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Chapter 12: History of Mars

Chapter 12: History of Mars. Rover’s view of Mars. Why Mars is prime target for search for life:. 1. Direct evidence that Mars had liquid water in past – and possibility of subsurface water now. 2. Has an atmosphere of CO 2 and N 2

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Chapter 12: History of Mars

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  1. Chapter 12: History of Mars Rover’s view of Mars

  2. Why Mars is prime target for search for life: 1. Direct evidence that Mars had liquid water in past – and possibility of subsurface water now. 2. Has an atmosphere of CO2 and N2 3. Planet is cold and dry – good for preserving organic remains of life. (see C. Mckay’s article in our book)

  3. Mars Rover: Mission Objectives • Search for and characterize a variety of rocks and soils that hold clues to past water activity. Samples will include: those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity. • Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites. • Determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering. • Perform "ground truth" -- calibration and validation -- of surface observations made by Mars orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.

  4. Search for iron-containing minerals, identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates. • Characterize the mineralogy and textures of rocks and soils and determine the processes that created them. • Search for geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life.

  5. Orbit of Mars – and several recent oppositions (25” angular size at best e= 0.093, a=1.52 AU, aphelion = 1.67 AU, perihelion = 1.38 AU, -> variation in light during Martian year of 45%

  6. Mars/Earth Comparison: • Mean Distance from Sun: 1.52 AU 1 AU • Average Surface Pressure: 0.5 – 1kPa 101.3 kPa • Diameter: 4,220 miles 7,926 miles • Tilt of Axis: 25 degrees 23.5 degrees • Length of Year: 687 Earth Days 365.25 Days • Length of Day: 24 hours 37 minutes 23 hours 56 minutes • Temperature Average -60 degrees C Average +15 degrees C • Incident solar radiation: 149 W/sq m. 344 W/sq m.

  7. Space craft images of Mars Polar cap Hubble Space Telescope Image Viking (1976)

  8. Mars – in true colour (Viking mission image) Northern hemisphere – rolling volcanic (lunar-like) plains. Southern hemisphere – heavily cratered highlands 5 km above lowlands in north. Major feature: Tharsis bulge, which is 10 km higher than rest of surface

  9. Map by Mars Global Surveyor – used laser altimeter

  10. Hellas Basin – lowest region on Mars, 3000 km across and 6km below average level of Martian surface; impact crater?

  11. Surface of Mars – Northern hemisphere & sourthern highlands • Northern hemisphere: rolling volcanic plains (like lunar maria); much larger lava plains than on Earth or Moon; less cratered than southern highlands – therefore younger • b) Southern highlands: cratered and 5 km above northern hemisphere; original Martian crust

  12. Tharsis - the only continent on surface of Mars… Tharsis bulge – major geological feature of Mars - less cratered than northern plains so is relatively young: 2-3 billion years old - depressions hundreds of km wide, up to 7 km deep - Vallis Marineris; crustal forces push out Tharsis region, and this valley is where crust cracked; feature is 4000km long (Grand Canyon fits into small crack in this structure)

  13. Comparison, to scale, with the Grand Canyon which is 20km wide and 2 km deep. Cracks in Valles Marineris at least 2 billion yrs old.

  14. Olympus Mons –largest volcano known in the solar system: 700 km base and 25 km in height…! Compare Mauna Kea: base 120 km, height 9 km from ocean bottom

  15. Volcanism on Mars • Volcanoes on Mars sit on top of hot spots in the underlying Martian mantle (like “shield” volcanoes – Hawaiin islands) • No indication of “continental drift” on Mars – no volcanic activity of this kind • Height of volcano – lower surface gravity of planet (40% of Earth) -> volcano can be built up 2.5 times higher than on Earth (assuming similar strength of crusts) • Tharsis active 100 million yrs ago (based on cratering record)

  16. Martian Atmosphere Pressure is 1/150th of Earth’s atmosphere Composition (by volume) 95.3% CO2 2.7% N 1.6% Argon 0.13% Oxygen 0.03% water vapor (Earth: 21% O; 78% N) Noon; summertime T=300K Night; little heat retention T drops by 100 K Storms; begin in southern hemisphere, carrying dust into stratosphere; covering the planet On average, temperatures on Mars are 50 K cooler than Earth

  17. Polar caps – frozen Carbon Monoxide and Water Ice Freezing point of CO2: 150 K; CO evaporates during Martian summer leaving small cap of water ice; CO2 refreezes during Martian winter producing a larger cap. Addition and subtraction of CO2 from atmosphere mcauses large pressure fluctuations over a season (30%). Southern (left,) and northern caps (right – mostly water) in summer; 350 and 1000 km diam.

  18. Water on Mars: Impact cratering, and runoff channels a) Large lunar crater (Copernicus) - powdery ejecta b) Mars’ crater Yuty (18 km diam) – fluid-like ejecta; permafrost melted during the impact

  19. Runoff channel on Mars – 400 km long, 5 km wide Compare Mars channel, with Red River running to Mississippi

  20. Flow around obstacles (craters) • The flow rates around these obstacles were about 100 times larger than the flow rate of water through the Amazon river. “Islands” in this image are 40 km long. • (Flow through Amazon is 100,000 tons per second – largest river system on Earth). • Flooding shaped these channels 3 billion yrs ago.

  21. Where did all the water go? • Mars had rivers, lakes, and possibly oceans . • 4 billion years ago, climatic change leads to freezing of rivers, water forming permafrost (like Canadian tundra) • Giant flash floods occur 3 billion years ago in wake of volcanic activity that melts the permafrost. • Once volcanic activity ceased, water froze into permafrost. Site of ancient ocean on Mars?

  22. How much water was/is there? • To explain existing erosional features; need 0.001 – 0.01 Earth oceans worth • Evidence for more water earlier; high levels of deuterium in Mars atmosphere -> most of hydrosphere lost to space -> more than 0.1 Earth oceans • Shorelines of northern basin: measured by Mars Global Surveyor’s (MGS) laser altimeter: -> could hold .01 Earth oceans within basin. • Minerals: From MGS infrared spectrometer – measure infrared spectra to find an iron oxide (“grey hematite”), which *may* be related to formation in presence of water. -> strategy for surface rovers….

  23. Properties of water on Mars; - Triple point of water is 0.61 kPa; water does not exist at liquid at lower pressures -> low present pressure on Mars means water is absent in liquid form. - at surface pressure of 1kPa, water boils at 7C. Even at 0C, water close to boiling and this carries away a lot of heat. • Relevance to Mars: - low elevation of northern plains -> pressure is higher and above the triple point of water (0.7 kPa) … so liquid water could be present - high elevation of southern polar regions has too low a pressure -> liquid water unstable

  24. Roving Mars for water, and life ….

  25. Opportunity at Victoria crater

  26. Design of Viking experiments: • Prolytic release exp (PR): - detect microbes in soil, consuming CO2 and using light • Gas exchange exp (GEx): - detect gas release by microbes when organics added to soil Result: rapid O2 release when soil exposed to just water vapour; response persists even after soil sterilization. ( not biological) • Labelled release exp (LR): - detect release of CO2 from microbes when radioactively tagged organic nutrients added Result: release of CO2 eliminated on sterlization (biological?)

  27. Gas Chromatograph Mass Spectrometer (GCMS): - no detection of organics in soil to one part per billion. - major reason why results of exps interpreted as due to reactivity of martion soil. Why? In Atacama desert (driest place on Earth), even soil without detectable microbes have detectable organics • Caveats: Exps based on trying to culture microbes – this is now kown that culture exps on Earth fail 90% of the time. - develop culture free methods for future exps.

  28. Is there life on Mars? Viking lander results Soil samples taken by Viking lander looked for gas release due to metabolic activity – no evidence for metabolism “Martian meteorite” contains PAHs and perhaps long, rod-like bacteria (0.5 microns long)? No concrete evidence yet for life – however presence of water beneath surface very important. ALH84001

  29. Rovers:Physical evidence for water; spherules seen in Eagle Crater rock outcrop site. Not volcanic… but gypsum (most common sulfate mineral) crystals. Fell out of sedimentary rock perhaps due to wind erosion.

  30. Rover results: Opportunity in Eagle crater Rock outcrops in crater hold evidence that liquid water was stable and present on Mars: • Mossbauer spectrometer results (gamma ray spectroscopy): iron-rich sulfate (hydrated minerals) called “jarosite”, requiring presence of water to form. • Evaporation sequence of minerals: variation in concentrations of elements going down through rock, progressively deposited as water evaporated • Spherules…eroded out of rock • Layering of rock, angled, “cross bedded” sedimentary rock laid down in flowing water.

  31. History of water on Mars: • Origin of water: Earth water acquired from late impacts of large Mars sized planetesimals? - for Mars, such collisions would be destructive – must have accreted from many smaller impacts - implies Mars gets water from asteroids and comets, delivering total of 1/20 – ¼ Earth ocean’s worth – with D/H = 2 times Earth ocean. - 2nd possibility; local origin, Mars formed in a cooler, wetter part of nebula: water ice added directly during its formation locally?

  32. Warm climate on early Mars? - Heating by green house requires much more CO2 than on Earth because i) solar luminosity lower at earlier times by 70% ii) Mars is more distant than Earth, so black body T is lower to begin with, -> needed atmosphere with several times pressure of Earth’s and 10,000 times pressure of CO2 than Earth! - greenhouse gas eventually lost to space - test idea using N(15)/N(14) isotopic ratios…

  33. Drying and freezing of Mars: - High erosion rates on early Mars due to warm and wet surface conditions - eg. heavy erosion of large impact craters in older southern hemisphere material - on younger terrains, much less erosion (possibly by several thousand times) -> early and quick end to wet era. - water loss tested by D/H measurements: i) 5 times Earth ocean ii) 3 times ancient Mars meteorites iii) much less than loss on Venus -> water stored by trapping in crust?

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