Mars: Canals. thinking. Chasma.

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2 Mars: Canals Schiaparelli noted canali, which in italian means channels, not canals. Percival Lowell saw canals which he attributed to an intelligent civilization coping with global draught. Most canals turned out to be products of poor observing (opticalillusions) and wishful thinking. Some canal features are real albedo markings: e.g., Juventae Fons oasis is Juventae Chasma.

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4 Mars: Physical Properties (I) Mean radius (km) Equatorial radius (km) Polar radius (km) Surface area (106 km2) N. polar cap (106 km2) S. Polar cap (106 km2) Volume (km3) Mass (kg) Mean density (g.cm-3) Equatorial gravity (m.s-2) Polar gravity (m.s-2) Equatorial escape velocity (km.s-1) / / x 1011 (53% of Earth) x 1023 (11% of Earth) /

5 Mars: Physical Properties (II) Sidereal revolution period (Earth days) Mean synodic period (Earth days) Orbital eccentricity Orbital inclination to ecliptic Mean orbital velocity (km.s-1) Inclination of equator to orbit Sidereal rotation period (Earth hours) Solar constant at 1.52 AU (W.m-2) Mean surface temperature (K) Surface temperature range (K) Mean surface pressure (mbar) Annual pressure range (mbar) Mean atmospheric mass (kg) o o (43% less than at Earth) x 1016 Mars: Bulk Mars has a relatively low density (d = g.cm-3): Although its volume is 53% of Earth s, its mass is only 11% of Earth s.

6 Mars: Temperatures Calculated Surface Equilibrium Temperature: On Mars: Teq 216 On Earth: Teq ~ 253 K Global Average Surface Temperature: On Mars: Tav 220 ~ Teq On Mars, greenhouse warming is weak. On Earth: Tav ~ 288 K > Teq On Earth, greenhouse warming is significant. Mars: Orbital Characteristics Mars s orbital eccentricityis relatively high compared to that of the Earth: e ~ vs Mars receives ~ 45% more insolation at perihelion than at aphelion. Orbital perturbations due to Jupiter and the Sun induce considerable changes in Mars s orbital eccentricity over time: 0 < e < 0.14.

7 Sidebar: Orbital Parameters a = semimajor axis 2a = major axis or length of the ellipse ra apoapsis distance from focus rp = periapsis distance from focus e = (ra rp) / (ra + rp) ra + rp = 2a ra (1 + e) rp = a (1 e)

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9 Mars: Topography Mars topography distribution is strongly bimodal Hemisphericcrustal dichotomy Origin of this hemispheric crustal dichotomy is unknown: Exogenic explanation: Giant impact? - Endogenic explanation: Early tectonic evolution dissymmetry? Highlands in southern hemisphere (60% of planet) are heavily cratered Ancient Lowlands in northern hemisphere are less cratered Younger Tharsis bulge (rise) is a large (largest) volcanic province. OlympusMons is the largest (shield) volcano known: (D ~ 600 km at base; h =27 km above datum; basal scarp cliffs: 6 km high; summit caldera: 80 km in diameter). VallesMarineris is a large (largest) canyon system: 4000 km long (30oW to110ow), up to 600 km wide, up to 7-9 km deep. Origin by extensional faulting connected to rise of Tharsis bulge?

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13 From The Grand Tour of the Solar System, by W. K. Hartmann and R. Miller

14 Mars: Internal Structure Internal structure of Mars is inferred from bulk physical properties and geochemical models. Three-layer internal structure: Crust (silicates) Depth range: 0 to km (1.00 to ~ 0.98 RM) Crust is thickest under Tharsis bulge. Mantle (silicates) Depth range: 100 to 1630 km (~ 0.98 to 0.48 RM) Basal pressure: ~ kbar Basal temperature: ~ 1900 K Mean density: ρ ~ 3.5 Core (metallic: Fe-FeS) Depth range: 1630 to 3390 km (0.48 to 0 RM) Central pressure: ~ kbar Central temperature: ~ 3000 K Mean density: ρ ~ 7.3 Mass: ~ 21% of Mars s total mass. N2 Ar O2 O3 Mars: Atmosphere: Composition Gas CO2 CO H2O NO Ne HDO Kr Xe Abundance % 2.70 % 1.60 % 0.13 % 0.08 % 0.03 % (variable) ~ 100 ppmat 120 km 2.5 ppm / ppm 0.3 ppm 0.08 ppm ~ ppm(var.) Source Outgassing& Evaporation Outgassing Outgassing(40K), primordial CO2 photolysis CO2 photolysis Evaporation & Desorption Photochemistry (N2, CO2) Outgassing, primordial Evaporation & Desorption Outgassing, primordial Outgassing, primordial Photochemistry (CO2) Sink Condensation Escape as N None Photoreduction Photooxidation Condensation & adsorption Photochemistry None Condensation & adsorption None None Photochemistry

15 Mars: Atmosphere: Isotopes Isotopic ratio D / H 12C / 13C 14N / 15N 16O / 17O 16O / 18O 36Ar / 38Ar 40Ar / 36Ar 129Xe / 132Xe Observed value (9 +/- 4) x 10-4 (7.8 +/- 0.3) x / / / / / / / or -1 Data source IR spectroscopy IR spectroscopy Viking mass spectrometer Viking mass spectrometer IR spectroscopy Viking mass spectrometer IR spectroscopy Viking mass spectrometer Viking mass spectrometer Viking mass spectrometer Mars: Atmosphere: Chemistry CO2 is converted to CO and O2 by solar UV. Abundances of CO2, O2, and CO cannot be explained by direct recombination of CO and O to CO2, as the latter is a very slow process. Catalytic help from OH radicals (produced by photolysis of H2O) and from O atoms would do the trick. Solar UV flux on Mars is ~ 800 greater than at the surface of the Earth. Solar UV photolysis of atmospheric gases happens all the way down to the surface. H2O2 (hydrogen peroxide) is produced and reacts with soil to produce aggressive peroxide chemistry likely explanation for activity detected by Viking some life detection experiments.

16 Mars: Atmosphere: CO2 cycle Mars s orbital eccentricity results in pronounced seasons. Southern winters are extremely cold: Tmin ~ 140 K Southern summers are relatively warm: Tmax ~ 300 K As a consequence of these seasonal temperature changes, during the southern winter, a substantial fraction of the martianatmospheric CO2 condenses out onto the surface, producing a (whopping) global pressure change of 37% (2.4 mbar) relative to the global mean pressure (6.36 mbar). For condensible gases (CO2, H2O, ): Column densities and mixing ratios are seasonally variable as a result of this seasonal condensation and sublimation of CO2. For non-condensible gases (N2, Ar, Ne, Kr, Xe, ): Mixing ratios will vary with the seasonal condensation and sublimation of CO2, but NOT their column densities. Mars: Surface: Landers All successful Mars landers have touched down in the northern lowlands: Viking Lander 1 (Chryse Planitia) and Viking Lander 2 (Utopia Planitia) are on opposite sides of Mars. Mars Pathfinder is located 850 km SE of Viking Lander 1.

17 Mars: Surface: Composition Mass% Na2O MgO Al2O3 SiO2 SO3 Cl K2O CaO TiO2 Fe2O3 Thppm Uppm Brppm Rb ppm Srppm Other Total Mars / / / / / / Viking Lander < ~ 80 < / Viking Lander 2 2 =VL1? =VL1? < present / Phobos / / / / / / / / / Pathfinder (Rocks) 2.5 +/ / / / / / / / / / Pathfinder (Soil) 2.3 +/ / / / / / / / / / Mars: Surface: Thermal Inertia

18 Small valley networks Runoff channels Outflow channels Gullies Some landforms are suggestive of ground ice and past glaciation(s). Many landforms are suggestive of past flow of liquid H2O: H2O is presently thermodynamically unstable on Mars, mainly because of the low surface atmospheric pressure. Some locations are transient exceptions. If water is present there, it would be stable at the surface (e.g., mid pm in Summer on floor of Hellas Basin). Total H2O inventory, based on estimated accretionary endowment and on cumulative outflow channel discharges, suggest an amount equivalent to a global liquid layer km deep. H2O is present on Mars today at least in the atmosphere, in both polar caps, and in the near-surface regolith (within topmost meter or so); might also be present in abundance as deeper ground ice and liquid water, but not yet detected. Mars: H2O

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23 Epithermal Neutron Flux Thermal Neutron Flux

24 Mars: Craters: Transition Sizes Simple impact craters (bowl-shaped) D < km Complex impact craters with central peak km < D < km Complex impact craters with ring of peaks km < D < 1000 km Multi-ringed impact basins 1000 km < D

25 Mars: Geologic Ages Surface Ages: Rule of thumb based on apparent crater densities: Craters crowded rim to rim: > 3.5 GY Craters scattered: 3.0 GY GY Craters sparse or absent: < 500 MY Highest preserved crater density on Mars: Arabia Oldest surface on Mars in terms of preservation of large-scale geographic features. Oldest eroded craters in Arabia probably formed GY ago (?). Moon: Heavy Bombardment: GY ago. Note: Impactor flux at Mars ~ 2-3 x that on Moon (Bottke, Ivanov) Surface Ages: Caution with designation. A Noachian surface, as defined by the density of say craters > 1 km in diameter, may be covered by a thin Hesperian lava flow and a younger Amazoniandrift mantle EARTH Amazonian Hesperian Noachian MARS