Astronomy Chapter 9

5 features on Mars and explanations

1. Hellas Basin- one of large impact craters that scars southern hemisphere of Mars. caused by impact craters 2. Olympus Mons- shallow sloped but towering mountain (tallest known in solar system). affects northern plains more. most volcanoes concentrated on or near Tharsis Bulge. caused by volcanism 3. Tharsis bulge- 4000 km across and most of it rises above average Martian surface level. created by long-lived plume of rising mantle material that bulged the surface upward and provided the molten rock for the eruptions that built the giant volcanoes. caused by volcanism 4. Valles Marineris- most prominent tectonic feature is this deep system of valleys. no one knows how they are formed. caused by tectonics 5. extensive crack on western edge of Valles Marineris run up against Tharsis Bulge caused by tectonics 6. dried up riverbeds caused by erosion

3 requirements for global magnetic field

1. Interior region of electrically conducting fluid (liquid or gas), such as molten metal 2. Convection in that layer of fluid 3. At least moderately rapid rotation Earth only terrestrial world that meets all 3 requirements Mar's doesn't retain enough heat to drive core convection Venus's convection of rotation period is too slow to generate magnetic field Mercury is perplexing b/c it has measurable magnetic field although it is small and has slow rotation, could be its huge metal core

Lithosphere

Category of rock strength that planet's outer layer consists of which is relatively cool and rigid rock and essentially floats on warmer, softer rock beneath. Encompasses the crust and part of the mantle of each world. Smaller worlds have thicker litho spheres. Mars Mercury and Moon (smaller) have lithosphere a that extend to core while Earth and Venus have it that extend short way into their upper mantles

How interiors cool off

Convection, conduction, radiation

Large planets retain internal heat longer

Due to extra layers off rock acting as insulation

Heat from differentiation

Undergoing differentiation means sinking of dense materials and rising of less-dense materials, meaning that mass moves inwards , losing gravitational potential energy. Energy is converted into thermal energy by the friction generated as materials separate by density

erosion

breakdown or transport of surface rock through the action of ice, liquid, or gas. examples: valleys carved by glacial ice, canyons carved by rivers, sand dunes shaped by wind, river deltas made of sediments carried downstream includes Grand Canyon

geological history of moon

bright, heavily cratered regions are lunar highlands, smooth dark regions are lunar maria. craters covered Moon's entire surface during bombardment period. some impacts violent enough to fracture Moon's lithosphere beneath which huge craters were created. Moon's interior had already cooled since its formation so there was no molten rock to flood these craters. lava floods came hundreds of millions of years later b/c of heat released by decay of radioactive elements of interior. mantle material melted 3-4 billion years ago and welled up through cracks in lithosphere flooding the impact craters.

formation of mountain ranges on earth

built by tectonic processes. formed when partially molten mantle material rose up and pushed surface rock higher. and can be formed through collisions of continent-bearing plates

formation of rift valleys on earth

created by plates pulling apart.

Earth's geology destined from birth?

1. impact cratering has affected all worlds similarly. 2. volcanic and tectonic activity are related to planetary size (bigger= more) 3 cannot use fundamental properties to explain plate tectonics. Conclusion: likely that broad geological histories of terrestrial worlds were destined from birth by the properties of size, distance from Sun, and rate of rotation

Impact cratering

Forms when one of the leftover planetesimals from solar system's formation ( asteroid or comet) slams into a solid surfaced. Speed causes impact to release enough energy to vaporize solid rock and blast out a crater. Examples are craters on moon (tycho crater on moon) and Earth (meteor crater in Arizona)

How interiors get hot

Heat of accretion, heat from differentiation , heat from radioactive decay

Core

Highest-density material, consisting primarily of metals such as nickel and iron, resides in a central core

4 major geological processes

Impact cratering, volcanism, tectonics, erosion

Global magnetic field

Interior heat helps create. Earth's is created by charged particles moving with the molten metal in earth's liquid outer core. Internal heat causes liquid metal to rise and fall (convection) while Earth's rotation twists and distorts the convection pattern. Results in electrons in the molten metal move w/in Earth's outer core in much same way as in an electromagnet, generating Earth's magnetic field

no liquid water on Mars

Mars is so cold that any liquid water would freeze into ice. when temperatures rises above freezing, air pressure is so low that liquid water would evaporate. liquid water unstable on Mars today.

Radiation

Objects emit thermal radiation characteristic of their temperatures. Radiation (light) carries energy away and therefore cools an object

Convection

Process by which hot material expands and rises while cooler material contracts and falls, thereby transporting heat upward

Heat from radioactive decay

Radioactive nuclei decay and causes subatomic particles to fly off at high speeds colliding with neighboring atoms and heating them, converts some of the mass-energy of radioactive nuclei to the thermal energy of the planetary interior

seafloor vs. continental crust (Earth's plate tectonics)

Seafloor crust- thinner, denser, younger. 5-10 km thick and primarily made of basalt (dense rock), less than 200 M years old continental crust- much thicker (20-70 km thick), but sticks up only slightly higher than seafloor crust b/c its weight presses it down farther into mantle . made mostly of rock w/ lower density. can be up to 4 B years old

Crust

The lowest-density Rock, such as granite and basalt (common form of volcanic rock), forms a thin crust, essentially representing the world's outer skin

Conduction

Transfer of heat from hot material to cooler material through contacts occurs through microscopic collisions of individual atoms or molecules when two objects are in close contact, b/c the faster-moving molecules in the hot material tend to transfer some of their energy to the slower-moving molecules of the cooler material

repaving of Venus

Venus shows no features of plate tectonics but has its relatively few impact craters distributed uniformly suggesting surface is about same age everywhere. concludes that entire surface was repaved about 750 M years ago erasing all craters that were formed earlier. don't know how much was due to tectonic processes and how much to volcanism

terrestrial worlds' size, distance from sun, and rotation rate controlling erosion

erosion arises from weather phenomena like wind and rain and has links with all 3 fundamental properties. size affects erosion b/c erosion requires atmosphere and terrestrial world can have atmosphere only if it is large enough to have had significant volcanic outgassing and if gravity is strong enough to have prevented the gas from escaping to space distance from sun is important b/c of its role in temperature. higher temperatures on a world closer to Sun will make it easier for atmospheric gases to escape into space, while the colder temperatures of terrestrial world further may cause atmosphere gases to freeze out. and water erosion is much more effective with liquid water than with water vapor or ice and is strongest when moderate temp allows water vapor to condense into liquid form. rotation rate is important b/c it is primary driver of winds and other weather, faster rotation means stronger winds and storms

formation of Mercury's cliffs

formed when tectonic forces compressed the crust, causing the surface to crumple. crumpling would have shrunk surface of portions it affected, Mercury could not have stayed the same size unless other parts of the surface expanded. Mercury's large iron core shows that it gained and retained more internal heat from accretion and differentiation than the Moon and this heat caused Mercury's core to swell in size. when core cooled later it contracted and mantle and lithosphere contracted too generating tectonic stresses that created cliffs and closed off any remaining volcanic vents, ending Mercury's volcanism

formation of faults on earth

forms in places where plates slip sideways relative to eachother which create fractures in lithosphere. rough surfaces of plates catch and stress builts up until it is so great that it forces a rapid and violent shift, causing an earth quake

lack of plate tectonics on Venus

highest expectation is lithosphere resists fracturing into plates b/c it is thicker and stronger than earth's. lithospheres may differ b/c Venus's high surface temperature is so hot that any water in its crust and mantle has probably been baked out over time, so loss of water would have thickened and strengthened Venus' lithosphere since water softens and lubricates rock

terrestrial worlds' size, distance from sun, and rotation rate controlling impact cratering

impacts are random events and creation of craters are not controlled by fundamental planetary properties. number of remaining impact craters is controlled by fundamental properties since impact craters can be destroyed over time. size is primary factor. larger worlds have more volcanism and tectonics (and sometimes erosion) that tend to cover up or destroy ancient impact craters. more geological activity causes less impact craters

formation of islands on earth

islands created in ocean and plate motion carries them toward bigger mainlands, where subduction continues to take seafloor crust downward into the mantles. b/c islands were made of lower-density continental crust, they remained on surface and attached to edge of mainland

terrestrial worlds' size controlling volcanism and tectonics

larger planets have more internal heat and thus more volcanic activity and tectonic activity

rigid outer layer of planet

lithosphere

formation of lunar maria

melted mantle material welling up through cracks and flooding impact craters gave maria circular shape and dark color. flat surface shows that lunar lava spread easily and far (runniest lava). relatively few tectonic features are surface wrinkles

geological history of mercury

molten lava later covered up some of the craters formed on Mercury during heavy bombardment. had as much volcanism as Moon. largest impact craters (basis) formed from impacts so large and violent that they melted surface rock that then flowed over and filled them.

craters and aging

more craters indicate older geological age of surface. geological age refers to age of surface as it now appears. Moon has many more impact craters than Earth indicating that we are looking at surface that has stayed virtually unchanged for billions of years. Earth's is younger surface b/c scars of ancient impacts have been erased over time by other geological processes such as volcanic eruptions or erosion

conveyor belt of plate tectonics

over millions of years movement in plate tectonics act like a giant conveyor belt for Earth's lithosphere. Mid-ocean ridges occur at places where mantle material rises upward, creating new seafloor crust and pushing plates apart. new crust cools and contracts as it spreads sideways from central ridge giving seafloor spreading regions ridged shape. over millions of years, seafloor crust gradually makes its way across ocean bottom and gets recycled into mantle in process of subduction (occurs when seafloor plate meets continental plate). beneath subduction zone, descending seafloor heats up and may begin to melt as it moves into mantle if enough melting, molten rock may erupt and caused active volcanoes. conveyor like process of plate tectonics driven by heat flow from mantel convection. continental crust does not get recycled back into mantle and contients have been built up by it over billions of eyars. but continents always reshaped by volcanism and stress associated with plate tectonics and erosion

longest lasting heat source responsible for geological activity

radioactive decay

tectonics

refers to the building of surface features by stretching, compression, or other forces acting on the lithosphere. goes hand in hand with volcanism b/c both require internal heat and most tectonic activity is a direct or indirect result of mantle convection. crust can be compressed in places where adjacent convection cells push rock together. examples: Appalachian mountains and ceranius Valleys on Mars (cracks and valleys)

plate tectonics of Earth

slow motion of plates that float over the mantle, gradually moving over, under and around each other as convection moves Earth's interior core. Earth's lithosphere broken into more than a dozen plates. theory traced to continental drift (idea that continents gradually drifted across surface of Earth)

formation of continents on earth

subducting seafloor crust partially melts and low-density material melting first erupts from volcanoes as new continental crust which builds up since continental crust does not get recycled back inot mantle. and are continually reshaped by volcanism and stresses from plate tectonics and erosion.

formation of seafloors on earth

subduction occurs at ocean trenches (where seafloor meets continental plate) and dense seafloor pushes under less dense continental crust, returning seafloor crust to mantle. new seafloor crust is created by eruptions of subducting seafloor curst at mid-ocean ridges where plates spread apart

3 major geological features of Venus and formation

1. Ishtar Terra- formed by impact craters has a few large craters but lacks small craters most common on other worlds b/c small objects that could make such craters burn up completely when they enter thick atmosphere of Venus. 2. Lada Terra- formed by step stratovolcanoes built from thick lava. venus has abundant evidence of volcanism w/ variety of lava types b/c both lava plains and volcanic mountains (steeper sides indicate thicker lava) 3. Aphrodite Terra- formed by tectonic forces fracturing and twisting the crust. entire surface has been contorted and fractured by tectonic forces . large circular coronae are one of the features

evidence of water on Mars in past

1. orbital evidence: rims of many large craters and lack of small craters argue for ancient rainfall which eroded crater rims and erased small craters. water once flowed b/w two ancient crater lakes. river delta where water flowed into an ancient crater and spectra indicate presence of lay minerals on crater floor. some evidence suggests ocean on norther plains. radar data suggests that rock along proposed shoreline is sedimentary rather than volcanic 2. surface evidence: 3 rovers have found abundant mineral evidence of past liquid water. rocks contained tiny spheres (blueberries) composed of minerals that suggest formation ina salty environment (pond, lake). clumps of pebbles with rounded surfaces and ssedimentary layers found indicating flowing water. suggestions that region was covered by highly acidic water and lake of pure water. 3. photographs of smaller-scale water flows in more recent times

Heat of accretion

Accretion deposits energy brought from afar by colliding planetesimals

Differentiation

Causes layering of interiors from core to mantle to crust due to less dense materials being driven to top and resulting in layers made of different materials. Terrestrial worlds underwent differentiation at some time in the past meaning all worlds must have once been hot enough inside for their interior rock and metal to melt

Volcanism

Occurs when underground molten rock finds a path to the surface. Molten rock rises for three main reasons: 11. Less dense than solid rock 2. Solid rock surrounding chamber of molten rock can squeeze the molten rock, driving it upward under pressure 3. Molten rock often contains trapped gases that expand as it rises. Lavas (molten rock) can flow across surface at different eases , runniest lavas can flow farm before cooling and solidifying, thickest lavas tend to collect in one place. Examples of thickets lavas: Mount Fuji, Mount Kilamanjaro, Mount Hood. Runnier lavas: mountains of Hawaiian islands and Olympus Mons on Mars. Runniest lavas: lava plains up Columbia plateau b/w Washington and Oregon and vast lava plains that make smooth regions (Maria) on moon

Mantle

Rocky material of moderate density-mostly minerals that contain silicon, oxygen and other elements, forms a thick mantle that surrounds the core

outgassing

waters and gases from more distant reaches of the solar system crashing into growing planets got trapped in interiors of planets. volcanic eruptions release this gas in process known as outgassing, which occurs both with dramatic volcanic eruptions and the more gradual escape of gas from volcanic vents. virtually all gas that made atmospheres of Venus, Earth, and Mars and water vapor that rained down to form Earth's oceans originally was released from planetary interiors by outgassing