Our Solar System Origins of the Solar System Astronomy 12
Learning Outcomes (Students will…) -Explain the theories for the origin of the solar system -Distinguish between questions that can be answered by science and those that cannot, and between problems that can be solved by technology and those that cannot with regards to solar system formation. -Estimate quantities of distances in parsec. Estimate the age of the solar system. -Describe and apply classification systems and nomenclature used in the sciences. Classify planets as terrestrial vs. Jovian, inner vs. outer, etc. Classify satellites. Classify meteoroid, asteroid, dwarf planet, planet. Classify comets as long period vs. short period. etc -Formulate operational definitions of major variables. Given data such as diameter and density describe the properties that divide the planets and moons into groups. -Tools and methods used to observe and measure the inner and the outer planets and the minor members of the solar system
Our Solar System Our solar system is made up of: Sun Sun Eight planets Eight planets Their moons Their moons Asteroids & Meteroids Asteroids & Meteroids Comets Comets
Inner Planets The inner four rocky planets at the center of the solar system are: Mercury Mercury Venus Venus Earth Earth Mars Mars
Mercury Planet nearest the sun Planet nearest the sun Second smallest planet Second smallest planet Covered with craters Covered with craters Has no moons or rings Has no moons or rings About size of Earth’s moon About size of Earth’s moon
Venus Sister planet to Earth Sister planet to Earth Has no moons or rings Has no moons or rings Hot, thick atmosphere Hot, thick atmosphere Brightest object in sky besides sun and moon (looks like bright star) Brightest object in sky besides sun and moon (looks like bright star) Covered with craters, volcanoes, and mountains Covered with craters, volcanoes, and mountains
Earth Third planet from sun Third planet from sun Only planet known to have life and liquid water Only planet known to have life and liquid water Atmosphere composed of Nitrogen (78%), Oxygen (21%), and other gases (1%). Atmosphere composed of Nitrogen (78%), Oxygen (21%), and other gases (1%).
Mars Fourth planet from sun Fourth planet from sun Appears as bright reddish color in the night sky Appears as bright reddish color in the night sky Surface features volcanoes and huge dust storms Surface features volcanoes and huge dust storms Has 2 moons: Phobos and Deimos Has 2 moons: Phobos and Deimos
Asteroid Belt Separates the inner, terrestrial planets from the outer, Jovian planets Separates the inner, terrestrial planets from the outer, Jovian planets Contains ~100,000 asteroids. Contains ~100,000 asteroids. Largest known asteroid: 4 Vesta Largest known asteroid: 4 Vesta Largest object : Ceres (dwarf planet) Largest object : Ceres (dwarf planet)
Outer Planets The outer planets composed of gas are : Jupiter Jupiter Saturn Saturn Uranus Uranus Neptune Neptune
Jupiter Largest planet in solar system Largest planet in solar system Brightest planet in sky Brightest planet in sky At last count, 65 moons: 5 visible from Earth At last count, 65 moons: 5 visible from Earth Strong magnetic field Strong magnetic field Giant red spot Giant red spot Rings have 3 parts: Halo Ring, Main Ring, Gossamer Ring Rings have 3 parts: Halo Ring, Main Ring, Gossamer Ring
Saturn 6 th planet from sun 6 th planet from sun Beautiful set of rings Beautiful set of rings 62 moons 62 moons Largest moon, Titan, Largest moon, Titan, Easily visible in the night sky Easily visible in the night sky Voyager explored Saturn and its rings. Voyager explored Saturn and its rings.
Uranus 7 th planet from sun 7 th planet from sun Has a faint ring system Has a faint ring system 27 known moons 27 known moons Covered with clouds Covered with clouds Uranus sits on its side with the north and south poles sticking out the sides. Uranus sits on its side with the north and south poles sticking out the sides.
Neptune 8 th planet from sun 8 th planet from sun Discovered through math Discovered through math 12 known moons 12 known moons Triton largest moon Triton largest moon Great Dark Spot thought to be a hole, similar to the hole in the ozone layer on Earth Great Dark Spot thought to be a hole, similar to the hole in the ozone layer on Earth
A Dwarf Planet Pluto is a small solid icy planet is smaller than the Earth's Moon. Pluto is a small solid icy planet is smaller than the Earth's Moon.
Pluto Never visited by spacecraft Never visited by spacecraft Orbits very slowly Orbits very slowly Charon, its moon, is very close to Pluto and about the same size Charon, its moon, is very close to Pluto and about the same size
Two Types of Planets: Terrestrial and Jovian Why?
Asteroids Small bodies Small bodies Believed to be left over from the beginning of the solar system billions of years ago Believed to be left over from the beginning of the solar system billions of years ago 100,000 asteroids lie in belt between Mars and Jupiter 100,000 asteroids lie in belt between Mars and Jupiter Largest asteroids have been given names Largest asteroids have been given names
Comets Small icy bodies Small icy bodies Travel past the Sun Travel past the Sun Give off gas and dust as they pass by Give off gas and dust as they pass by
How was the Solar System Formed? A viable theory for the formation of the solar system must be: based on physical principles (angular momentum, the law of gravity, the law of motions) able to explain all (at least most) the observable facts with reasonable accuracy able to explain other planetary systems
How was the Solar System Formed? A viable theory for the formation of the solar system must account for 4 characteristics: 1.Patterns of motion 2.Two types of planets 3.Asteroids & comets 4.Exceptions to patterns
Patterns of Motion All the planets orbit the Sun in the same direction The rotation axis of most of the planets and the Sun are roughly aligned with the rotation axis of their orbits. Orientation of Venus, Uranus, and Pluto’s spin axes are not similar to that of the Sun and other planets. Why do they spin in roughly the same orientation? Why are they different?
Sun, a star, at the center Inner (rocky) Planets (Mercury, Venus, Earth, Mars) ~ 1 AU Asteroid Belt ~ 3 AU Outer (gaseous) Planets (Jupiter, Saturn, Neptune, Uranus) ~ 5-40 AU Kuiper Belt ~ 30 to 50 AU -includes Pluto Oort Cloud ~ 50,000 AU What does the solar system look like from far away?
Bode’s Law A rough rule that predicts the spacing of the planets in the Solar System To find the mean distances of the planets, beginning with the following simple sequence of numbers: 0 3 6 12 24 48 96 192 384 With the exception of the first two, the others are simple twice the value of the preceding number. Add 4 to each number: 4 7 10 16 28 52 100 196 388 Then divide by 10: 0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 38.8 Planet Actual Distance (AU) Bode’s Law Mercury0.390.4 Venus0.720.7 Earth1.001.0 Mars1.521.6 Jupiter5.205.2 Saturn9.5410.0 Uranus19.219.6 Neptune30.138.8 Works for moons too!
Most asteroids are located in two regions: Asteroid belt Orbit of Jupiter… the Hildas (the orange "triangle" just inside the orbit of Jupiter) and the Jovian Trojans (green). The group that leads Jupiter are called the "Greeks" and the trailing group are called the "Trojans" Hildas Jovian Trojans Where are the asteroids?
Where are the comets? Kuiper Belt A large body of small objects orbiting (the short period comets <200 years) the Sun in a radial zone extending outward from the orbit of Neptune (30 AU) to about 100 AU. Pluto maybe the biggest of the Kuiper Belt object. Oort Cloud Long Period Comets (period > 200 years) seems to come mostly from a spherical region at about 50,000 AU from the Sun.
Exceptions to Patterns Uranus has different axial tilt Some moons larger than others Some moon have unusual orbits
Planetary Nebula or Close Encounter? Historically, two hypothesis were put forward to explain the formation of the solar system…. #1 - Gravitational Collapse of Planetary Nebula #1 - Gravitational Collapse of Planetary Nebula Solar system formed form gravitational collapse of an interstellar cloud of gas #2 - Close Encounter (of the Sun with another star) #2 - Close Encounter (of the Sun with another star) Planets are formed from debris pulled out of the Sun during a close encounter with another star. But, it cannot account for The angular momentum distribution in the solar system, The angular momentum distribution in the solar system, Probability for such encounter is small in our neighborhood… Probability for such encounter is small in our neighborhood… Astronomers favour Hypothesis #1
The Nebular Theory * of Solar System Formation Interstellar Cloud (Nebula) Protoplanetary DiskProtosun Gravitational Collapse Terrestrial Planets AccretionNebular Capture Jovian Planets Asteroids Leftover Materials Comets Leftover Materials Metal, Rocks Condensation (gas to solid) SunGases, Ice Heating Fission/Fusion * It is also called the ‘Protoplanet Theory’. (depends on temperature)
Collapse of the Solar Nebula Gravitational Collapse 1.Heating Protosun Sun In-falling materials loses gravitational potential energy, which were converted into kinetic energy. The dense materials collides with each other, causing the gas to heat up. Once the temperature and density gets high enough for nuclear fusion to start, a star is born. 2.Spinning Smoothing of the random motions Conservation of angular momentum causes the in-falling material to spin faster and faster as they get closer to the center of the collapsing cloud. 3.Flattening Protoplanetary disk. The solar nebular flattened into a flat disk. Collision between clumps of material turns the random, chaotic motion into a orderly rotating disk. This process explains the orderly motion of most of the solar system objects! Denser region in a interstellar cloud, maybe compressed by shock waves from an exploding supernova, triggers the gravitational collapse.
The Solar Nebula Hypothesis Basis of modern theory of planet formation. Planets form at the same time from the same cloud as the star. Sun and our solar system formed ~ 5 billion years ago. Planet formation sites observed today as dust disks of T Tauri stars.
Evidence for Ongoing Planet Formation Many young stars in the Orion Nebula are surrounded by dust disks: Probably sites of planet formation right now!
Dust Disks around Forming Stars Dust disks around some T Tauri stars can be imaged directly (HST).
The Story of Planet Building Planets formed from the same protostellar material as the sun, still found in the sun’s atmosphere. Rocky planet material formed from clumping together of dust grains in the protostellar cloud. Mass of less than ~ 15 Earth masses: Planets can not grow by gravitational collapse Mass of more than ~ 15 Earth masses: Planets can grow by gravitationally attracting material from the protostellar cloud Earthlike planets Jovian planets (gas giants)
Extrasolar Planets An extrasolar planet, or exoplanet, is a planet beyond our solar system, orbiting a star other than our Sun Information obtained primarily from wikipedia.org
Types of Extrasolar Planets Hot Jupiter A type of extrasolar planet whose mass is close to or exceeds that of Jupiter (1.9 × 10 27 kg), but unlike in the Solar System, where Jupiter orbits at 5 AU, hot Jupiters orbit within approximately 0.05 AU of their parent stars (about one eighth the distance that Mercury orbits the Sun) Example: 51 Pegasi b
Types of Extrasolar Planets Pulsar Planet A type of extrasolar planet that is found orbiting pulsars, or rapidly rotating neutron stars Example: PSR B1257+12 in the constellation Virgo
Types of Extrasolar Planets Gas Giant A type of extrasolar planet with similar mass to Jupiter and composed on gases Example: 79 Ceti b
Methods of Detecting Extrasolar Planets Transit Method If a planet crosses ( or transits) in front of its parent star's disk, then the observed visual brightness of the star drops a small amount. The amount the star dims depends on the relative sizes of the star and the planet.
Methods of Detecting Extrasolar Planets Astrometry This method consists of precisely measuring a star's position in the sky and observing how that position changes over time. If the star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. If the star is large enough, a ‘wobble’ will be detected.
Methods of Detecting Extrasolar Planets Doppler Shift (Radial Velocity) A star with a planet will move in its own small orbit in response to the planet's gravity. The goal now is to measure variations in the speed with which the star moves toward or away from Earth. In other words, the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines (think ROYGBIV) due to the Doppler effect. A red shift means the star is moving away from Earth A blue shift means the star is moving towards Earth
Methods of Detecting Extrasolar Planets Pulsar Timing A pulsar is a neutron star: the small, ultra-dense remnant of a star that has exploded as a supernova. Pulsars emit radio waves extremely regularly as they rotate. Because the rotation of a pulsar is so regular, slight changes in the timing of its observed radio pulses can be used to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it has a planet. Calculations based on pulse- timing observations can then reveal the geometry of that orbit
Methods of Detecting Extrasolar Planets Gravitational Microlensing The gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect.
Methods of Detecting Extrasolar Planets Direct Imaging Planets are extremely faint light sources compared to stars and what little light comes from them tends to be lost in the glare from their parent star. It is very difficult to detect them directly. In certain cases, however, current telescopes may be capable of directly imaging planets.