Lecture 2: Course Overview Introduction to the Solar System

Home , 1862 Apollo, 433 Eros, Concentric spheres

AST2003 Section 6218 - Spring 2012

Instructor: Professor Stanley F. Dermott

Office: 216 Bryant Space Science Center

Phone: 352 294 1864

email [email protected]

Lecture time and place: Tuesdays (4th period: 10:40 am – 11:30 am)

Thursdays (4th and 5th period) (10:40 am – 12:35

pm), FLG 210

Office hours: Tuesdays 11:45 – 12:45 pm,

Thursdays 12:45 pm - 1:45 pm

or by appointment

Teacher Assistant: Dr Naibi Marinas (Help with Mastering Astronomy and

Exam Reviews)

Office: 312 Bryant Space Science Center

Phone: 325 294 1848

Email: [email protected]!!

Class Website: http://www.astro.ufl.edu/~marinas/astro/AST2003.html A bit about myself Russian Translation Worked with Carl Sagan while at Cornell Carl Sagan: Author and presenter of COSMOS Two papers in Nature

Radar images of hydrocarbon lakes on Titan taken by Cassini spacecraft

This movie, comprised of several detailed images taken by Cassini's radar instrument, shows bodies of liquid near Titan's north pole. Biggest Discovery!

Published in Nature in 1994

Structure in Debris DebrisDisks disks imply >km planetesimals around Debris disks imply >km main sequence stars, but planetesimals around also evidence for planets: main sequence stars, but •! inner regions are empty, also evidence for planets: probably cleared by planet formation •! inner regions are empty, probably cleared by •! disks are clumpy/ planet formation asymmetric, probably caused by unseen •! disks are clumpy/ equivalent of Neptune asymmetric, probably caused by unseen Planets are lower mass equivalent of Neptune and further out than those detected with other means

Planets are lower mass and further out than those detected with other means OVERVIEW OF THE COURSE spring 2012 calendar

This is a tentative schedule and it will change !!

! January

10 - Introduction and course Overview!

12 - course overview

17 - charting the heavens (chapter 1)

19 - charting the heavens!! (Chapter 1)

24 - the copernican revolution!!! (Chapter 2)

26 - the copernican revolution!!! (Chapter 2)

31 - radiation!!! (Chapter 3)

February

02 - spectroscopy and telescopes!!! (Chapters 4 & 5)

07 - review exam 1

09 - exam 1 (Chapters 1-5) 1. Evolving perspectives - a historical prologue

• The wandering planets move in a narrow track against the unchanging background stars, and some of these vagabonds can suddenly turn around, apparently moving in the opposite direction before continuing on their usual course.

• The ancient Greeks noticed that the Earth always casts a curved shadow on the Moon during a lunar eclipse, demonstrating that our planet is a sphere.

• For centuries, astronomers tried to describe the observed planetary motions using uniform, circular motions with the stationary Earth at the center and with the distant celestial sphere revolving about the Earth once a day.

• Around 145 AD, Claudius Ptolemy devised an intricate system of uniform motion around small and large circles to model the motions of the Sun, Moon and planets around a stationary Earth; his model was used to predict their location in the sky for more than a thousand years. 1. Evolving perspectives - a historical prologue • The stars seem to be revolving around the Earth each night, but the Earth is • Theinstead wandering spinning planets beneath move the in stars. a narrow This trackrotation against also thecauses unchanging the Sun to move backgroundacross the sky stars, each and day. some of these vagabonds can suddenly turn around, apparently moving in the opposite direction before continuing on their usual • course.Mikolaj Kopernik, better known as Nicolaus Copernicus, argued in 1543 that the Earth is just one of several planets that are whirling endlessly about the Sun, • Theall movingancient inGreeks the same noticed direction that the but Earth at different always castsdistances a curved from shadow the Sun on and the with Moonspeeds during that decrease a lunar eclipse, with increasing demonstrating distance. that our planet is a sphere.

•• ForAlmost centuries, four centuriesastronomers ago, tried Johannes to describe Kepler the used observed accurate planetary observations, motions usingobtained uniform, by Tycho circular Brahe, motions to conclude with the that stationary the planets Earth move at the in center ellipses, and or with ovals, thewith distant the Sun celestial at one sphere focus, revolving and to infer about a precise the Earth mathematical once a day. relation between the mean orbital distance and period of each planet. • Around 145 AD, Claudius Ptolemy devised an intricate system of uniform • motionMore distantaround planets small and take large longer circles to move to model once the around motions the of Sun the and Sun, they Moon move andwith planets slower around speeds; a theirstationary orbital Earth; periods his are model in proportion was used to to predict the cubes their of their locationdistances. in the sky for more than a thousand years.

•• TheAstronomy stars seem is anto beinstrument-driven revolving around science the Earth in which each night, novel buttelescopes the Earth and is new insteadtechnology spinning enable beneath us to discoverthe stars. cosmic This rotation objects alsothat causesare otherwise the Sun invisibleto move and acrosshitherto the unknown. sky each day.

•• MikolajMany major Kopernik, astronomical better known discoveries as Nicolaus have Copernicus,been unanticipated argued andin 1543 that theserendipitous, Earth is just made one of while several new planets telescopes that arewere whirling used to endlessly study other, about known the Sun, allcosmic moving objects; in the thesame earliest direction of these but ataccidental different discoveries distances from include the theSun four and largewith speedsmoons that of Jupiter, decrease the with planet increasing Uranus, distance. and the ﬁrst known asteroid, Ceres,

• Almost four centuries ago, Johannes Kepler used accurate observations, obtained by Tycho Brahe, to conclude that the planets move in ellipses, or ovals, with the Sun at one focus, and to infer a precise mathematical relation between the mean orbital distance and period of each planet.

• More distant planets take longer to move once around the Sun and they move with slower speeds; their orbital periods are in proportion to the cubes of their distances.

• Astronomy is an instrument-driven science in which novel telescopes and new technology enable us to discover cosmic objects that are otherwise invisible and hitherto unknown.

• Many major astronomical discoveries have been unanticipated and serendipitous, made while new telescopes were used to study other, known cosmic objects; the earliest of these accidental discoveries include the four large moons of Jupiter, the planet Uranus, and the ﬁrst known asteroid, Ceres,

The Geocentric Paradigm Below is an image of the universe as conceived of by Aristotle and Ptolemy.!

The earth is composed of four elements:! Earth, Water, Fire and Air.!

It is in the center (notice the trees, mountains and water).! In this cosmology, the earth does not revolve around anything else or rotate around its own axis.!

It is surrounded by ten concentric spheres made of a perfectly transparent substance known as "quintessence."!

These spheres revolve around the earth, carrying the other celestial bodies.!

As you can see, one is the sphere "of the Moon" ("Lunae"), two is Mercury ("Mercurii"), three is Venus ("Veneris"), four is the Sun ("Solis"), ﬁve is Mars ("Martis"), six is Jupiter ("Iovis"), seven is Saturn ("Saturni"), and spheres eight, nine and ten hold the "ﬁxed stars" (so-called because they do not move relative to each other, unlike the planets, which move among the other stars).! (The symbols by the names of the planets are the traditional astrological symbols for them.!

The symbols in spheres eight, nine and ten are for the twelve astrological constellations, Gemini, Ares, etc.)!

Beyond the tenth sphere is, as the words in the periphery say in Latin,

"The Kingdom of Heaven, the Abode of God and of the Elect."!

This photograph shows the apparent movements of the planets against the background stars. Mars, Jupiter and Saturn appear to stop in their orbits, then reverse direction before continuing on – a phenomenon called retrograde motion by modern astronomers. Ptolemy: Epicycles - “Wheels within wheels” To explain the occasional retrograde loops in the apparent motions of Mars, Jupiter and Saturn, astronomers in ancient times imagined that each planet travels with uniform speed around a small circle, known as the epicycle. The epicycle’s center moves uniformly on a larger circle, the deferent. A similar scheme was used by Ptolemy (ﬂ. AD 150) to explain the wayward motions of the planets in his Almagest. In the Ptolemaic system, the Earth was displaced from the center of the large circle, and each planet traveled with uniform motion with respect to another imaginary point, the equant, appearing to move with variable speed when viewed from the Earth. Mikolaj Kopernik, better known as Nicolaus Copernicus, argued in 1543 that the Earth is just one of several planets that are whirling endlessly about the Sun, all moving in the same direction but at different distances from the Sun and with speeds that decrease with increasing distance.

Almost four centuries ago, Johannes Kepler used accurate observations, obtained by Tycho Brahe, to conclude that the planets move in ellipses, or ovals, with the Sun at one focus, and to infer a precise mathematical relation between the mean orbital distance and period of each planet. A Sun-centered model of the solar system explains the looping path of Mars in terms of the relative speeds of the Earth and Mars. The Earth travels around the Sun more rapidly than Mars does. As Earth overtakes and passes the slower moving planet (points 2 to 4), Mars appears to move backward (points B to D) for a few months. Mikolaj Kopernik, better known as Nicolaus Copernicus, argued in 1543 that the Earth is just one of several planets that are whirling endlessly about the Sun, all moving in the same direction but at different distances from the Sun and with speeds that decrease with increasing distance.

Almost four centuries ago, Johannes Kepler used accurate observations, obtained by Tycho Brahe, to conclude that the planets move in ellipses, or ovals, with the Sun at one focus, and to infer a precise mathematical relation between the mean orbital distance and period of each planet. Each planet moves in an ellipse with the Sun at one focus. The length of a line drawn from the Sun, to a planet and then to the empty focus, denoted by the dashed line, is always 2a, or twice the semi-major axis, a. The eccentricity, or elongation, of the planetary ellipse has been greatly overdone in this ﬁgure; planetary orbits look much more like a circle. In his Principia, published in 1686, Isaac Newton showed how the laws of motion and universal gravitation describe the movements of the planets and everything else in the Universe.

The solar system is held together by the Sun’s gravitational attraction, which keeps the planets in their orbits; they move at precisely the right speed required to just overcome the pull of solar gravity.

The gravitational attraction between two objects increases in proportion to the product of their masses and in inverse proportion to the square of the distance between them. 14 - the solar system: comparative planetology (chapter 6)

16 - the solar system: comparative planetology (chapter 6)

21 - The earth (chapter 7)

23 - the moon and mercury (chapter 8)

28 - venus and mars (chapters 9 and 10)

March

01 - jupiter and saturn (Chapters 11 and 12)

6 /8 - No Class / Spring Break

13 - Jupiter and saturn!!! (Chapters 11 and 12)

15 - uranus and neptune (chapter 13)

20 - review exam 2

22 - Exam 2 (chapters 6 - 13) 4. Planet formation Mercury, Venus, Earth Mars and Venus, Mercury, Jupiter, Saturn, Uranus and Neptune and Uranus Saturn, Jupiter, (a dwarf planet) dwarf (a + Pluto Pluto +

So, where did all these planetary systems come from? The eight major planets can be divided into two groups –

the four rocky, dense terrestrial planets, Mercury, Venus, Earth and Mars, located relatively near the Sun, and the four giant, low-density planets,

Jupiter, Saturn, Uranus and Neptune, that are further from the Sun. Many major astronomical discoveries have been unanticipated and serendipitous,

made while new telescopes were used to study other, known cosmic objects; the earliest of these accidental discoveries include he four large moons of Jupiter, the planet Uranus, and the ﬁrst known asteroid, Ceres, discovered respectively by

Galileo Galilei in 1610,

William Herschel in 1781, and Giuseppe Piazzi in 1801. Asteroids and Trojans The exact locations of ﬁve thousand ﬂying rocks, called asteroids or minor planets, whose orbits are accurately known. The vast majority of the asteroids orbit the Sun

in the main belt located between the orbits of Mars and Jupiter.

A few of them pass inside the orbit of Earth, while others move

about 60 degrees ahead of and behind Jupiter in similar orbits. The planet Neptune was discovered in 1846, near the location predicted by mathematical calculations under the assumption that the gravitational pull of a large,

unknown world, located far beyond Uranus, was causing Uranus’ observed positions to deviate from its predicted ones. The new, close-up view from space

• • The space-age investigation of the solar system began in a cold war • competition between the Soviet Union, which launched the first artificial The new, close-up view from space • satellite, and the United States, which won the race to the Moon. • • The Voyager 1 and 2 flyby •spacecraftThe space-age transformed investigation our understanding of the solar of system began in a cold war • the four giant planets, Jupiter,• competitionSaturn, Uranus between and Neptune, the Soviet and Union, revealed which launched the first artificial • fascinating, unexpected aspects of their moons and rings. • satellite, and the United States, which won the race to the Moon. • The Giotto spacecraft was the first to provide a close-up view of a comet, • The Voyager 1 and 2 flyby spacecraft transformed our understanding of • showing that its nucleus is a black, city-sized chunk of water ice and dust • that emits sunward jets of• waterthe when four passinggiant planets, near the Jupiter, Sun. Saturn, Uranus and Neptune, and revealed • fascinating, unexpected aspects of their moons and rings. • Orbiting spacecraft have greatly increased the time for study of the planets • and moons, revealing ancient• waterThe Giottoflow on spacecraft Mars, vast was outpourings the first to of provide lava a close-up view of a comet, • on Venus, Jupiter’s volcanic• moonshowing Io and that an iceits nucleuscovered isocean a black, on its city-sized satellite chunk of water ice and dust • Europa, and Saturn’s marvelous• that rings, emits water-spewing sunward jets satellite of water Enceladus, when passing near the Sun. • and haze-shrouded moon Titan. • Orbiting spacecraft have greatly increased the time for study of the planets • Three rovers have explored• the andsurface moons, of Mars revealing and provided ancient evidencewater flow on Mars, vast outpourings of lava • for water flow across its surface• on roughly Venus, 4.0 Jupiter’s billion years volcanic ago. moon Io and an ice covered ocean on its satellite • Europa, and Saturn’s marvelous rings, water-spewing satellite Enceladus, • The Huygens Probe and radar• fromand haze-shroudedthe orbiting Cassini moon spacecraft Titan. have • discovered rain, rivers and lakes of liquid methane on Saturn’s moon Titan. • Three rovers have explored the surface of Mars and provided evidence • for water flow across its surface roughly 4.0 billion years ago.

• The Huygens Probe and radar from the orbiting Cassini spacecraft have • discovered rain, rivers and lakes of liquid methane on Saturn’s moon Titan. The new, close-up view from space

• • The space-age investigation of the solar system began in a cold war • competition between the Soviet Union, which launched the ﬁrst artiﬁcial • satellite, and the United States, which won the race to the Moon.

• The Voyager 1 and 2 ﬂyby spacecraft transformed our understanding of • the four giant planets, Jupiter, Saturn, Uranus and Neptune, and revealed • fascinating, unexpected aspects of their moons and rings.

• The Giotto spacecraft was the ﬁrst to provide a close-up view of a comet, • showing that its nucleus is a black, city-sized chunk of water ice and dust • that emits sunward jets of water when passing near the Sun.

• Orbiting spacecraft have greatly increased the time for study of the planets • and moons, revealing ancient water ﬂow on Mars, vast outpourings of lava • on Venus, Jupiter’s volcanic moon Io and an ice covered ocean on its satellite • Europa, and Saturn’s marvelous rings, water-spewing satellite Enceladus, • and haze-shrouded moon Titan.

• Three rovers have explored the surface of Mars and provided evidence • for water ﬂow across its surface roughly 4.0 billion years ago.

• The Huygens Probe and radar from the orbiting Cassini spacecraft have • discovered rain, rivers and lakes of liquid methane on Saturn’s moon Titan. Giant red spot and Galilean satellites

Europa

Ganymede

Callisto The new, close-up view from space

• The VoyagerVolcanic 1 and activity 2 ﬂyby on Io spacecraft transformed our understanding of • the four giant planets, Jupiter, Saturn, Uranus and Neptune, and revealed • fascinating, unexpected aspects of their moons and rings.

• Three rovers have explored the surface of Mars and provided evidence • for water ﬂow across its surface roughly 4.0 billion years ago.

• The Huygens Probe and radar from the orbiting Cassini spacecraft have • discovered rain, rivers and lakes of liquid methane on Saturn’s moon Titan. • • Massive eruptions continuously disﬁgure the surface of Jupiter’s satellite Io, • the most volcanically active body in the solar system. Water oozes out from Jupiter’s moon Europa The new, close-up view from space

• Three rovers have explored the surface of Mars and provided evidence • for water ﬂow across its surface roughly 4.0 billion years ago.

• The Huygens Probe and radar from the orbiting Cassini spacecraft have • discovered rain, rivers and lakes of liquid methane on Saturn’s moon Titan. Saturn's• realm • Massive eruptions continuously disﬁgure the surface of Jupiter’s satellite Io, • the most volcanically active body in the solar system.

The magniﬁcent rings of Saturn encircle the planet, never touching its cloud tops. From the outside in there are the bright A and B rings separated by the Cassini Division.

The narrow Encke Gap in the outer

A ring is also visible, as is the dark

C ring nearest to the planet. The new, close-up view from space

• Three rovers have explored the surface of Mars and provided evidence • for water ﬂow across its surface roughly 4.0 billion years ago.

The magniﬁcent rings of Saturn encircle the planet, never touching its cloud tops. From the outside in there are the bright A and B rings separated by the Cassini Division.

The narrow Encke Gap in the outer

A ring is also visible, as is the dark

CSaturn’s ring nearest rings to open the planet. up

These images were taken from the Hubble Space Telescope during a four-year period, from 1996 to 2000 (left to right), as Saturn moved along one seventh of its 29-year journey around the Sun. Tiger stripes on Enceladus

Saturn’s enigmatic moon Enceladus is a jumbled world of fresh snow plains (middle), old cratered terrains (top), and prominent tiger stripe fractures (bottom, false color blue).

The ﬁssures spray ice particles, water vapor and organic compounds outward, some of them forming Saturn’s E ring and others falling back on the moon. Enceladus vents water jets

Saturn’s enigmatic moon Enceladus is a jumbled world

of fresh snow plains (middle), old cratered terrains (top),

and prominent tiger stripe fractures (bottom, false color blue).

The ﬁssures spray ice particles, water vapor and organic

compounds outward, some of them forming Saturn’s E ring

and others falling back on the moon.

Dramatic plumes, both large and small, spray water ice particles, water vapor and organic compounds

out from many locations along tiger stripe fractures near the south pole of Saturn’s moon Enceladus. 27 - solar system debris (chapter 14)

29 - solar system debris (chapter 14)

April

03 - the formation of planetary systems!! (Chapter 15)

05 - the formation of planetary systems!! (chapter 15)

10 - the sun!!! (Chapter 16)

12 - life in the universe (chapter 28)

17 - life in the universe (chapter 28)

19 - review exam 3

24 -! Exam 3 (chapters 14-16, 28)

May

02 - optional ﬁnal (ﬂg 210 from 3:00 to 5:00 pm)

Saturn’s enigmatic moon Enceladus is a jumbled world ofLakes fresh of snow methane plains and (middle ethane), old on crateredSaturn’s terrains moon Titan(top), and prominent tiger stripe fractures (bottom, false color blue).

The ﬁssures spray ice particles, water vapor and organic compounds outward, some of them forming Saturn’s E ring and others falling back on the moon.

Dramatic plumes, both large and small, spray water ice particles, water vapor and organic compounds out from many locations along tiger stripe fractures near the south pole of Saturn’s moon Enceladus.

A radar image shows a bright, central island in a dark, smooth lake, surrounded by a bright shoreline with numerous inlets. The island is about 90 kilometers across. This is one of many large lakes formed at high latitudes on Titan, with more in the northern polar regions than the southern ones. Seasonal rains of liquid methane and ethane probably ﬁll these lakes. The radar instrument aboard Cassini obtained this image Saturn’s enigmatic moon Enceladus is a jumbled world

of fresh snow plains (middle), old cratered terrains (top),

Theand tiltedprominent planet tiger stripe fractures (bottom, false color blue).

The ﬁssures spray ice particles, water vapor and organic

compounds outward, some of them forming Saturn’s E ring

and others falling back on the moon.

Dramatic plumes, both large and small, spray water ice particles, water vapor and organic compounds

out from many locations along tiger stripe fractures near the south pole of Saturn’s moon Enceladus.

A radar image shows a bright, central island in a dark, smooth lake, surrounded by a bright shoreline with

numerous inlets. The island is about 90 kilometers across. This is one of many large lakes formed at high

latitudes on Titan, with more in the northern polar regions than the southern ones. Seasonal rains of liquid

methane and ethane probably ﬁll these lakes. The radar instrument aboard Cassini obtained this image

Thin, spidery rings and several small moons encircle Uranus. The planet is tipped on its side, so its equator, rings and direction of rotation are almost perpendicular to the plane of the planet’s orbital motion around the Sun. Saturn’s enigmatic moon Enceladus is a jumbled world of fresh snow plains (middle), old cratered terrains (top), and prominent tiger stripe fractures (bottom, false color blue).

The ﬁssures spray ice particles, water vapor and organic compounds outward, some of them forming Saturn’s E ring and others falling back on the moon.

Nereid, the outermost of Neptune’s satellites, travels in a highly inclined, eccentric orbit, in the same direction as that of the planet’s rotation. Triton, the largest satellite of Neptune, travels around Neptune in a circular obit, but, unlike any other largest satellite of the giant planets, it travels in the opposite retrograde direction to the rotation of Neptune. In addition, careful analysis of Triton’s motions shows that the satellite is in a decaying orbit and is slowly being pulled toward Neptune. Triton, the largest moon of Neptune Asteroids and meteorites

• There are billions of asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.

• The asteroid belt is largely empty space, and a spacecraft may safely travel through it.

• Hundreds of Trojan asteroids circle the Sun in the same orbit as Jupiter. These asteroids are located near the two Lagrangian points where the gravity of the Sun balances that of Jupiter.

• The Earth resides in a swarm of asteroids. Many of these near-Earth asteroids travel on orbits that intersect the Earth’s orbit, with the possibility of an eventual devastating collision with our planet. Near-Earth asteroids

Asteroids and meteorites

• There are billions of asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.

• The asteroid belt is largely empty space, and a spacecraft may safely travel through it.

• Hundreds of Trojan asteroids circle the Sun in the same orbit as Jupiter. These asteroids are located near the two Lagrangian points where the gravity of the Sun balances that of Jupiter.

The paths of three representative near-Earth asteroids, 1221 Amor, 1862 Apollo and 2062 Aten, all come closer to the Sun than most asteroids, located in the main belt beyond the orbit of Mars. Amor crosses the orbit of Mars, and almost reaches the Earth’s orbit. Apollo crosses the orbits of Mars, Earth and Venus (not shown). Aten is always fairly close to the Earth’s orbit. Asteroid 433 Eros, a solid rock Asteroids and meteorites

• There are billions of asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.

• The asteroid belt is largely empty space, and a spacecraft may safely travel through it.

• Hundreds of Trojan asteroids circle the Sun in the same orbit as Jupiter. These asteroids are located near the two Lagrangian points where the gravity of the Sun balances that of Jupiter.

The paths of three representative near-Earth asteroids, 1221 Amor, 1862 Apollo and 2062 Aten, all come

closer to the Sun than most asteroids, located in the main belt beyond the orbit of Mars. Amor crosses the orbit

of Mars, and almost reaches the Earth’s orbit. Apollo crosses the orbits of Mars, Earth and Venus (not

shown). Aten is always fairly close to the Earth’s orbit.

This global view of the S-type asteroid 433 Eros was obtained by the NEAR Shoemaker spacecraft on 29 February 2000 from a distance of 200 kilometers. This perspective highlights the major features of the asteroid’s northern hemisphere. The asteroid’s largest crater (top) measures 5.5 kilometers wide and sits opposite from an even larger 10-kilometer, saddle-shaped depression (bottom). Studies of the spacecraft’s orbit around the asteroid indicate that 433 Eros is a solid rock. Asteroids and meteorites

• There are billions of asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.

• The asteroid belt is largely empty space, and a spacecraft may safely travel through it.

• Hundreds of Trojan asteroids circle the Sun in the same orbit as Jupiter. These asteroids are located near the two Lagrangian points where the gravity of the Sun balances that of Jupiter.

As illustrated in this image of Africa, the Arabian Peninsula, and the Indian Ocean, the Earth's surface consists of continents and oceans. Continents cover a little more than one-quarter of the Earth's surface, while ocean water covers almost three-quarters of the surface. Our home planet has a thin atmosphere with white clouds of water ice, and enough transparency that you can usually look right through it. The Antarctica ice cap gleams white at the bottom. Apollo 17 astronauts took this image in December 1972 as they left the Earth en route to our Moon. (Courtesy of NASA.) Asteroids and meteorites

• There are billions of asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.

• The asteroid belt is largely empty space, and a spacecraft may safely travel through it.

• Hundreds of Trojan asteroids circle the Sun in the same orbit as Jupiter. These asteroids are located near the two Lagrangian points where the gravity of the Sun balances that of Jupiter.

TheEarth’s paths moving of three platesrepresentative near-Earth asteroids, 1221 Amor, 1862 Apollo and 2062 Aten, all come closer to the Sun than most asteroids, located in the main belt beyond the orbit of Mars. Amor crosses the orbit of Mars, and almost reaches the Earth’s orbit. Apollo crosses the orbits of Mars, Earth and Venus (not shown). Aten is always fairly close to the Earth’s orbit.

The Earth's lithosphere is broken into numerous plates. They move in the directions shown by the arrows at rates of a few tenths of a meter per year. The lithosphere dives into the underlying asthenosphere at zones of subduction. They are denoted by the thick line with triangles, forming the famous ring of fire around the edge of the Pacific and Nazca Plates. Most of the Earth's earthquake and continental volcanic activity is concentrated along the subduction zones. Continental fit

The continents ﬁt together like the pieces of a puzzle. Rise in Earth’s atmospheric carbon dioxide

6 The average monthly concentration of atmospheric carbon dioxide, or CO2 for short, in parts per million (10 ),

abbreviated ppm, of dry air plotted against time in years observed since 1958 at the Mauna Loa Observatory,

Hawaii.

The continents ﬁt together like the pieces of a puzzle. The full Moon An enormous Moon

6 The average monthly concentration of atmospheric carbon dioxide, or CO2 for short, in parts per million (10 ),

abbreviated ppm, of dry air plotted against time in years observed since 1958 at the Mauna Loa Observatory,

Hawaii.

The continents ﬁt together like the pieces of a puzzle.

In this awesome picture, a man and child seem enveloped by the Earth’s Moon, which looks huge in comparison to the tree in the foreground. When the Moon is overhead, alone in an otherwise empty sky, there are no other objects to gauge its distance; we then think the Moon is smaller than at the horizon. Moon illusion

6 The average monthly concentration of atmospheric carbon dioxide, or CO2 for short, in parts per million (10 ),

abbreviated ppm, of dry air plotted against time in years observed since 1958 at the Mauna Loa Observatory,

Hawaii.

The continents ﬁt together like the pieces of a puzzle.

We make decisions about size because of our perceptions of distance. The two black disks in this ﬁgure are the same size, but we see the bottom one as smaller because we think it is closer. The top disk seems larger because it appears to be farther away. The Moon on the horizon is similarly thought to be huge because comparisons with objects on the ground make us think it is far away - also see Figure 5.6. When people look straight up at the Moon, in an otherwise empty sky, they no longer have land clues to compute the Moon's distance and it is perceived as being closer and smaller. Kepler Discovers a Tiny Solar System

Jan. 11, 2012:! Astronomers using data from NASA's Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars.

Kepler in Brief

A Nutshell Description of the Kepler Mission

Why?

The Kepler Mission is a NASA Discovery Program for detecting potentially life-supporting planets around other stars. All of the extrasolar planets detected so far by other projects are giant planets, mostly the size of Jupiter and bigger. Kepler is poised to ﬁnd planets 30 to 600 times less massive than Jupiter.

How?

By a method known as the transit method of planet ﬁnding. When we see a planet pass in front of its parent star it blocks a small fraction of the light from that star.When that happens, we say that the planet is transiting the star. If we see repeated transits at regular times, we have discovered a planet! From the brightness change we can tell the planet size. From the time between transits, we can tell the size of the planet's orbit and estimate the planet's temperature.These qualities determine possibilities for life on the planet.

What?

The Kepler satellite has a 0.95-meter diameter telescope that is a photometer having a ﬁeld of view a bit over 10 degrees square (and area of sky the size of about two open hands). It is designed to continuously and simultaneously monitors brightnesses of 100,000 stars brighter than 14th magnitude in the constellations Cygnus & Lyrae.

To detect an Earth-size planet, the photometer must be able to sense a drop in brightness of only 1/100 of a percent. This is akin to sensing the drop in brightness of a car's headlight when a fruitﬂy moves in front of it! The photometer must be spacebased to obtain this precision.

When?

Kepler was launched in March 2009. Kepler in Brief

A Nutshell Description of the Kepler Mission

Why?

How?

What?

When?

Kepler was launched in March 2009. Kepler in Brief Kepler in Brief

A Nutshell Description of the Kepler Mission AKepler Nutshell in Brief Description of the Kepler Mission

Why?Why?A Nutshell Description of the Kepler Mission TheThe Kepler Kepler Mission Mission is a NASAis a NASA Discovery Discovery Program Programfor detecting for potentially detecting life-supporting potentially life-supporting planetsplanetsWhy? around around other other stars. stars. All of All the ofextrasolar the extrasolar planets detected planets so detectedfar by other so projects far by areother projects are giant planets, mostly the size of Jupiter and bigger. Kepler is poised to find planets 30 to 600 timesgiantThe Kepler less planets, massive Mission mostly than is aJupiter. NASAthe size Discovery of Jupiter Program and bigger.for detecting Kepler potentially is poised life-supporting to find planets 30 to 600 timesplanets less around massive other stars. than All Jupiter. of the extrasolar planets detected so far by other projects are How?giant planets, mostly the size of Jupiter and bigger. Kepler is poised to find planets 30 to 600 How?times less massive than Jupiter. By a method known as the transit method of planet finding. When we see a planet pass in front ofHow? its parent star it blocks a small fraction of the light from that star.When that happens, we say thatBy thea method planet is known transiting as the the star. transit If we methodsee repeated of transitsplanet atfi nding.regular times,When we we have see a planet pass in front discoveredofBy its a method parent a planet! known star itFrom as blocks the the transit brightness a small method fraction change of planet we of canfi thending. tell light the When planetfrom we size. thatsee a From star.Whenplanet the pass time in that front happens, we say betweenthatof its the parent transits, planet star weitis blocks transitingcan tell a smallthe sizethe fraction ofstar. the Ifofplanet's wethe lightsee orbit repeatedfrom and that estimate star.When transits the planet's at that regular happens, times, we say we have temperature.Thesediscoveredthat the planet a isplanet! transiting qualities From thedetermine star. the Ifbrightness wepossibilities see repeated change for lifetransits onwe the atcan planet.regular tell thetimes, planet we have size. From the time betweendiscovered transits, a planet! weFrom can the tell brightness the size change of the we planet's can tell theorbit planet and size. estimate From the the time planet's What?between transits, we can tell the size of the planet's orbit and estimate the planet's temperature.Thesetemperature.These qualities qualities determine determine possibilities possibilities for life on for the lifeplanet. on the planet. The Kepler satellite has a 0.95-meter diameter telescope that is a photometer having a field of viewWhat?What? a bit over 10 degrees square (and area of sky the size of about two open hands). It is designed to continuously and simultaneously monitors brightnesses of 100,000 stars brighter thanTheThe 14thKeplerKepler magnitude satellite satellite hasin the hasa 0.95-meter constellations a 0.95-meter diameter Cygnus diameter telescope & Lyrae. telescope that is a photometer that is a havingphotometer a field ofhaving a field of view a bit over 10 degrees square (and area of sky the size of about two open hands). It is Toviewdesigned detect a bit anto overcontinuouslyEarth-size 10 degrees planet, and simultaneouslythe square photometer (and must monitorsarea be of able brightnessessky to the sense size a of drop of 100,000 about in brightness stars two brighter open of hands). It is onlydesignedthan 1/10014th magnitude ofto acontinuously percent. in theThis constellations is and akin simultaneouslyto sensing Cygnus the &drop Lyrae. monitors in brightness brightnesses of a car's headlight of 100,000 when stars brighter athan fruitfl 14thy moves magnitude in front of in it! the The constellations photometer must Cygnus be spacebased & Lyrae. to obtain this precision. To detect an Earth-size planet, the photometer must be able to sense a drop in brightness of When? Toonly detect 1/100 anof a Earth-size percent. This planet, is akin theto sensing photometer the drop must in brightness be able of to a sensecar's headlight a drop whenin brightness of a fruitfly moves in front of it! The photometer must be spacebased to obtain this precision. Kepleronly 1/100 was launched of a percent. in March This 2009. is akin to sensing the drop in brightness of a car's headlight when aWhen? fruitfly moves in front of it! The photometer must be spacebased to obtain this precision.

When?Kepler was launched in March 2009.

Kepler was launched in March 2009. National Aeronautics and Space Administration

NASA Ames Research Center/W. Stenzel (OSC)/Artist’s Concept Stenzel (OSC)/Artist’s Center/W. NASA Ames Research

Kepler Mission: A Search for Habitable Planets www.nasa.gov

National Aeronautics and Space Administration Milky Way photo by Carter Roberts Carter by photo Way Milky

The Kepler Mission Star Field www.nasa.gov Astronomers see more planets than stars in galaxy

By SETH BORENSTEIN AP Science Writer Published: Wednesday, January 11, 2012 at 4:04 p.m.

Last Modiﬁed: Wednesday, January 11, 2012 at 4:04 p.m.

The more astronomers look for other worlds, the more they ﬁnd that it's a crowded and crazy cosmos. They think planets easily outnumber stars in our galaxy and they're even ﬁnding them in the strangest of places.

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This handout illustration provided by San Diego State University, shows a newly discovered planet, called Kepler 35, that circles not one but two stars. Scientists thought this type of two- sun system _ made famous as the home planet of the ﬁctional Luke Skywalker _ is too unstable to support planets. But so far they’ve found three of these planets with two suns, showing that planets seem to be everywhere. The study is in this week’s journal Nature. (AP Photo/Lynette R. Cook, San Diego State University)

And they've only begun to count.

Three studies released Wednesday, in the journal Nature and at the American Astronomical Society's conference in Austin, Texas, demonstrate an extrasolar real estate boom. One study Astronomers see more planets than stars in galaxy

By SETH BORENSTEIN AP Science Writer Published: Wednesday, January 11, 2012 at 4:04 p.m.

Last Modiﬁed: Wednesday, January 11, 2012 at 4:04 p.m.

Enlarge

And they've only begun to count.

Three studies released Wednesday, in the journal Nature and at the American Astronomical Society's conference in Austin, Texas, demonstrate an extrasolar real estate boom. One study