Formation of Planetary System Extra-solar planetary systems Lecture 16

Other theory Tidal Hypothesis Early attempt to explain the dichotomy of planets. 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!

Planet Formation : Summary

Core-accretion Model

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! Clearing remnant gas by winds

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

Disk-instability Model Core-accretion model takes too long to create “cores” while gas depletes in less than ~10 Myrs! 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. 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. 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. Not enough info to confirm/reject b/w these two competing models. Computer simulation of the disk- instability.

Radial Velocity Method Detecting the radial reflex motion of a star due to an invisible massive planet. 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. 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 confirmed RV planets as of late 2011 Searching for Extrasolar Planets

Radial Velocity Method Detecting the radial reflex motion of a star due to an invisible massive planet. 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. 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 confirmed RV planets as of late 2011 Searching for Extrasolar Planets 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?

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). Searching for Extrasolar Planets

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

Mercury Transits (2006, Nov 8) Transit of Venus Transit of Venus 2012 June June 6 Transit of Mercury Transit of Mercury 2016 May May Nov Nov 11

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

As of 2011 Summer… 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 Kepler : Space Transit Survey

Great sensitivity from Kepler!!

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

Direct Imaging of Exo-Planets (Jovian Planets) Reflected light detection of Jovian planets requires contrast ratio at  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’“young” = planets are still ‘hot’ thus, much brighter than older planets! thus, much brighter than older planets! “ nearby ” = large separation between stars and planets!“nearby” = large separation between stars and planets! normal stars (old & distant)young distant starsyoung & nearby stars!!!

Coronagraph Blocking the bright region to see nearby faint stuffs…

Power of Adaptive Optics

Need for a confirmation! Actual Example from Keck AO Actual Example from Keck AO

Need for a confirmation!

Some early discoveries… European Very Large Telescope European Very Large Telescope 2M1207b  central obj is a brown dward 2M1207b  central obj is a brown dward AB Pic b  companion is a BD AB Pic b  companion is a BD GSC B  companion is a BD GSC B  companion is a BD

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

Fomalhaut direction of Fomalhaut movement

HR 8799

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

4 th planet was discovered in th planet was discovered in 2010

HR 8799 A Scaled-up version of the Solar System A Scaled-up version of the Solar System

If we replace HR8799 with our Sun… Our Solar System Planets JupiterNeptuneUranusSaturn 5 AU30 AU19 AU9.5AU Observed HR 8799 planetary system ebcd After replacing the central star with our Sun HR8799 is about 2.5 times more massive than our Sun.

Future Simulation of a planet detected with GPI. Simulation of a planet detected with GPI. First light in early 2012 First light in early 2012 Will look at about 1000 nearby young stars 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 M Jupiter a young (100Myr) Sun-like star at 55 Lyrs Gemini Planet Imager (34 million USD device)

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

In summary… Important Concepts 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 Important Terms Hot Jupiters Astrometry Transit Planetesimal Skip section 8-3 Chapter/sections covered in this lecture : sections 8-5 through 8-7