1. Today’s APODAPOD  Begin Chapter 8 on Monday– Terrestrial Planets  Hand in homework today  Quiz on Oncourse The Sun Today A100 – Ch. 7 Extra-Solar Planets

2. Today’s Topics  Solar systems around other stars  How do we find them  What are they like?  How are they similar to our solar system? How do they differ  What kinds of stars have planets?

3. Worlds around other Suns  Evidence exists for planets around other nearby stars  The new planets are not observed directly, but rather by their gravitational effects on their parent star  These new planets are a surprise - they are huge planets very close to their parent stars Note: All of these images are artists’ conceptions

4. Our Solar System Gas Giants Ice Giants Terrestrial Planets Plutoids

5. Searching for Planets  More than 300 “extra-solar” planets have been discovered  How are planets discovered? Radial velocity Transits  Gravitational lensing  Wobbles in stars’ positions

6. oThe Doppler Shift! oAbsorption lines shift left or right if stars move toward or away from us oPlanetary orbits cause stars’ radial velocities to change Discovering Planets from Spectra

7. The Electromagnetic Spectrum

8. What is Wavelength ???  Some phenomena are periodic  They repeat in equal intervals of time  The time between successive peaks is called wavelength  Wavelength = Color  Red light has longer wavelengths  Blue light has shorter wavelengths Time

9. Where does light come from?  Thermal radiators emit light at all wavelengths  Atomic emission occurs only at particular wavelengths THERMAL EMISSION ATOMIC EMISSION

10. The Doppler Shift Police Siren Doppler Pumpkin Johan Christian Doppler

11. The Doppler Effect  How does light tell us the speed of a distant object?  How does light tell us the rotation rate of an object? Doppler Principles (Police Traffic Radar Handbook) The Doppler Shift of Sound Waves What's Happening?

12. The Doppler Shift for Light  Astronomers us the Doppler effect to measure the “radial” velocities of astronomical objects  Radial velocities are motions toward or away from us

13. Measuring the Shift Stationary Moving Away Away Faster Moving Toward Toward Faster Doppler shift tells us ONLY about the part of an object’s motion toward or away from us The amount of blue or red shift tells us an object’s speed toward or away from us:

14. The Doppler Shift in YOUR Life

15. Periodic velocity changes due to orbiting planet VERY high precision is needed to measure these very small velocity changes Velocity vs. Time

16. Velocity of 51 Peg About 7 orbits in 30 days P=4.2 days

17. A Planet around  Eridani  A planet orbits the star  Eridani at a radius of 3.2 A.U.   Eridani is similar to our Sun   Eridani is only 10.5 light years away  The planet is similar to Jupiter  The planet orbits  Eridani in 7 years   Eridani has at least one more planet

18. The star  And has at least 3 planets terrestrial planets

20. If the Earth lies in the same plane as the orbit of a planet we see a transit The planet passes across the face of the star Some of the starlight is blocked by planet and the star appears dimmer Planetary Transits

21. Seeing planets near stars is hard Looking for an Earthlike planet around a nearby star is like standing on the East Coast of the United States and looking for a pinhead on the West Coast — with a VERY bright grapefruit nearby.  Very large telescopes will help

22. Imaging Planets? This photo shows an image of the faint star GQ Lupi taken in the infrared. The faint object to the right of the star is a possible planetary companion. It is 250 times fainter than the star itself and it located 0.73 arcsecond west. At the distance of GQ Lupi, this corresponds to a distance of roughly 100 astronomical units. The planet probably has a mass of about 2 x Jupiter.

23.  Location of brown dwarf Possible planet Another possible planet  Orbiting the brown dwarf ~225 light years away  Young, temp near 1000K  Further from its “sun” than Pluto is from ours (brown dwarf is blocked out)

24. Properties of KNOWN Extra-Solar Planets SURPRISES!  All are gas giants like Jupiter and Saturn  Most are larger than Jupiter  Many orbit very close to their parent stars  Some are in systems with multiple planets

25. Many Known Planets Are Close to Stars The Sun (Masses are given as Jupiter masses)

26. Hot Jupiters Did these hot Jupiters form further out, and migrate inward as they eject smaller bodies from their planetary systems

27. BUT: Selection Effects  Close-in, massive planets are easier to detect  Far-out planets and light-weight planets are MUCH HARDER to detect  So far, we’ve only been able to detect massive, close-in planets  Techniques, sensitivity are improving  Terrestrial planets soon!

28. Planet Mass Distribution  The number of planets discovered decreases as planet mass increases  There are few planets much more massive than Jupiter  Most planets are <2 Jupiter masses

29. How Far Are Planets from their Stars?  Planets with semi-major axes > 3AU have periods comparable to or longer than the length of most Doppler surveys, so the distribution is incomplete beyond that distance. incomplete

30. Period Distribution for Hot Jupiters  A “pile-up” of planets with orbital periods near 3 days – very close to central star  Why???

31. What are the planets’ orbits like?  What are the eccentricities of our sun’s planets?  Planets within 0.1 AU are probably tidally circularized  Beyond 0.1 AU, the distribution of eccentricities appears essentially uniform between 0 and 0.8  Very different from our solar system!

32. Looking for Another Earth  So far, we don’t have the right instruments to detect Earth-like planets  Requires large ground-based telescopes or large, specially equipped space telescopes  Stay tuned!

33. ASSIGNMENTS this week  Begin Chapter 8 – Terrestrial Planets  HAND IN HOMEWORK Dates to Remember