2000 February 3, SPS 1020 (Introduction to Space Sciences) - Read TNSS Chs. 7 (Mercury) and 8 (Venus), and PBD Chs. 11 and 12 by Tuesday, February 8. - There will be a reading quiz on TNSS Chapters 7 (Mercury), 8 (Venus), 10 (The Earth's Moon), 11 (Mars), and PBD Chapters 11 and 12 on Tuesday, February 8. ------------------------------------------------------------------------- MARS (TNSS Chapter 11)- --------------------- The most Earth-like of planets. Has atmosphere, weather, clouds, polar caps, water (mostly ice), snow, seasons. Radius ~ 1/2 Earth's radius Total area ~ land area of Earth (Earth's Moon: area ~ of N. America) Acceleration of gravity ~ 1/3 Earth's (Earth's Moon ~ 1/6 Earth) Obliquity (tilt of axis, to orbital plane) = 25 degrees => shows seasons, like Earth => seasonal changes, before ~ 1965 attributed to vegetation Now known to be _global dust storms_ (Sagan) Mars year = 687 days = 1.88 Earth years Rotation period = 24h 37m Temperatures: Gets very cold (< -100 C) every night: heat escapes from thin atmosphere. Steep temperature gradient, above ground. Polar caps: both seasonal (CO_2 ice) and permanent (water ice) Atmosphere present, but we can't breathe it: - 95% CO_2 composition, pressure ~ 7 millibars, about like outside a jet airliner window (1 bar = Earth standard) - At -166 C, CO_2 sublimates into dry ice: Mars "snows" its own atmosphere! - Also icy water clouds, 20-30 km altitude, over volcano summits 2 small natural satellites: Phobos and Deimos. Captured asteroids? 1894: Percival Lowell established Lowell Observatory, Flagstaff, Arizona. Mapped "canals" on Mars (first seen be Schiaparelli, 1877). These later prove to be optical illusions, from chains of craters near eye's resolution limit. Lowell attributed them to intelligence (engineering projectsof dying civilization), book "Mars as the Abode of Life". => Popularized idea of life on Mars. Also H.G.Wells sci-fi novel (1898), "The War of the Worlds"; Edgar Rice Burroughs "John Carter" series Spacecraft exploration: -------------------------- Mariner 4 (1965), also Mariners 6 and 7 (1969) flybys: a real shock! No canals or any sign of life. Only cratered terrain, "like the Moon." Calls to end Mars exploration ("we understand it"); had seen < 1/2 of it (like Mercury now) Mariner 9 (1971): first Mars orbiter - stunning success! (Mariner 8 duplicate: in Atlantic.) Arrived during global dust storm: would have been failure, if a flyby - First features to settle out: four great _shield volcanoes_ in Tharsis Regio. - Valles Marineris: a really Grand Canyon! - Dendritic channels (dendritic = tree-like): like dry river beds, from running liquid water! Can't have been lava (too viscous), but: Atmosphere is too tenuous for liquid water to exist on Mars today => warmer and wetter in past 4 primary geological processes: _all_ are important on Mars - 1) Impact cratering: S. Hemisphere of Mars is mostly ancient, cratered terrain. (Late Heavy Bombardment, 3.8 billion years old) Not entirely dominant, though. much water erosion in S.: dendritic channels => Still, great age of features shows that surface is not very actively resurfaced. 2) Tectonism: less important, since no global plate tectonics: planet is smaller than Earth, had insufficient interior heat. No tectonic (folding) mountains, like Earth's; all volcanic. However, one spectacular feature: *Valles Marineris* ("Mariner Valley" or "The Big Valley:). One great fault, from volcanic uplifting. Valley 5000 km long, 700 km wide at widest, rims 4 miles high! Has slumping, from avalanches! 3) Volcanism: giant shield volcanoes, biggest in Solar System. Olympus Mons ~ 15 miles tall. Impossible to have mountains this tall of Earth, because of isostasy. *Lack* of plate tectonics allows Martian volcanoes to attain their huge size. Hawaii moves, along Pacific. Pateras (Latin, "saucer"): ancient collapsed shield volcanoes? (Unknown on Earth) 4) Gradation: - Wind (aeolean) erosion common (sand dunes, craters with debris trails) - Water erosion, in many cases: - Rampart craters (e.g. Yuty): from splashes! - Dry _runoff channels_ in south: look like Earth river beds, with tributaries - Outflow channels: were massive outpourings. From flash floods? - Chaotic terrain (irregular blocks of rock and fractures, on E end of Vallis Marineris): from groundwater, fed outflow channels SNC ("snick") meteorites, from Mars: contain water, and hyrated minerals (clays) Also _claimed_ signs of life: more later. Back to exploration history: Landers, modern exploration - -------------------------------------------------------- Viking 1 and 2 (launched 1976): $1G pair of orbiters and landers. Orbiters: global maps at 20-m resolution. Landers: first successful landings on another planet. First search for life on another world; found none (more later). Viking 1 lander: in Chryse Planitia Viking 2 lander: in Utopia Planitia Sites chosen for spacecraft safety, not geological interest: boring plains Mars Observer: $1G mission lost in 1993. Aiiiiigh!!!! MO, Hubble, & Galileo => "faster, cheaper, better" (Dan Goldin, NASA Administrator since 1992) "The Mars Invasion": ------------------- Mars Pathfinder (lander), deployed Sojourner rover (1997) - spectacular technological development, excellent science too. Documented history of water, climate on Mars; analyzed rock compositions; discovered dust devils. Novel landing technique (airbags and bouncing) => site chosen for geological interest, Ares Vallis floodplain. Flooded at least 5 times. Found rounded pebbles, conglomerate rocks (many pebbles cemented together). Removed all doubt that water once flowed! Mars Global Surveyor, arrived 1997 September: obtaining highest-resolution images ever (5-m). - Magnetometer data: ancient Martian plate tectonics? Discovered because survey was stretched out, because spacecraft arrived damaged. - Oceanus Borealis (Northern Ocean) - over 1700 m deep over N. half of Mars, > 3 billion years ago (!) Very new evidence, from topography data from Mars Global Surveyor orbiter (operating now); but still hasn't found "shoreline" Nozomi (Japan, launched 1998): to study magnetism. Little global magnetic field. Cool interior => weak or no dynamo, to make magnetic field. Fuel consumption problem => will arrive 4 years late, in December 2003. NASA plans to send two spacecraft to Mars every opposition (closest approach, every 26 months), for next 3-4 oppositions: Mars Surveyor (Climate) Orbiter: launched 1998 December, arrived 1999 September, but burned up in atmosphere, due to English-to-metric units mixup! Mars Surveyor (Polar) Lander: launched 1999 January, to land on S. Pole of Mars, 1999 December; attempted deploying two Deep Space 2 penetrators. Again, total failure. Mars Surveyor 2001 Orbiter & Lander, Mars Surveyor 2003 Orbiter & Lander, Mars Express (European, 2003) orbiter and lander, Mars Surveyor 2005 Orbiter & Lander (sample return, Europe involved): All planned, but because of recent failures, program will now undergo a throrough review. Whither "Cheaper, Faster, Better?" ------ Terraforming? Might it be possible to change the climate of Mars, to make it warmer and wetter? Robert Zubrin (The Case for Mars) and Carl Sagan (Cosmos book) discuss this: plant plants at poles, absorb more sunlight, make planet warmer. The details have been left as an exercise for the student... MAJOR unsolved question: Where did the atmosphere go? Mars is less massive than Earth, so some gases would escape, but this doesn't explain all atmospheric loss.