1 / 33

AST 111

AST 111. Exoplanets I. Exoplanets. Exoplanets : Planets orbiting stars other than the Sun. Exoplanets. Remember: 99.9% of our Solar System is in the Sun Stars are so far that it is very difficult to image their planets

sydney
Download Presentation

AST 111

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. AST 111 Exoplanets I

  2. Exoplanets Exoplanets: Planets orbiting stars other than the Sun

  3. Exoplanets • Remember: 99.9% of our Solar System is in the Sun • Stars are so far that it is very difficult to image their planets • Light from stars 1,000,000,000x stronger than from planets, and the starlight gets blurred • Only 10 have been directly imaged

  4. A Picture • From the book: • 1 to 10 billion scale: • The Sun is a grapefruit • Earth is the head of a pin 15 meters away • Jupiter is a marble 80 meters away • Distance to nearest star is distance across U.S. • You’re in San Francisco looking at Washington D.C. • The grapefruit is hard enough to find! Good luck with the pinhead!

  5. Exoplanets • But technology now moves at an astounding rate. As I was writing this, I received this!! Credit: ESO

  6. Exoplanets • YOU CAN OBSERVE EXOPLANETS. • A 10” scope with a CCD camera is all that’s needed. ($4k) • It’s even a homework problem in the book: Chapter 13, Problem 54

  7. Exoplanets • Before 1990’s, all we knew about planets was our own Solar System • 1200 exoplanets (and more every day!) have been counted

  8. Lots of Earths!

  9. 51 Pegasi • First exoplanet discovered (1995) • Surface temp of 1340 oF

  10. How do we find them? • Exoplanets are indirectly observed by: • Gravitational wobble • Astrometric technique • Doppler technique • Transits and eclipses • Direct detection

  11. Gravitational Wobble • Objects in a solar system orbit the center of mass • The star appears to “wobble”

  12. Gravitational Wobble • Larger mass planets cause more wobble • More planets add their own wobbles to the star • Our Sun: • Jupiter creates a wobble • Saturn’s effect is perceptible • Other planets’ effects hard to see

  13. Gravitational Wobble (Astrometric) • Astrometric method: • Precisely measure stellar position • 10 LY away: • Large planet at 5AU from Sun-like star causes the star to move “the width of a human hair… seen at 3 miles” • Best for massive planets orbiting close stars • Takes many years of observing– ONE exoplanet found with this method

  14. Gravitational Wobble (Doppler) • 51 Pegasi discovered by alternating blue and red shifts • Recall spectra: • Blueshifts if moving toward us • Redshifts if moving away

  15. Gravitational Wobble (Doppler)

  16. Gravitational Wobble (Doppler) • Doppler technique accurate to 1 m/s • Period of graph is the planet’s orbital period • Kepler’s laws give distance from star

  17. Gravitational Wobble (Doppler) • Can determine orbital shape • More elliptical orbit, more “skewed” graph

  18. Gravitational Wobble (Doppler) • The Doppler technique does not work from bird’s eye view! • Recall that there must be relative motion toward or away from observer.

  19. Gravitational Wobble (Doppler) • Works best with more massive, closer stars • More gravitational pull • More wobble • Less time wait for doppler shifts

  20. Mass Estimate • Conservation of Momentum: Mstarvstar = Mplanetvplanet Mplanet = Mstarvstar vplanet • Doppler technique gives vstar. Know Mstar. _____________

  21. Mass Estimate • Kepler’s Laws give the radius of orbit • Doppler effect gives period of planet’s orbit • Also, vplanet = 2paplanet pplanet Mplanet = Mstarvstarpplanet 2paplanet ___________ ____________________

  22. Mass Estimate • 51 Pegasi: • 2.12 x 1030 kg (star’s mass) • 57 m/s (star’s velocity) • Radius of orbit: 7.82 x 109 m • Planet’s orbital period: 3.65 x 105 seconds • Mass of 51 Pegasi works out to 0.47 MJupiter

  23. Transits and Eclipses • Transit: Planet passes in front of star • Eclipse: Planet passes behind the star • Can’t actually see the dot moving across the star • Measure brightness changes

  24. Transits and Eclipses • Requires correct alignment (edge-on)

  25. Transits and Eclipses • Amount of “dip” in brightness gives planet’s radius • Have mass from Kepler’s Laws • Can get density: • Looks like terrestrial? • Looks like Jovian?

  26. Transits and Eclipses • Can show composition of upper atmosphere • During transit, starlight passes through the planet’s atmosphere

  27. Planet Size • From brightness measurements: Fraction of light blocked = area of planet’s disk = pr2planet area of star’s disk pr2star = r2planet r2star ________________________________ ________________ __________

  28. Example: HD209458 • rplanet = rstar x (fraction of light blocked)1/2 • Star HD209458: • Radius of 800,000 km • Planet blocks 1.7% of light (0.017) • rplanet = 800,000 km x (0.017)1/2 • rplanet =100,000 km

  29. Transits and Eclipses • One can observe the system in infrared during eclipse • Planets glow in infrared • Decrease in IR part of spectrum shows how much IR the planet gives • Can calculate planet’s temperature • Can identify greenhouse gases

  30. Direct Detection • Works for very large planets • Far from parent star

  31. Direct Detection

  32. Direct Detection

  33. Exoplanets • From the book: Although it is too soon to know for sure,it seems ever more likely that our MilkyWay Galaxy is home to billions of planetarysystems.

More Related