant rift valley

Vallis Marineris, Mars:

Largest canyon known

in Solar System

Mars Odyssey

(Thermal Emission Imaging System multi-band camera

Ascreus Mons

Pavonis Mons

Arsia Mons

Tharsis volcanoes

Hawaiian eruptions and shield volcanoes:

effusive activity forms long lava flows

Basaltic lavas

Mauna Loa from SIR-C Credit: S. Rowland

Arsia Mons

(Mars Global Surveyor)

A giant Tharsis shield

volcano

Topography (MOLA,

MGS) over Viking

image

Caldera ~ 110 km across

Possible skylights on Arsia Mons

The Solar System’s largest volcano

Olympus Mons:

600 km diameter,

26 km high

Lack of plate

tectonics allows

huge constructs!

Image from MOC,

Mars Global

Surveyor

Olympus Mons: scarp and caldera

3D view from NASA Mars Observer

MOLA topographic data superimposed with

MOC wide-angle image mosaic.

“

Olympus Mons is ~600 km diameter, 24km high

Nested calderas ~60x90km across

caldera walls ~3km high

ESA Mars Express

HRSC image

At least 6 coalescing depressions

suggest a sequence of at least six

episodes of caldera collapse [Hauber

and Neukum, 2006]. Crater counts of

the caldera floors reveal an age of 100

to 200 Ma [Neukum et al., 2004].

Olympus Mons: Sequence of collapse and approximate ages

Unusual compared to calderas of other Martian volcanoes: ages of five caldera

floors cluster around 100-200 Myr ago (error ~50 Myr). Imply formation or

resurfacing within a narrow time span ~150 Myr ago.

From: Mouginis-Mark, Harris and Rowland (2004)

Olympus Mons: a giant shield volcano

Olympus Mons scarp and aureole: how did they form?

“The most persistent

explanation, however, has

been landslides. Large

masses of shield material

can be found in the

aureole area.”

HRSC (Mars Express)

HiRISE image ~ 1km wide (MRO) shows

N edge of scarp, nearly 7 km high at this

location. “Most scientists think the the

cliffs formed by landslides. This collapse

is driven by the weight of the huge

volcano exceeding the strength of the

rocks it is built of. ”

Michael Carroll’s

view of a volcanic

eruption on Mars

triggering flash

flooding

Erosion by water: river gulleys

Newton Basin, picture ~1.5 km (1.1 mi) across

Explosive eruptions

Mount St. Helens:

1980 eruption (Plinian)

Mars: evidence for explosive volcanism

Hecates Tholus (Elysium)

Caldera ~10 km diameter

tholus (tholeii) = small dome-shaped hill

MRO HiRISE

image of cone

on the flank of

Pavonis Mons

SP crater near

Flagstaff,

Arizona

On Mars, atmospheric pressure is sufficiently

low that explosive eruptions can form easily

if the magma has sufficient amount of

dissolved gases

Mars: evidence for explosive volcanism

Tyrrhena Patera (THEMIS

mosaic, Mars Odyssey):

Colder nighttime

temperatures (blue hues)

indicate parts likely covered

with finer-grained materials

(pyroclastics). Warm (red)

area likely a rocky surface

Mars Exploration Rovers: Spirit and Opportunity

• Landed January 2004, designed to

operate for 3 months.

• Each has found evidence of long-ago

Martian environments where water

was active and conditions may have

been suitable for life.

• Spirit got stuck and batteries died,

Opportunity still sending back data Meteorite found by

Opportunity, Sept 2010

Erosion and impact cratering:

Victoria Crater

Diameter 750 m

Depth 70 m

Path of rover Opportunity

Opportunity imaged by the Mars Reconnaissance Orbiter

Curiosity: sending the geologist to Mars

Curiosity on the parachute Imaged by MRO

How to get the Data:

All spacecraft data are public and archived

Depending on purpose of search, specific websites

are useful

• Public outreach and education

• Browsing data

• Missions

• Research

Planetary Photojournal

http://photojournal.jpl.nasa.gov

Excellent resource for general perusal of images and processed data,

teaching, illustrations

Click on a planet (for example, for Io or Europa, click on Jupiter)

Pages for individual missions: http://saturn.jpl.nasa.gov

Getting the Data: Planetary Data System http://pds.jpl.nasa.gov/