Chapter 10: Mars A Near Miss for

Life?• Orbital Properties

• Physical Properties

• Seasons

• Surface Features

• Atmosphere

• Satellites

• Comparison to Earth and Venus

Objectives

• After completing this chapter, you should be able to: • compare the general physical properties of Mars, Earth,

Venus, Mercury, and the Moon. • compare the orbital and rotational properties of Mars, Earth,

Venus Mercury, and the Moon. • describe the atmosphere, hydrosphere, lithosphere,

magnetosphere, and biosphere of Mars and• compare to the terrestrial planets and explain their differences. • describe Mars' cycle of visibility as seen from the Earth. • describe the physical properties and origin of the Martian

moons. • describe the "geologic" history of Mars and compare it to the

other terrestrial planets.

Planetary Configurations• In their orbital cycles, planets assume various

configurations relative to the Sun-Earth line.

• For a planet farther from the Sun than Earth:

–opposition - planet is closest to Earth and appears to be opposite the Sun

(from Earth).

–conjunction - planet is farthest from the Earth and the Sun lies between the

planet and Earth.

–quadrature - planet is 90o from the Sun-Earth line.

Earth-Sun line

Conjunction

Opposition

Quadrature

Superior Planet Configurations

Mars from Earth• Mars appears largest and brightest when it is at

opposition.• If also at perihelion, Mars

– is within 0.38 AU (56 million miles) of Earth,

– has an angular size of 25”,

– has surface features as small as 100 km across that can be resolved by Earth-based telescopes (about the same size as objects on the Moon resolved by unaided eye).

– Will occur again in August 2003.

• Mars appears less bright than Venus.– Twice as far from the Sun

– surface area about 30% that of Venus

– less reflective surface - only 15% of incident light reflected

Distance from Mars to Earth

• Mars becomes easily visible about once every two years (780 days OR the period between oppositions), when it is

– closest to the Earth,

– visible all night long, and

– highest in the sky at midnight.

• At maximum brightness, it is the second brightest planet.

Earth-based Studies of Mars• First telescopic observations by Galileo.• Small angular size of Mars, Earth’s atmospheric

turbulence limit observations– show daily changes in surface due to rotation– seasonal changes in colors of regions– length of day– tilt of rotation axis

• 19th century observations by Schiaparelli interpreted surface as criss-crossed by straight lines, called canali.

• U.S. astronomer Percival Lowell also observed the features in 1896; others did not.

• Debate continued over half a century.

Mars in Two Views

Early Exploration from Space• In 1965, Mariner 4 passed near Mars and sent

back 22 photographs of the surface.

First picture of Mars from Mariner 4

First picture of craters on surface of Mars

Early Exploration from Space• In 1971, Mariner 9 was the first spacecraft to orbit

another planet and sent back a series of photographs showing volcanoes (Olympus Mons), valleys (Valles Marineris), craters, and channels.

Early Exploration from Space• The Viking missions each had 2 spacecraft,

orbiter and lander, to obtain high resolution images of the surface, examine the surface geology, and search for evidence of life.

Recent Missions to Mars

• Pathfinder w/ Sojourner explored the Martian surface in 1997.• Mars Global Surveyor: arrived in Martian orbit Sept. 12, 1997.• Mars Polar Explorer: Lost contact December, 1999

Mars Global SurveyorMars Global Surveyor: arrived in Martian orbit Sept. 12, 1997.

Plateau in Valles Marineres

Possible evidence of ponding in

Martian crater

Chasm in Valles Marineris

Current Mission: Mars Odysseyhttp://www.jpl.nasa.gov/odyssey/

• Mars Odyssey carries three scientific instruments designed to tell us what the Martian surface is made of and about its radiation environment:

– a thermal-emission imaging system,

– a gamma ray spectrometer and

– a Martian radiation environment experiment.

• Odyssey arrived at Mars on October 24, 2001, when it fired its main engine and was captured into Mars' orbit.

Odyssey

Current Mission: Mars Odyssey

Current Mission: Mars Odyssey

This thermal infrared image was the first acquired by Mars Odyssey's thermal emission imaging system on October 30, 2001. It is late spring in the Martian southern hemisphere. The extremely cold, circular feature shown in blue is the Martian south polar carbon dioxide ice cap at a temperature of about -120 °C (-184 ° F). Clouds of cooler air blowing off the cap can be seen in orange extending across the image to the left of the cap. The thin blue crescent along the upper limb of the planet is the Martian atmosphere. (NASA/JPL)

http://www.jpl.nasa.gov/odyssey/

Mars Statistics•Satellites: 2

•Diameter: 6,785 km (0.52x Earth)

•Mass: 0.11 x Earth

•Density: 3.9 g/cm3 (Moon=3.3,Earth=5.5)

•Surface Gravity: 0.38 x Earth

•Escape Speed: 5.0 km/sec

•Length of Solar Day: 24 hrs 37 min

•Length of year: 687 Earth days

•Orbital semi-major axis: 1.52 AU

•Tilt of Axis: 23o59”

•Orbital eccentricity: 0.093

•Minimum Distance from Sun: 205 million km (128 million miles)

•Maximum Distance from Sun: 249 million km (155 million miles)

•Temperature: 150K to 310K ( -116oF to 34oF), 218K average

•Surface magnetic field: 1/800 X Earth

Seasons on Mars

•Mars’ axial tilt only slightly greater than Earth’s.

– expect seasons similar to Earth.

•Mars’ orbital eccentricity greater than Earth’s.

– S-hemisphere closest to Sun during summer, and farthest from the Sun during winter.•Summers warmer in S-hemisphere than N-hemisphere.

•Winters colder in S-hemisphere than N-hemisphere.

•Prediction for polar ice caps and variations with season?

Martian Sunset

Picture taken by Mars Pathfinder mission.The color of the Sun is not correct since it is overexposed (should appear white or bluish-white).

Atmospheric Composition of Mars• Composition

– 95.3% carbon dioxide– 2.7% nitrogen– 1.6 % argon– 0.13 % oxygen– 0.07% carbon monoxide– 0.03 % water vapor

• Atmospheric pressure at the surface of Mars is ~ 1/100 x Earth’s.

– may vary by 30% throughout Mars year because of variations in solar heating.

• No recorded lightning or thunder.

Atmosphere of Mars•Troposphere where convection and "weather" occur. – Two types clouds:

• water vapor w/ carbon dioxide; – white – appear in low-lying areas in morning – near poles in late summer/early fall

• dust– yellowish– high speed surface winds (>100mph)

•At noon in the summertime, surface temperatures may reach >300 K.

•At night, – temperatures drop up to 100 K,– convection ceases, and – troposphere vanishes.

Atmosphere: Pressure and Temperature• Atmospheric pressure changes seasonally as carbon

dioxide freezes and then evaporates from polar caps. • During southern hemisphere winters,

the global air pressure drops by 30%. • Seasonal changes are also affected by Mars' distance

from the Sun, and are also the cause of planet-wide dust storms that can obscure the planet's surface.

• Diurnal temperature changes are quite extreme ranging from -225 F at night to 63 F during the day. – The greatest extremes occur in the southern hemisphere. – Occasionally carbon dioxide and water vapor clouds form

because of the low temperature in the atmosphere. – Also frost can form on the ground.

Martian Dust Storms

Martian Dust Devil

animation file:///H|/phys1050-fall2001/pictures/dustdevil.gif

Comparing Terrestrial Atmospheres

PLANET COMPOSITION PRESSURE

Earth Nitrogen/Oxygen 1 atmosphere

Venus Carbon dioxide 100 atmosphere

Mars Carbon dioxide 0.01 atmosphere

Goldilocks and the

3 Planets:A story about

the Greenhouse

Effect

Atmospheric History1. Primary and secondary atmospheres similar to

Earth and Venus. 2. Moderate greenhouse effect warms surface and

allows liquid water to form. 3. Water dissolves carbon dioxide to form carbonate

rocks. 4. Reduced carbon dioxide content diminishes

greenhouse effect, so planet cools. 5. The surface atmospheric pressure decreases so

that most of the liquid water is frozen. 6. Steps #4 & 5 propagate a runaway ice age effect.

Assuming no weathering, no life, and no gases escaping,

atmospheres of the terrestrial planets would be:

VENUS EARTH MARS

Nitrogen 3.4% 1.9% 1.7%

Oxygen Trace Trace Trace

Argon 40 ppm 190 ppm 850 ppm

Carbon dioxide 96.5% 98% 98%

Pressure 0.88 atm 0.7 atm 0.02 atm

Water depth 9 m 3 km 30 m

Martian Hydrosphere• Liquid water is not expected on surface of Mars today. • The pressure and temperature combination is too low

for liquid water to be stable, except possibly at the bottom of a deep canyon.

– Only Earth in the inner Solar System has large amounts of liquid water.

• Very little water vapor in the Martian atmosphere. – Less than Earth or Venus, but the relative humidity is 100%!

• A comparison of atmospheric and ground water shows:

PLANET ATMOSPHERE GROUNDMars 0.01 mm 10-160 m

Venus 30 mm 9 m

Earth 100 mm 3000 m

Evidence for Recent Water at Surface

Images from Surveyor suggest geologically recent seeps of water to the Martian surface in gully landforms observed from latitudes of 300 - 700 in both hemispheres.

Martian Climate Changes

• Mars is currently locked in a global ice age. It may not have always been that way in the past.

• Changes in the tilt of its axis, orbital eccentricity, and/or precession of its rotation axis caused by the gravitational influence Jupiter could have greatly altered the Martian climate.

• It may have been possible for liquid water to exist on the surface or Mars in the past.

Polar Regions of Mars• Polar ice caps composed of

– water ice – carbon dioxide ice.

• In summer, dry ice in N-cap sublimates and leaves water ice remnant.

• S-cap retains some dry ice year round.

• Layering observed in polar deposits implies periodic sedimentation from long-term, repetitive climate changes.

N-pole cap

S-pole capMariner 9 images

Evidence of Water on Mars?

Runoff channels: resemble Earth’s river systems, ~4 billion years old

Water Erosion?

Outflow channel: relic of catastrophic flooding ~3 billion years ago.

Run-off Channels

Observations suggest that this water may have melted in the past causing huge floods. Other evidence points to runoff channels that might have formed under rainy conditions.

(Photo from MOLA, Mars Global Surveyor)

Evidence of Water in the Past

Sedimentary rock layers like these in Mars's Holden Crater suggest that the Red

Planet was once home to ancient lakes.

Martian gullies in Newton Crater. Scientists hypothesize that liquid water burst out from

underground, eroded the gullies, and pooled at the bottom of this crater as it froze and evaporated.

New Information from Mars Global Surveyor

•Wide-spread presence of olivine at surface suggests drier and colder throughout history than previously theorized.

•green (yellow/green) - sulfates red - sulfate-free blue - olivine and pyroxenes (both volcanic) magenta - coarse-grained hematite

Seismic Activity on Mars

• Each Viking lander carried a seismometer; only one worked.

• Showed that Mars does have some seismic activity, but that the activity per unit area on Mars is less than on Earth.

• Mars quakes that were recorded lasted about a minute.– Earthquakes last seconds– moonquakes last hours

• Internal structure of Mars more similar to Earth than Moon.

The Surface of Mars

• Mars Viking landers answered “why is Mars red?”

• Viking soil analysis showed surface to consist of – mostly silicate rocks– large fraction (20%) as iron oxide

• Soil is magnetic.

• High surface abundance of iron combined with the overall density implies that Mars should not have much of an iron core. That is, Mars should show little differentiation.

Mars: Internal Structure• No direct measurements to

constrain models of interior.

• Average density and volcanic history imply some interior melting and differentiation.

– thin crust (65-80 km)

– rocky mantle more dense than Earth

– small iron-rich core, possibly w/ sulfur

• Lack of detectable magnetic field implies core is non-metallic and/or non-liquid.

• No widespread geological activity in last ~2 billion years.

Martian Interior and Tectonics• There are no seismic data from Mars,

because this equipment failed on one of the Viking landers.

• Other indirect evidence suggests that Mars probably has no large iron core, and that the interior is not well differentiated.

• The mantle must have been hot to cause volcanoes and rift valleys, but the crust may be too thick to allow plate tectonics to begin.

• The planet probably froze solid before plate tectonics could begin.

Plate Tectonics

• The mantle must have been hot to cause volcanoes and rift valleys, but the crust may be too thick to allow plate tectonics to begin.

• The planet probably froze solid before plate tectonics could begin.

Crustal Thickness

Crustal thickness may be inferred from gravity observations made by Mars Global Surveyor.

North

Red - thin

Blue - thick

Martian Magnetosphere

• No magnetic field has been detected, so the solar wind can interact directly with the Martian atmosphere.

• No magnetic field suggests Mars has no or a very small liquid metallic core.

Martian Lithosphere

Viking 1 view from surface of Mars

Surface Features:

A view from HST

Terrains on Mars• Highlands - 60%–ancient –heavily cratered terrain–southern hemisphere

• Northern Lowlands - 20%–younger, lightly cratered–resemble lunar maria–average elevation 4 km below highlands–dune fields, rift valleys, dry riverbeds, water flow patterns

• Volcanic Highlands - 20%–Tharsis volcanic province– immense bulge the size of North America–volcanic plains, 10 km above surroundings –crowned by 4 volcanoes that rise another 15 km–few impact craters

The Surface of Mars• Mars Global Surveyor has been recording thermal

emission spectra from the surface of Mars.• Analysis of the data suggests

– low albedo regions composed of • volcanic basalts in the S-hemisphere

• andesitic volcanics in N-hemisphere

– high albedo regions show anomalous spectra consistent with atmospheric dust

Maps from Mars Global Surveyor: Hellas region

Craters on Mars Highlands

• This mosaic of Viking images shows a portion of a cratered highland region on Mars (U.S. Geological Survey; data from NASA)

Craters on Mars

Copernicus: typical impact crater on the Moon, ejecta appears as dry, powdery material

Yuty: impact crater on Mars, ejecta appears liquid, “splosh” crater

Maps from Mars Global Surveyor: Utopia region

Northern Lowlands

• The northern hemisphere lowlands have a number of very interesting landscapes.

• Large dune fields have been detected from orbiting spacecraft. – The largest of these fields is about the size of

Colorado or Nebraska with combined groups the size of Texas.

– The amount of sand in these dunes is comparable to the volume of Mars' smallest moon (Deimos).

Maps from Mars Global Surveyor: Tharsis region

Olympus Mons

Largest known volcano in our solar system, shield volcano with 3 x elevation of Mt. Everest on Earth

Olympus Mons -Perspective

Base: 700 km diameter Caldera: 80 km across Height: 25 km higher than surrounding plains and surrounded by a 6 km high cliff

Alba Patera

Two views of Alba Patera with topography draped over a Viking image mosaic. The vertical exaggeration is 10:1. (Credit: MOLA Science Team)

Arisa Mons

Two views of Arsia Mons, the southern most of the Tharsis montes, shown as topography draped over a Viking image mosaic. MOLA topography clearly shows the caldera structure and the flank massive breakout that produced a major side lobe. The vertical exaggeration is 10:1. (Credit: MOLA Science Team)

Valles Marineris• Discovered by Mariner 9

• On Earth, would

stretch from Los Angeles to New York

Valles Marineris: The Grand Canyon of Mars

Cause: tectonic fracture of crust Length: ~4000 km Depth: to 7 km Width: to 120 km

Flow from Highlands to Lowland Plain

Ancient riverbeds on Mars. At the lower center are several river channels showing northward flow (upward in the figure) from the edge of a highland scarp to a lowland plains region called Amazonis Planitia. (U.S. Geological Survey; data from NASA)

Martian Biosphere• MARTIAN SCIENCE FICTION

– Percival Lowell – War of the Worlds

• THE VIKING LANDER RESULTS – All data gathering can be explained by non-biological

processes. – No organic compounds found. – Soil appears to have the properties of peroxide (antiseptic!).– It is possible that life formed but is now extinct.

• MARTIAN METEORITES

– Martian meteorites appear to have structures that resemble microfossils.

– No definitive conclusion has been reached yet.

NASA’s Plan to Look for Life on Mars• Options for Search

– Look for life • fossils

• extant organisms

– Look for evidence of life • chemical processes

• biological/chemical signatures

– Search for environments which might have sustained life

• ancient groundwater environments

• surface water environments

• modern groundwater environments

Life Sustaining Environments

• Ancient groundwater environments– possible warm groundwater circulation in highlands

– deposits exposed at surface in ejecta from recent impact craters

• Surface water environments– liquid water flowed and pooled in low-lying regions

– solar heating provided energy for biology

– evidence in water lain sediments in valley systems and basins in highlands

• Modern groundwater environments– life survived from early epoch in places beneath the

surface where liquid water is present today.

Four basic experiments.Samples were isolated in chambers and exposed to a variety of gases, radioactive isotopes and nutrients to look for evidence of

respiration by living animals, absorption of nutrients offered to any organisms present, andan exchange of gases between the soil and its surroundings.

Another sample was pulverized and analyzed for organic (carbon-bearing) materials.

These experiments were built around the hypothesis that if there were life on Mars it would have a similar metabolism to life on Earth, and it would have a similar biochemistry based on the same organic compounds important to life on Earth.

Viking 1&2 ExperimentsA Search for

Earth-like Life on Mars

The results of these experiments were complex. The first

three gave positive results, but the complete absence of any organic

compounds in the Martian soil according to the mass spectrometer

experiment suggests that the positive results for the first three

were not evidence for life, but rather evidence for a complex

inorganic chemistry in the Martian soil. Thus, the Viking verdict

was that there was no evidence for present or past life on Mars.

Results of the Viking Expeditions

Geologic History

1. Condensation from the solar nebula. 2. Accretion of planetesimals into the planet. 3. Short period of completely molten state. 4. Partial differentiation. 5. Formation of thick rigid crust. 6. Impact cratering. 7. Volcanic and tectonic activity, but no plate tectonics. 8. Interior cools. 9. Relatively inactive today,

but some geologic processes exist.

Moons of Mars

Deimos15 km diameter,

smoother, less cratered,30 hour orbital period

Phobos27 km diameter,Stickney crater,

7.5 hour orbital period

Irregular shape, pitted with craters, density = 2 g/cm3, circular orbits in equatorial plane.

Martian Moons• Phobos and Deimos are both extremely small

(about 20 miles across). • They may be captured asteroids, because Mars

lies on the inner edge of the asteroid belt. • They appear to be rich in carbon compounds

and show some evidence of volcanic vents. • Phobos revolves around Mars in just 7.5 hours,

so it rises in the west and sets in the east. • Both moons exhibit synchronous rotation with

the same side of the moon always facing Mars. • The motions of these moons were used to

determine the mass of Mars in 1877.

Spheres: Earth, Venus, Mercury, Mars and the Moon

REALM

EARTH VENUS MARS MERCURY MOON

Atmosphere

Very Active

Active Active Very thin None

Hydrosphere

Very Active

None ActiveVery

inactiveVery

inactive

Magnetosphere

Very Active

Very Weak None Very weak None

Lithosphere

Very Active

Active ActiveVery

inactiveVery

inactive

Biosphere

Very Active

None None? None None

Overview of Mars from Earth• Fourth planet from the Sun.

• Half the size and 1/10 the mass of Earth.

• Characteristic reddish color with light and dark areas that appear to change appearance throughout the Martian year as winds cover and uncover various surfaces.

• Polar ice caps fade in Martian summer and grow during the winter.

• Clouds are observed in the atmosphere.

Overview of Mars from Space• Surface

– Northern hemisphere • lava-covered plains with volcanoes as large as USA states.

• size possibly evidence against continental drift.

– Southern hemisphere• strongly cratered, older basalt highlands

– Equatorial region• gigantic valley near equator: Valles Marineris

• volcanic plateau: Tharsis complex

• Red color from relatively large amount of iron in surface rocks.– implies Mars not as differentiated as other terrestrial planets,

has smaller core, no magnetic field.

Overview of Mars from Space (continued)

• Evidence for liquid water at surface in past– surface features that resemble Earth’s riverbeds,

sandbars, and floodplains– permafrost suggested in layering of surface deposits

of sand and ice, as well as in landslides– polar ice caps contain frozen carbon dioxide and

water ice– new images suggest recent water at surface in crater

rims near poles.

• Evidence against liquid water at surface in past– wide-spread deposits of olivine on surface

Properties of Earth, Venus, and Mars Earth Venus Mars

Semi-major axis (AU)

1.00 0.72 1.52

Period (Earth yrs) 1.00 0.61 1.88

Mass (Earth=1) 1.00 0.82 0.11

Diameter (Earth=1) 1.00 12,756 km

0.95 12,140 km

0.52 6788 km

Density (g/cm3) 5.5 5.2 3.9

Surface gravity(Earth=1) 1.00 0.91 0.38

Rotation period 23.9 hrs -243 days 24.6 hrs

Surface area (Earth=1) 1.00 0.94 0.28

Atmos. pressure(bar) 1.00 90 0.007

Surface magnetic field (Earth=1)

1.00 1/1000 1/800

Atmospheric Compositions (in %) of Earth, Venus, and Mars

Venus Mars Earth

Carbon dioxide (CO2) 96.5 95.3 0.03

Nitrogen (N2) 3.5 2.7 78.1

Argon (Ar) 0.006 1.6 0.93

Oxygen (O2) 0.003 0.15 21.0

Neon (Ne) 0.001 0.003 0.002