11c. Red Planet Mars• Mars data• Earth-based observations of Mars• Early observations mistaken as evidence of life• Spacecraft find craters, volcanoes & canyons• Surface features indicate flowing water• Earth & Mars began alike, evolved differently• Rovers explored the Martian surface• The Martian atmosphere changes seasonally• Martian moons resemble captured asteroids

Mars Data (Table 13-1)

Mars Data: Numbers• Diameter: 6,794 km 0.53 . Earth

• Mass: 6.4 . 1023 kg 0.107 . Earth

• Density: 3.9 . water 0.72 . Earth

• Orbit: 2.3 . 108 km 1.52 AU

• Day: 24h.37m 23s 1.02 . Earth

• Year: 686.98 days 1.88 . Earth

Mars Data: Special Features• Mars is farthest terrestrial planet from the Sun• Mars is the second smallest terrestrial planet• Mars has < 1% the Earth’s atmosphere

– Mars’ atmosphere is ~ 95% CO2 & 3% N2

• Mars has rapidly changing polar ice caps• Mars has two very different hemispheres

– The “north” is covered with volcanoes & lava flows– The “south” is covered with numerous craters

• Mars holds some Solar System records– Olympus Mons: The tallest mountain (a

volcano)– Valles Marineris: The longest canyon

• Mars will be the first planet visited by humans

Earth-Based Observations of Mars• Mars is the closest superior planet to Earth

– Conjunction

Always superior [far side of the Sun]• Mars is overhead at local solar noon• Mars is farthest from Earth & appears smallest

– Opposition• Mars is overhead at local solar midnight• Mars is closest to Earth & appears largest

• Mars’ orbit is rather highly elliptical– Mars oppositions vary in favorability

• August oppositions are most favorable– 28 August 2003 closest in nearly 60,000 years

• February oppositions are least favorable– Mars looks very small even at favorable oppositions

• Hubble Space Telescope cannot identify impact craters

Future Mars OppositionsMay 22, 2016

July 27, 2018

October 13, 2020

Orbits of Earth & Mars

Mars: Hubble Space Telescope

Old Mars Observations From Earth• Giovanni Schiaparelli 1877

– Reported seeing canali on Mars• Italian Means⇒ “channels” & is ambiguous

– Natural stream channels

• English Translated⇒ “canals” & has

implications– Artificial shipping routes

– Long viewing sessions & poor seeing conditions• He “saw” what was not actually there

• He incorrectly interpreted what he did not actually see

Observations As Evidence of Life• Seasonal color changes do occur on Mars

– Winter Fine red dust settles on large lava flows• Areas look relatively light Field stubble on

Earth

– Summer Wind removes thin cover of dust• Areas look relatively dark Verdant fields on

Earth

• The human eye plays tricks– Astronomers stare at bright red areas on Mars

• Most of Mars has a distinct red color

– Astronomers see cyan [blue-green] in dark areas• Tendency of retinal fatigue to see complementary color

• Misinterpretation– “Canals” + summer greening = Intelligent life

Martian Canali & Craters

Martian Global Topography

Spacecraft Find Craters & Volcanoes• Mariner 4, 5 & 7

– First close-up pictures of Mars– Two distinctly different hemispheres on Mars

• Boundary tilted ~ 30° to the Martian equator• Northern hemisphere Relatively low & relatively

smooth• Southern hemisphere Relatively high & heavily

cratered• Unusual features

– Valles Marineris

Fly-over• Longest, widest & deepest canyon in the Solar System

– Would reach from San Francisco to New York– Many side canyons are as large as the Grand Canyon

– Mars shows no evidence of plate tectonics• As on Venus, lack of oceans may be critical here

– Olympus Mons

Fly-over• Solar System’s largest volcano• Clear evidence of hot-spot volcanism

Valles Marineris: Hemispheric View

Olympus Mons: Solar System Champ

Surface Features Indicate Water• Earth-like streamflow clearly existed on Mars

– Dendritic stream channels flow down mountains• Most of these appear to be relatively old

– Parallel stream channels flow down slopes• Many of these appear to be remarkably young• Permafrost may be just beneath the Martian surface

• Catastrophic floods clearly existed on Mars– Teardrop-shaped islands around crater rims

• Remarkably similar to Glacial Lake Missoula floods• ≥ 109 floods from ~ 15,500 to ~ 13,500 years ago• Biggest floods ~ 500 cubic miles of water past Portland

• Evidence for a Great Northern Ocean– Strandlines on northern hemisphere slopes

• Notches cut by wave action along shorelines

Dendritic Stream Channels on Mars

Parallel Stream Channels on Mars

Evidence of Sheet Flow on Mars

Water F

low

D

irection

Teardro

p-S

hap

ed

Island

Mars Orbiter: “Dao Valley”

Mars Orbiter: “Reull Channels”

A Possible Water History on Mars

Ancient Modern

Earth & Mars Evolved Differently• Historic observations

– 1800’s Astronomers saw Martian clouds– 1965 Mariner 4 measured very high CO2

levels• Martian cirrus clouds contain both H2O & CO2 ice crystals

• Atmospheric warming effects– CO2 on Earth raises temperature ~ 36°C

• Much terrestrial CO2 is locked in carbonate rocks– Subduction recycles CO2 back into Earth’s atmosphere

– CO2 on Mars raises temperature ~   5°C• Mars quickly cooled & solidified because it is so small

– No subduction recycling of CO2 back into Mars’ atmosphere

• Rainfall dissolved CO2 & removed it from the atmosphere– Runaway icehouse effect on Mars– Stabilized at present levels

The Martian Atmosphere• Early atmosphere

– Probably very similar for Venus, Earth & Mars• Abundant volcanic activity during Mars’ early history• Abundant H2O, CO2 & SO2

– Being very small, Mars ran out of heat & magma• Once outgassing decreased, the oceans disappeared

– Water dissociated into H & O, which escaped Mars’ weak gravity• Remaining volcanic gases entered the atmosphere

• Present atmosphere– Chemically Remarkably similar to Venus

• ~ 95.3% CO2 & ~ 2.7% N2– Expected due to little remaining volcanic outgassing

– Physically Remarkably different from Earth• ~ 0.63% as much atmospheric gas as Earth

– Expected due to weak gravity & little replenishment

Atmospheres of Earth & Mars

Viking & Pathfinder Explored Mars• Viking spacecraft 1976

– Experiments looking for signs of life• Water Peroxides & superperoxides released

O2

• Nutrients No obvious organic waste products• Heated Mass spectrometer analyzes gases• C14 added None taken up by possible organisms

• Mars Pathfinder spacecraft 4 July 1997– Sojourner was the small rover on Mars Pathfinder

• Controlled from Earth with some autonomous functions• Discovered an abundance of andesite

– Volcanic rock moderately rich in quartz– Rock type first described in South America’s Andes Mountains

• Surprisingly different from Mars’ southern basalt– Volcanic rock very poor in quartz– Common in Earth’s ocean basins & the Moon’s maria

Mars Viking Lander

http://en.wikipedia.org/wiki/File:Sagan_Viking.jpg

Mars Pathfinder & Sojourner Rover

Mars Exploration Rovers• Overall mission

– Search for clues to ancient water• 2 rovers on opposite sides of Mars• Expected operating lifetime of 3 months

– Ultimately a search for life• Mars Exploration Rover – A Spirit

– Landed 4 January 2004• Crater Gusev

Appears to have been affected by water• First intentional grinding of a rock on Mars

– Operated until 22 March 2010• Mars Exploration Rover – B Opportunity

– Landed 25 January 2004• Landed in Meridiani Planum• Came to rest in Eagle Crater, a small impact crater

– Still operating as of 22 February 2013

Mars Opportunity Before Launch

http://en.wikipedia.org/wiki/File:Opportunity_Lander_Petals_PIA04848.jpg

Mars Spirit & Opportunity Rovers

http://en.wikipedia.org/wiki/File:NASA_Mars_Rover.jpg

Mars Opportunity “Blueberries”

Mars Opportunity “Meridiani Meteorite”

93% iron & 7% nickel

6 inches

Mars Opportunity “Escher Rock”

Mars Opportunity at Endurance Crater

Mars Curiosity Rover• Mars Science Laboratory (MSL) mission

– Spacecraft components• Earth–Mars fueled cruise stage

Skycrane• Entry–descent-landing (EDL) system• Curiosity rover with instrument package

– Soft-landed in Gale Crater on 6 August 2012• Unique “sky crane” landing strategy

• General mission objectives– Assess Martian climate & geology– Assess favorability of conditions for microbial life– Assess habitability for future human exploration

• Specific Curiosity objectives– Biological– Geological & geochemical– Planetary process– Surface radiation

MSL Cruise Stage Before Launch

http://en.wikipedia.org/wiki/File:MSL-Cruise_Stage_Test.jpg

Opportunity, Sojourner & Curiosity

http://en.wikipedia.org/wiki/File:Mars_Science_Laboratory_mockup_comparison_.jpg

Mars’ Atmosphere Is Very Dynamic• Diurnal changes

– Mars Pathfinder –76°C to –10°C– Daytime heating generates dust devils

• Weak clear-air tornadoes• Pressure dropped as dust devils passed Pathfinder

• Seasonal changes– Basic patterns ~ 20% seasonal pressure

changes• Winter Frigid temperatures freeze out much

CO2• Spring Warm temperatures thaw out much

CO2• Summer Frigid temperatures freeze out much

CO2• Fall Warm temperatures thaw out much

CO2

– Hemispheric differences• Northern summer Mars is at aphelion

– Clear skies warm northern summer much more than expected• Southern summer Mars is at perihelion

– Dust storms cool southern summer much less than expected

Martian Dust Devil From Above

http://lightsinthedark.files.wordpress.com/2012/03/dustdevil.jpg

Mars Global Dust Storm

http://science.nasa.gov/media/medialibrary/2001/10/11/ast11oct_2_resources/0131w.jpg

Cloud Caps on Martian Volcanoes

Cloud Cap On Mount Hood

http://fox12weather.files.wordpress.com/2010/09/lenticular-cropped1.jpg

Mars Craters & Mounds at Sunset

Mars Odyssey (Themis scanner)

Mars’ Moons Resemble Asteroids• Discovery

– Asaph Hall Favorable opposition of 1877• Named after chariot horses of the Greek god of war• Might be captured asteroids

• Details– Phobos Fear

• Closest to    Mars &  largest  in size• Orbital period of ~ 7 hours 39 minutes

– Races from West to East from horizon to horizon in ~ 5.5 hours– Comparable to artificial satellites in low Earth orbit

• Several times brighter than Venus appears from Earth– Deimos Panic

• Farthest from Mars & smallest in size• Orbital period of ~ 6 days

– Creeps from East to West from horizon to horizon in ~ 3.0 days• About as bright as Venus appears from Earth

The Martian Moons (Asteroids?)

• Mars data– Diameter only ~ 53% that of Earth– Mass 10.7% & density 72% of Earth– Highly elliptical orbit– Same day & axial tilt as Earth

• Early Mars observations– Schiaparelli reported seeing canali– Seasonal color change was confusing

• Seasonal dust storms rearrange dust• Retinal fatigue produces cyan color

• Many spacecraft have visited Mars– Mariner 4, 5 & 7

• Two very different hemispheres– Viking landers

• Looked for signs of life; none found– Mars Pathfinder

• Included the Sojourner rover– Mars Orbiter

• Mars’ dynamic atmosphere– Diurnal changes– Seasonal changes

• Atmospheric pressure varies ~ 20%• H2O & CO2 clouds can occur on Mars

• Mars has two small natural satellites– Phobos Fear

• Fast West-to-East sky crossing– Deimos Panic

• Slow East-to-West sky crossing

Important Concepts