Intro to the Solar System PDF

Tour of the Solar System- 1/15/25 -​ Solar system is mostly empty space -​ Earth ~150M km from Sun (1 AU) -​ Jupiter 5.5 AU from Sun -​ Neptune 30 AU from Sun -​ Oort Cloud ~50,000 AU from Sun Light year = 9.46 trillion km -​ Next star (Alpha Proxima) 4.3 light ye...

Tour of the Solar System- 1/15/25 -​ Solar system is mostly empty space -​ Earth ~150M km from Sun (1 AU) -​ Jupiter 5.5 AU from Sun -​ Neptune 30 AU from Sun -​ Oort Cloud ~50,000 AU from Sun Light year = 9.46 trillion km -​ Next star (Alpha Proxima) 4.3 light years away Astronomical Unit (AU): 1 AU = 149.6M kilometers (93M miles) Sun: -​ over 1M Km in diameter (Earth ~13,000 Km) -​ If Sun was size of basketball, Earth would be 150 basketballs away -​ Medium sized, middle-aged star -​ Diameter is 1.39M km -​ Fit over 100 Earths along equator -​ Surface temp = 5770 K -​ Core temp = over 15M K Stars are clouds of hydrogen and helium gas held together by gravity -​ Pressure converts hydrogen to helium -​ Most of the visible universe is hydrogen and helium -​ Cecelia Payne determined that the sun is mostly hydrogen in 1925 by examining absorption lines in the solar spectrum -​ Henry Russel, a prominent astronomer on her PhD committee discouraged her from publishing her conclusions -​ 4 years later (1929), Russel came to the same conclusion using a different method -​ He published his results, and his findings were confirmed and accepted by the scientific community -​ Russel did acknowledge Payne’s contributions, but for many years she didn’t receive the credit she deserved E = MC^2 -​ If you smash 4 hydrogen atoms together, you can make one helium atom -​ A small amount of mass can be converted into a large amount of energy -​ Stars take 4 hydrogen atoms and create a helium atom, converting mass into energy, radiating into space -​ Want to do it on Earth for unlimited, clean energy Chemical Reaction- 1.2x10^8 J/kg (burning hydrogen) Nuclear fusion- 6x10^14 J/kg (fusing hydrogen into helium) Stars are powered by nuclear fusion- Pressure and temperature in the core fuses hydrogen atoms to form helium -​ Every second, the sun burns ~600M tons of hydrogen, converting it into helium and energy. Every 70,000 years, the sum=n consumes a mass of hydrogen = mass of the Earth  -​ The “missing” mass is converted into energy (E = MC^2) Mercury: -​ 2440 km radius -​ ~6% the mass of Earth -​ 57.9M km (.39 AU) from the Sun -​ Density 5.43 g/cm^3 -​ Heavily cratered (generated by high-velocity impacts) Density (mass/volume) -​ Provides clues to composition -​ Water has a density of 1g/cm^3 -​ Typical rocks have densities of ~2.5-3.5g/cm^3 -​ The high density of Mercury means that it's not just rocky material -​ Air- 1.225 kg/m^3 -​ Liquid water- 1000 kg/m^3 -​ Rocky material- ~2500-3300 kg/m^3 -​ Solid iron (1 atm. pressure)- 7874 kg/m^3 If you can measure the density of an object in the solar system, you can start making an educated guess about its composition Venus: -​ Similar to Earth in size (0.815 Earth mass), composition, and distance to the Sun (0.72 AU) -​ Earth’s twin (evil >:)) -​ Clouds of sulfuric acid and a crushing CO2 atmosphere obscure the surface -​ Temperature hot enough to melt lead -​ Clouds of sulfuric acid -​ Dense atmosphere produces run-away greenhouse effect and obscures the surface from view -​ Carbon dioxide prevents infrared light from escaping, absorbs the radiation -​ Increasing carbon dioxide warming the planet by keeping heat from escaping -​ Magellan spacecraft revealed Venus’ complex surface using radar, which can penetrate the atmosphere. -​ Revealed a diverse landscape with jagged mountains, abundant volcanic features, but very few craters. Earth: -​ Only planet in our solar system that has abundant liquid water at its surface -​ Surface temperatures range from -73 up to 48C, but are mostly in the range where liquid water can exist La bella Luna: -​ 1738 km radius -​ ~1% the mass of the Earth -​ Lower density than Earth (3.3 g/cm^3 vs 5.4 g/cm^3) Mars: -​ ~11% Earth’s mass -​ 1.5 AU (= ~50% as much solar energy)  -​ Extensive past volcanism (some pretty recent) -​ Evidence for past water -​ Mars was warm and wet for the first billion years, but today it’s cold and dry Venus and Mars are two different extremes of the greenhouse effect Earth is kept in balance for now The Outer Planets 1/17/25 Asteroid Belt: between the orbits of Mars and Jupiter lies the asteroid belt, composed of millions of bodies ranging from less than a km in size to nearly 1000 kn -​ Most meteorites derive from here -​ 4 Vesta is the second largest asteroid in the belt, diameter 525 km -​ It’s thought to be the source of a special class of achondrite meteorites called Eucrites -​ Images taken by the Dawn spacecraft while in orbit around Vesta in 2011 -​ On October 20, 2020, Osiris Rex successfully “tagged” the asteroid Bennu, collecting ~122 g of fine material from the asteroid’s surface -​ Material was returned to Earth for study on September 24, 2024 Jupiter: -​ 318x the mass of Earth -​ Larger than all other planets combined -​ Low density (1.33 g/cm^3) gas giant -​ It is not a failed star. Jupiter is big, but the minimum mass for nuclear fusion is ~75x that of Jupiter -​ Has a dense atmosphere composed mostly of hydrogen and helium, though methane and other gases are also present -​ Rotates very rapidly (a “day” is 9.9 hrs) -​ Rapid rotation combined with convection driven by heat from the interior helps produce the stark atmospheric banding, severe and long-lived storms (Great Red Spot) and unimaginable winds -​ At the equator, winds can reach velocities of 150 m/s (540 km/hr) -​ Has 95 known satellites -​ 4 largest (Callisto, Ganymede, Europa, and Io) are called the “Galilean satellites” -​ Callisto has a radius larger than our moon (2403 km vs 1738 km), though it’s much less massive bc of its low density (1.85 g/cm^3), reflecting its composition of a mixture of rock and ice -​ Its surface is heavily cratered, revealing that Callisto has been inactive for a long time -​ Ganymede is the largest Galilaean satellite (radius=2634 km) -​ Similar in composition to Callisto -​ Although parts of Ganymede’s surface are heavily cratered, others are less so. Massive fractures and grooves cut across the planet, suggesting a much more active past than Callisto -​ Europa is denser than Ganymede and Callisto (2.99 g/cm^3), primarily rock rather than ice -​ It has an icy surface that is only lightly cratered and which is covered with a very complex network of cracks, ridges, and grooves  -​ Young (sparsely cratered), complex terrains suggest Europa’s surface has been reworked by cryovolcanism -​ Gravitational interaction with Jupiter and other Galilean satellites results in tidal heating, which warms Europa’s interior -​ Europa likely hides an ocean of liquid water several hundred km thick -​ On Earth, deep-sea hydrothermal vents team with life, and may have been home to the earliest life forms -​ Could similar vents beneath Europa’s icy crust provide a habitat for life? -​ Io is a world where tidal heating has gone mad -​ Io is the most volcanically active body in the solar system -​ Io’s high density (3.53 g/cm^3) indicates a rocky composition -​ No impact craters. Io’s surface is constantly being reworked by volcanism Saturn: -​ 95x the mass of Earth -​ Very low density (0.69 g/cm^3), would float in water -​ Massive atmosphere of H, He, and methane (similar to Jupiter) -​ Most famous for its rings -​ Saturn’s rings are composed of countless small icy particles, ranging in size from ~1 meter to 10 km/s. As they descend, friction causes the meteoroid to heat and surface layers melt and ablate, starting at a height of ~120 km. -​ Ionization of the surrounding atmosphere causes it to glow, producing the streak of light we know as a meteor or shooting star. -​ If the meteoroid survives passage through the atmosphere, it becomes a meteorite. -​ Most of the meteors we observe in the night sky are caused by particles roughly the size of a grain of sand. Most of these do not survive the journey.  -​ Meteors enter our atmosphere at a minimum velocity of ~11 km/s. Air friction causes them to heat up and glow. What happens to all the dust that escapes comets during their approach to the sun? -​ Some of it becomes Interplanetary Dust Particles (IDPs). -​ Although large particles (grain of sand) usually burn up in the Earth’s atmosphere, small particles are slowed down by the atmosphere high enough that they do not burn up, and settle slowly down. -​ Many IDPs represent comet dust minus the icy components. These particles can be analyzed in laboratories. Meteorite finds are found and collected long after they fall to Earth. In some places, meteorites are easier to find than others because they stick out from their surroundings, as here in the Sahara desert. Meteorite falls are observed falling to Earth, and can be collected soon after impact. This means that falls are generally fresher and less contaminated than finds, and are therefore scientifically more valuable. -​ The moving Antarctic ice sheets act as a conveyor belt collecting and concentrating meteorites in certain regions, where they stick out like a sore thumb against the icy landscape. Types of meteorites: Stony meteorites: -​ Chondrites are mixtures of silicate and metal phases, and most contain chondrules. These represent different objects formed directly from the solar nebula with little subsequent processing. -​ Achondrites have experienced melting and differentiation processes occurring on or within a planetesimal. Iron meteorites: -​ As the name implies, these are made mostly of iron, along with nickel. These derive from planetesimals that were large and hot enough to experience differentiation, or density separation of metal and silicate components. Stony irons: -​ Macroscopic mixtures of silicate and metal phases. In some cases these may sample the core/mantle boundary of differentiated planetesimals. Major spectral classes of asteroids S: Stony asteroids. Probably differentiated bodies. -​ Source of achondrite meteorites? C: Carbonaceous, dark. Probably very primitive. -​ Source of chondrite meteorites? M: Metallic, probably mostly iron and nickel. Differentiated bodies. -​ Source of iron meteorites? About 90% of falls are chondritic in composition. About 5% are iron meteorites, 1% are stony-ron, and the rest (~5%) are achondrites. In contrast to falls, about 40% of finds are iron meteorites. Chondrite meteorites represent primitive mixtures of the various components present in the solar nebula. They provide our best estimate of the composition of the nebula.  -​ Refractory phases called CAIs (calcium-aluminum inclusions) formed by condensing from hot gas -​ Round Chondrules formed by flash heating/melting of dust accumulations, possibly due to shock waves in the disk The relative abundances of most elements in chondrite meteorites are very similar to the elemental abundances seen in the Sun’s atmosphere, confirming that chondrites are primitive samples of the Solar Nebula. Carbonaceous chondrites like Murchison and Tagish Lake contain significant quantities of organic carbon, including amino acids not found on Earth. -​ Some scientists think that the early Earth may have been “seeded” with organic compounds from comets and meteorites, and that these compounds were necessary for the origin of life on Earth. In contrast to chondrites, achondrites and iron meteorites have been subjected to melting and differentiation processes occurring on or within the planetesimals from which they came. -​ Surprisingly, although achondrites and iron meteorites come from bodies with a more complicated geologic history than chondrites, they are almost the same age as chondrites. Many achondrites have compositions broadly similar to the terrestrial volcanic rock basalt and appear to be partial melts separated from initially chondritic planetesimals. They likely represent the crust of planetesimals that became hot enough to melt early in solar system history. A special class of achondrite meteorites called HED meteorites (for Howardite, eucrite, and diogenite) are believed to all derive from the large asteroid 4 Vesta, which has a diameter of ~530 km. Whereas achondrites represent the mantle and crust of differentiated planetesimals, iron meteorites derive from planetesimal cores. If a planetesimal gets hot enough to melt, the dense iron can sink to the middle, even in the weak gravity present in objects 10s to100s of km in size. Question: What does the existence of achondrites and iron meteorites tell us about the thermal history of the planetesimals from which they derived? Achondrites and iron meteorites derive from differentiated planetesimals – the iron and silicates have separated due to density differences. -​ This requires that the planetesimal was once partially molten. The existence of iron meteorites further indicates that these planetesimals were later destroyed through impacts. Widmanstaetten patterns form when iron- and nickel-rock crystals grow during slow cooling of planetesimal cores. Crystal size is related to cooling rate-slow cooling results in big crystals. From this, scientists can estimate the cooling rate (0.5-500 K/ma) and therefore size (less than a few 100 km) of the parent bodies. Today, we consider it self-evident that craters such as these are produced by hyper-velocity impacts of asteroids or comets with planetary surfaces. However, before the Apollo program, the origins of the moon’s craters were hotly debated, and many believed that they were volcanic features. 2/3/25 Meteorites, impacts, and cratering What does the existence of achondrites and iron meteorites tell us about the thermal history of the planetesimals from which they derived? -​ Whereas achondrites represent the mantle and crust of differentiated planetesimals, iron meteorites derive from planetesimal cores. If a planetesimal gets hot enough to melt, the dense iron can sink to the middle, even in the weak gravity present in objects 10s to100s of km in size. “Onion shell” model for origin of chondrites (undifferentiated), achondrites, and iron meteorites. -​ Achondrites and iron meteorites derive from differentiated planetesimals – the iron and silicates have separated due to density differences. -​ This requires that the planetesimal was once partially molten. -​ The existence of iron meteorites further indicates that these planetesimals were later destroyed through impacts. Widmanstaetten patterns form when iron- and nickel-rich crystals grow during slow cooling of planetesimal cores. Crystal size is related to cooling rate-slow cooling results in big crystals. From this, scientists can estimate the cooling rate (0.5-500 K/ma) and therefore size (less than a few 100 km) of the parent bodies. Today, we consider it self-evident that craters such as these are produced by hyper-velocity impacts of asteroids or comets with planetary surfaces. However, before the Apollo program, the origins of the moon’s craters were hotly debated, and many believed that they were volcanic features. How do we know that Meteor Crater formed from a meteor impact, and not from a volcanic explosion like the crater shown below? How do we tell the difference? Gene Shoemaker carefully mapped Meteor Crater, Arizona (before the name gave the answer away). Evidence he documented included: -​ Iron meteorite fragments (duh!) -​ Doubled-over layers of rock (ejecta blanket) -​ Highly fractured, or brecciated rock -​ Impact glass, shocked quartz, and other evidence for very high pressures. Shocked quartz top right and bottom left) looks very different from normal quartz (top left). The planar deformation features form when quartz grains are suddenly subjected to pressures of 5-8 GPa (~50,000-80,000 atmospheres) The extreme pressures generated by impact can cause rocks at the base of a crater to melt, producing impact melt that may also incorporate material from the impactor. In very large events, such as the Sudbury crater, melt and brecciated rock may form a pseudotachylite Tektites form as molten ejecta following ballistic trajectories that can carry the material thousands of miles from the impact site. The aerodynamic shapes result from atmospheric friction. Microtektites are often preserved in deep-sea sediments, and provide a record of cratering processes on Earth. Sometimes tektite fields provide clues to location of impact. Nearly 200 impact structures have been identified on Earth, and more are discovered every year. Clearly, Earth has not been spared the cosmic pounding that produced the heavily scarred lunar surface. Debris from space will impact the Earth at a minimum velocity of ~11.2 km/s (Earth’s escape velocity). What happens during a hypervelocity impact? Asteroids hit the Earth with an average velocity of ~17 km/s, and comets collide at up to 70 km/s (for a head-on collision). -​ Hypervelocity impacts produce shock waves very similar to those produced by explosions. The cratering process can be divided into stages: 1)​ Compact and compression occur as the impactor makes contact. Shock waves pass into the target and disrupt it. Peak pressures can exceed 100 GPa, and both impactor and target may vaporize or melt. 2)​ The shock wave is followed by a rarefaction (release) wave. Material moves upwards and outwards in an expanding ejecta curtain, producing a transient bowl cavity. 3)​ Modification depends on the size of the crater and the strength of the target. Debris may partially fill the cavity, or the walls of the crater may slump to form terraces. Rebound of the central cavity may produce a central peak. The final shape of the excavated crater will vary with the size of the crater. -​ Small craters (on Earth, 26,000 Seismograph stations on the moon: 5, no longer functioning Seismograph stations on Mars: 1 (no longer functioning) Structure of the Earth: -​ Crust: ~10–70 km thick, solid, intermediate composition -​ Mantle: ~2900 km thick, (mostly) solid, ultramafic composition -​ Outer core: ~2200 km thick, liquid, mostly iron -​ Inner core: ~1500 km thick, solid, mostly iron Much of the detailed knowledge we have about Earth’s interior comes from seismology. What about other planets and moons in our solar system? Differentiation: -​ Heat from accretion (impacts) and from radioactive decay causes melting in planet or planetesimal interiors. -​ Denser components (e.g., iron-nickel metal) sink to form the core.  -​ Less dense materials (e.g., rocky material composed of Si, Mg, Al) rises to form mantle and crust. PLATE TECTONIC THEORY: -​ 12 rigid outer plates moving over a softer (but still solid) upper mantle; Continents carried along for the ride. Plate Tectonics: -​ what drives the process? -​ Over 200 million years ago, all the continents were assembled into one “supercontinent”-Pangea (“All land”) -​ By ~150 Ma, the continents had started to break apart. The Atlantic ocean was born where rifting occurred. -​ The continents are still moving today, carried by currents within the mantle. There are three main types of plate boundaries. Most of the exciting stuff in geology happens at these boundaries. -​ Divergent: plates move apart and create new lithosphere -​ Occur at zones of upwelling mantle -​ Produces new oceanic crust!!! -​ Volcanism and shallow earthquakes -​ Eg. Mid-Atlantic ridge -​ Transform: plates slide horizontally past each other -​ The friction of the two plates sliding past each other can produce large earthquakes. -​ The San Andreas fault in California is an example of a transform plate boundary. -​ Convergent: plates collide and one is pulled into the mantle and recycled -​ The heavier (usually older) plate sinks beneath the lighter plate = SUBDUCTION -​ Subduction is associated with volcanic islands, deep ocean trenches, coastal mountain ranges and earthquakes. Much more dangerous than divergent margins. -​ The Andes Mountains of South America are an example of a convergent plate boundary 2/12/25 Planetary Internal Structure, Dynamics, and Volcanism Plate tectonics on other planets? -​ Hallmarks of plate tectonics include long, linear chains of mountains, deformation, volcanism. On Earth, two types of crust, thick, old continental crust and thin, younger oceanic crust. -​ Earth has two types of crust – continental and oceanic. Continental crust is thicker (40-70 km vs ~6-8 km and is less dense (~2.7 g/cm3 vs. ~3.0 g/cm3) -​ These different types of crust are a result of processes linked to plate tectonics and are reflected in the distribution of elevations around the globe (the hypsometric distribution). -​ Hallmarks of plate tectonics include linear regions of focused volcanism, mountain belts, or areas of crust deformation, evidence for transform (side-to-side) plate motion, and bimodal distribution of elevations (distinct crust types). The surface of Venus is also divided into highlands (thick crust) and lowlands (thinner crust). But, the entire surface appears to be roughly the same age-about 200 million years! -​ Although Venus has plenty of volcanic features, we do not see the linear patterns of volcanism or deformation characteristic of plate tectonics. -​ Crater density shows age The distribution of elevations can provide clues to the presence or absence of plate tectonics. On Earth, we have two different types of crust (continental and oceanic) with very different elevations. On Venus, there only appears to be one type of crust. -​ Venus has LOTS of volcanoes. Over 1600 volcanic features have been identified on Venus. Many of these appear to be very young. However, the volcanoes appear more or less randomly distributed over the entire planet, not organized in linear arrays. -​ Venus is active, but it doesn’t have plate tectonics. How can the entire surface be the same, relatively young age? -​ One possibility is that Venus experiences periodic catastrophic overturns. -​ During periods of inactivity, heat builds up in the interior. Once the heat build-up is too large, mantle upwelling produces a giant pulse of volcanism that resurfaces the entire planet. Although Mars appears to be (mostly) inactive today, it clearly has had a more protracted history of volcanism and other tectonic processes than, for example, Mercury. How is Mars similar to or different from the Earth? -​ The Martian crust can be divided into the very old, heavily cratered southern highlands and the younger northern lowlands. -​ Many very large volcanic features, including Olympus Mons, can be found near the Tharsis Bulge. Magnetic stripes on Mars? Tectonics early on? -​ On Earth, oceanic crust records the Earth’s magnetic field as it forms at mid-ocean ridges. Variations in the field over time result in oceanic crust having a “striped” pattern. -​ Mars doesn’t have a magnetic field today, but it did early in its history. Are the magnetic “stripes” preserved in the martian crust a result of early plate tectonics on Mars? The Earth’s magnetic field protects us from harmful ionized particles from space. -​ Convection in the outer core generates the Earth’s magnetic field. -​ The existence of the magnetic field tells us that the core is rapidly convecting. Geodynamo: Self-exciting Dynamo A conducting material (e.g., metal) moving through a magnetic field generates an electrical current. Electrical currents in turn generate magnetic fields. Rapid convection of Earth’s liquid iron outer core basically converts kinetic energy into electrical currents and the magnetic field. Planetary magnetic fields -​ Mercury: Weak field, about ~1% the strength of Earth’s field. -​ Venus: No magnetic field. It is thought that Earth’s rotation helps “stir” our liquid outer core, so maybe Venus’ very slow rotation doesn’t allow this stirring. -​ Earth: Our magnetic field varies in strength and direction, periodically flipping its polarity.  -​ Mars: Mars doesn’t have a magnetic field today, but it did in the past. As Mars’ interior cooled down, convection in the core stopped, shutting down the dynamo. Why have some planetary bodies remained geologically active longer than others? -​ The main controls are size and the presence or absence of internal sources of heat. -​ Internal heat comes primarily from stored heat (from the time of planetary accretion), and heat produced by radioactive decay. The abundance of radioactive elements like uranium is therefore important. Question: What do radiators and elephants’ ears have to do with planetary dynamics and why Earth is tectonically and volcanically active, but the moon is not? Planet interiors cool as heat is conducted from the interior to the surface, and then radiated into space. -​ Conduction is controlled by surface area, which for a sphere is given by: 4pR2 -​ In contrast, the amount of heat stored or produced in a planet’s interior is a function of composition and volume, which is given by: 4pR3/3 The Volume-to-surface area ratio therefore increases as radius increases. Smaller planets have a lower (volume)/(surface area) ratio and so their interiors cool faster than larger planets. Volcanism is one of the most important processes that shape the surfaces of rocky or icy worlds. Volcanism on all of the terrestrial worlds is similar in many respects (e.g., composition of most lavas), but important differences also exist that are influenced by planet size, atmospheric thickness and other variables. -​ On Earth, there are two main types of magma that generally correspond with eruption style and tectonic setting: -​ Mafic volcanism occurs where mafic (or basaltic) lavas are produced. These lavas have modest silica contents (~45-50% SiO2) and relatively high magnesium content (~10% MgO). -​ Basaltic lavas are usually very hot (~1000-1250 oC) and so are very fluid. They usually have fairly low contents of dissolved gases like water vapor or CO2. -​ Felsic volcanism produces material that has much higher silica content (up to ~70% SiO2) but lower magnesium. Silicic magmas are colder (~700 oC) and have a much higher viscosity. -​ Felsic magmas typically have higher concentrations of dissolved gases, which have difficulty escaping due to the high viscosity of the magma. The two main styles of volcanism are explosive and effusive. Eruptive style is controlled by: -​ Viscosity, or how fluid a melt is; and Volatile content or how much gas (water vapor and CO2 a melt initially contains. -​ Viscosity is controlled by the composition and temperature of a melt. So how are melts generated in the mantle, and how does this affect the type of volcanic activity we see at the surface? -​ Divergent margins and areas of mantle upwelling (mantle plumes like Hawaii) -​ As the hot mantle rises in response to spreading plates or in mantle plumes, the decrease in pressure causes the mantle to melt, forming basaltic magmas. Low SiO2 Lavas: Basalts -​ Very fluid – erupts at 1000 to 1200°C -​ Low silica and high temperature means low viscosity -​ Flows very quickly and covers large areas