Extrasolar Planets. Attendance Quiz Are you here today? (a) yes (b) no (c) Captain, the sensors indicate a class M planet orbiting this star Here!

Extrasolar PlanetsExtrasolar Planets

Attendance Quiz

Are you here today?

(a) yes

(b) no

(c) Captain, the sensors indicate a class M planet orbiting this star

Here!

Special Public LectureSpecial Public Lecture

Are We Alone?*

Dr. Jill TarterDirector for SETI ResearchSETI Institute

Friday, May 67pmUrsa Major C*5 clicker points extra credit for attending

Are We Alone?*

Dr. Jill TarterDirector for SETI ResearchSETI Institute

Friday, May 67pmUrsa Major C*5 clicker points extra credit for attending

Exam #2 (again)Exam #2 (again)• The second midterm exam is next Monday, 5/9, during the first half of class

- please come on time (or better yet, early)

• It will be multiple choice, and you will take it using a 50-question scantron, so make sure to bring one to class!

• It will cover the material in Chapters 6, S2, 13, 14, 15, 16 of the optional textbook (what we covered in class since the last midterm through Wednesday)

• The format will be the same as the first midterm

• Most questions will look something like the in-class “Conceptual Questions” or the Lecture Tutorial and Ranking Task questions - your LT book is your textbook to study from

• Cell phones must be off and put away during the exam (as they should be in every class). If I see or hear a cell phone that is grounds to fail the exam!

• There will be no second half of class, so once you are done you will have the afternoon off. Don’t have too much fun! :)

• The second midterm exam is next Monday, 5/9, during the first half of class - please come on time (or better yet, early)

• It will be multiple choice, and you will take it using a 50-question scantron, so make sure to bring one to class!

• It will cover the material in Chapters 6, S2, 13, 14, 15, 16 of the optional textbook (what we covered in class since the last midterm through Wednesday)

• The format will be the same as the first midterm

• Most questions will look something like the in-class “Conceptual Questions” or the Lecture Tutorial and Ranking Task questions - your LT book is your textbook to study from

• Cell phones must be off and put away during the exam (as they should be in every class). If I see or hear a cell phone that is grounds to fail the exam!

• There will be no second half of class, so once you are done you will have the afternoon off. Don’t have too much fun! :)

Today’s TopicsToday’s Topics

• Extrasolar Planets - the problem• Formation of our Solar System• Doppler Detection of Extrasolar Planets• Properties of Extrasolar Planets• Effect on Models of Solar System Formation• Other Techniques of Extrasolar Planet Detection

• Extrasolar Planets - the problem• Formation of our Solar System• Doppler Detection of Extrasolar Planets• Properties of Extrasolar Planets• Effect on Models of Solar System Formation• Other Techniques of Extrasolar Planet Detection

The ProblemThe Problem• Until 1995, we only knew of one Solar

System - our own• We had suspected for hundreds of years,

and had confirmed as long ago as the 1800s (by stellar parallax) that the stars were extremely distant Suns

• Only their extreme intrinsic brightness makes them visible over such vast distances

• Planets shine by reflected light and are much smaller than stars, so direct detection of planets around other stars is extremely difficult (Jupiter would be 1 billionth as bright as the Sun from outside the Solar System)

• As we will see, the first detections of extrasolar planets came indirectly

• Until 1995, we only knew of one Solar System - our own

• We had suspected for hundreds of years, and had confirmed as long ago as the 1800s (by stellar parallax) that the stars were extremely distant Suns

• Only their extreme intrinsic brightness makes them visible over such vast distances

• Planets shine by reflected light and are much smaller than stars, so direct detection of planets around other stars is extremely difficult (Jupiter would be 1 billionth as bright as the Sun from outside the Solar System)

• As we will see, the first detections of extrasolar planets came indirectly

Formation of our Solar SystemFormation of our Solar System• Before we consider extrasolar planets, let’s first discuss our own Solar System• Two main features of our Solar System that any theory of formation must

explain

1. Organized, nearly circular orbits of the planets

2. 2 major categories of planetsa) Inner, small, rocky, terrestrial planets (Mercury, Venus, Earth, Mars)

b) Outer, large, gaseous (H, He) jovian planets (Jupiter, Saturn, Uranus, Neptune)

• Before we consider extrasolar planets, let’s first discuss our own Solar System• Two main features of our Solar System that any theory of formation must

explain

1. Organized, nearly circular orbits of the planets

2. 2 major categories of planetsa) Inner, small, rocky, terrestrial planets (Mercury, Venus, Earth, Mars)

b) Outer, large, gaseous (H, He) jovian planets (Jupiter, Saturn, Uranus, Neptune)

Formation of our Solar SystemFormation of our Solar System• As we saw in Chapter 16, stars form from spinning clouds

of hydrogen gas that contract by gravity• As the cloud contracts, it spins faster, much as a spinning

skater spins faster as she draws in her arms

Spinning Platform Demo• The disk will be densest (and hottest) in the center; the

temperature drops as one moves further from the star

• As we saw in Chapter 16, stars form from spinning clouds of hydrogen gas that contract by gravity

• As the cloud contracts, it spins faster, much as a spinning skater spins faster as she draws in her arms

Spinning Platform Demo• The disk will be densest (and hottest) in the center; the

temperature drops as one moves further from the star

Formation of our Solar SystemFormation of our Solar System• Let’s focus on the second of our

features of the Solar System, namely the 2 major categories of planetsa) Inner, small, rocky, terrestrial planets

b) Outer, large, gaseous (H, He) jovian planets

• This feature can be explained by considering the temperature gradient in the solar nebula and the condensation temperature of common materials in the solar nebula

• In the inner solar system (inside the “ice line”, minerals and metals can condense but water and other hydrogen compounds (CH4, NH3) cannot, so the planets formed are rocky and small (minerals and metals make up ~ 0.6% of the nebula)

• Let’s focus on the second of our features of the Solar System, namely the 2 major categories of planetsa) Inner, small, rocky, terrestrial planets

b) Outer, large, gaseous (H, He) jovian planets

• This feature can be explained by considering the temperature gradient in the solar nebula and the condensation temperature of common materials in the solar nebula

• In the inner solar system (inside the “ice line”, minerals and metals can condense but water and other hydrogen compounds (CH4, NH3) cannot, so the planets formed are rocky and small (minerals and metals make up ~ 0.6% of the nebula)

H2O freezes

Mars

Interactive Figure 8.6

Formation of our Solar SystemFormation of our Solar System

H2O freezes

Mars

Jupiter


• In the outer solar system, outside the “ice line”, hydrogen compounds can condense (freeze) so there is ~3x as much material to form solid (icy) planetesimals

• These planetesimals become large enough to gravitationally capture hydrogen and helium gas, growing into gas giants, which have icy-rocky cores

• Models show that a core of 3-20 Mearth will lead to planets like Uranus (14 Mearth) and Jupiter (318 Mearth)

• In the outer solar system, outside the “ice line”, hydrogen compounds can condense (freeze) so there is ~3x as much material to form solid (icy) planetesimals

• These planetesimals become large enough to gravitationally capture hydrogen and helium gas, growing into gas giants, which have icy-rocky cores

• Models show that a core of 3-20 Mearth will lead to planets like Uranus (14 Mearth) and Jupiter (318 Mearth)

Planet Formation Quiz IPlanet Formation Quiz I

Which of the following types of planets would form in the early solar system at locations hot enough for liquid water to boil into a gas?

a) rocky terrestrial planets

b) jovian gas giant planets

Which of the following types of planets would form in the early solar system at locations hot enough for liquid water to boil into a gas?

a) rocky terrestrial planets

b) jovian gas giant planets

Lecture Tutorial: Temperature and Formation of the Solar System, pp. 103-104

Lecture Tutorial: Temperature and Formation of the Solar System, pp. 103-104

• Work with one or more partners - not alone!

• Get right to work - you have 10 minutes

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another. Take time to understand it now!!!!

• Come to a consensus answer you all agree on.

• Write clear explanations for your answers.

• If you get stuck or are not sure of your answer, ask another group.

• If you get really stuck or don’t understand what the Lecture Tutorial is asking, ask me for help.









Planet Formation Quiz IIPlanet Formation Quiz IIThe standard model of solar system formation offers what explanation for the different compositions of the terrestrial and Jovian planets?

a) During condensation, the heavier elements tended to sink nearer the Sun and, being rare, only provided enough material to build the relatively small terrestrial planets.

b) During the collapse of the gaseous nebula, most of the material tended to collect far from the Sun because of the large centrifugal forces, which provided the necessary material to build the large Jovian planets.

c) The large gravitational forces of Jupiter tended to prevent planet formation in the inner solar system and eventually attracted most of the material into the region of the Jovian planets.

d) The terrestrial planets were formed near the Sun where, because of the high temperatures, only heavier elements were able to condense.

The standard model of solar system formation offers what explanation for the different compositions of the terrestrial and Jovian planets?

a) During condensation, the heavier elements tended to sink nearer the Sun and, being rare, only provided enough material to build the relatively small terrestrial planets.

b) During the collapse of the gaseous nebula, most of the material tended to collect far from the Sun because of the large centrifugal forces, which provided the necessary material to build the large Jovian planets.

c) The large gravitational forces of Jupiter tended to prevent planet formation in the inner solar system and eventually attracted most of the material into the region of the Jovian planets.

d) The terrestrial planets were formed near the Sun where, because of the high temperatures, only heavier elements were able to condense.

Detection of Extrasolar PlanetsDetection of Extrasolar Planets• In 1995, the first planet around a main

sequence star was detected• Since direct detection is currently impossible,

how was it found?• To answer this, consider the Sun and Jupiter

• Although Kepler considered the planets to be orbiting a stationary Sun, Newton showed that all pairs of bodies orbit a common center-of-mass (COM)

• In the case of the Sun and Jupiter, the COM is near the edge of the Sun

• Thus, every 12 years, as Jupiter orbits at an average distance of 5 AU, the Sun conducts a small loop of radius equal to the Sun’s radius with the same period

• The speed of the Sun in this orbit is much smaller than vjupiter = 412 m/s, about 13 m/s

• In 1995, the first planet around a main sequence star was detected

• Since direct detection is currently impossible, how was it found?

• To answer this, consider the Sun and Jupiter• Although Kepler considered the planets to be

orbiting a stationary Sun, Newton showed that all pairs of bodies orbit a common center-of-mass (COM)

• In the case of the Sun and Jupiter, the COM is near the edge of the Sun

• Thus, every 12 years, as Jupiter orbits at an average distance of 5 AU, the Sun conducts a small loop of radius equal to the Sun’s radius with the same period

• The speed of the Sun in this orbit is much smaller than vjupiter = 412 m/s, about 13 m/s


Detection of Extrasolar PlanetsDetection of Extrasolar Planets• Although this speed is small, if one looked

carefully at the absorption line spectrum of the Sun, one would see the lines redshifted and blueshifted as the Sun executed its (near-)circular orbit

• The size of this Doppler shift would be tiny (about 40 parts per billion) about 20 106 nm shift in wavelength at 500 nm

• Since the Doppler shift is due to the tug of gravity by the planet on the star, the size of the shift grows as1. the planet mass gets larger relative to the star’s

mass

2. the planet’s orbit is closer to the star

• Although this speed is small, if one looked carefully at the absorption line spectrum of the Sun, one would see the lines redshifted and blueshifted as the Sun executed its (near-)circular orbit

• The size of this Doppler shift would be tiny (about 40 parts per billion) about 20 106 nm shift in wavelength at 500 nm

• Since the Doppler shift is due to the tug of gravity by the planet on the star, the size of the shift grows as1. the planet mass gets larger relative to the star’s

mass

2. the planet’s orbit is closer to the star

€

Fgrav ∝Mstarmplanet

rs-p2

so astar =Fgrav

Mstar

∝mplanet

rs-p2

Artist’s conception

Detection of Extrasolar PlanetsDetection of Extrasolar Planets

• In 1995, a planet was discovered orbiting the star 51 Pegasi

• As the planet orbited the star, the star was tugged back and forth (like the Sun), leading to a Doppler shift in the star’s absorption lines which, when converted to velocities looked like the figure

• Notice the scale ( 57 m/s), about 4 times the shift of the Sun, but still very small

• Also note the time-scale (4 day period!)• The planet must be very close to the star (a

~ 0.05 AU < 0.39 AU for Mercury)

Kepler’s 3rd Law• From the size of the Doppler shift, the

mass of the planet is ~ 0.5 Mjupiter

• In 1995, a planet was discovered orbiting the star 51 Pegasi

• As the planet orbited the star, the star was tugged back and forth (like the Sun), leading to a Doppler shift in the star’s absorption lines which, when converted to velocities looked like the figure

• Notice the scale ( 57 m/s), about 4 times the shift of the Sun, but still very small

• Also note the time-scale (4 day period!)• The planet must be very close to the star (a

~ 0.05 AU < 0.39 AU for Mercury)

Kepler’s 3rd Law• From the size of the Doppler shift, the

mass of the planet is ~ 0.5 Mjupiter

Interactive Figure“How orbital properties…”

Detection of Extrasolar PlanetsDetection of Extrasolar Planets• All of this assumes we are viewing the orbit

edge-on• If the orbit is tilted, the velocity along the

line-of-sight (which is what causes th Doppler shift) is smaller, so the mass estimate is a lower limit

• To date, over 200 extrasolar planets have been discovered around nearby stars - most detected by the “Doppler” technique

• Note that • most of them have masses more similar to

Jupiter than Earth, • are at distances closer than Jupiter, and • many are in highly eccentric orbits

• Why?• Recall • The method is biased towards large, close

planets

• All of this assumes we are viewing the orbit edge-on

• If the orbit is tilted, the velocity along the line-of-sight (which is what causes th Doppler shift) is smaller, so the mass estimate is a lower limit

• To date, over 200 extrasolar planets have been discovered around nearby stars - most detected by the “Doppler” technique

• Note that • most of them have masses more similar to

Jupiter than Earth, • are at distances closer than Jupiter, and • many are in highly eccentric orbits

• Why?• Recall • The method is biased towards large, close

planets

€

astar ∝mplanet

rs-p2

Summary of Doppler TechniqueSummary of Doppler Technique1. The star and planet are orbiting the COM with the same period

• Thus, the observed period of the star is equal to the period of the planet

2. The period of the orbit gives the size of the orbit (Kepler’s 3rd Law)3. At every moment, the star and planet are moving in opposite directions

• Thus, when the planet is moving away from the Earth, the star is moving towards the Earth, and vice versa

4. We observe the star’s spectrum• Thus, when we see a redshift (positive velocity), the star is moving away from the Earth,

and the planet is moving towards the Earth, and vice versa

• The mass of the planet relative to the star and the distance between the star and planet determine the size of the Doppler shift1. Higher planet mass larger Doppler shift2. Closer distance larger Doppler shift

1. The star and planet are orbiting the COM with the same period• Thus, the observed period of the star is equal to the period of the planet

2. The period of the orbit gives the size of the orbit (Kepler’s 3rd Law)3. At every moment, the star and planet are moving in opposite directions

• Thus, when the planet is moving away from the Earth, the star is moving towards the Earth, and vice versa

4. We observe the star’s spectrum• Thus, when we see a redshift (positive velocity), the star is moving away from the Earth,

and the planet is moving towards the Earth, and vice versa

• The mass of the planet relative to the star and the distance between the star and planet determine the size of the Doppler shift1. Higher planet mass larger Doppler shift2. Closer distance larger Doppler shift

Extrasolar Planets Quiz IExtrasolar Planets Quiz I

To detect an extrasolar planet by means of the Doppler shift, you look for a periodic shift of the spectrum lines

a) of the planet

b) of the star the planet is orbiting

c) of the star and the planet

To detect an extrasolar planet by means of the Doppler shift, you look for a periodic shift of the spectrum lines

a) of the planet

b) of the star the planet is orbiting

c) of the star and the planet

Lecture Tutorial: Motion of Extrasolar Planets, pp. 117-120

Lecture Tutorial: Motion of Extrasolar Planets, pp. 117-120

















Extrasolar Planets Quiz IIExtrasolar Planets Quiz II

The orbital period of an unseen planet

a) will be the same as period of the star’s Doppler shift

b) will be much larger than the star’s

c) will be much smaller than the star’s

The orbital period of an unseen planet

a) will be the same as period of the star’s Doppler shift

b) will be much larger than the star’s

c) will be much smaller than the star’s

Extrasolar Planets Quiz IIIExtrasolar Planets Quiz III

The shorter the period of the Doppler curve

a) the farther the unseen planet is from the star b) the closer the unseen planet is to the starc) the greater the mass of the planetd) the smaller the mass of the planete) (b) and (c)

The shorter the period of the Doppler curve

a) the farther the unseen planet is from the star b) the closer the unseen planet is to the starc) the greater the mass of the planetd) the smaller the mass of the planete) (b) and (c)

Extrasolar Planets Quiz IVExtrasolar Planets Quiz IV

The larger the mass of the unseen planet

a) The larger the Doppler shift of the star

b) The smaller the Doppler shift of the star

c) The faster the period of the star’s Doppler shift

d) The slower the period of the star’s shift

e) (a) and (c)

The larger the mass of the unseen planet

a) The larger the Doppler shift of the star

b) The smaller the Doppler shift of the star

c) The faster the period of the star’s Doppler shift

d) The slower the period of the star’s shift

e) (a) and (c)

Extrasolar Planets Quiz VExtrasolar Planets Quiz V

Given the location marked with the dot on the star’s radialvelocity curve, at what position (1-4) would you expect the planet to be located at this time?

a) 1b) 2c) 3d) 4


a) 1b) 2c) 3d) 4

2

1

3

4

Earth

Orbit of planet

Orbit of star

Extrasolar Planets Quiz VIExtrasolar Planets Quiz VI


a) 1b) 2c) 3d) 4


a) 1b) 2c) 3d) 4

2

1

3

4

Earth

Orbit of planet

Orbit of star

Comparison of our Solar System to Extrasolar Planets

Comparison of our Solar System to Extrasolar Planets

• Consider the masses, orbital distances, and eccentricities of the known extrasolar planets

• How does this information affect our model for our Solar System in which gas giants form outside the “ice-line” in nearly circular orbits?

• This simple model must change• These new planets, like many new

scientific discoveries, has challenged the simple theory and will require it to be modified

• One idea is that large planets can migrate from where they form towards the central star

• Consider the masses, orbital distances, and eccentricities of the known extrasolar planets

• How does this information affect our model for our Solar System in which gas giants form outside the “ice-line” in nearly circular orbits?

• This simple model must change• These new planets, like many new

scientific discoveries, has challenged the simple theory and will require it to be modified

• One idea is that large planets can migrate from where they form towards the central star

Planetary MigrationPlanetary Migration• This migration occurs when a large

planet sets up waves in the remaining protostellar disk

• These waves act back on the planet, causing drag which leads the planet to spiral closer to the star

• However, this idea can work too well - some computer models suggest the planets would then spiral into the star so fast that we wouldn’t see any planets

• Also, why didn’t Jupiter migrate?• This is an area of intense research

interest, and eventually, a solution will be found, and a new model born

• This migration occurs when a large planet sets up waves in the remaining protostellar disk

• These waves act back on the planet, causing drag which leads the planet to spiral closer to the star

• However, this idea can work too well - some computer models suggest the planets would then spiral into the star so fast that we wouldn’t see any planets

• Also, why didn’t Jupiter migrate?• This is an area of intense research

interest, and eventually, a solution will be found, and a new model born

My ResearchMy ResearchUsing the James Clerk Maxwell Telescope, located on the summit of Mauna Kea, in Hawaii, we observed the disks around young stars from which planets form, studying their structure and rotation

Using the James Clerk Maxwell Telescope, located on the summit of Mauna Kea, in Hawaii, we observed the disks around young stars from which planets form, studying their structure and rotation

My ResearchMy Research• Eventually, we will also observe these disks using

a satellite called Herschel, a joint project of NASA and the European Space Agency (ESA), launched 14 May 2009

• The primary mirror is 3.5-m (11.5-ft) in diameter: the largest mirror ever to be launched into space

• This infrared satellite will give us an unprecedented look at the details of the disks that form planets

• Eventually, we will also observe these disks using a satellite called Herschel, a joint project of NASA and the European Space Agency (ESA), launched 14 May 2009

• The primary mirror is 3.5-m (11.5-ft) in diameter: the largest mirror ever to be launched into space

• This infrared satellite will give us an unprecedented look at the details of the disks that form planets

Herschel’s 3.5-m (11.5-ft) primary mirror

Transit-Eclipse Detection of Extrasolar PlanetsTransit-Eclipse Detection of Extrasolar Planets• The other main technique of detecting extrasolar planets is transits or eclipses

Note: Mercury transited the Sun in November 2006 (next one in 2016)

• The other main technique of detecting extrasolar planets is transits or eclipses

Note: Mercury transited the Sun in November 2006 (next one in 2016)

Transit-Eclipse Detection of Extrasolar PlanetsTransit-Eclipse Detection of Extrasolar Planets• Recall that in eclipsing binary stars, one star occults the other, causing a dip in the

combined amount of light from both stars• When a planet transits a star, it blocks a small amount (less than 1%) of the star’s

light; when the planet is behind the star, its thermal (infrared) radiation is blocked• Note: this technique only works when we view the planetary orbit nearly edge-on

• Recall that in eclipsing binary stars, one star occults the other, causing a dip in the combined amount of light from both stars

• When a planet transits a star, it blocks a small amount (less than 1%) of the star’s light; when the planet is behind the star, its thermal (infrared) radiation is blocked

• Note: this technique only works when we view the planetary orbit nearly edge-on

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Kepler is searching for Earth-sized planetsKepler is searching for Earth-sized planets

• Kepler is a NASA satellite that is searching for earth-sized planets

• It was launched in March 2009 and uses the transit method

• The dips in star-light it is searching for are smaller than typical variations in starlight

• However, by looking for periodic dips, it can distinguish planets from other variations

• To confirm a planet, it will have to see multiple transits

• By 2012, we should know if there are earth-sized planets around other, nearby stars

• Kepler is a NASA satellite that is searching for earth-sized planets

• It was launched in March 2009 and uses the transit method

• The dips in star-light it is searching for are smaller than typical variations in starlight

• However, by looking for periodic dips, it can distinguish planets from other variations

• To confirm a planet, it will have to see multiple transits

• By 2012, we should know if there are earth-sized planets around other, nearby stars

The search for habitable extrasolar planetsThe search for habitable extrasolar planets

Documents

Extrasolar Planets. Attendance Quiz Are you here today? (a) yes (b) no (c) Captain, the sensors indicate a class M planet orbiting this star Here!