Formation of Planetary System Extra-solar planetary systems

1. Formation of Planetary SystemExtra-solar planetary systems Lecture 16

2. Other theory Tidal Hypothesis • Early attempt to explain the dichotomy of planets. Problem? tidal force strong enough to “draw out” a filament from stars will effectively disperse it before it could condense into planets!

3. Planet Formation : Summary

4. Core-accretion Model

5. Clearing remnant gas by winds After about 10 million years of the gravitational contraction, the central star begins a nuclear fusion at its center (i.e., start shining!!)  strong star-light and other small particles emanating from the star “sweep out” remaining gas but not large dust or rocks!

6. Simulation of core-accretions Problem: This process takes too long!?!

7. Disk-instability Model • Core-accretion model takes too long to create “cores” while gas depletes in less than ~10 Myrs! • Gas of the outer solar nebula are “bumpy” and clumps can collapse onto themselves similar to the collapsing solar nebula. • This single step collapse can be very fast (<1 Myr). At a later stage, massive gas planets attract nearby “rocks/planetesimals” which then settled down to the center forming a rocky core. • Not enough info to confirm/reject b/w these two competing models. Computer simulation of the disk-instability.

8. Searching for Extrasolar Planets Radial Velocity Method Detecting the radial reflex motion of a star due to an invisible massive planet. While the planet may be too faint to observe directly, astronomers can detect its presence by monitoring the absorption lines in the star’s spectrum. 372 confirmed RV planets as of late 2011

9. Searching for Extrasolar Planets Radial Velocity Method Detecting the radial reflex motion of a star due to an invisible massive planet. While the planet may be too faint to observe directly, astronomers can detect its presence by monitoring the absorption lines in the star’s spectrum. 372 confirmed RV planets as of late 2011 Quite unexpected discovery was many hot Jupiters around many stars. Based on the model of solar system formation, there should not be massive planets so close to the star. Then, how?

10. Searching for Extrasolar Planets Astrometric Method Detecting the reflex motion of a star (on the projected sky-plane) due to an invisible massive planet. While the planet may be too faint to observe directly, astronomers can detect its presence by monitoring the positions of the star very accurately (no planet has been discovered by this method yet).

11. Searching for Extrasolar Planets Detecting a tiny change of star’s brightness during a transit by an invisible planet.

12. Mercury Transits (2006, Nov 8) • Transit of Venus • 2012 June 6 • Transit of Mercury • 2016 May 9 • 2019 Nov 11

13. Searching for Extrasolar Planets Transit method  can even obtain a spectrum of planetary atmosphere!

14. Kepler : Space Transit Survey 0.95m space telescope looking at the same field over-and-over for 4 years. 105 square degrees of FoV (0.25% of the entire sky). 42 CCDs As of 2011 Summer…

15. Great sensitivity from Kepler!!

20. Searching for Extrasolar Planets Light “bends” around a massive object. Microlensing(Never repeats) Simultaneous monitoring hundreds of thousands stars  statistics on planets.

21. Direct Imaging of Exo-Planets (Jovian Planets) • Reflected light detection of Jovian planets requires 10-9 contrast ratio at  0.5 • Current state-of-the-art achieves 10-4~-5 at 1.0 sensitivity curve

22. How can we do then? Focus on nearby young stars • “young” = planets are still ‘hot’ thus, much brighter than older planets! • “nearby” = large separation between stars and planets! normal stars (old & distant) young distant stars young & nearby stars!!!

23. Coronagraph Blocking the bright region to see nearby faint stuffs…

24. Power of Adaptive Optics

25. Need for a confirmation! • Actual Example from Keck AO

26. Need for a confirmation! • Actual Example from Keck AO

27. Some early discoveries… • European Very Large Telescope • 2M1207b  central obj is a brown dward • AB Picb companion is a BD • GSC 8047-0232 B  companion is a BD

28. Recent Discoveries • In 2008, by Canadians, about 350 lightyears away in a star forming region… • In 2010, common proper motion was confirmed. • Wide separation (about 300 AU)  probably not formed as a planet.

29. Fomalhaut direction of Fomalhaut movement

30. HR 8799

31. Direct Imaging of Planetary System! Science (2008) C. Marois, B. Macintosh, T. Barman, B. Zuckerman, Inseok Song, J. Patience, D. Lafreniere, R. Doyon

32. 4th planet was discovered in 2010

33. HR 8799 • A Scaled-up version of the Solar System

34. If we replace HR8799 with our Sun… HR8799 is about 2.5 times more massive than our Sun.

35. Future Gemini Planet Imager (34 million USD device) Simulation of a planet detected with GPI. First light in early 2012 Will look at about 1000 nearby young stars  capable of imaging true Solar System analogs (i.e., a Jupiter at 5AU) 10 yr orbit of a 2 MJupiter a young (100Myr) Sun-like star at 55 Lyrs

36. Darwin Future European mission NASA collaboration Launch in 2015? In a coming decade, we will have dozens of (if not hundreds) exoplanet images And, we will have spectra of those exoplanets  able to check their habitabilities and eventual biosignatures!

37. In summary… Important Concepts Important Terms Hot Jupiters Astrometry Transit Planetesimal Skip section 8-3 • Solar system formation models • core-accretion model • disk-instability model • tidal hypothesis (wrong one!) • Various exoplanet detection methods • Radial velocity • Astrometry • Transit • Microlensing • Direct-imaging • Chapter/sections covered in this lecture : sections 8-5 through 8-7