Presentation on theme: "Survey of Solar Systems"— Presentation transcript:
1Survey of Solar Systems Chapter 8Survey of Solar SystemsCopyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2Upon completing this chapter you should be able to: Identify the primary components of the Solar System, and describe their distinctive properties.Discuss the differences between terrestrial, Jovian, and dwarf planets, and their satellites, and recount why astronomers reclassified Pluto.Explain how astronomers measure masses and radii for bodies in the Solar System, and carry out a calculation to find a body's density from these measurements.Describe the densities of different classes of objects in the Solar System and relate this to their composition.
3Upon completing this chapter you should be able to: Recall the age of the Solar System and explain how it is determined.Describe the steps in the formation of the Solar System according to the nebular theory and relate these to the properties of the planets and other bodies.Explain why disks are expected to form around stars, and describe the observations that indicate disks are present around yound stars.Describe the role of planetesimals in planet formation and modification, and where some can still be found.
4Upon completing this chapter you should be able to: Discuss the roles of rocky, icy, and gaseous materials in the formation of planets and their atmospheres.Explain the various methods currently being used to detect exoplanets, the information each provides about an exoplanet, and the limitations of these methods.Discuss the ways in which exoplanetary systems appear to differ from the Solar System.
5The Solar System consists of the Sun and the bodies in its gravitational domain: the eight planets, dozens of dwarf planets, and swarms of moons, asteroids, and comets.Although we have only walked on the Earth and the Moon, we have detailed pictures sent to us from spacecraft of most of the planets and their satellites. Some are baren balls of rock; others are mostly ice. Some have thin, frigid atmospheres so cold that ordinary gases crystallize as snow on their cratered surfaces; others have thick atmospheres that constistency of molten lava and no solid surface at all.All the planets circle the Sun in the same direction, and most of them spin in the same direction. The moons also form flattened systems, generally orbiting in the same direction.
6The Solar SystemThe Solar System is occupied by a diversity of objects, but shows an underlying order in the dynamics of their movementsThe planets form two main families:solid rocky inner planets (terrestrial)gaseous/liquid outer planets (Jovian)Astronomers deduce that the Solar System formed some 4.5 billion years ago out of the collapse of a huge cloud of gas and dust
7The Sun: the only star in our solar system Image of the Sun made with ultraviolettelescope that reveals high temperaturegases in the Sun's atmosphere.The Sun is a star, a ball of incandescent gas whose output is generated by nuclear reactions in its coreComposed mainly of hydrogen (71%) and helium (27%), it also contains traces of nearly all the other chemical elements
8The SunIt is the most massive object in the Solar System – 700 times the mass of the rest of the Solar System combinedEmits its ownlightIts large mass provides the gravitational force to hold all the Solar System bodies in their orbital patterns around the Sun
9The Planets Orbits are almost circular lying in nearly the same plane They emit no visible light of their own but shine by reflected sunlightMercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
10The PlanetsThe orbits are shown in the correct relative scale in the 2 drawings. Because of the great difference in scale, the inner and outer Solar System are displayed separately.
11The PlanetsAll of the planets travel counterclockwise around the Sun (as seen from high above the Earth’s north pole)Six planets rotate counterclockwise; Venus rotates clockwise (retrograde rotation), and Uranus appears to rotate on its side
12The PlanetsThe planets' orbits from the side. The drawf planets Ceres, Pluto, and Eris are also shown, illustrating their highly inclined orbits.This view also shows that while Pluto sometimes gets closer to the Sun than Neptune, its orbit actually remains well separated from Neptune's.
13According to the IAU, a planet is a celestrial body that is in orbit around the sun, is massive enought for its self-gravity to create a nearly round shape, and has cleared the neighborhood around its orbit.By this definition, our solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.Some astronmers call these the major planets.
14Instead of "inner" and "outer" planets, astronomers sometimes use "terrestrial" and "Jovian" to describe the two types of planets.The terrestrial planets (Mercury to Mars) are so named because of their resemblance to the Earth.The Jovian planets (Jupiter to Neptune) are named for their resemblance to Jupiter.
15Inner PlanetsMercury, Venus, Earth, MarsSmall rocky (mainly silicon and oxygen) bodies with relatively thin or no atmospheresAlso known as terrestrial planetsIt is believed that only the rocky material could condense at the higher temperatures of the inner part of the solar nebula.
16Outer Planets Jupiter, Saturn, Uranus, and Neptune Gaseous, liquid, or icy (H2O, CO2, CH4, NH3)Also referred to as Jovian planetsJovian planets are much larger than terrestrial planets and do not have a well-defined surfaceCompared to the Terrestrial planets, the Jovian planets have many satellites.
17A drawf planet shares all the characteristics of a planet except that it has not cleared the neighborhood around its orbit.Ceres, Pluto, Haumea, Makemake, and Eris fall into this category...
18In 2008, dwarf planets that orbit beyond Neptune are called Plutoids. Pluto (it has not cleared its neighborhood) and similar objects fail to fit into either familyRecently, scientists have discovered more than 200 similar objects orbiting the Sun at the same distance as PlutoIn 2008, dwarf planets that orbit beyond Neptune are called Plutoids.In 2006, a new family was introduced – the dwarf planetsMassive enough to pull themselves sphericalOrbits have not been swept clear of debris
19Spins and Axial TiltsMost planets spin (rotate) in the same direction, clounterclockwise as viewed from above the north pole.Venus and Uranus are exceptionsAxial tilts range from 0º to 98º.
20Asteroids and Comets Composition and size Asteroids are rocky or metallic bodies ranging in size from a few meters to 1000 km across (about 1/10 the Earth’s diameter)Comets are icy bodies about 10 km or less across that can grow very long tails of gas and dust as they near the Sun and are vaporized by its heatAlthough the majority of comets probably originate in the Oort cloud, some come from the Kuiper belt. Together they probably contain more than 1 trillion comet nuclei, only a few of which get close enough to the Sun to be detected.
21Asteroids and Comets Their location within Solar System Most asteroids are in the asteroid belt between Mars and Jupiter indicating that these asteroids are the failed building-blocks of a planetSome comets may also come from a disk-like swarm of icy objects that lies beyond Neptune and extends to perhaps 1000 AU, a region called the Kuiper ( KY -per) Belt
22Asteroids and CometsMost comets orbit the Sun far beyond Pluto in the Oort cloud, a spherical shell extending from 40,000 to 100,000 AU from the Sun
24Bode's Rule: The search for order In the 1700's astronomers noticed that the spacing between the orbits of the planets seems to follow a fairly regular progression.This mathematical progression may indicate something about the natural spacing between orbits of large bodies, or it may be a chance pattern ...
26Bode’s RuleVery roughly, each planet is about twice as far from the Sun as its inner neighbor. The progression of distance from the Sun can be expressed by a simple math relation...Bode's Rule.First noted in 1766, formalized mathematically by J. E. Bode in 17780, 3, 6, 12 ,24, 48, 96, 192, (nine numbers...)4, 7, 10, 16, 28, 52, 100, 196, "0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, "Does a pretty good job, up to a point...
27Measuring Composition: Density A planet’s average density is determined by dividing a planet’s mass by its volumeMass determined from Kepler’s modified third lawVolume derived from a planet’s measured radius
28Measuring Composition Since the inner and outer planets differ dramatically in composition, it is important to understand how composition is determinedA planet’s reflection spectrum can reveal a planet’s atmospheric contents and the nature of surface rocksSeismic activity has only been measured on Earth for the purposes of determining interior composition
29Measuring Composition: Density Once average density known, the following factors are taken into account to determine a planet’s interior composition and structure:Densities of abundant, candidate materialsVariation of these densities as a result of compression due to gravitySurface composition determined from reflection spectraMaterial separation by density differentiationMathematical analysis of equatorial bulges
30Analysis Concludes:The terrestrial planets, with average densities ranging from 3.9 to 5.5 g/cm3, are largely rock and iron, have iron cores, and have relative element ratios similar to the Sun except for deficiencies in lightweight gasses
31Analysis Concludes:The Jovian planets, with average densities ranging from 0.71 to 1.67 g/cm3, have relative element ratios similar to the Sun and have Earth-sized rocky cores
32Satellites The number of planetary satellites changes frequently as more arediscovered!Jupiter 63Saturn 60Uranus 27Neptune 13Mars 2Earth 1Mercury and Venus are moonlessEven Pluto and Eris have moons!
33Age of the Solar SystemAll objects in the Solar System seem to have formed at nearly the same time, out of the same original cloud of gas and dustRadioactive dating of rocks from the Earth, Moon, and some asteroids suggests an age of about 4.5 billion yrsA similar age is found for the Sun based on current observations and nuclear reaction rates
34Formation of Planetary Systems A theory of the Solar System’s formation must account for the following:Planets orbit in the same direction and in the same planeRocky inner planets and gaseous/liquid/icy outer planetsCompositional trends in the solar systemAll Solar System bodies appear to be less than 4.5 billion years oldOther details – structure of asteroids, cratering of planetary surfaces, detailed chemical composition of surface rocks and atmospheres, etc.
36The Solar Nebula Hypothesis Derived from 18th century ideas of Laplace and KantProposes that Solar System evolved from a rotating, flattened disk of gas and dust (an interstellar cloud), the outer part of the disk becoming the planets and the inner part becoming the Sun
37The Solar Nebula Hypothesis This hypothesis naturally explains the Solar System’s flatness and the common direction of motion of the planets around the SunInterstellar clouds are common between the stars in our galaxy and this suggests that most stars may have planets around them
38Interstellar CloudsCome in many shapes and sizes – one that formed Solar System was probably a few light years in diameter and 2 solar massesTypical clouds are 71% hydrogen, 27% helium, and traces of the other elements
39Interstellar CloudsClouds also contain tiny dust particles called interstellar grainsGrain size from large molecules to a few micrometersThey are a mixture of silicates, iron and carbon compounds, and water ice
40Formation of the Solar Nebula Triggered by a collision with another cloud or a nearby exploding star, rotation forces clouds to gravitationally collapse into a rotating disk
41The Solar NebulaA few million years pass for a cloud to collapse into a rotating disk with a bulge in the centerThis disk, about 200 AU across and 10 AU thick, is called the solar nebula with the bulge becoming the Sun and the disk condensing into planetsThe jovian planets has a composition that most resembles the original solar nebula.
42Disk ObservationsA) The small blobs in this are stars in the process of formation and their surrounding disk of dust and gas. These are in the Orion Nebula, a huge gas cloudabout 1500 ly from Earth.B) Dust ring that surounds the star Fomalhaut. A small mask in the telescope blots out the star's direct light, which would otherwise overexpose the image.
43Temperatures in the Solar Nebula Before the planets formed, the inner part of the disk was hot, heated by gas falling onto the disk and a young Sun – the outer disk was colder than the freezing point of water
44CondensationCondensation occurs when gas cools below a critical temperature at a given gas pressure and its molecules bind together to form liquid/solid particlesThe process in which a gas cools and its molecules stick together to form liquid particles ....
45Condensation in the Solar Nebula Iron vapor will condense at 1300 K, silicates will condense at 1200 K, and water vapor will condense at room temperature in airIn a mixture of gases, materials with the highest vaporization temperature condense firstCondensation ceases when the temperature never drops low enoughSun kept inner solar nebula (out to almost Jupiter’s orbit) too hot for anything but iron and silicate materials to condenseOuter solar nebula cold enough for ice to condense
46Formation of PlanetsAn artist's dipiction of how the planets may have formed in the nebula.nebular hypothesis: Interstellar cloud, solar nebula, accretion, collisions between planetesimals, planets.
47AccretionNext step is for the tiny particles to stick together, perhaps by electrical forces, into bigger pieces in a process called accretionAs long as collisions are not too violent, accretion leads to objects, called planetesimals, ranging in size from millimeters to kilometersAstronomers believe that the satellites of the Jovian planets were planetesimals orbiting the growing planet.
48PlanetesimalsPlanetesimals in the inner solar nebula were rocky-iron composites, while planetesimals in the outer solar nebula were icy-rocky-iron compositesPlanets formed from “gentle” collisions of the planetesimals, which dominated over more violent shattering collisions
49Formation of the Planets Simulations show that planetesimal collisions gradually lead to approximately circular planetary orbitsAs planetesimals grew in size and mass their increased gravitational attraction helped them grow faster into clumps and rings surrounding the Sun
50Formation of the Planets Planet growth was especially fast in the outer solar nebula due to:Larger volume of material to draw uponLarger objects (bigger than Earth) could start gravitationally capturing gases like H and He
51Final Stages Rain of planetesimals cratered surfaces Remaining planetesimals became small moons, comets, and asteroids
52Continuous Bombardment Continued planetesimal bombardment and internal radioactivity melted the planets and led to the density differentiation of planetary interiors
53Formation of MoonsMoons of the outer planets were probably formed from planetesimals orbiting the growing planetsNot large enough to capture H or He, the outer moons are mainly rock and ice giving them solid surfaces
54Formation of Atmospheres Atmospheres were the last planet-forming processOuter planets gravitationally captured their atmospheres from the solar nebulaInner planets created their atmospheres by volcanic activity and perhaps from comets and asteroids that vaporized on impactObjects like Mercury and the Moon are too small – not enough gravity – to retain any gases on their surfaces
55Evidence exists for planets around other nearby stars Exosolar PlanetsEvidence exists for planets around other nearby starsThe new planets are not observed directly, but rather by their gravitational effects on their parent starThese new planets are a surprise - they have huge planets very close to their parent starsThe recent discovery that planets more massive than Jupiter orbit nearby stars in small orbits surprising because according to the nebular hypothesis, massive planets should only form away from their star.
56Exosolar PlanetsIdea: The huge planets formed far from their stars as current theory would project, but their orbits subsequently shrankThis migration of planets may be caused by interactions between forming planets and leftover gas and dust in the disk
57Detecting ExoplanetsWe can detect planets around other stars by using the doppler shift method.A planet and its stars revolve around a common center of mass.As the star approaches us in its motion around the center of mass, its spectrum will be blue-shifted.As it recedes, the spectrum will be red-shifted.
58Gravitational Lensing Method Another method utilizes a prediction of General Relativity called gravitational lensing.Gravity bends the path of light when it passes near a massive object.If that object is a star with companion planets, we can use the lensing effect to detect them.We have not found many planetary systems using this method, but it has the potential to find low-mass planets!
59Transit Method We can also use the transit method for detection. Look for dimming of light from the central star.