Our Solar SystemOur 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 SystemOur Solar System

Our solar system is made Our solar system is made up of:up of:

SunSunEight planets Eight planets Their moonsTheir moonsAsteroids & MeteroidsAsteroids & MeteroidsCometsComets

Inner PlanetsInner Planets

The inner four rocky planets The inner four rocky planets at the center of the solar at the center of the solar system are:system are:

MercuryMercuryVenusVenusEarthEarthMarsMars

MercuryMercury

Planet nearest the sunPlanet nearest the sunSecond smallest planetSecond smallest planetCovered with cratersCovered with cratersHas no moons or ringsHas no moons or ringsAbout size of Earth’s moonAbout size of Earth’s moon

VenusVenus

Sister planet to EarthSister planet to EarthHas no moons or ringsHas no moons or ringsHot, thick atmosphereHot, thick atmosphereBrightest object in sky besides sun and Brightest object in sky besides sun and

moon (looks like bright star)moon (looks like bright star)Covered with craters, volcanoes, and Covered with craters, volcanoes, and

mountainsmountains

EarthEarth

Third planet from sunThird planet from sunOnly planet known to have life and Only planet known to have life and

liquid waterliquid waterAtmosphere composed of Nitrogen Atmosphere composed of Nitrogen

(78%), Oxygen (21%), and other gases (78%), Oxygen (21%), and other gases (1%).(1%).

MarsMars

Fourth planet from sunFourth planet from sunAppears as bright reddish color in the Appears as bright reddish color in the

night skynight skySurface features volcanoes and huge Surface features volcanoes and huge

dust stormsdust stormsHas 2 moons: Has 2 moons: Phobos and DeimosPhobos and Deimos

Asteroid BeltAsteroid Belt

Separates the inner, terrestrial planets Separates the inner, terrestrial planets from the outer, Jovian planetsfrom the outer, Jovian planets

Contains ~100,000 asteroids.Contains ~100,000 asteroids.Largest known asteroid: 4 VestaLargest known asteroid: 4 VestaLargest object : Ceres (dwarf planet)Largest object : Ceres (dwarf planet)

Outer PlanetsOuter Planets

The outer planets composed The outer planets composed of gas are :of gas are :

JupiterJupiterSaturnSaturnUranusUranusNeptuneNeptune

JupiterJupiter

Largest planet in solar systemLargest planet in solar system Brightest planet in skyBrightest planet in sky At last count, 65 moons: 5 visible from EarthAt last count, 65 moons: 5 visible from Earth Strong magnetic fieldStrong magnetic field Giant red spotGiant red spot Rings have 3 parts: Halo Ring, Main Ring, Rings have 3 parts: Halo Ring, Main Ring,

Gossamer RingGossamer Ring

SaturnSaturn 66thth planet from sun planet from sun Beautiful set of rings Beautiful set of rings 62 moons62 moons Largest moon, Titan, Largest moon, Titan, Easily visible in the night Easily visible in the night

skysky Voyager explored Saturn Voyager explored Saturn

and its rings.and its rings.

UranusUranus 77thth planet from sun planet from sun Has a faint ring systemHas a faint ring system 27 known moons27 known moons Covered with cloudsCovered with clouds Uranus sits on its side with the north Uranus sits on its side with the north

and south poles sticking out the and south poles sticking out the sides.sides.

NeptuneNeptune

88thth planet from sun planet from sunDiscovered through mathDiscovered through math12 known moons12 known moonsTriton largest moonTriton largest moonGreat Dark Spot thought to be a Great Dark Spot thought to be a

hole, similar to the hole in the hole, similar to the hole in the ozone layer on Earthozone layer on Earth

A Dwarf PlanetA Dwarf Planet

Pluto is a small solid icy Pluto is a small solid icy planet is smaller than the planet is smaller than the Earth's Moon.Earth's Moon.

PlutoPluto

Never visited by Never visited by spacecraftspacecraft

Orbits very slowlyOrbits very slowly

Charon, its moon, is Charon, its moon, is very close to Pluto very close to Pluto and about the same and about the same sizesize

Two Types of Planets: Terrestrial and Jovian

Why?

AsteroidsAsteroids Small bodies Small bodies Believed to be left over Believed to be left over

from the beginning of from the beginning of the solar system billions the solar system billions of years agoof years ago

100,000 asteroids lie in 100,000 asteroids lie in belt between Mars and belt between Mars and JupiterJupiter

Largest asteroids have Largest asteroids have been given namesbeen given names

CometsComets

Small icy bodiesSmall icy bodiesTravel past the SunTravel past the SunGive off gas and dust as Give off gas and dust as

they pass bythey pass by

Anatomy of a Comet

Anatomy of a Comet

Anatomy of a Comet

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 motion2. Two types of planets3. Asteroids & comets4. Exceptions to patterns

Patterns of MotionPatterns 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

PlanetPlanet Actual Distance (AU)Actual Distance (AU) Bode’s LawBode’s Law

Mercury 0.39 0.4

Venus 0.72 0.7

Earth 1.00 1.0

Mars 1.52 1.6

Jupiter 5.20 5.2

Saturn 9.54 10.0

Uranus 19.2 19.6

Neptune 30.1 38.8

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"

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 Planetary Nebula or Close Encounter?Encounter?

Historically, two hypothesis were put forward to explain the formation of the solar Historically, two hypothesis were put forward to explain the formation of the solar system….system….

#1 - Gravitational Collapse of Planetary Nebula#1 - Gravitational Collapse of Planetary NebulaSolar system formed form gravitational collapse of an interstellar cloud of gasSolar system formed form gravitational collapse of an interstellar cloud of gas

#2 - Close Encounter #2 - Close Encounter (of the Sun (of the Sun with another starwith another star))Planets are formed from debris pulled out of the Sun during a close encounter Planets are formed from debris pulled out of the Sun during a close encounter with another star. But, it cannot account forwith 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 TheoryThe Nebular Theory** of Solar System of Solar System FormationFormation

Interstellar Cloud (Nebula)

Protoplanetary DiskProtosun

Gravitational Collapse

Terrestrial Planets

Accretion Nebular Capture

Jovian PlanetsAsteroids

Leftover Materials

Comets

Leftover Materials

Metal, Rocks

Condensation (gas to solid)

Sun Gases, 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

HypothesisBasis 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.

Beta Pectoris dust disk

Planetesimals forming planets

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 planetsJovian 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 JupiterA type of extrasolar planet whose mass is close to or exceeds that of Jupiter (1.9 × 1027 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 PlanetA 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 GiantA 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.