Our Solar SystemOur Solar SystemChapter 29Chapter 29

All the planets, as well as most of All the planets, as well as most of their moons, also called satellites, their moons, also called satellites, orbit the Sun in the same direction, orbit the Sun in the same direction, and all their orbits, except Pluto’s, lie and all their orbits, except Pluto’s, lie near the same plane. near the same plane.

The planets of our solar system have The planets of our solar system have various sizes, surface conditions, and various sizes, surface conditions, and internal structures. internal structures.

Overview of Our Solar Overview of Our Solar SystemSystem

Earth is one of nine (wrong) eight Earth is one of nine (wrong) eight planets revolving around, or planets revolving around, or orbiting, the Sun. orbiting, the Sun.

Early IdeasEarly Ideas When viewed from Earth, the planets slowly When viewed from Earth, the planets slowly

change position each night relative to the change position each night relative to the position of the stars. position of the stars.

Ancient astronomers assumed that Ancient astronomers assumed that the Sun, planets, and stars orbited a the Sun, planets, and stars orbited a stationary Earth in what is now stationary Earth in what is now known as a geocentric model, known as a geocentric model, meaning “Earth centered.”meaning “Earth centered.”

Early IdeasEarly Ideas Some aspects of planetary motion were difficult Some aspects of planetary motion were difficult

to explain with a geocentric model. to explain with a geocentric model.

– The normal direction of motion for The normal direction of motion for all planets, as observed from Earth, all planets, as observed from Earth, is toward the east. is toward the east.

– Retrograde motionRetrograde motion is when a is when a planet occasionally will move planet occasionally will move toward the west across the sky. toward the west across the sky.

Early IdeasEarly Ideas In 1543, Polish scientist Nicolaus Copernicus In 1543, Polish scientist Nicolaus Copernicus

suggested that the Sun was the center of the suggested that the Sun was the center of the solar system.solar system.

– In a Sun-centered, or heliocentric, model, In a Sun-centered, or heliocentric, model, the inner planets move faster in their the inner planets move faster in their orbits than the outer orbits than the outer planets do. planets do.

– As Earth bypasses a slower-moving outer As Earth bypasses a slower-moving outer planet, it appears that the outer planet planet, it appears that the outer planet temporarily moves backward in the sky.temporarily moves backward in the sky.

Early IdeasEarly IdeasMars appears to Mars appears to move from east to move from east to west (positions 3 west (positions 3 and 4) for a short and 4) for a short time during its time during its retrograde motion. retrograde motion. Retrograde motion Retrograde motion is similar to passing is similar to passing a slower car in the a slower car in the freeway. It appears freeway. It appears that the slower car that the slower car is moving is moving backward relative backward relative to the background. to the background. (not to scale)(not to scale)

Early IdeasEarly Ideas

Kepler’s First LawKepler’s First Law– From 1576–1601, Danish astronomer From 1576–1601, Danish astronomer

Tycho Brahe made accurate observations Tycho Brahe made accurate observations of planetary positions. of planetary positions.

– Using Brahe’s data, Johannes Kepler Using Brahe’s data, Johannes Kepler demonstrated his first law which states demonstrated his first law which states that each planet orbits the Sun in a shape that each planet orbits the Sun in a shape called an ellipse.called an ellipse.

– An ellipse is an oval shape that is An ellipse is an oval shape that is centered on two points called the foci centered on two points called the foci instead of a single point, as in a circle. instead of a single point, as in a circle.

Early IdeasEarly Ideas

Kepler’s First LawKepler’s First Law– The major axis, the maximum diameter of The major axis, the maximum diameter of

the ellipse, is the line that runs through the ellipse, is the line that runs through both foci, one of which is always the Sun.both foci, one of which is always the Sun.

Early IdeasEarly Ideas

Kepler’s First LawKepler’s First Law– An An astronomical unitastronomical unit (AU), 1.496 (AU), 1.496 ×× 10 1088

km, is the average distance between the km, is the average distance between the Sun and Earth. Sun and Earth. – The average distances between the Sun The average distances between the Sun

and each planet are measured in and each planet are measured in astronomical units.astronomical units.

Early IdeasEarly Ideas

Kepler’s Second and Third LawsKepler’s Second and Third Laws– Kepler’s second law states that because a Kepler’s second law states that because a

planet moves fastest when close to the planet moves fastest when close to the Sun and slowest when far from the Sun, Sun and slowest when far from the Sun, equal areas equal areas are swept out in equal are swept out in equal amount of time. amount of time.

Early IdeasEarly Ideas– Italian scientist Galileo Galilei proved, by Italian scientist Galileo Galilei proved, by

discovering four moons orbiting the discovering four moons orbiting the planet Jupiter, that not all celestial bodies planet Jupiter, that not all celestial bodies orbit Earth, and therefore, Earth is not orbit Earth, and therefore, Earth is not necessarily the center of the solar system. necessarily the center of the solar system. – In 1684, English scientist Isaac Newton In 1684, English scientist Isaac Newton

published a mathematical and physical published a mathematical and physical explanation of the motions explanation of the motions of celestial bodies. of celestial bodies.

Gravity and OrbitsGravity and Orbits Through observations, Newton realized that Through observations, Newton realized that

any two bodies attract each other with a force any two bodies attract each other with a force that depends on their masses and the distance that depends on their masses and the distance between the two bodies. between the two bodies.

The force grows stronger in The force grows stronger in proportion to the product of the two proportion to the product of the two masses, but diminishes as the square masses, but diminishes as the square of the distance between them of the distance between them increases. increases.

Gravity and OrbitsGravity and Orbits

GravityGravity– Newton’s law of universal gravitation Newton’s law of universal gravitation

states that every pair of bodies in the states that every pair of bodies in the universe attract each other with a force universe attract each other with a force that is proportional to the product of their that is proportional to the product of their masses and inversely proportional to the masses and inversely proportional to the square of the distance between them.square of the distance between them.

The Terrestrial PlanetsThe Terrestrial Planets The nine (wrong) eight planets of The nine (wrong) eight planets of

our solar system can be grouped into our solar system can be grouped into two main categories according to two main categories according to their basic properties. their basic properties. – The The terrestrial planetsterrestrial planets are the inner are the inner

four planets of Mercury, Venus, Earth, four planets of Mercury, Venus, Earth, and Mars that are close to the size of and Mars that are close to the size of Earth and have solid, rocky surfaces. Earth and have solid, rocky surfaces.

– The The gas giant planetsgas giant planets are the outer are the outer planets of Jupiter, Saturn, Uranus, and planets of Jupiter, Saturn, Uranus, and Neptune which are much larger, more Neptune which are much larger, more gaseous, and lack solid surfaces. gaseous, and lack solid surfaces.

MercuryMercury Mercury is the closest planet to the Mercury is the closest planet to the

Sun and has no moons. Sun and has no moons. Mercury is about Mercury is about

one-third the size of one-third the size of Earth and has a Earth and has a smaller mass and smaller mass and radius. radius.

Mercury has a slow Mercury has a slow spin of 1407.6 spin of 1407.6 hours; in two of hours; in two of Mercury’s years, Mercury’s years, three of Mercury’s three of Mercury’s days have passed.days have passed.

MercuryMercury

AtmosphereAtmosphere– Mercury has essentially Mercury has essentially

no atmosphere, and what little does exist is no atmosphere, and what little does exist is composed primarily of oxygen and sodium. composed primarily of oxygen and sodium.

– The daytime surface temperature on Mercury The daytime surface temperature on Mercury is 700 K (427ºC), while temperatures at night fall is 700 K (427ºC), while temperatures at night fall to 100 K (–173ºC).to 100 K (–173ºC).

MercuryMercury

SurfaceSurface– Most of what we know about Mercury is based on radio observations and images from a United States space probe mission, called Most of what we know about Mercury is based on radio observations and images from a United States space probe mission, called Mariner 10Mariner 10. . – Mercury’s surface is covered with craters and plains. Mercury’s surface is covered with craters and plains. – The plains of Mercury’s surface are smooth and relatively crater free. The plains of Mercury’s surface are smooth and relatively crater free. – Mercury has a planetwide system of cliffs, called scarps, that may have developed as Mercury’s crust shrank and fractured early in the planet’s geological Mercury has a planetwide system of cliffs, called scarps, that may have developed as Mercury’s crust shrank and fractured early in the planet’s geological

history.history.

MercuryMercury

InteriorInterior– The high density of Mercury suggests that it has an extensive nickel-iron core, filling about 42 percent of Mercury’s volume. The high density of Mercury suggests that it has an extensive nickel-iron core, filling about 42 percent of Mercury’s volume. – The detectable magnetic field suggests that Mercury has a molten zone in its interior. The detectable magnetic field suggests that Mercury has a molten zone in its interior. – Mercury’s small size, high density, and probable molten interior zone resemble what Earth might be like if its crust and Mercury’s small size, high density, and probable molten interior zone resemble what Earth might be like if its crust and

mantle were removed. mantle were removed.

MercuryMercury

VenusVenus Venus, the second planet Venus, the second planet

from the Sun, has no moons. from the Sun, has no moons.

Venus’s high albedo (brightness) Venus’s high albedo (brightness)

and its proximity to Earth make it the and its proximity to Earth make it the brightest planet in Earth’s nighttime brightest planet in Earth’s nighttime sky.sky.

The surface of Venus is very hot, and The surface of Venus is very hot, and it rotates slowly counterclockwise it rotates slowly counterclockwise with one day equaling with one day equaling 243 Earth days. 243 Earth days.

Venus has been explored by radar and Venus has been explored by radar and

spacecraft. spacecraft.

VenusVenusAtmosphereAtmosphere

– Venus is the hottest planet in the solar system with an average surface temperature of about 737 K (464°C).Venus is the hottest planet in the solar system with an average surface temperature of about 737 K (464°C).– The atmospheric pressure on The atmospheric pressure on

Venus is equivalent to Venus is equivalent to 92 Earth atmospheres. 92 Earth atmospheres.

– An efficient greenhouse effect An efficient greenhouse effect is achieved with an atmosphere is achieved with an atmosphere that is primarily carbon dioxide that is primarily carbon dioxide and nitrogen with clouds of and nitrogen with clouds of sulfuric acid.sulfuric acid.

VenusVenusSurfaceSurface

– The 1989 The 1989 MagellanMagellan missions of the United States used radar reflection measurements to map the surface of Venus in detail. missions of the United States used radar reflection measurements to map the surface of Venus in detail. – The surface has been smoothed by volcanic lava flows, and it has only a few impact craters. The surface has been smoothed by volcanic lava flows, and it has only a few impact craters. – The most recent global episode of volcanic activity took place about 500 million years ago.The most recent global episode of volcanic activity took place about 500 million years ago.– There is little evidence of current tectonic activity There is little evidence of current tectonic activity

on Venus, and there is no well-defined system of on Venus, and there is no well-defined system of crustal plates.crustal plates.

VenusVenusInteriorInterior

– The size and density of Venus are similar to Earth, so the internal structure is most likely similar. The size and density of Venus are similar to Earth, so the internal structure is most likely similar. – It is theorized that Venus has a liquid metal core that extends halfway to the surface. It is theorized that Venus has a liquid metal core that extends halfway to the surface. – There is no measurable magnetic field despite this liquid core, which is probably due to Venus’s slow rotation rate.There is no measurable magnetic field despite this liquid core, which is probably due to Venus’s slow rotation rate.

VenusVenus

EarthEarth Earth, the third planet from the Sun, Earth, the third planet from the Sun,

has many unique properties.has many unique properties.– Its distance from the Sun Its distance from the Sun

and its nearly circular orbit and its nearly circular orbit allow liquid water to exist allow liquid water to exist on its surface in all three on its surface in all three states: solid, liquid, and states: solid, liquid, and gas. gas.

– Liquid water is required for Liquid water is required for life.life.

– Earth’s moderately dense Earth’s moderately dense atmosphere (78 percent atmosphere (78 percent nitrogen and 21 percent nitrogen and 21 percent oxygen) and a mild oxygen) and a mild greenhouse effect support greenhouse effect support conditions suitable for life.conditions suitable for life.

MarsMars Mars is the fourth Mars is the fourth

planet planet from the Sun and the from the Sun and the outermost of the outermost of the terrestrial terrestrial planets. planets.

Mars is smaller and less Mars is smaller and less dense than Earth and has dense than Earth and has two irregularly-shaped two irregularly-shaped moons, Phobos and Deimos.moons, Phobos and Deimos.

Mars has been explored by Mars has been explored by telescopes on Earth and with probes telescopes on Earth and with probes beginning in the 1960s that have beginning in the 1960s that have flown by, orbited, or landed. flown by, orbited, or landed.

MarsMarsAtmosphereAtmosphere

– The composition of Mars’s atmosphere is similar to Venus’s atmosphere, but The composition of Mars’s atmosphere is similar to Venus’s atmosphere, but with much lower density with much lower density and pressure.and pressure.

– The thin atmosphere is turbulent, which creates a The thin atmosphere is turbulent, which creates a constant wind on Mars. constant wind on Mars.

– Martian dust storms may last for weeks at a time. Martian dust storms may last for weeks at a time.

MarsMarsSurfaceSurface

– The southern hemisphere of Mars is a heavily cratered, highland region, while the northern hemisphere is dominated by plains that are sparsely cratered. The southern hemisphere of Mars is a heavily cratered, highland region, while the northern hemisphere is dominated by plains that are sparsely cratered. – Four gigantic shield volcanoes including Olympus Mons, the largest mountain in the solar system, are located in the northern hemisphere. Four gigantic shield volcanoes including Olympus Mons, the largest mountain in the solar system, are located in the northern hemisphere. – The Martian surface contains erosional features that suggest that liquid water once existed on the surface The Martian surface contains erosional features that suggest that liquid water once existed on the surface

of Mars.of Mars.– Mars has polar ice caps of frozen carbon dioxide covering both poles that grow and shrink with the seasons on Mars. Water ice lies beneath the northern cap.Mars has polar ice caps of frozen carbon dioxide covering both poles that grow and shrink with the seasons on Mars. Water ice lies beneath the northern cap.

MarsMarsInteriorInterior

– Astronomers are unsure about the internal structure Astronomers are unsure about the internal structure of Mars. of Mars.

– It is thought to have a core of iron and nickel, and possibly sulfur which is covered by a mantle. It is thought to have a core of iron and nickel, and possibly sulfur which is covered by a mantle. – Because Mars has no magnetic field, the core is probably solid. Because Mars has no magnetic field, the core is probably solid. – There is no evidence of current tectonic activity or tectonic plates on the surface of the crust. There is no evidence of current tectonic activity or tectonic plates on the surface of the crust.

MarsMars

The Gas Giant Planets The Gas Giant Planets The interiors of the gas giant planets The interiors of the gas giant planets

are composed of fluids, either are composed of fluids, either gaseous or liquid, and possibly gaseous or liquid, and possibly small, solid cores. small, solid cores. They are composed primarily of They are composed primarily of lightweight elements such as lightweight elements such as hydrogen, helium, carbon, nitrogen, hydrogen, helium, carbon, nitrogen, and oxygen, and they are very cold and oxygen, and they are very cold at their surfaces. at their surfaces.

The gas giants have many satellites The gas giants have many satellites as well as ring systems, and they are as well as ring systems, and they are all very large.all very large.

JupiterJupiter Jupiter is the largest planet, Jupiter is the largest planet,

making up 70 percent of all making up 70 percent of all planetary matter in our solar planetary matter in our solar system, and system, and the fifth planet from the Sun.the fifth planet from the Sun. Jupiter has a banded appearance as a result Jupiter has a banded appearance as a result

of flow patterns in its atmosphere. of flow patterns in its atmosphere. Jupiter has four major satellites in addition Jupiter has four major satellites in addition

to at least 12 smaller ones.to at least 12 smaller ones. Jupiter has been explored by several United Jupiter has been explored by several United

States space probes which detected States space probes which detected volcanic activity on Jupiter’s closest major volcanic activity on Jupiter’s closest major moon, Io.moon, Io.

JupiterJupiterAtmosphereAtmosphere

– Jupiter has a low density, 1326 kg/mJupiter has a low density, 1326 kg/m33, for its huge size because it is composed of lightweight elements. , for its huge size because it is composed of lightweight elements.

– Hydrogen and helium make up the Hydrogen and helium make up the majority of Jupiter’s atmospheric gas. majority of Jupiter’s atmospheric gas.

– Below the liquid hydrogen, there is Below the liquid hydrogen, there is a layer of liquid metallic hydrogen.a layer of liquid metallic hydrogen.

– Liquid metallic hydrogenLiquid metallic hydrogen is a form of hydrogen that has properties of both a is a form of hydrogen that has properties of both a liquid and a metal, which can exist only under conditions of very high pressure. liquid and a metal, which can exist only under conditions of very high pressure.

JupiterJupiterAtmosphereAtmosphere– Electric currents flow within the layer of liquid metallic Electric currents flow within the layer of liquid metallic

hydrogen and generate Jupiter’s magnetic field.hydrogen and generate Jupiter’s magnetic field.

– At less than 10 hours, Jupiter has the shortest day in the solar system. At less than 10 hours, Jupiter has the shortest day in the solar system.

– Jupiter’s rapid rotation causes its clouds to flow rapidly in alternating cloud types called Jupiter’s rapid rotation causes its clouds to flow rapidly in alternating cloud types called belts and zones. belts and zones.

– Jupiter’s Great Red Spot is a storm that has been rotating around Jupiter for more than 300 years. Jupiter’s Great Red Spot is a storm that has been rotating around Jupiter for more than 300 years.

JupiterJupiterMoons and RingsMoons and Rings

– Jupiter’s four largest moons, Io, Europa, Ganymede, and Callisto, are called Galilean satellites. Jupiter’s four largest moons, Io, Europa, Ganymede, and Callisto, are called Galilean satellites.

– Io has been heated by Jupiter’s gravitational force to the point of becoming almost completely molten inside and undergoes constant volcanic eruptions. Io has been heated by Jupiter’s gravitational force to the point of becoming almost completely molten inside and undergoes constant volcanic eruptions.

– Astronomers hypothesize that Europa has a subsurface ocean of liquid water. Astronomers hypothesize that Europa has a subsurface ocean of liquid water.

– Jupiter, like the other three gas giant planets, Jupiter, like the other three gas giant planets, has rings. has rings.

JupiterJupiter

SaturnSaturn

Saturn is the sixth Saturn is the sixth planet from the Sun planet from the Sun and the second-and the second-largest planet in the largest planet in the solar system. solar system.

In 2004, the United States In 2004, the United States CassiniCassini mission, mission, launched in 1997, become the fifth probe to launched in 1997, become the fifth probe to visit the planet.visit the planet.

It will also release a probe into the It will also release a probe into the atmosphere of Titan, Saturn’s largest moon, atmosphere of Titan, Saturn’s largest moon, to explore surface conditions there.to explore surface conditions there.

SaturnSaturnAtmosphereAtmosphere– Saturn is not quite as large as Jupiter and has an average density that is lower than that of water. Saturn is not quite as large as Jupiter and has an average density that is lower than that of water.

– Saturn rotates rapidly for its size Saturn rotates rapidly for its size and has flowing belts and zones. and has flowing belts and zones.

– Saturn’s atmosphere is Saturn’s atmosphere is dominated by hydrogen dominated by hydrogen and helium but it also and helium but it also includes ammonia ice. includes ammonia ice.

SaturnSaturnInteriorInterior– The internal structure of Saturn is most likely fluid The internal structure of Saturn is most likely fluid

throughout with a small, solid core.throughout with a small, solid core.

– Saturn’s strong magnetic field is aligned with its Saturn’s strong magnetic field is aligned with its rotational axis, which is unusual among the planets.rotational axis, which is unusual among the planets.

SaturnSaturnMoons and RingsMoons and Rings

– Saturn’s ring system has much broader and brighter rings than those of the other gas giant planets. Saturn’s ring system has much broader and brighter rings than those of the other gas giant planets.

– There are seven major rings composed of narrower rings, called ringlets, and many open gaps. There are seven major rings composed of narrower rings, called ringlets, and many open gaps.

– The rings are less than 200 m thick, and are aligned with Saturn’s equatorial plane. The rings are less than 200 m thick, and are aligned with Saturn’s equatorial plane.

– The ring particles are probably debris left over when The ring particles are probably debris left over when a moon was destroyed either by a collision or a moon was destroyed either by a collision or Saturn’s gravity. Saturn’s gravity.

SaturnSaturn

Moons and RingsMoons and Rings– The 18 known satellites of Saturn include the giant Titan, seven The 18 known satellites of Saturn include the giant Titan, seven

intermediate-sized moons, and a number of small moons. intermediate-sized moons, and a number of small moons.

– Titan is larger than Earth’s moon, and its atmosphere Titan is larger than Earth’s moon, and its atmosphere is made of nitrogen and methane. is made of nitrogen and methane.

SaturnSaturn

UranusUranus

The seventh planet from The seventh planet from the Sun, Uranus, was the Sun, Uranus, was discovered accidentally in discovered accidentally in 1781. 1781.

Uranus has at least 18 moons and 10 rings. Uranus has at least 18 moons and 10 rings. In 1986, the United States In 1986, the United States Voyager 2Voyager 2

mission visited Uranus. mission visited Uranus.

UranusUranusAtmosphereAtmosphere– Uranus is 4 times as large and 15 times as massive as Earth and has a blue, velvety appearance.Uranus is 4 times as large and 15 times as massive as Earth and has a blue, velvety appearance.

– Uranus’s atmosphere is Uranus’s atmosphere is composed of helium and composed of helium and hydrogen and methane gas hydrogen and methane gas and has no distinct belts and has no distinct belts or zones. or zones.

–Uranus’s atmosphere keeps Uranus’s atmosphere keeps the planet at a temperature of the planet at a temperature of 58 K (–215°C).58 K (–215°C).

UranusUranusInteriorInterior

– Its internal structure is completely fluid except for Its internal structure is completely fluid except for a small, solid core and a small, solid core and it has a strong magnetic field. it has a strong magnetic field.

– The rotational axis of Uranus is tipped over so far that the north pole almost lies in its orbital plane.The rotational axis of Uranus is tipped over so far that the north pole almost lies in its orbital plane.

UranusUranus

Moons and RingsMoons and Rings– The known moons and rings of Uranus orbit in the planet’s equatorial plane. The known moons and rings of Uranus orbit in the planet’s equatorial plane.

– New moons are frequently being discovered causing frequent changes in the count. New moons are frequently being discovered causing frequent changes in the count.

– Uranus’s rings are very dark—almost black.Uranus’s rings are very dark—almost black.

NeptuneNeptune

The existence of The existence of Neptune Neptune was predicted, based on was predicted, based on small deviations in the small deviations in the motion of Uranus, before motion of Uranus, before

it was discovered. it was discovered.

In 1846, Neptune was discovered In 1846, Neptune was discovered where astronomers had predicted it. where astronomers had predicted it.

The The Voyager 2Voyager 2 probe flew past probe flew past Neptune in 1989.Neptune in 1989.

NeptuneNeptuneAtmosphereAtmosphere

– Neptune is slightly smaller and denser than Uranus, but it is still about four times as large as Earth.Neptune is slightly smaller and denser than Uranus, but it is still about four times as large as Earth.

– Other similarities between Other similarities between Neptune and Uranus include Neptune and Uranus include their bluish color, atmospheric their bluish color, atmospheric compositions, temperatures, compositions, temperatures, magnetic fields, interiors, magnetic fields, interiors, and particle belts.and particle belts.

– Neptune does have distinctive clouds and Neptune does have distinctive clouds and atmospheric belts and zones similar to those atmospheric belts and zones similar to those of Jupiter and Saturn. of Jupiter and Saturn.

NeptuneNeptuneMoons and RingsMoons and Rings

– Neptune has many moons, the largest being Triton. Neptune has many moons, the largest being Triton.

– Triton has a retrograde orbit, which means that it orbits backward, unlike virtually every other large satellite in the solar system. Triton has a retrograde orbit, which means that it orbits backward, unlike virtually every other large satellite in the solar system.

– Triton also has a thin atmosphere and nitrogen geysers. Triton also has a thin atmosphere and nitrogen geysers.

– Neptune has six rings that are composed of microscopic-sized dust particles. Neptune has six rings that are composed of microscopic-sized dust particles.

Uranus & NeptuneUranus & Neptune

PlutoPluto Pluto was discovered in 1930. Pluto was discovered in 1930.

Pluto is very different from the other Pluto is very different from the other eight planets of our solar system and eight planets of our solar system and does not fit into either the terrestrial does not fit into either the terrestrial group or gas giant group.group or gas giant group.

The density of Pluto indicates that it is The density of Pluto indicates that it is made of half ice and half rock, and it made of half ice and half rock, and it is smaller than is smaller than Earth’s moon. Earth’s moon.

The atmosphere is composed of The atmosphere is composed of methane and nitrogen, but in methane and nitrogen, but in unknown quantities. unknown quantities.

PlutoPluto The orbit of Pluto is every elliptical. The orbit of Pluto is every elliptical.

Moveing from 30 AU to 50 AU from the Sun. Moveing from 30 AU to 50 AU from the Sun.

Pluto’s satellite, Charon, orbits in Pluto’s satellite, Charon, orbits in synchronous rotation at Pluto’s synchronous rotation at Pluto’s equatorial plane. equatorial plane.

Many of Pluto’s properties are more Many of Pluto’s properties are more similar to those of the gas giants’ similar to those of the gas giants’ large moons than they are to those of large moons than they are to those of any other planet. any other planet.

PlutoPluto

Formation of Our Solar Formation of Our Solar SystemSystem

Astronomers use Earth-based Astronomers use Earth-based observations and data from probes observations and data from probes to derive theories about how our to derive theories about how our solar system formed. solar system formed.

The significant observations related The significant observations related to our solar system’s formation to our solar system’s formation include the shape of our solar include the shape of our solar system, the differences among the system, the differences among the planets, and the oldest planetary planets, and the oldest planetary surfaces, asteroids, meteorites, and surfaces, asteroids, meteorites, and comets.comets.

A Collapsing Interstellar A Collapsing Interstellar CloudCloud

Stars and planets form from clouds of Stars and planets form from clouds of gas and dust, called interstellar clouds, gas and dust, called interstellar clouds, which exist in space between the stars which exist in space between the stars and consist mostly og hydrogen and and consist mostly og hydrogen and helium. helium. Our solar system may have begun Our solar system may have begun when interstellar gas started to when interstellar gas started to condense as a result of gravity and condense as a result of gravity and became concentrated enough to became concentrated enough to form the Sun and planets. form the Sun and planets.

A Collapsing Interstellar A Collapsing Interstellar CloudCloud

DON’T WRITE THIS DOWNDON’T WRITE THIS DOWN– The collapse is initially slow, but it The collapse is initially slow, but it

accelerates and the cloud soon becomes accelerates and the cloud soon becomes much denser at its center. much denser at its center.

– Rotation slows the collapse in the Rotation slows the collapse in the equatorial plane, equatorial plane, and the cloud becomes flattened. and the cloud becomes flattened.

– The cloud eventually becomes a rotating The cloud eventually becomes a rotating disk with a dense concentration at the disk with a dense concentration at the center.center.

Sun and Planet Sun and Planet FormationFormation

Elements and Elements and compounds that were compounds that were able to condense close able to condense close to the Sun, where it to the Sun, where it was warm, are called was warm, are called refractory elements, refractory elements, and far from the Sun, and far from the Sun, where it was cool, where it was cool, volatile elements could volatile elements could condense. Refractory condense. Refractory elements, such as iron, elements, such as iron, comprise the comprise the terrestrial planets, terrestrial planets, which are close to the which are close to the Sun. Volatile elements, Sun. Volatile elements, such as ices and gases such as ices and gases like hydrogen, like hydrogen, comprise the planets comprise the planets further from the Sun, further from the Sun, where it is cool.where it is cool.

Sun and Planet Sun and Planet FormationFormationThe Growth of ObjectsThe Growth of Objects

– Once the condensing slowed, the tiny grains of condensed material Once the condensing slowed, the tiny grains of condensed material started to accumulate and merge together to form larger bodies. started to accumulate and merge together to form larger bodies.

– PlanetesimalsPlanetesimals formed as smaller particles collided formed as smaller particles collided and stuck together. and stuck together.

– Further growth continued through collisions and mergers of planetesimals resulting in a smaller number of Further growth continued through collisions and mergers of planetesimals resulting in a smaller number of larger bodies: the planets.larger bodies: the planets.

Sun and Planet Sun and Planet FormationFormation

Merging into PlanetsMerging into Planets– Jupiter was the first large planet to develop in the Jupiter was the first large planet to develop in the

outer solar system.outer solar system.

– The inner planets also formed by the merging of The inner planets also formed by the merging of planetesimals.planetesimals.

– The Sun’s gravitational force is theorized to have The Sun’s gravitational force is theorized to have swept up much of the gas in the area of the inner planets, preventing them from acquiring much additional swept up much of the gas in the area of the inner planets, preventing them from acquiring much additional material. material.

– The inner planets initially ended up with no satellites. The inner planets initially ended up with no satellites.

Sun and Planet Sun and Planet FormationFormation

DebrisDebris– The amount of interplanetary debris thinned out as it crashed into planets or was diverted out of the solar system. The amount of interplanetary debris thinned out as it crashed into planets or was diverted out of the solar system.

– The planetesimals in the area between Jupiter and Mars, known as the asteroid belt, remained there because The planetesimals in the area between Jupiter and Mars, known as the asteroid belt, remained there because Jupiter’s gravitational force prevented them from merging to form a planet.Jupiter’s gravitational force prevented them from merging to form a planet.

Planet FormationPlanet Formation

AsteroidsAsteroids AsteroidsAsteroids comprise the thousands and comprise the thousands and

thousands of bodies that orbit the Sun within the thousands of bodies that orbit the Sun within the planetary orbits that are leftovers from the planetary orbits that are leftovers from the formation of the solar system. formation of the solar system.

Asteroids range from a few Asteroids range from a few kilometers to about 1000 km in kilometers to about 1000 km in diameter and have pitted, irregular diameter and have pitted, irregular surfaces. surfaces.

Most asteroids are located between Most asteroids are located between the orbits of Mars and Jupiter within the orbits of Mars and Jupiter within the asteroid belt. the asteroid belt.

AsteroidsAsteroidsPieces of AsteroidsPieces of Asteroids– As the asteroids orbit, they occasionally collide and As the asteroids orbit, they occasionally collide and

break into fragments. break into fragments. A A meteoroidmeteoroid is a asteroid fragment or any other interplanetary is a asteroid fragment or any other interplanetary

material that falls toward Earth and enters Earth’s atmosphere.material that falls toward Earth and enters Earth’s atmosphere.

A A meteormeteor is the streak of light produced when a is the streak of light produced when a meteoroid burns up in Earth’s atmosphere. meteoroid burns up in Earth’s atmosphere.

A A meteoritemeteorite is part of a meteoroid, that does not is part of a meteoroid, that does not completely burn up, that collides with the ground. completely burn up, that collides with the ground.

CometsComets CometsComets are small, icy bodies that have highly are small, icy bodies that have highly

eccentric orbits around the Sun and are remnants eccentric orbits around the Sun and are remnants from solar system formation.from solar system formation.

Comets are made of ice and rock, Comets are made of ice and rock, and they range from 1 to 10 km in and they range from 1 to 10 km in diameter. diameter.

CometsCometsThe Orbits of CometsThe Orbits of Comets

– When a comet nears the sun in its highly eccentric orbit, it begins to evaporate and form a head and one or more tails.When a comet nears the sun in its highly eccentric orbit, it begins to evaporate and form a head and one or more tails.

– The The comacoma is an extended is an extended volume of glowing gas volume of glowing gas flowing from a comet’s head.flowing from a comet’s head.

– The The nucleusnucleus of a comet is the small solid core of a comet is the small solid core that releases gases and dust particles that that releases gases and dust particles that form the coma and tails when it is heated. form the coma and tails when it is heated.

CometsCometsPeriodic CometsPeriodic Comets

– Comets that repeatedly orbit into the inner solar system are known as periodic comets. Comets that repeatedly orbit into the inner solar system are known as periodic comets.

– Meteor showers Meteor showers occur when Earth intersects a cometary orbit and numerous particles from occur when Earth intersects a cometary orbit and numerous particles from the comet burn up upon entering Earth’s upper atmosphere.the comet burn up upon entering Earth’s upper atmosphere.

– Most meteors are caused by dust particles from comets, while most meteorites, Most meteors are caused by dust particles from comets, while most meteorites, the solid chunks of rock or metal that reach Earth’s surface, are fragments of the solid chunks of rock or metal that reach Earth’s surface, are fragments of asteroids.asteroids.

Comets and MeteorsComets and Meteors