Other Solar Systems

1

Week 15 (Chapter 13): Other Planetary Systems

Nov. 30

Please pickup your grade sheet at front. Please pickup your grade sheet at front. We’ll discuss at end of class.We’ll discuss at end of class.

Other Solar Systems

• First one (51 Pegasi) discovered in 1995

• Currently 268 exoplanets in >180 solar systems identified (61 added since last spring)

• Mostly bigger than Jupiter (Mj)– Selection Effect f(mass, orbit)

• All very close to parent stars (<5AU)– Selection Effect f(time)

• Detection based on extremely precise observations

Detection TechniquesDetection Techniques

• Direct: Pictures or spectra of the planets themselves

• Indirect: Measurement of stellar properties revealing the effects of orbiting planets– Astrometric → measuring “wobble”

– Doppler → measuring Doppler shift

Direct DetectionDirect Detection• Brown Dwarf 2M1207 (blue

object on right) and planetary companion.

• About 150 light years distant.S n like stars are billion times• Sun-like stars are ~billion times brighter than reflected light from planets

• Equivalent to standing in San Francisco and seeing a pinhead in Washington, D. C. illuminated by a grapefruit-sized searchlight 15 meters away from the pinhead!

Indirect: AstrometricIndirect: Astrometric• REM: The Barycenter?• Sun and Jupiter orbit

around their common center of massS h f bbl• Sun therefore wobbles around that center of mass with same period as Jupiter

• Only 1 successful exoplanet detected by this method.

Astrometric in TheoryAstrometric in Theory• Sun’s motion around

solar system’s center of mass depends on tugs from all the planetsplanets

• Astronomers around other stars could determine masses and orbits of all our planets by deconvolving combined effects

2

Indirect: DopplerIndirect: Doppler

• Measuring a star’s Doppler shift can tell us its motion toward and away from usand away from us

• Current techniques can measure motions as small as 1 m/s (walking speed)

First Extrasolar PlanetFirst Extrasolar Planet• Doppler shifts of star

51 Pegasi indirectly reveal a planet with 4-day orbital period

• Short period means small orbital distance

• Works best for BIG planets with SHORT periods

First Extrasolar PlanetFirst Extrasolar Planet

Planet around 51 Pegasi has mass similar to Jupiter, M = 1Mj, but very close to star → 1st Hot Jupiter

Other Extrasolar PlanetsOther Extrasolar PlanetsLower mass Higher mass

• Doppler data curve tells us about a planet’s mass and the shape of its orbit

Highly eccentric orbit

Farther away from star

Transits and EclipsesTransits and Eclipses

• A transit is when a planet crosses in front of a star• The resulting eclipse reduces the star’s apparent

brightness and tells us planet’s radius

Direct Detection?Direct Detection?2M1207

• Special techniques can eliminate light from brighter objects

• These techniques are enabling direct planet detection

3

Known OrbitsKnown Orbits• Most of the detected

planets have orbits smaller than Jupiter’s

Pl• Planets at greater distances are harder to detect with Doppler technique (need more time)

Selection EffectsSelection Effects• You will see what you are looking for in the time

span you are looking.• We have not been looking very long• Our instruments can only detect Doppler shifts on• Our instruments can only detect Doppler shifts on

planets parallel to the direction we are looking• Hence, we are currently finding:

– Massive Planets– Close in to their parent stars (fast orbits)– Planets with highly eccentric orbits

Orbits of Extrasolar PlanetsOrbits of Extrasolar Planets

• Orbits of known extrasolar planets are much more elongated (greater g (geccentricity) than those in our solar system

• An example of Selection Effect

SemiSemi--Major AxisMajor Axisvalues forvalues forvalues for values for

178 178 exoplanetsexoplanets

Mass DistributionMass Distribution

• Most that have been detected are more massive than Jupitermassive than Jupiter

• Planets with smaller masses are harder to detect with Doppler technique

How do known extrasolar planets compare with our solar system?

4

Surprising CharacteristicsSurprising Characteristics• Not a very good sample…• Many highly elliptical

orbits• Some very close to their

stars: Hot Jupitersstars: Hot Jupiters• Blur the line between a

large planet and a small star (Brown Dwarfs)

• Do not fit well with nebular hypothesis

Extrasolar Earths?Extrasolar Earths?

Goldilocks Goldilocks ZoneZone

MostMost--recent direct detectionrecent direct detection

Oops. One more last week…Oops. One more last week… Missing Link?Missing Link?• Corot-EXO-3B• Supergiant Planet or a

SubStellar Object (SSO)

• Between a BrownBetween a Brown Dwarf and a planet– Slightly smaller then

Jupiter, but 21X the mass– Twice the density of lead– Orbital period 4 days, 6

hours– 680 light years away

5

Revisiting theRevisiting theNebular TheoryNebular Theory

• Nebular theory predicts that massive Jupiter like planets should not form insideJupiter-like planets should not form inside the frost line (at << 5 AU)

• Discovery of Hot Jupiters has forced reexamination of nebular theory

• Planetary migration, gravitationalwaves or close encounters may explain?

Gravitational EncountersGravitational Encounters

• Close gravitational encounters between two massive planets can eject one planet while flinging the other into a highly elliptical

bitorbit

• Multiple close encounters with smaller planetesimals can also cause inward migration

Rogue Planets IRogue Planets I

• AKA: planetars• Lone planets not in

orbit around any star.

• Normal creation process, then ejected by gravitational close encounters…

• Or, accretion in cold gas/dust clouds

Rogue Planets IIRogue Planets II• Earth-sized rogue

planets could have enough internal heat, from radioactive decay and tidal heating ifand tidal heating, if moon(s) present, to remain geologically active.

• Dynamicists suggest up to 5% of all planets?

Modifying the Nebular Theory?Modifying the Nebular Theory?

• Exoplanet observations, even if biased, show nebular theory is incomplete

• Effects like planet• Effects like planet migration and gravitational encounters might be more important than previously thought

• Or we might be looking at another class of solar systems

Planets: Common or Rare?Planets: Common or Rare?

• Preliminary Conclusions:

• One in ten stars surveyed thus far haveeasily-detectable planetseasily detectable planets– Should be about half

• Others may have smaller (Earth-sized) planets that current techniques cannot detect

• Are these the “normal” solar systems?

6

What’s normal? Transit MissionsTransit Missions• NASA’s Kepler

mission is scheduled to begin looking for transiting planets in 2009.

• Designed to measure the 0.008% decline in brightness when an Earth-mass planet eclipses a Sun-like star

Astrometric MissionsAstrometric Missions

• GAIA: A European mission planned for 2010 that will use interferometry to measure precise motions of a billion stars

SIM A NASA i i• SIM: A NASA mission planned for 2011 that will use interferometry to measure star motions even more precisely (to 10-6 arcseconds)

Measures physical parallax ofMeasures physical parallax ofwobbling starswobbling stars

Direct DetectionDirect Detection• Determining whether

Earth-mass planets are really Earth-like requires direct detection

• Missions capable ofMissions capable of blocking enough starlight to measure the spectrum of an Earth-like planet require interferometry

• NASA mission currently on hold due to lack of funding.

Terrestrial Planet Finder (TPF)

Ad AstraAd Astra

• Voyager 1 crossed terminator shock 2004 @ 94 AU– But most instruments had failed by then

• IBEX: Interstellar Boundary Explorer– Launched October 19th 2008 to boldly go…

My Other Vehicle is aMy Other Vehicle is aGalaxyGalaxy--class Starshipclass Starship

7

What about people?What about people?

NearNear--TermTerm• Orion CEV (back to the Moon)

– Shuttle retirement ~2010

• DTO (Direct-to-Orbit) hypersonic aircraft, > Mach 15

• Mars Direct & Mars NetMars Direct & Mars Net

Mars NetMars Net• Continue robotic surface

exploration– Find water and map look for life– Find landing sites with potential

for sustainabilityy– 2030 timeframe

• Sample Return doubtful?• Satellite Relay Constellation• Safely land crew return vehicle

w/ supplies• Then send people

– Why?

The Years AheadThe Years Ahead• Ongoing Spirit and Opportunity missions.• Completion of Cassini mission at Saturn.• Kepler, GAIA and SIM exoplanet missions.• New Horizons 2015 KBO flyby.

l l ki f i• Luna GLOB polar rover looking for water ice.• Project Constellation (LEO and return to the Moon)

– Multiple missions in 2018 to 2030 timeframe

• Mars robotic base construction• Europa aquabot (Enceladus too?)• Mars Direct (piloted mission) ≈ 2035?• Titan Direct ≈ 2075?

The Days AheadThe Days Ahead• Understanding your Grade Sheet information…

• Open Q&A time for Exam #4 is now

• Wednesday, Dec. 9th @ 6 PM is Exam #4y, @

• Exam #4 (the Final) will cover:– Chapters 10, 11, 12, and 13.

– Class notes from Weeks 12, 13, 14, and 15.

– Exact questions from Term Exams 1-3.

– Objective Questions: 30 @ 2 points each.

– Essays: 4 @ 10 points each.

(Semi(Semi--) Final Averages) Final Averages• Column 1 is a real grade

• Columns 2 & 3 are speculative

• Column 1: “Grade now w/ 4%” is your class grade today without taking TE4.

Thi i th “ lk ” b– This is the “walk away” number.

– Even if you “blow the final”, your grade cannot get worse than this number.

– If you already have an “A”, please do not come to TE4 (the final exam).

• Column 2 is what your final grade would be if you make as much on the final as you did on your highest TE 1-3 grades.

• Column 3 is what your final grade would be if you made 100% on TE4 (the final).

8

Quick 1102 updateQuick 1102 update• No final exam

• Final grade will be based on your earned points divided by 1000.

• Plus a % curve to be calculated after 12/4.

• Last exercise still pending:– Assignment 10 (Extrasolar Systems) due 12/4.

• All old exercises are open for partial credit. If you need ‘em…..go get ‘em.