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Planet

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defined as a celestial body that: -is in orbit around the sun -has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape -has cleared the neighborhood around its orbit

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8 planets in the Solar System

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Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune

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dwarf planet

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an object the size of a planet, but is not a planet or a moon (ex. pluto)

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Comparative Planetology

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is the comparison of worlds—planets, moons, asteroids, comets—with each other to better understand their similarities and differences

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Values of Comparative Planetology

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-reveals similarities and differences among the planets that have helped guide the development of our theory of solar system formation that, in turn, gives us a better understanding of how we came to exist on the Earth -new insights into the physical processes that have shaped Earth and other worlds -knowledge of our own solar system can be applied to understanding the many recently discovered planetary systems around other stars

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Water Freezes

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32°F / 0°C / 273 K

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Water Boils

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212°F / 100°C / 373 K

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Sun

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-radius: 695,000 km -mass: 333,000 Earth masses -surface temperature of about 5,800 K (5,527°C or 9,980°F) -surface is a roiling sea of hot hydrogen and helium gas -through nuclear fusion the Sun converts 4 million tons of hydrogen into energy per second -has shone steadily for 5 billion years and will shine for 5 billion more years

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Mercury

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-distance from Sun: 0.39 AU -radius: 2,440 km -mass: 0.055 Earth mass -virtually no atmosphere -day side hot (425°C) and night side cold ( 150°C) -surface of craters, lava flows, steep cliffs -made mostly of iron

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Venus

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-distance from Sun: 0.72 AU -radius: 6,051 km -mass: 0.815 Earth mass -extreme greenhouse effect bakes the surface: 450°C -thick atmosphere but contains no oxygen -surface has mountains, valleys, craters, lava flows

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Earth

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-distance from Sun: 1.00 AU -radius: 6,378 km -mass: 1.00 Earth mass -only planet with oxygen -water oceans cover ¾ of the surface -first planet on tour with a moon

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Mars

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-distance from Sun: 1.52 AU -radius: 3,397 km -mass: 0.107 Earth mass (10% of Earth) -has 2 tiny moons -surface has large volcanoes, valleys, polar caps made of frozen CO2 and water ice, and evidence of a past that was warm and wet -atmospheric pressure is low (1% of Earth) -surface temperature is cold most of the time

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Jupiter

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-distance from Sun: 5.20 AU -radius: 71,492 km -mass: 317.9 Earth masses -volume is more than 1,000 times that of Earth -made primarily of hydrogen and helium -no solid surface -has 67 moons and a thin set of rings

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Galilean moons

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-Jupiters Four Largest Moons -Lo, Europa, Ganymede, Callisto

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Lo

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active volcanoes all over

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Europa

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with a possible subsurface ocean

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Ganymede

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which is the Largest moon in solar system (and bigger than Mercury)

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Callisto

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which is a large, cratered "ice ball"

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Saturn

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-distance from Sun: 9.54 AU -radius: 60,268 km -mass: 95.18 Earth masses -is less dense than water -made primarily of hydrogen and helium -no solid surface -has enormous ring system -62 moons orbit the planet

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Titan

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Saturns largest moon, and the only moon in the solar system with an atmosphere, methane-rich atmosphere is being replenished by a layer of methane ice underneath its surface

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Uranus

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-distance from Sun: 19.19 AU -radius: 25,559 km -mass: 14.54 Earth masses -made of hydrogen, helium, and methane (which gives the planet its pale green color) -no solid surface -27 moons and a set of rings -entire system is tipped on its side compared to the rest of the planets

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William Herschel

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discovered Uranus on March 13, 1781

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Neptune

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-distance from Sun: 30.06 AU -radius: 24,764 km -mass: 17.13 Earth masses -very similar to Uranus but a more striking blue in color -has rings and at least 13 moons -large moon Triton orbits the planet "backward"

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Johann Galle

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discovered Neptune on September 23, 1846, based on a prediction by Frenchman Urbain Le Verrier

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Methane Gas

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absorbs red light, but transmits blue light that reflects off the clouds making planets like Neptune and Uranus appear blue

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Pluto

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-distance from Sun: 39.54 AU -radius: 1,160 km -mass: 0.0022 Earth mass -made mostly of ice -elliptical orbit is highly inclined (17°) -actually comes closer to the Sun than Neptune for 20 of its 248-year orbit -has more in common with Kuiper belt objects -now classified as a dwarf planet -has large moon Charon that is about half of Pluto's size plus four more recently discovered smaller moons: Nix, Hydra, Kerberos (P4/discovered in 2011), and Styx (P5/discovered 2012)

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Eris

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67.9 AU (38.2-97.5 AU); orbital period: 559 yrs; inclination: 43.99°; e = 0.438; radius ≈ 1,200 km; radius ≈ 0.188 REarth; ices/rock; surface temp: 33 K; 1 moon (Dysnomia)

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Ceres

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discovered January 1, 1800, by Giuseppe Piazzi; distance: 2.544 AU (perihelion)-2.987 AU (aphelion); located in the main asteroid belt; largest asteroid; orbital period: 4.599 years; orbital inclination: 10.587°; e = 0.080; radius = 488 x 455 km (303 × 282 mi); radius ≈ 471 km or 0.0738 REarth; mass = 0.000158 MEarth; composition: mostly rock; density: 2.08 g/cm3; surface temperature: 167 K; no moon(s); re-categorized as a dwarf planet in August 2006

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Makemake

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discovered March 31, 2005, by Brown, Trujillo, and Rabinowitz; distance: 38.509 AU (perihelion)- 53.074 AU (aphelion); located in the Kuiper Belt; 4th dwarf planet; orbital period: 309.88 years; orbital inclination: 28.96°; e = 0.159; radius ≈ 750 km (466 mi) or 0.118 REarth; mass = 0.0006696 MEarth; no moon(s); composition: mostly ice; density ≈ 2 g/cm3; surface temperature: 30 K; surface is likely covered with methane, ethane, and nitrogen ices that give it a reddish color; second brightest KBO after Pluto; named for the creator of humanity in the Rapa Nui mythology of Easter Island

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Haumea

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discovered December 28, 2004, by Brown; distance: 34.721 AU (perihelion)-51.544 AU (aphelion); located in the Kuiper Belt; 5th dwarf planet; orbital period: 283.28 years; orbital inclination: 28.22°; e = 0.195; dimensions: 1960 × 1518 × 996 km; mass = 0.0007031 MEarth; 2 moons; composition: largely rock with ice covering; density ≈ 2.6-3.3 g/cm3; ellipsoidal shaped; surface temperature: < 50 K; surface is bright and appears icy; third brightest KBO after Pluto; named for the Hawaiian goddess of child birth; 2 moons named after her daughters

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Albedo

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is the term for the depth of color of a planet, i.e., its lightness or darkness, and hence its reflectivity. A black planet, reflecting no light, has an albedo of 0.0; a gray planet, reflecting half the light incident on it. has albedo 0.5; and a white one, reflecting all incident light, has albedo 1.0.

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Layout of Solar System

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-patterns of motion -terrestrial planets -jovian planets -asteroids and comets -exceptions to the rule

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Patterns of Motion

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-all planetary orbits are nearly circular and lie nearly in the same plane (the ecliptic) -all planets orbit the Sun in the same direction—counter-clockwise as viewed from high above Earth's North Pole -most planets rotate in the same direction in which they orbit (counterclockwise), with fairly small axis tilt; the Sun also rotates in this same direction -most of the solar system's large moons exhibit similar properties in their orbits around their planets

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Terrestrial Planets

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-Mercury, Venus, Earth, Mars -smaller size and mass -made mostly of rock and metal -solid surface; warmer surfaces -few, if any, moons and no rings -closer to the Sun; closer together

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Jovian Planets

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-Jupiter, Saturn, Uranus, Neptune -larger size and mass -lower density -made mostly of hydrogen, helium, and hydrogen compounds -rings and many moons -farther from the Sun; farther apart -cool temperatures at cloud tops

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Dwarf Planets

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-Pluto, Eris, Makemake, Haumea, Ceres -small like terrestrial planets -solid surface -less dense—made of ice and rock -orbits are more elliptical and have greater inclination -3 moons for Pluto; 1 moon for Eris; 0 moons for Makemake; 2 moons for Haumea; no rings for any of them -Pluto (and Eris, Makemake, Haumea) are of a class of objects that inhabit the outer solar system— Trans-Neptunian Objects (TNOs) that are sometimes referred to as Kuiper Belt Objects (KBOs)

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Small Solar-System Bodies

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-IAU defined all other objects—excluding planets, dwarf planets and satellites of planets or dwarf planets— that orbit the Sun -covers most of the solar system's asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies

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Asteroids

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-small rocky bodies -smaller in size than planets -most found in the asteroid belt between Mars and Jupiter -orbit the Sun in the same direction and plane as the planets - >10,000 have been identified

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Comets

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-small objects that orbit the Sun -estimated 1012 inhabit the far outer reaches of the solar system -made mostly of ices-water ice, ammonia ice, methane ice -found in the Kuiper belt (30-50 AU from Sun); orbit in same direction and nearly same plane as the planets -Pluto is probably a large Kuiper belt object -beyond Kuiper belt is Oort cloud (that may extend ¼ of the distance to the nearest star or 50,000-100,000 AU) and is spherical in shape (orbits inclined at every possible angle)

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Exceptions to the Rules

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-Uranus and Pluto rotate nearly on their sides -Venus rotates "backward" (clockwise rather than counterclockwise) -Neptune's large moon Triton orbits in the opposite direction -Earth has one of the largest moons in the solar system, which is unusual considering the size of the planet our Moon orbits

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Successful Solar System Formation

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-patterns of motion - why planets fall into the two major categories: rocky terrestrial planets near the Sun and large jovian gas giants farther out -existence of asteroids and comets that reside primarily in the asteroid belt, Kuiper belt, and Oort cloud -all general patterns while at the same time making allowances for exceptions to the general rules, such as the odd axis tilt of Uranus and the existence of Earth's large Moon

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Nebular hypothesis (nebular theory)

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proposed the solar system formed from the gravitational collapse of an interstellar cloud of gas, first proposed by Immanuel Kant in 1775 then by Pierre-Simon Laplace 40 years later

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Close Encounter Hypothesis

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-could not account for observed orbital motions of the planets -could not account for the two planet types (terrestrial/jovian) -relied on an encounter that is statistically very unlikely

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Solar Nebula

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Collapsed part of an interstellar gas cloud

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Elements of the universe after big bang

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the universe is composed of hydrogen (75%) and helium (25%) with a small amount of lithium.

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Solar Nebula Gas

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made up of billions of years of galactic recycling that occurred before our solar system was born—giving the 98% H + He / 2% heavier elements we see in the Sun today

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Star Stuff

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what our solar system and us are made of

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Solar Nebula Theory Evidence

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comes from observations of other gas clouds, such as the Orion nebula, in which we can see stars that appear to be in the process of formation

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The Shrinking Nebula heats up

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because gravitational P.E. is being converted into K.E., which heats the gas molecules (and follows the law of conservation of energy)

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The Shrinking Nebula spins or rotates

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due to the conservation of angular momentum; a fast rotation insures that not all of the material in the nebula will collapse to the center

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The Shrinking Nebula flattens into a disk

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due to collisions between particles in a spinning cloud

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Shrinking Nebula Process Produces

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-highest density and temperature at the center (i.e., the Sun) -orderly motion -nearly circular orbits (collisions cause highly elliptical orbits to become more circular)

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Seeds

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-planets began from them -solid chunks of matter that could gravitationally attract other chunks and grow into planets

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Seed Formation

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due to condensation of solid particles at very low temperatures

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Ingredients of Solar Nebula

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-H AND He GAS (98%) remained gaseous -H COMPOUNDS (1.4%)—methane (CH4), ammonia (NH3), and water (H2O)—solidify into ices below 150 K -ROCK (e.g., silicon-based minerals) (0.4%) condenses at 500-1,300 K -METALS (e.g., Fe, Ni, Al) (0.2%) condense at 1,000-1,600 K

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Frost Line

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occurs between the orbits of Mars and Jupiter where temperatures remain <150 K -This explains the existence of rocky and metal-rich inner planets and gaseous outer planets and icy moons and comets in the outer regions of the solar system

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Accretion

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the process of growth by colliding and sticking

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Planetesimals

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large accretions of mass that are pulled into a spherical shape by gravity

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icy planetesimals

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could grow very large because of low temperatures and abundance of gas far from the Sun

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large planetesimals

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-could attract and capture even more gas, growing into the giant, low-density planets we see today

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Accretion and Gas Capture Model

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large planetesimals also caused gas to form flattened disks around them, leading to the accretion of many small planetesimals that ultimately became the numerous moons of the gas giants

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Solar Wind

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has swept most of the H and He gas into interstellar space

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theory of angular momentum transfer

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The strong magnetic field and solar wind of the young Sun transferred significant angular momentum via charged particles from the Sun into space, leaving the Sun with much less angular momentum and a much slower rotation

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Young Stars

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-rotate much faster than mature stars, leading to very strong solar winds that clear gas and debris fairly quickly from planetary disks -produce strong jets of gas that carry material away from them

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Asteroid

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rocky leftover planetesimals of the inner solar system

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Comet

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icy leftover planetesimals of the outer solar system

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Oort Cloud Comets

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probably came from icy planetesimals ejected from the region of the gas giants

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Kuiper Belt Comets

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-less affected by the gravity of the jovian planets, so they continue to orbit in the plane of planetary orbits -Though the outer regions of the solar system are lower in density, these comets could continue their accretion, growing into moon-sized objects like Pluto (and its moon Charon) as well as the larger recently discovered Eris

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Heavy Bombardment Period

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In the first few hundred million years of the solar system's existence, there were vast numbers of collisions between planetesimals

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Impact Crater

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evidence of this period of bombardment

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Water on Earth

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come from the impact of icy planetesimals originating beyond the orbit of Mars

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Capture Moons

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moons with backwards rotation

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Asaph Hall

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discovered the two moons of Mars—Phobos and Deimos—in 1877 at the U.S. Naval Observatory

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Measure the Age of Rock

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through radiometric dating that uses the principle of radioactive decay in certain isotopes

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Oldest Earth Rocks

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about 4.28 billion years old, though the oldest material are zircons dated to nearly 4.4 billion years old

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Oldest Lunar Rocks

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4.4 billion years old

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Planetary Geology

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the study of surface features and the processes that create them and is applied to the study of any solid world, whether planet or moon

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Seismic Waves

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-waves of energy that travel through the Earth's layers that are a result of an earthquake, explosion, or volcano -monitoring them allows us to obtain detailed information about the Earth's interior

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Two types of Seismic waves

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P waves and S waves

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P waves

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primary or pressure waves that are similar to sound waves, they can travel through almost any material

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S waves

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secondary or shear waves that can only travel through solids, since they are stopped by liquids, detailed analysis of them tells us that the Earth has a liquid layer in its outer core

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Layering by Denisty

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core, mantle, crust

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Core

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highest-density material, consisting primarily of metals (Fe and Ni) reside in the core

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Mantle

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rocky material composed of a variety of minerals that contain Si and O (and other elements) forms the thick mantle that surrounds the core

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Crust

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lowest-denisty rock, such as granite and basalt, form the World's outer skin

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Lithosphere

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is the outer layer of relatively rigid rock and encompasses the crust and part of the upper mantle

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differentiation

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the process by which gravity separates materials by density, the terrestrial planets all underwent this process in the past

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The 5 worlds

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earth, venus, mars, mercury, moon

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Earth World

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-small lithosphere and large mantle -solid inner core -molten (liquid or plastic) core

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Venus World

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-small lithosphere and large mantle like Earth -probably similar core structure to Earth but this cannot yet be verified

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Mars World

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proportionally very large lithosphere and small core

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Mercury World

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-core is much larger in proportion to its overall size than any other world -probably due to closeness to Sun as more metal-rich planetesimals came together -too hot for much rock to condense as readily close in -giant impact that also blew away much of its mantle is also a most likely contributing cause to its composition

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Moon World

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proportionally large lithosphere and very small core

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Layering by Strength - Lithosphere

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-solid rock can deform and flow under the influence of gravity -gravity will make any rocky object more than 500km in diameter into a sphere within 1 billion years -strength of rock depends on three characteristics: composition, temperature, surrounding pressure

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How interiors get hot

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-heat of accretion -heat from differentiation -heat from radioactive decay

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heat of accretion

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impact release KE from gravitational PE; KE converts to thermal energy

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heat from differentiation

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dense materials sink, gravitational PE converts to thermal energy

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heat from radioactive decay

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mass-energy converted to thermal energy

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how interiors cool off

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convection, conduction, radiation

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convection

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occurs when hot rock expands and rises from within the mantle, cools and contracts at the top of the mantle and falls back to start the process over

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convection cells

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arise within the mantle

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Three requirements for a global magnetic field

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-an interior region of electrically conducting fluid such as molten metal -convection in that layer of fluid -moderately rapid rotation

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Four basic Geological Processes

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impact cratering, volcanism, tectonics, erosion

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impact cratering

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blasting of bowl shaped craters by asteroids or comets striking a planet's surface

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volcanism

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eruption of molten rock, or lava, from a planet's interior onto its surface

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tectonics

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the disruption of a planet's surface by internal stresses

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erosion

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the wearing down or building up of geological features by wind, water, ice, or other phenomena of planetary weather

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