Planetary Surfaces 4 major processes affect planetary surfaces
- Slides: 32
Planetary Surfaces 4 major processes affect planetary surfaces: Impact cratering – from collisions with asteroids and comets Volcanism – eruption of molten rocks Tectonics – disruption of a planet's surface by internal stresses Erosion – wearing down or building up geological feature by wind, water, ice, etc.
Impact Cratering: The most common geological process shaping the surfaces of rigid objects in the solar system (Terrestrial planets, moon, asteroids)
EROSION: the breakdown and transport of rocks and soil by an atmosphere, liquids and/or ices. Mars Venus
Volcanism Ø Source of current atmospheres o Terrestrial planets o Jovian moons Ø Erases craters Ø A source of water Mars
Tectonics: refers to the action of internal forces and stresses on the lithosphere to create surface features, i. e. , “geological processes” Can only occur on planets or moons with convection in the mantle Earth & Venus Europa Ganymede?
Tectonics… • raise mountains • create huge valleys (rifts) and cliffs • create new crust • generate volcanoes (maintain atmospheres) • can move large segments of the lithosphere (plate tectonics)
Portion of Valles Marineris on Mars – created by tectonic stresses
Tectonic plates
divergent plate boundary (plates move away from each other). Ø Atlantic Ocean Ø Great Rift Valley in Africa Ø Valles Marineris (Mars)
Øconvergent plate boundary with subduction : plates move towards each other & one slides beneath the other. Ø Nazca plate being subducted under the South American plate to form the Andes Mountain Chain. Ø Island arc system
Ø convergent plate boundary without subduction : plates move towards each other and compress. Ø Formation of Himalayas.
Plates sliding past each other: earthquakes, valleys, mountain building
Half of the world’s volcanoes surround the Pacific plate Tectonic plates
ATMOSPHERES
Atmospheric Basics Ø Layer of gas surrounding a planet. Ø Usually very thin for terrestrial planets (exception Venus). Ø Affects conditions on the planet. Ø We would like to understand how each of the terrestrial planets ended up having such different atmospheres. Venus’s thick atmosphere
All terrestrial planets probably had minimal atmospheres at some point after they formed: “primary” atmosphere of H, He These original atmospheres were swept away from the terrestrial planets early in their life. Current atmospheres are “secondary” atmospheres, formed primarily by outgassing (mostly carbon dioxide - CO 2)
Holding onto an atmosphere requires gravity Ø The strength of gravity determines the escape velocity from the planet. Ø The temperature and composition of an atmosphere determines the velocities of atoms and molecules in the atmosphere; lighter molecules will move faster. At a given temperature, H and He will have higher velocities than more massive elements or molecules (recall that K. E. = 1/2 mv 2)
Holding onto an atmosphere requires gravity Ø The strength of gravity determines the escape velocity from the planet. Ø The temperature and composition of an atmosphere determines the velocities of atoms and molecules in the atmosphere. Ø If the constituents of an atmosphere are moving faster than escape velocity, then a planet or moon will be unable to hold onto an atmosphere.
Larger (stronger gravity), cooler (slower moving molecules) planets can hold onto atmospheres better than smaller (weaker gravity), hotter (faster moving molecules) planets
● Moon and Mercury are “Airless” worlds Ø gravity too weak to hold onto an atmosphere Ø “black Ø sky” The little atmosphere that exists consists of particles of the solar wind that are temporarily trapped.
● Mars Ø Very little atmosphere today (mainly CO 2) Ø Mars had standing and running water on its surface in the past. Ø Therefore, it must have had a more substantial atmosphere in the past Ø Does it have water today? Yes - frozen in polar ice caps and beneath its soil
● Venus Ø Densest atmosphere of all Terrestrials Ø Mostly CO 2 Ø Temperature at surface hot enough to melt lead Ø Pressure at the surface ~ 90 times that on Earth Ø Perpetual cloud cover, sulfuric acid rain Ø Weather forecast “awful” all the time.
● Earth Ø A moderate atmosphere today Ø Mostly nitrogen (N 2), with some oxygen (O 2: arises from photosynthetic life), carbon dioxide (CO 2), etc. Ø Enough to enable liquid water to exist (temperature and pressure adequate) Ø Together the air & water produce erosion
The Jovian planets (high gravity, cool/cold atmospheres) have very substantial atmospheres, primarily H & He. We see the tops of clouds
LAYERING OF ATMOSPHERES Structure is created within an atmosphere through interactions of atmospheric gasses with light
Exosphere hottest layer, v. rarified Thermosphere absorbs X-rays, ionized, ionosphere, reflects some radio, aurora Mesosphere • weakly absorbs UV Stratosphere • strongly absorbs UV, ozone (O 3), stratified (no convection), Earth only Terrestrial planet with one. Troposphere • absorbs IR (greenhouse); convective; weather
From the perspective of life, stratosphere & troposphere are the most important Stratosphere absorbs harmful UV Troposphere provides greenhouse effect
A magnetic field creates “magnetosphere” that deflects away solar wind particles. In the absence of a “magnetosphere”, the solar wind will slowly strip away an atmosphere.
The greenhouse effect Ø Planets heat up by absorbing the Sun’s visible light Ø Planets cool off by radiating infrared out to space Ø Greenhouse gasses trap infrared radiation in troposphere (lowest level of atmosphere), thereby heating the lower atmosphere. ● greenhouse gasses (e. g. , H 2 O, CO 2, CH 4 - methane) transmit visible light but absorb infrared light
● ● Greenhouse effect raises temperature of lower atmosphere Greenhouse effect is critical to the existence of life on Earth – it raises temperatures to “habitable” level, permits liquid water
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