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
• Orbit:
2.3 . 108 km 1.52
• Day:
• Year:
0.72
.
Earth
AU
24h.37m 23s
1.02
.
Earth
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 isfarthest fromEarth & 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 Oppositions
May 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
– Summer
Field stubble on Earth
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
• Solar System’s largest volcano
• Clear evidence of hot-spot volcanism
Fly-over
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
– Parallel
relatively old
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
Teardrop-Shaped
Island
Water Flow
Direction
Mars Orbiter: “Dao Valley”
Mars Orbiter: “Reull Channels”
A Possible Water History on Mars
Ancient
Modern
Earth & Mars Evolved Differently
• Historic observations
– 1800’s
– 1965
Astronomers saw Martian clouds
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
Nutrients
Heated
C14 added
Peroxides & superperoxides released O2
No obvious organic waste products
Mass spectrometer analyzes gases
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”
Mars Opportunity “Escher Rock”
Mars Opportunity at Endurance Crater
Mars Curiosity Rover
• Mars Science Laboratory (MSL) mission
– Spacecraft components
• Earth–Mars fueled cruise stage
• Entry–descent-landing (EDL) system
• Curiosity rover with instrument package
Skycrane
– 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
•
•
•
•
Winter
Spring
Summer
Fall
~ 20% seasonal pressure changes
Frigid temperatures freeze out much CO2
Warm temperatures thaw out much CO2
Frigid temperatures freeze out much CO2
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?)
Important Concepts
•
Mars data
–
–
–
–
•
Early Mars observations
• 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
Diameter only ~ 53% that of Earth
Mass 10.7% & density 72% of Earth
Highly elliptical orbit
Same day & axial tilt as Earth
– Schiaparelli reported seeing canali
– Seasonal color change was confusing
•
•
• 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