Surface of Mars Lecture #20: Geology and Geologic Processes View from the Surface History/Evolution of the surface Reading: Chapter 9.4 The Main Points Mars has had a geologically active past that has included volcanic, tectonic, impact, and erosional processes Today, Mars geology is dominated by erosional processes, and we don t know if the planet is still volcanically or tectonically active Astro 102/104 1 Astro 102/104 2 Geology of Mars Mars is a geologically exciting place! Abundant evidence of past volcanism Abundant evidence of past tectonism Abundant evidence of past impact cratering Abundant evidence of past and current erosion Much of our knowledge comes from orbital imaging (Viking, MGS, Odyssey, MRO) Augmented at five specific landing sites Astro 102/104 3 The View from the Surface Three landers and two rovers have successfully returned images and other data from the surface of Mars Viking Lander 1 600 kg landed mass, powered by two 238 Pu RTGs Landing site: Chryse Planitia (22.697 N, 48.222 W) Operated from July 20, 1976 to November 13, 1982 Viking Lander 2 Landing site: Utopia Planitia (48.269 N, 225.990 W) Operated from September 3, 1976 to April 11, 1980 Mars Pathfinder 360 kg landed mass (Rover = 16 kg), powered by solar panels Landing site: Ares Valles (19.33 N, 33.55 W) Operated from July 4, 1997 to September 27, 1997 Mars Exploration Rovers (Spirit and Opportunity) 174 kg mobile mass, powered by solar panels Landing sites: Gusev Crater and Meridiani Planum Operated from January 2004 to??? Astro 102/104 4 1
Viking Landers (1976-1982) Mars Pathfinder (1997) Trenches at VL2 VL1 Astro 102/104 5 Frost at VL2 Dunes, boulder at VL1 Astro 102/104 6 Mars Exploration Rovers (2003-2008) Volcanism Two large volcanic provinces on Mars Tharsis: An enormous 10 km bulge in the crust Elysium: Smaller, localized elevated region Relative age dating from crater counts indicates that these volcanoes are relatively young (< 100 million years?) Mars may be volcanically active today, though we have not seen direct evidence... Astro 102/104 7 Astro 102/104 8 2
Olympus Lava flows in Tharsis Elysium Lava flows that partially buried another volcano Tectonism Spectacular rifting of the Martian crust has occurred Triggered by bulging of Tharsis? Largest rift: Valles Marineris canyon system 5000 km long, 100 km wide, 8 km deep ( ~ 5 miles deep!!) Few signs of compression (e.g., folded or uplifted mountains) Speculations, but no conclusive evidence for Earth-like plate tectonics on Mars Astro 102/104 9 Astro 102/104 10 Extensional Graben Canyons Impact Cratering Thousands of impact craters on Mars Sizes range from a few meters to 1500 km Many more craters in the south (older) But even "young" areas have many craters Fractured Astro 102/104 Terrain Rift Valley 11 Astro 102/104 12 3
"Splosh" Craters Degraded Craters "Pedestal" Craters Impact Basins Age of the surface based on craters Craters used to develop the stratigraphy of the Martian surface Absolute ages have large uncertainties Most recent volcanism: from 0.1 to 2.0 billion years ago? Radial Ejecta Craters on Astro 102/104 Volcanoes! 13 Astro 102/104 14 Erosional Features Evidence for substantial movement of materials on Mars Gravity Landslides, Slumps, Ejecta Blankets Wind Dunes, Streaks, Dust Storms, Dust Devils Water Outflow channels, Runoff channels (valley networks) Ice? Astro 102/104 15 Runoff Channel Outflow Channel Landslide Astro 102/104 Streamlined Islands 16 4
Seeps? Dust Devils in Motion Dust Devil & Tracks Dunes Wind Streaks This movie clip shows several dust devils moving from right to left across a plain inside Mars' Gusev Crater. The clip consists of frames taken by Spirit's navigation camera during the rover's 543rd martian day, or sol (July 13, 2005). The total time elapsed during the taking of these frames was 12 minutes, 17 seconds. Astro 102/104 17 Astro 102/104 18 Topography of Mars General trend: North is low (blues); South is high (reds) Crater density: north "young", south "old" Reference elevation: 6.1 mbar pressure Enormous range of elevations on Mars! Mars Topography: Broad range of elevations Distinct northern/southern dichotomy - Southern highlands; Northern lowlands Highest high: +25 km (Olympus Mons) Lowest low: -5 km (Hellas Basin) Factor of 20 in atmospheric pressure! Astro 102/104 19 % of surface area Astro 102/104 20 5
The Martian Interior The relatively low density (3.9 g/cm 3 ) implies less iron or metal in the interior than Earth or Venus Mars appears to be differentiated Spacecraft measurements of the gravity field of Mars are consistent with the presence of a metallic core of radius 1300-2000 km (1/3 to 1/2 the planet's radius) No seismic networks on Mars (yet), so the existence of a core and details about the interior are still just theories... Astro 102/104 21 Is (or Was) Mars Magnetic? Mars has no global magnetic field today If Mars has (or had) a molten iron core like the Earth, then why doesn't it have a magnetic field? Data from the Mars Global Surveyor mission reveal regions of the surface that appear to retain a remnant magnetism Was the core molten long ago? Consistent with early volcanism But what does it mean? Astro 102/104 22 Summary Mars is a fascinating geologic world Largest volcanoes in the solar system Enormous rift valleys and canyon systems Complex impact structures on all scales Active erosion by wind and gravity Extensive erosion by water early in Mars history? 3 landers and two rovers have studied the environment in detail Spacecraft data indicate that Mars is differentiated Will humans one day go to Mars? Astro 102/104 23 Next Lecture... Martian Climate Change? The Martian Climate Evidence for climate change Did it rain on Mars? Implications for Earth's climate... Reading: Chapter 10.4 Reading: Astro 102/104 24 6