AST 105 Intro Astronomy The Solar System MIDTERM II: Tuesday, April 5 4 Processes that Shape Surfaces Volcanism Eruption of molten rock onto surface Impact cratering Impacts by asteroids or comets Tectonics Creating features on a planet s surface by internal stresses Erosion Rocks act like silly putty How can solid rock be bent, squished, stretched, and cracked? Behavior depends on the time scales of the stresses Long time scales flows and bends Short time scales cracks and breaks Also depends on temperature High Temp. rock flows more easily Low Temp. rock more brittle, breaks & cracks
Compression Tectonics Extension 4 Processes that Shape Surfaces Volcanism Eruption of molten rock onto surface Impact cratering Impacts by asteroids or comets Convection of the mantle creates stresses in the crust Tectonics Can be global or just local. Plate tectonics may be unique to Earth Erosion Requires a warm interior Disruption of a planet s surface by internal stresses Surface changes made by wind, water, or ice Erosion Colorado River continues to carve Grand Canyon Glaciers carved the Yosemite Valley Erosion is the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather. Weather is important for erosion! Without weather there would be much less movement of wind, water, and ice Rotation needed to cause weather Wind wears away rock and builds up sand dunes Erosion can create new features by depositing debris Liquid water also important Water is the dominant cause of erosion
Planets Have Three Basic Fundamental Properties Size (mass & radius) Distance from Sun Rotation rate Size, distance and rotation rate affect: Gravity Internal temperature Surface temperature Atmosphere (existence, weather) and these affect the four geological processes! Volcanism Size? Distance from the Sun? Rotation rate? Volcanism Size! Large planets are warm inside have thin lithospheres so lava can easily erupt onto the surface Volcanism doesn t depend on distance from the Sun or rotation rate
Is volcanism affected by size, Is volcanism affected by size, Impact Cratering How does (did) it depend on Size? Distance from the Sun? Rotation rate? Impact Cratering How does (did) it depend on Size? - Nope (not per area) Distance from the Sun? - No Rotation rate? - Nada
Is impact cratering (the act of being hit, per unit area) affected by size, Is impact cratering (the act of being hit, per unit area) affected by size, Tectonics Size? Distance from the Sun? Rotation rate? Tectonics Size! Large planets are warm inside Have more internal convection Have thinner, more deformable lithospheres Tectonics does not depend on distance from the Sun or rotation rate.
Is tectonics affected by size, Is tectonics affected by size, Erosion Size? Distance from the Sun? Rotation Rate? Erosion Size Larger gravity means it can hold on to any atmosphere it creates Distance from the Sun Surface temp can effect whether liquid water can form Temperature of atmosphere also effect whether gas escapes planets grasp Rotation Rate Rotation needed for weather patterns
Is erosion affected by size, Is erosion affected by size, What would Mars look like (today) if it were twice as big? A. More volcanoes, more tectonics, more B. Fewer volcanoes, more tectonics, fewer C. Fewer volcanoes, fewer tectonics, more D. More volcanoes, more tectonics, fewer E. Fewer volcanoes, fewer tectonics, fewer What would Mars look like (today) if it were twice as big? A. More volcanoes, more tectonics, more B. Fewer volcanoes, more tectonics, fewer C. Fewer volcanoes, fewer tectonics, more D. More volcanoes, more tectonics, fewer E. Fewer volcanoes, fewer tectonics, fewer
Don t get confused Venus mostly re-surfaced by Earth heavily volcanism/ re-worked tectonics surface SIZE determines Internal Temp Not distance from the Sun Not pressure inside a planet DISTANCE determines Surface Temp More on this when we get to atmospheres Mercury - lots of, little volcanism Terrestrial Worlds Next: Light as Information Bearer Mars - some volcanism, south heavily cratered, past geological activity Moon - volcanism stopped 3.2 BY ago, lots of Colors of Light We can separate light into its different wavelengths (spectrum). By studying the spectrum of an object, we can learn its: Composition Temperature Velocity White light is made up of many different colors
The Electromagnetic Spectrum 400-700 nm Four Ways in Which Light can Interact with Matter 1. Emission matter releases energy as light 2. Absorption matter takes energy from light 3. Transmission matter allows light to pass through it 4. Reflection matter repels light in another direction Wave-Particle Duality of Light Light can behave like a wave Frequency, wavelength, amplitude Light can also behave like a particle Photons = little bundles (bullets) of energy Light as a WAVE Wavelength is the distance between peaks Wavelength can be measured in any length unit. Ex: m, nm, Å (Angstroms) Typically represented as λ (lambda) For light this ranges from kilometers to smaller than atoms
Light as a WAVE Wavelength is the distance between peaks Light as a WAVE Wavelength is the distance between peaks Frequency is the number of times (per second) that the wave moves up and down Frequency is measured in Hertz (cycles per second). Represented as f The higher the frequency, the more cycles pass per second Frequency is the number of times (per second) that the wave moves up and down All light travels with a constant speed Speed of light often represented by c. c = 300,000 km/s c = 3x10 8 m/s c = 671,000,000 mph Light as a WAVE Wavelength is the distance between peaks Light as a WAVE Wavelength is the distance between peaks Amplitude measures the height of the wave Frequency is the number of times (per second) that the wave moves up and down All light travels with a constant speed Amplitude represents the brightness (or intensity) of the light. Frequency is the number of times (per second) that the wave moves up and down All light travels with a constant speed λ x f = c OR f = c / λ OR λ = c / f The shorter the wavelength, the higher the frequency