the planets. midterm! ► in next week part i (take home exam, including 10 points from mastering...

The planets

Midterm!Midterm!► In next week In next week Part I Part I (take home exam, (take home exam,

including 10 points from Mastering including 10 points from Mastering Astronomy, Astronomy, 50 pts50 pts)) will bewill be available, due available, due October 26October 26thth, noon, noon

► In 2 weeks, In 2 weeks, Part IIPart II ( (in class examin class exam, , 50 pts50 pts.).) Taken in 3Taken in 3rdrd hour hour (week of 10/22 to 10/25) (week of 10/22 to 10/25) Bring SCANTRON (882 form) and #2 pencilBring SCANTRON (882 form) and #2 pencil Based on “Review Questions” handout, available Based on “Review Questions” handout, available

now!now!

►Also: 10 of the 25 extra credit points are due Also: 10 of the 25 extra credit points are due by October 26by October 26thth, noon., noon.

© Sierra College Astronomy Department 3

Lecture 7: A Planetary OverviewLecture 7: A Planetary Overview

Comparative PlanetologyComparative Planetology

► In this chapter we wish to look at the solar system In this chapter we wish to look at the solar system as whole and compare the worlds to each other, as whole and compare the worlds to each other, seeking to understand their similarities and seeking to understand their similarities and differences – differences – comparative planetologycomparative planetology

► Planetology broadly includes moons, asteroids, and Planetology broadly includes moons, asteroids, and comets as well as the planets.comets as well as the planets.

► We can see that the solar system is not a random We can see that the solar system is not a random collection of worlds collection of worlds



Comparative PlanetologyComparative Planetology

► We see several values to comparative planetology We see several values to comparative planetology (CP):(CP): CP has revealed similarities and difference in the planets CP has revealed similarities and difference in the planets

have helped guide the development of our theory of solar have helped guide the development of our theory of solar system formationsystem formation

CP gives us deep new insights into the physical CP gives us deep new insights into the physical processes that have shaped the Earth and other worldsprocesses that have shaped the Earth and other worlds

CP allows us to apply lessons from our own solar system CP allows us to apply lessons from our own solar system to the study of other solar systems.to the study of other solar systems.



Solar System Roll CallSolar System Roll Call

►TheThe Sun Sun thethe is largest and brightest object in is largest and brightest object in the solar systemthe solar system

►The Sun is hot (5800 K on surface)The Sun is hot (5800 K on surface)►The Sun is gaseous and converts matter into The Sun is gaseous and converts matter into

energy in coreenergy in core►The Sun has the greatest influence on the The Sun has the greatest influence on the

rest of the solar system (light, solar wind…)rest of the solar system (light, solar wind…)

Sun




► Mercury Mercury is the smallest planet in the solar is the smallest planet in the solar system system

► It rotates every 58.6 days and revolves every It rotates every 58.6 days and revolves every 88 days and is tidally locked to the Sun88 days and is tidally locked to the Sun

► The produces 88 days of daylight and 88 The produces 88 days of daylight and 88 days of night, making temperatures extreme days of night, making temperatures extreme (425(425°C to -150°C; 800°F to -240°F).°C to -150°C; 800°F to -240°F).

► One spacecraft has visited Mercury and One spacecraft has visited Mercury and another is another is on its wayon its way

Mercury

Tidal




► Venus Venus is often called Earth’s “twin” because it is nearly the is often called Earth’s “twin” because it is nearly the same size as the Earth. But it’s nothing like the Earth…same size as the Earth. But it’s nothing like the Earth…

► It rotates backwards (or upside down) very slowlyIt rotates backwards (or upside down) very slowly

► It is covered with an atmosphere of mostly COIt is covered with an atmosphere of mostly CO22 which allows a which allows a

runaway greenhouse effect to occur raising the temperature to runaway greenhouse effect to occur raising the temperature to 470470°C (880°F) planetwide°C (880°F) planetwide

► Its surface pressure in 90 times greater than the Earth and Its surface pressure in 90 times greater than the Earth and there are clouds of sulfuric acid near the surface of the planetthere are clouds of sulfuric acid near the surface of the planet

► TheThe Venus Express Venus Express currently orbits Venuscurrently orbits Venus

Venus




► Earth Earth is only world that we know of that has or had is only world that we know of that has or had life on itlife on it

► It is the only world with a significant amount of It is the only world with a significant amount of oxygen in the atmosphereoxygen in the atmosphere

► It is the only world with significant amounts of liquid It is the only world with significant amounts of liquid waterwater

► It is the closest planet to the Sun to have a moon and It is the closest planet to the Sun to have a moon and our Moon is quite large compared to the Earthour Moon is quite large compared to the Earth

Earth




► Mars Mars may bear the closest resemblance to the Earthmay bear the closest resemblance to the Earth

► It has a thin atmosphere of mostly COIt has a thin atmosphere of mostly CO22

► It has polar caps made of COIt has polar caps made of CO22 and water-ice and water-ice

► In the past, water very likely flowed on the surfaceIn the past, water very likely flowed on the surface► It has great geological wonders such as a great canyon and It has great geological wonders such as a great canyon and

the largest volcano in the solar systemthe largest volcano in the solar system► It has two tiny moonsIt has two tiny moons► It is the most studied extraterrestrial planet and has several It is the most studied extraterrestrial planet and has several

spacecraft spacecraft present and proposed present and proposed to land or orbit Mars.to land or orbit Mars.

Mars

moons



Solar System Roll CallSolar System Roll Call► Jupiter Jupiter is largest planet in the solar system and is made is largest planet in the solar system and is made

mostly of gas with a Earth sized rocky-ice core in the mostly of gas with a Earth sized rocky-ice core in the centercenter

► It has more than 300 times the diameter and 1000 times It has more than 300 times the diameter and 1000 times the volume of the Earththe volume of the Earth

► Its atmosphere has many storms many of which have Its atmosphere has many storms many of which have lasted for hundreds of yearslasted for hundreds of years

► Its four largest moons (of 63) have interesting properties Its four largest moons (of 63) have interesting properties too (active volcanoes, subsurface water, magnetic fields)too (active volcanoes, subsurface water, magnetic fields)

Jupiter

Jupiter2

Gal Moons




► Saturn Saturn is another gaseous giant planet with a is another gaseous giant planet with a spectacular ring systemspectacular ring system

► The ring system is made of millions of ice-dust The ring system is made of millions of ice-dust chunks orbiting around the planetchunks orbiting around the planet

► Saturn has Saturn has 60 moons60 moons, a few of them midsize , a few of them midsize moons and one large one, Titan, which has a moons and one large one, Titan, which has a significant atmosphere.significant atmosphere.

► Currently, Currently, CassiniCassini is orbiting around Saturnis orbiting around Saturn

Saturn



Solar System Roll CallSolar System Roll Call► Uranus (YUR-uh-nus) Uranus (YUR-uh-nus) is a smaller gas giant with a green-blue color is a smaller gas giant with a green-blue color

due to methanedue to methane► It has several dozen moons a few of which are midsizeIt has several dozen moons a few of which are midsize► The entire system (planet, rings, moons) is tilted on their sideThe entire system (planet, rings, moons) is tilted on their side► Neptune Neptune is just a bit smaller than Uranus and bluer in coloris just a bit smaller than Uranus and bluer in color► It has It has aboutabout a dozen moons, one of which is large (Triton). Triton is a dozen moons, one of which is large (Triton). Triton is

the largest moon to go backward the largest moon to go backward (retrograde(retrograde) around the planet) around the planet► Both Neptune and Uranus has been visited by only one spacecraft Both Neptune and Uranus has been visited by only one spacecraft

(Voyager 2)(Voyager 2)

NeptuneUranus

Neptune2Uranus2Neptune3

Uranus3



Solar System Roll CallSolar System Roll Call► Pluto Pluto ((and the otherand the other Dwarf Planets Dwarf Planets)) are round objects which orbit are round objects which orbit

around the Sunaround the Sun► Pluto was discovered as a planet in 1930, but was an oddball world. Pluto was discovered as a planet in 1930, but was an oddball world.

One of its 3 moons is half its size (Charon). It will be visited One of its 3 moons is half its size (Charon). It will be visited by spacecraft in 2015by spacecraft in 2015..

► Soon in the 1990s other objects out where Pluto lived were being Soon in the 1990s other objects out where Pluto lived were being discovered. One of these, Eris, was found to be a little larger than discovered. One of these, Eris, was found to be a little larger than PlutoPluto

► In 2006, the phrase “dwarf planet” was defined for these objects and In 2006, the phrase “dwarf planet” was defined for these objects and asteroids (like Ceres) which were round but were found “nearby” asteroids (like Ceres) which were round but were found “nearby” other solar system objectsother solar system objects

Pluto

Eris

Ceres



Solar System featursSolar System featurs

► Looking at the general characteristics, there Looking at the general characteristics, there are 4 features which stand out:are 4 features which stand out:

1.1. Patterns of motion among large bodiesPatterns of motion among large bodies

2.2. Two major types of planetsTwo major types of planets

3.3. Asteroids and cometsAsteroids and comets

4.4. Exceptions to the rulesExceptions to the rules

StatSheet

StatSheet 2



Distances In The Solar SystemDistances In The Solar System

Measuring Distances in the Solar SystemMeasuring Distances in the Solar System

►Copernicus used geometry to determine Copernicus used geometry to determine relative distances to the planets.relative distances to the planets.

►Today we measure planetary distances Today we measure planetary distances using radar.using radar.

►Average distances to the planets from Average distances to the planets from the Sun range from .387 AU for Mercury the Sun range from .387 AU for Mercury to 39.53 AU for Pluto.to 39.53 AU for Pluto.



Feature 1:Feature 1: Patterns of MotionPatterns of Motion

► All planetary orbits are All planetary orbits are ellipsesellipses, but all are , but all are nearly circular.nearly circular.

► Each of the planets revolves around the Sun Each of the planets revolves around the Sun in the same direction.in the same direction.

► All planets - except Venus, Uranus - rotate in All planets - except Venus, Uranus - rotate in a counterclockwise direction.a counterclockwise direction.

► Most of the satellites revolving around Most of the satellites revolving around planets also move in a counterclockwise planets also move in a counterclockwise direction, though there are some exceptions.direction, though there are some exceptions.

orbits

StatSheet Stat

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Feature 1:Feature 1: Patterns of MotionPatterns of Motion

►InclinationInclination of a planet’s orbit is the angle of a planet’s orbit is the angle between the plane of a planet’s orbit and the between the plane of a planet’s orbit and the ecliptic planeecliptic plane ( (the plane of the Earth’s orbitthe plane of the Earth’s orbit).).

►The elliptical paths of all the planets are The elliptical paths of all the planets are very nearly in the same plane (inclination very nearly in the same plane (inclination about 0°), though Mercury’s orbit is inclined about 0°), though Mercury’s orbit is inclined at 7° and Pluto’s at 17°.at 7° and Pluto’s at 17°.

tilts



Planet DiametersPlanet Diameters

Diameters of Non-Earth PlanetsDiameters of Non-Earth Planets► Diameters are determined from distances (from Diameters are determined from distances (from

the Earth to the planet) and the planet’s angular the Earth to the planet) and the planet’s angular size via the small angle formula size via the small angle formula (Mathematical (Mathematical Insight 2.1) Insight 2.1)

► Diameter of Sun (1.39 Diameter of Sun (1.39 ×× 10 1066 km) is over 100 km) is over 100 times that of Earth (1.3 times that of Earth (1.3 ×× 10 1044 km). km).

► Jupiter’s diameter is 11 times that of Earth.Jupiter’s diameter is 11 times that of Earth.► Pluto’s diameter is 1/5 that of Earth.Pluto’s diameter is 1/5 that of Earth.



Planet MassesPlanet MassesMass of the PlanetsMass of the Planets► Kepler’s third law was reformulated by Newton Kepler’s third law was reformulated by Newton

to include masses to include masses ((Mathematical Insight 4.3Mathematical Insight 4.3):):

aa33//pp22 = = KK ( (MM11 + + MM22))► Newton’s statement of Kepler’s third law allows Newton’s statement of Kepler’s third law allows

us to calculate the mass of the Sun.us to calculate the mass of the Sun.► Consider the orbits of planets around the Sun.Consider the orbits of planets around the Sun.

Since one of the masses to the Sun (the other Since one of the masses to the Sun (the other being a planet), the sum of the two is being a planet), the sum of the two is essentially equal to the mass of the Sun, and essentially equal to the mass of the Sun, and the equation can be rewritten as:the equation can be rewritten as:

aa33//pp22 = = KMKM



Planet MassesPlanet Masses

► We can do the same sort of calculation for We can do the same sort of calculation for planets as long as they have satellites planets as long as they have satellites orbiting themorbiting them

► The masses of 7 of the 9 known planets can The masses of 7 of the 9 known planets can be calculated based on the distances and be calculated based on the distances and periods of revolution of these planets’ natural periods of revolution of these planets’ natural satellites.satellites.

► For Mercury and Venus, which do not For Mercury and Venus, which do not possess any natural satellites, accurate possess any natural satellites, accurate determinations of their respective masses determinations of their respective masses had to await orbiting or flyby space probes.had to await orbiting or flyby space probes.



Feature 2:Feature 2: Classifying the PlanetsClassifying the Planets

► The planets (except Pluto) fit into two groups: The planets (except Pluto) fit into two groups: the inner the inner terrestrial terrestrial planets and the outer planets and the outer JovianJovian planets. planets.

Size, Mass, and DensitySize, Mass, and Density► The Jovian planets have much bigger The Jovian planets have much bigger

diameters and even larger masses than the diameters and even larger masses than the terrestrial planets.terrestrial planets.

► Terrestrial planets are more dense, however.Terrestrial planets are more dense, however.► Earth is the densest planet of them all.Earth is the densest planet of them all.

StatSheet

Insidethe planets

StatSheet 2



Classifying the PlanetsClassifying the Planets

Satellites and RingsSatellites and Rings► The Jovian planets have more satellites than The Jovian planets have more satellites than

the terrestrials.the terrestrials.► 4 Jovian planets: 4 Jovian planets: 163163 total satellites as of total satellites as of

September 2007September 2007 (63 for Jupiter, (63 for Jupiter, 6060 for for Saturn, 27 for Uranus, and 13 for Neptune).Saturn, 27 for Uranus, and 13 for Neptune).

► 4 terrestrial planets: 3 total satellites.4 terrestrial planets: 3 total satellites.► Pluto has 3 satellites. Pluto has 3 satellites. Eris has one satellite.Eris has one satellite.► Each Jovian planet has a ring or ring system. Each Jovian planet has a ring or ring system.

None of the terrestrial planets do.None of the terrestrial planets do.


Terrestrial JovianTerrestrial JovianNear the SunNear the Sun Far from the SunFar from the Sun

SmallSmall LargeLarge

Mostly solidMostly solid Mostly liquid & gasMostly liquid & gas

Low massLow mass Great massGreat mass

Slow rotationSlow rotation Fast rotationFast rotation

No ringsNo rings RingsRings

High densityHigh density Low densityLow density

Thin atmosphereThin atmosphere Dense atmosphereDense atmosphere

FewFew moonsmoons Many moonsMany moons

A comparison of planetary characteristics

StatSheet

StatSheet 2



Feature 3:Feature 3: Asteroids and CometsAsteroids and Comets

AsteroidsAsteroids► These rocky bodies orbit the Sun, but are These rocky bodies orbit the Sun, but are

much smaller than planets. Most lie between much smaller than planets. Most lie between Mars and JupiterMars and Jupiter

CometsComets► Small icy (water, ammonia, methane) objects Small icy (water, ammonia, methane) objects

which occasionally visit the inner solar system which occasionally visit the inner solar system and become visibleand become visible

► Comets originate from two regions: the Kuiper Comets originate from two regions: the Kuiper Belt and the Belt and the ÖÖort Cloudort Cloud

Asteroids

comets



Feature 4:Feature 4: Exceptions to the RulesExceptions to the Rules

► There are objects in the solar system that are There are objects in the solar system that are unusual or have characteristics which are unusual as unusual or have characteristics which are unusual as compared to the rest of the solar system. Some compared to the rest of the solar system. Some examples:examples: Venus and Uranus rotate differently (backwards and on its Venus and Uranus rotate differently (backwards and on its

side, respectively)side, respectively) Small moons of Jupiter and Saturn and the large moon Small moons of Jupiter and Saturn and the large moon

Triton (around Neptune) revolve in the opposite direction of Triton (around Neptune) revolve in the opposite direction of the rotation of the host planet.the rotation of the host planet.

While other terrestrial planets have no moons (Mercury, While other terrestrial planets have no moons (Mercury, Venus) or tiny moons (Mars) The Earth’s moon is large Venus) or tiny moons (Mars) The Earth’s moon is large compared to the Earth.compared to the Earth.

Asteroids

comets



Spacecraft Exploration of the Solar SystemSpacecraft Exploration of the Solar System

► Our knowledge of the solar system has been Our knowledge of the solar system has been dramatically increased by telescopic dramatically increased by telescopic observationsobservations

► We gone to the Moon to directly explore the We gone to the Moon to directly explore the surface and bring back moon rock samplessurface and bring back moon rock samples

► Other samples of the solar system have Other samples of the solar system have come to use via meteoritescome to use via meteorites

► But most of our recent knowledge of the solar But most of our recent knowledge of the solar system has come from robotic spacecraftsystem has come from robotic spacecraft




There are 4 broad categories in which robotic There are 4 broad categories in which robotic mission may be classified:mission may be classified:

► Flyby:Flyby: spacecraft goes by planet once spacecraft goes by planet once► Orbiter:Orbiter: spacecraft orbits planet allowing longer term spacecraft orbits planet allowing longer term

studystudy► Lander or ProbeLander or Probe:: spacecraft lands on planet (or spacecraft lands on planet (or

sends a probe to explore the planet), some may sends a probe to explore the planet), some may have rovers for mobile surveys of the planethave rovers for mobile surveys of the planet

► Sample return missionSample return mission: spacecraft lands gets a : spacecraft lands gets a sample of the surface and takes off to Earthsample of the surface and takes off to Earth

All these mission carry some sort of radio for All these mission carry some sort of radio for communication to and from the Earthcommunication to and from the Earth




Flybys:Flybys:► Generally, the cheapest of the spacecraft typesGenerally, the cheapest of the spacecraft types► Fuel is only used to change the course of the Fuel is only used to change the course of the

spacecraftspacecraft► Some spacecraft such a Some spacecraft such a Voyager 2Voyager 2 use gravity use gravity

assists (gravity slingshots) to help the assists (gravity slingshots) to help the spacecraft change direction and increase spacecraft change direction and increase speedspeed

► They carry telescopes, cameras and They carry telescopes, cameras and spectroscopes.spectroscopes.

Voy 2




Orbiters:Orbiters:► More expensive than flyby mission because they must carry More expensive than flyby mission because they must carry

more fuel so they can get into an orbitmore fuel so they can get into an orbit► Sometimes an orbit may be very large and elliptical and must Sometimes an orbit may be very large and elliptical and must

be changed to get it more circular and closer to the planetbe changed to get it more circular and closer to the planet► Some spacecraft have used a technique of Some spacecraft have used a technique of aerobrakingaerobraking or or

skimming the atmosphere to shrink the orbit to a smaller sizeskimming the atmosphere to shrink the orbit to a smaller size► Orbiters have equipment like flyby spacecraft plus instruments Orbiters have equipment like flyby spacecraft plus instruments

to detect magnetic fields and radar to measure precise to detect magnetic fields and radar to measure precise altitudesaltitudes

► Orbiters have been sent to the Moon, Venus, Mars, Jupiter, Orbiters have been sent to the Moon, Venus, Mars, Jupiter, Saturn and to the asteroid ErosSaturn and to the asteroid Eros




Landers or Probes:Landers or Probes:► One can get the closest to a planet by landing on it or sending a One can get the closest to a planet by landing on it or sending a

probe through the atmosphere.probe through the atmosphere.► GalileoGalileo sent a probe through Jupiter’s atmosphere sending sent a probe through Jupiter’s atmosphere sending

information about temperature, pressure, composition, and radiation information about temperature, pressure, composition, and radiation before the signal was too faint to be detected. It presumably was before the signal was too faint to be detected. It presumably was crushed by the high pressure atmosphere.crushed by the high pressure atmosphere.

► Planets with solid surfaces, landers can provide close up views and Planets with solid surfaces, landers can provide close up views and local weather monitoring. Some landers may have rovers which can local weather monitoring. Some landers may have rovers which can venture across the surface (like Spirit and Opportunity).venture across the surface (like Spirit and Opportunity).

► Landers require more fuel since they must land softly on the Landers require more fuel since they must land softly on the surface, but the spacecraft which brought the rovers “crashed-surface, but the spacecraft which brought the rovers “crashed-landed” on the surface using protective airbags. landed” on the surface using protective airbags.

► Landers have been sent to the Moon, Venus, Mars. A probe went Landers have been sent to the Moon, Venus, Mars. A probe went into Jupiter, and on Titan.into Jupiter, and on Titan.

Spritlanding




Sample Return Mission:Sample Return Mission:► The hardest mission of them all is to land on a The hardest mission of them all is to land on a

surface, gather sample and return home.surface, gather sample and return home.► The only sample return mission are the The only sample return mission are the ApolloApollo

mission to the moon, the Soviet robotic mission to mission to the moon, the Soviet robotic mission to the moon in the early 1970sthe moon in the early 1970s

► A slight variation to this occurred with A slight variation to this occurred with Stardust Stardust which collected comet dust and returned to the which collected comet dust and returned to the EarthEarth

► There are plans to have a sample return mission to There are plans to have a sample return mission to MarsMars




Combination spacecraft:Combination spacecraft:► Many mission have combined more than one type of Many mission have combined more than one type of

spacecraft.spacecraft.► The The VikingViking missions of the 1970s had an orbiter and missions of the 1970s had an orbiter and

two landerstwo landers► The The GalileoGalileo mission had an orbiter and a probe that mission had an orbiter and a probe that

went into the Jupiter atmospherewent into the Jupiter atmosphere► The The CassiniCassini mission had an orbiter and a probe mission had an orbiter and a probe

((HuygensHuygens) that went to Titan) that went to Titan

List of selected robotic missionsList of selected robotic missions

Cassini

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