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Astronomy 2021A/B Midterm: Asstronomy midterm 2 chap. 6-8

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Department
Astronomy
Course
Astronomy 2021A/B
Professor
Martin Zinke- Allmang
Semester
Fall

Description
Astronomy Test 2 Chapter 6: The Solar System All planets have nearly circular orbits going in the same direction in nearly the same plane, most large moons orbit their planets in this way and the sun rotates in this direction as well. 4 inner (terrestrial) planets: Mercury, Venus, Earth, Mars; they are all made of metal and rock, small, close to the sun, and no rings 4 outer (jovian) planets: Jupiter, Saturn, Uranus, Neptune; large, far from sun, made mostly of H, He and hydrogen, rings Most asteroids (metal + rock) located in asteroid belt which is between Mars and Jupiter, most comets (icy) located in Kuiper belt, even more comets located in the Oort cloud The Sun Radius: 700,000 km (108x Earth), Mass: 333,000x Earth (contains 99.8% of the solar system’s mass, 1000x bigger than everything else combined), Composition: 98% hydrogen and helium, 2% other elements Sunspots only appear darker because they are slightly cooler than everything else The core of the sun is source of the sun’s energy, each second nuclear fusion transforms about 600 million tons of the Sun’s hydrogen into 596 million tons of hydrogen (the missing 4 million turns into energy) Solar wind: charged particles flowing outward from the sun and interact with planetary magnetic fields and influence planetary atmospheres Responsible for virtually all the light in the solar system Mercury Distance from sun: .39 AU, Average surface temperature: 700K-100K, Mass: .06x Earth Smallest of the 8 planets, virtually no air, world of hot and cold extremes due to extremely slow rotation, lots of craters, very large iron core Venus Distance .72 AU, Average surface temperature: 740K, Mass: .82x Earth, Same size as earth, Rotates in opposite direction of Earth and on its axis (days and nights are very long) Surface is completely hidden by dense clouds, this planet is extremely hot due to the greenhouse effect Earth Average surface temperature: 290 K, has the largest moon by far compared to its size, closest planet to the sun that has a moon Mars Distance from the sun: 1.5 AU, Mass: .1x Earth, Average surface temperature: 220 K, lack of atmospheric ozone, barely any oxygen, barely any air pressure Jupiter Distance from the sun: 5 AU, Mass: 318x Earth, Cloud-top temperature: 125 K, Moons: 67 Saturn Distance from the sun: 9.5 AU, Mass: 95x Earth, Moons: 62, Big Rings Uranus Distance from the sun: 19 AU, Mass: 14x Earth, the entire Uranus system is tipped on its side compared to the rest of the planets (extreme tilt of axis) Neptune Distance from the sun: 30 AU, Mass: 17x Earth, Has a moon Triton that orbits backwards Nebular Theory of Solar System Formation Feature of the Solar System that provide clues -Patterns of motion among large bodies: orbit and rotate in generally circular ways and on the same plane, all planets orbit counter clockwise, most rotate in the direction in which they orbit -2 major types of planets -Asteroids and comets -Exceptions to the rules including: Venus rotates backwards, Uranus rotates nearly on its side, small moons have unusual orbits and finally, our moon is massive compared to most Nebular Theory -The one scientific theory that survived careful examination of evidence and repeated testing -Originally proposed by Kant -Solar system was created as a result of the collapse of an interstellar cloud of gas Close encounter Hypothesis -Popular theory in the 1900s -The planets were formed during the sun’s close encounter with another star, however calculations showed that this is likely false because it doesn’t explain the 2 different types of planets, it doesn’t explain orbital motions and it is very unlikely that the sun had a near collision with another star Origin of the Nebula -Great gas clouds contain hydrogen and helium from the Big Bang and heavier elements produced by stars Nebula in Detail -Large, roughly spherical cloud of very cold, low-density gas which could be light-years in diameter -Collapse may have been triggered by a cataclysmic event -As the nebular collapses, it: heats up, spins and flattens, which explains the motions in the solar system -There are 2 types of planets due to the varying distances from the sun (therefore differences in temperatures) which only certain elements can be condensed (rock can be condensed where the rocky planets are, the gas can be condensed where the jovian planets are) Accretion – process of which small “seeds” grew into planets Frost Line -separates where rocks and metal can condense, and where hydrogen compounds can condense Clearing the Nebula -solar winds and radiation from our young sun blew out the rest of the remaining gas that hadn’t settled into the planets or the sun Heavy bombardment -Era where the vast majority of the planetesimals battered the planet during the solar system’s first few hundred million years Moon formation -The moon was likely created due to a massive impact which blasted Earth’s outer layers into orbit Age of the Solar System -Planets began to form through accretion just over 4.5 billion years ago -Can measure the age of the solar system by calculating how old the oldest rocks are (process called radiometric dating) which is done through careful measurement of various atoms and isotopes within the rock Chapter 7: Earth and Terrestrial Worlds Why the Earth is Geologically Active -Clues tell us about a planet’s interior structure, on Earth and the Moon, we can measure seismic waves (vibrations that travel both through the interior and along the surface after an earthquake) Terrestrial Planets’ Interiors Core: highest density material, consisting primarily of metals, divided into a solid inner core and molten outer core; Mantle: rocky material of moderate density, mostly minerals, surrounds the core; Crust: lowest-density rock (granite and basalt), thin crust Lithosphere: planet’s outer layer of cool, rigid rock Differentiation: gravity pulls denser layers to the bottom and the less dense material to the top Larger planets retain internal heat much longer than smaller ones, and the heat drives geological activity Interior heat is also responsible for Earth’s global magnetic field, which is essential because it creates a magnetosphere that protects the Earth from the charged particles of the solar wind Geological Features All geological features can be explained by: cratering, volcanism, tectonics or erosion. We can estimate the age of any surface by counting the amount of impact craters Earth’s atmosphere and oceans were made from gases released from the interior by volcanic outgassing Earth’s underlying mantle convection fractured the lithosphere into more than a dozen “plates” and these plates move. All terrestrial planets have tectonics but plate tectonics is unique to Earth Erosion can both break down and build up geological features Earth’s atmosphere Our atmosphere protects us from the ultraviolet and x-ray radiation Moon Heavily cratered, however there are some smooth dark sections known as the lunar maria which were made by large impacts that fractured the lithosphere, which lava then arose to flood the craters and no has solidified to a smooth surface Mercury Mercury is low-key shrinking due to the swell in size (due to the heating of the core) and then the contraction of the core once it cooled down Mars Mars is not geologically dead like Mercury or the Moon, however it has no liquid water because of the lack atmospheric pressure and its temperature. It is estimated the liquid water did flow on Mars 2-3 billion years ago. Mars underwent permanent climate change about 3 billion years ago when it lost much of its atmospheric carbon dioxide and water to space (probably due to its small size) Venus Thick carbon dioxide atmosphere makes it so hot. Venus has no oceans because of the runaway greenhouse (water evaporates due to more heat, the water vapor in the atmosphere causes the planet to get hotter, more water evaporates and etc.) Earth Four features unique to Earth and important for life: surface liquid water, atmospheric oxygen, plate tectonics, climate stability Earth has remained habitable for billions of years because its climate is kept stable by the natural action of the carbon dioxide cycle Chapter 8: Jovian Planets Differences Jovian planets are all made mostly of hydrogen, helium, and hydrogen compounds, however they differ primarily in their relative proportions of hydrogen compounds All Jovian planets aside from Uranus generate a great deal of heat, creating lots of storms on the planets. Jovian Moons The largest jovial moons rival the smallest planets in size and geological activity, majority of the moons contain a substantial amount of ice as well as metal and rock. Io By far the most volcanically active world in our solar system and it is hot due to tidal heating (gravity from Jupiter and other moons affecting different areas of Io, creating lots of internal friction) Europa “Water World” full of ice and could contain liquid water due to tidal heating Ganymede and Callisto Both have surfaces of water ice, and even though they are farther from Jupiter and shouldn’t be as well heated, they somehow both have evidence that supports a subsurface ocean of liquid water (indicating a mysterious, interior heat source in both). Also Ganymede is that largest moon in the solar system Titan nd Saturn moon that is the 2 largest in the solar system, also is unique because if it’s thick atmosphere Enceladus Smallest geologically active moon (orbits Saturn) Jovian Planet Rings Made from countless ice particles ranging in size, new ring particles are released by impacts on small moons within the ringsnew ring particles are released by impacts on small moons within the rings Chapter 9: Asteroids, Comets, and Dwarf Planets Asteroids – rocky leftover planetesimals Meteorites – small pieces of asteroids that fall to Earth Meteor – the flash of light caused by the particle entering our atmosphere at high speed, not the particle itself Asteroids The total mass of all asteroids is much less than the mass of any terrestrial planet. Jupiter’s gravity is responsible for the asteroid belt and it is the reason why there is no planet where the asteroid belt is because through orbital resonances, it prevented the asteroids from accreting into a planet and still shapes their orbits today. 2 types of meteorites: Primitive meteorites (remnants from the birth of our solar system), Processed meteorites (parts of larger objects that underwent differentiation into a core- mantle crust structure) Comet Tails Comets grow tails as they enter the inner solar system due to the Sun heating the surface temperature, which creates a huge, dusty atmosphere called a coma 2 visible types of comet tails: Plasma tail (consists of gas ionized by ultraviolet light, affected by solar wind, extends directly away from the Sun), Dust tail (consists of dust sized particles, affected by radiation pressure, generally points away from the sun but has a slight curve back in the direction it came from) Comets ejecting sand-to-pebble sized particles that are too big to be affected at such high speeds, forming an invisible tail (responsible for most meteors and meteor showers) Where Comets come from Kuiper belt: ring of comets that orbit the sun from twice as far as Neptune Oort Cloud: 1 trillion comets farther out then the Kuiper belt, occasionally we see some of comets from both in our inner solar system Dwarf Planets Pluto is essentially a large comet and there are a bunch like it including Eris which is 27% larger Impacts on Earth Scientists have identified a total of 150 impact craters and they believe that’s what caused the extinction of the dinosaurs Small meteorites crash down somewhere on Earth every day and larger meteorites could be a major threat us Impacts causing significant damage have occurred at least twice in recent history: in 1908 over Tunguska and in 2013 over Chelyabinsk, Russia Every asteroid or comet that has impacted Earth since the end of the heavy bombardment was in some sense sent our way by the influence of Jupiter or one of the other Jovian planets Chapter 10: Other Planetary Systems Extrasolar planets: planets outside of our solar system Detecting other planets 2 ways of learning about a distant object: directly (obtaining images or spectra of the object) and indirectly (inferring the object’s existence/properties without actually seeing it) Indirectly Almost all extrasolar planets detected to date have been found indirectly rather than through direct observation There are 2 different types of indirect observation: Observing the motion of a star to detect the subtle gravitational tugs of orbital planets and observing the changes to a star’s brightness that occur when one of its planets passes in front of the star as viewed from Earth Gravitational movement
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