3_Grand Tour pt - Discussion Questions from Tuesday...

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Unformatted text preview: Discussion Questions from Tuesday Discussion Questions from Tuesday • How can we see through the clouds of Venus, and what is actually imaged? • What kind of structures occur in the Venusian crust, how are they distributed, and what do they signify? • Why did Venus turn out so different from the Earth? • What does the population of impact craters on Venus suggest about its history? • Why do we think the pressure and temperature environment on Mars was different in the past from what it is today? Grand Tour of the Grand Tour of the Solar System, Part 3 Mars, Asteroids, and the Jupiter system Discussion Questions for Today Discussion Questions for Today In what ways are the shield volcanoes of Mars similar to terrestrial shield volcanoes? In what ways are they different? What evidence is there to suggest not only that Mars’ early environment could support liquid water, but that there may have even been an ocean there? What is meant by the term “orbital resonance,” and how does it apply to the distribution of asteroids in the Main Belt? Why do we think some asteroids may have formed from larger, differentiated planetary bodies, while others seem more primitive? Mars (continued) Annual Atmospheric Pressure Annual Atmospheric Pressure Variations Dunes Polar Regions Rayed Impact Craters Rayed Impact Craters Tornabene, et al., 2005 Canyons Canyons Volcanoes Olympus Mons shield volcano 18 km above the surrounding plains (Mauna Loa rises 8.8 km above seafloor) 600 km diameter (Circumscribes 2.65 X area of Ohio) Basal cliff up to 6 km high (landslides) Young (perhaps still active) Why is it so big? (plume without plates) Tharsis Martian Meteorites All are igneous rocks of basaltic or ultramafic composition. SNC = shergottite (basalt or gabbro), nakhlite (clinopyroxenite), chassignite (dunite), ALH84001 (orthopyroxenite) Best evidence for Mars origin is trapped gases Radiometric ages of SNCs are generally very young, less than 1.3 b.y. The exception is ALH84001, which has an age of 4.5 b.y. Spirit rover in Gusev crater Bonus question: who took this photo? Humphrey Humphrey Normative Mineralogy Adirondack/Humphrey/Mazatzal Diopside Pyroxenes Olivine (Fo55/52/51) 14/13/13% Hypersthene 31/26/35% 6/13/0% Magnetite 1.2/1.3/1.7% 4.4/4.3/2.6% Ilmenite Chromite 0.9/1/0.9% 0.9/0.9/0.8% 41/39/44% Plagioclase (An43/45/40) Extrapolated to 0.3% S, Molar Fe2+/Fetotal from Mossbauer Apatite TES Surface Type 2 Obscured By Dust TES Surface Type 1 Interpretations of Spectral Compositions TES Surface Type 2 Obscured By Dust TES Surface Type 1 Basaltic Andesitic Bandfield et al., 2000 Basaltic Andesitic Hamilton et al., 2001 Basaltic Wyatt and McSween., 2002 Altered Basalt Vastitas Borealis Formation Asteroids Asteroids Asteroids: Nature Asteroids: Nature Asteroid is Greek for "star-like“. Asteroids are small rocky objects that look like stars in Asteroids small telescopes, except that they move across the sky like planets and are part of the Solar System. and Most asteroids are found in the Main Belt between Mars and Most Main Jupiter and in the Kuiper Belt beyond Neptune. Kuiper Many exist in near-Earth space too and are known as NearMany NearEarth Asteroids or NEAs. Other smaller populations exist too: Trojans, Apollos, Amors, Other Centaurs,… Centaurs,… There may be 1,000,000+ asteroids >1 km in diameter. Asteroids: The Main Belt Asteroids: The Main Belt • The Main Belt extends from about 2.2 to 3.3 AU • Most of the orbits lie at or near (±10° to 20°) the plane of the ecliptic • More than 20,000 Main Belt asteroids have wellknown orbital parameters • The number known has been recently increasing by a few thousand per year because of new telescopic search programs Edge on view Asteroids: The Largest Ones Asteroids: The Largest Ones 1 Ceres (1801): D = 940 km, a = 2.77 AU Discovered by Guiseppe Piazzi in 1801 Piazzi was searching for a "missing planet" between Mars and Jupiter 2 Pallas (1802): D=540 km, a=2.77 AU 4 Vesta (1807): D=510 km, a=2.36 AU 13 Main Belt asteroids have D > 250 km Asteroids: Size Distribution Asteroids: Size Distribution • The number of asteroids of a given diameter D is proportional to 1/D2 collisional distribution • For example: 3 > 500 km 13 > 250 km hundreds > 100 km 10,000+ > 10 km (?) Total: >1,000,000 > 1 km (?) Number of Near-Earth Asteroids (a model) • Most of the mass is in the largest few asteroids • Total mass of all asteroids is only ~5-10% mass of the Moon Asteroids: Gaps & Resonances Asteroids: Gaps & Resonances • Astronomer Daniel Kirkwood (1886) noticed that the Main Belt has gaps in which asteroids are “missing”. • The Kirkwood Gaps are locations where resonances with Jupiter’s orbit occur, i.e., where gravitational disturbances by Jupiter are the strongest. • May explain why no planet there: Jupiter only allowed small bodies to coalesce and prevented a larger planet from forming. Asteroids: Other Groups Asteroids: Other Groups Trojans 889 asteroids leading and trailing Jupiter by 60° Centaurs 67 asteroids found between Jupiter & Neptune Kuiper Belt Objects More than 400 large asteroids beyond Neptune Near­Earth Asteroids (NEAs) 103 Atens: orbits interior to Earth's 593 Apollos: orbits that cross Earth's 595 Amors: orbits exterior to Earth's (e.g. 433 Eros) All these populations remain incompletely inventoried. Asteroids: NEAs Asteroids: NEAs Thousands of NEAs have been discovered through recent surveys. Asteroids: Composition Asteroids: Composition Spectroscopy and radar observations of asteroids reveal four main classes: C Type: dark, "carbon rich", albedo ~5% D Type: dark, very red spectra S Type: brighter, “stony", albedo ~20% M Type: rare "metallic" type, very radar bright C,D,S Types are possibly all primitive. M Types and other anomalous classes might be from differentiated parent bodies. Much debated. Asteroids: Spectral Distribution Composition varies systematically with distance from the Sun. Suggests that asteroids might preserve the conditions of planetary formation in the Early Solar System. Asteroids: Geology Asteroids: Geology 4 asteroids visited up close by spacecraft 951 Gaspra: Galileo flyby in 1991 243 Ida: Galileo flyby in 1993 253 Mathilde: NEAR flyby in 1997 433 Eros: NEAR orbital mission in 2000­2001 Also: Spacecraft images of Martian moons Phobos and Deimos: captured asteroids? Abundant evidence for impacts, and surprising evidence for erosion and tectonism on these small bodies 951 Gaspra S Type 16 x 11 x 10 km 243 Ida S Type 60 x 25 x 19 km Dactyl Ida's moon! D = 1.5 km 253 Mathilde C Type 66 x 48 x 46 km (large!) Many large craters Density only 1.3 g/cm3 May be 50% "empty" 433 Eros (2 views) S Type 31 x 13 x 13 km Many large craters Density about 2.6 g/cm3 433 EROS As seen by the NEAR (NearEarth Asteroid Rendezvous) Spacecraft. Tectonics: Eros may have been compressed and possibly even twisted during its history... Last image from NEAR before its landing: very fine-grained regolith. Rock is ~4m across Fine-grained regolith appears to be moving downhill on Eros: erosion. The Dawn Mission • Launched in 2007 • Arrives at Vesta in October ‘11, leaves in May ‘12 • Arrives at Ceres in Aug ‘15 • Will map the chemical and mineral composition, morphology, topography, etc. of these two very different large asteroids. Outer Planet Satellites Outer Planet Satellites Gas Giant Satellites Gas Giant Satellites Giant Planet Jupiter Medium Satellites 0 Small Satellites 24 Saturn Large Satellites 4 Galilean Satellites Titan 6 23 Uranus 0 5: 16 Triton M,A,U,T,O 0 7 Neptune 24 23 16 • Distinct and important differences in density, composition, and orbital properties Jupiter System: The Galilean Satellites Io Volcanically active No H2O! Rock Differentiated. Europa Smooth icy crust “Ocean” suspected beneath Ice, Liquid Water (?), and Rock Differentiated. Ganymede Tectonic grooves Ice and Rock Differentiated Magnetic field! Callisto Battered by impacts. Ice and Rock. Only partially differentiated Io Io: Tidal Heating Io: Tidal Heating Io is in synchronous rotation around Jupiter (always shows the same side to Jupiter) and is stretched into a football shape along the Jupiter­pointing axis. Because Io’s orbit is eccentric, this football shape is not constant but waxes and wanes (flexes) as the gravity differential changes along Io’s orbit. This flexing heats Io’s interior by shear friction. The situation is prevented from damping out (Io’s orbital eccentricity is maintained) by resonances with Europa and Ganymede. Io: Volcanic Activity Plumes such as the one below imaged along the limb of Io provide clear evidence that Io is volcanically active. Io: Volcanic Activity Io’s surface is devoid of impact craters and must therefore be very young. Resurfacing (renewal of the surface) is very active on Io. The multicolored deposits on Io are due to various sulfur­rich compounds emplaced by Io’s volcanic activity. Bright white deposits are due to SO2 (sulfur dioxide) frost. There is no evidence for H2O on Io. Io’s initial endowment in H2O must now be gone. The H escaped and the O recombined with sulfur S to form SO 2. Io: Volcanic Activity Io: Volcanic Activity Between 1979 and 1981: patterns of volcanic deposits clearly changed as well. Io: Hot Spots As a result of tidal heating, Io experiences volcanic activity on a global scale. When viewed in the thermal IR, Io’s surface reveals several active hot spots. They are sites of ongoing activity. Io: Volcanic Activity Io: Volcanic Activity Io has lakes of molten sulfur, plumes of SO2, and low viscosity basaltic lavas Virtually all H2O has been “boiled” off. Volcanic calderas are several km deep. Mountains are not volcanoes. Europa Europa: Flatland Europa is the second Galilean Satellite outward from Jupiter (after Io). On a global scale, Europa’s surface is extremely smooth and flat. Europa has varied surface textures all consistent with a fractured icy crust. Europa: Ice Rafting Tectonics Europa: Ice Rafting Tectonics Europa’s surface patterns were likely formed by multiple episodes of a floating ice crust splitting, colliding, grinding, and rewelding over an “ocean” of fluid material, liquid H2O? Europa: Refrozen Ice Rafts Image showing ~100 km strip of Europa’s surface, acquired by NASA’s Galileo spacecraft. Europa: A Subsurface Ocean ? Beneath Europa’s icy crust, there may be an ocean of liquid water or slush. Europa: Is there Life? Two key lines of evidence make Europa a possible habitat for Life: 1) Morphologic + Theoretical evidence for sustained presence of liquid H2O. 2) Spectral evidence for the presence of reddish, possibly organic­rich, salts. Ganymede Ganymede: Craters & Tectonics Ganymede: Craters & Tectonics Ganymede is the largest moon in the Solar System. Larger than Mercury! Surface was shaped by impact cratering and some form of tectonic activity. Ganymede: Ancient & Young Ganymede: Ancient & Young Grooved terrain is sparsely cratered: younger than heavily cratered terrain. Callisto Callisto: Impact Cratering Callisto: Impact Cratering An extended record of impact cratering is preserved on Callisto, from ancient basins (e.g., Valhalla) to relatively young crater chains (impacts a la SL­9?). The Valhalla Basin was formed by a giant impact early in Callisto’s history. The impact left a set of concentric wave­like structures in the moon’s icy crust. Galilean Satellites: Interiors Galilean Satellites: Interiors The relative abundance of H2O ice increases with radial distance from Jupiter. Discussion Questions for Today Discussion Questions for Today In what ways are the shield volcanoes of Mars similar to terrestrial shield volcanoes? In what ways are they different? What evidence is there to suggest not only that Mars’ early environment could support liquid water, but that there may have even been an ocean there? What is meant by the term “orbital resonance,” and how does it apply to the distribution of asteroids in the Main Belt? Why do we think some asteroids may have formed from larger, differentiated planetary bodies, while others seem more primitive? ...
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