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Mars. Moons of Mars. Exploration of Mars. ~1800: Herschel and others discover ice caps and clouds 1877: Phobos and Deimos discovered; also Schiaparelli (It.) refers to ‘ canali ’ 1890 ’ s: Lowell interprets markings as canals, implying intelligent Martian life
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Exploration of Mars • ~1800: Herschel and others discover ice caps and clouds • 1877: Phobos and Deimos discovered; also Schiaparelli (It.) refers to ‘canali’ • 1890’s: Lowell interprets markings as canals, implying intelligent Martian life • 1965 Jul: 1st close-up photos by Mariner 4 • 1971 Nov: 1st orbital probe in Mariner 9 • 1976 Jul: Viking 1 lander – no life • 1997 Jul: Mars Pathfinder • 1997 Sept: Mars Global Surveyor • 2001 Oct: Mars Odyssey • 2004 Jan: Spirit (Rover) • 2006: Mars Reconnaissance Orbiter • 2007: Phoenix lander
Properties of Mars • Iron core of 1500 km in radius • Low magnetic field (about 0.1% of Earth’s), because molten core has largely cooled • Resurfacing from past volcanic activity • Polar caps of dry ice • No surface water • Thin CO2 atmosphere • Red coloration from oxidized iron minerals
Water on Mars • Evidence for channels and sea beds (?) • H2O in clouds and polar caps, but only trace • Mars Odyssey implies subsurface water ice So maybe Mars warmer and wetter in past (even oceans?), and perhaps a lot of that water exists as permafrost below the surface (although in a warmer Mars, water vapor is close to escaping low gravity of Mars)
Methane in the Martian Atmosphere • Methane gas was recently detected in Mars’ atmosphere using groundbased telescopes • The methane gas distribution is patchy and changes with time • Most methane in Earth’s atmosphere is produced by life, raising questions about its origin on Mars View of Mars colored according to the methane concentration observed in the atmosphere. Warm colors depict high concentrations.
Recent Release of Methane • Methane in the atmosphere should be destroyed by UV light within a few hundred years • Methane observed now must therefore have been produced recently • Variations in space and time suggest that it was recently released from the subsurface in localized areas UV photons have enough energy to break molecules apart
The Big Picture surface methane liquid water hot rock ~2 µm methane bacteria • Where can the methane come from? From analogy with Earth, there are two leading theories for the origin of recent subsurface methane at Mars: • Methane is produced by water-rock interactions • Methane is produced by bacteria, in regions where liquid water is found Either theory implies that the Martian subsurface is dynamic • However, Curiosity has so far FAILED to detect any methane Methane on Mars could be produced chemically through liquid/rock interactions (top) or biologically (bottom)
Martian Weather • Mars tilt like Earth, hence similar seasons • Mars has e~0.1, so 10% closer at perihelion and 10% farther at aphelion • S. summer is warmer, receiving 50% more light compared to N. summer • Dust storms: greater heating in S. leads to more convection and lifting of dust; storms can last for several weeks
Terrestrial Atmospheres • Terrestrials have secondary atmospheres, which are produced by outgassing from the planet interior • Comets have likely influenced our atmosphere, possibly supplying some water for oceans during early bombardment era
Details of Outgassing: volcanos yield mainly CO2 and H2O Comparative Planetology: Venus and Mars have CO2 atmospheres, but not Earth, but Earth has oceans, so that the CO2 is in carbonate rocks Why O2 at Earth? Photosynthesis from plants. Earth O-poor until 2.5 Gyrs ago, and earliest plant fossils are 2 Gyrs old Where did H2O go at Venus? Break up molecule and H2 escapes Some Details…
