formation of planetary system extra-solar planetary systems lecture 16
TRANSCRIPT
Formation of Planetary SystemExtra-solar planetary systems
Lecture 16
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!
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!
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.
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
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
Searching for Extrasolar Planets
Quite unexpected discovery wasmany 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• 2012 June 6
Transit of Mercury• 2016 May 9• 2019 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 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!!!
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• 2M1207b central obj is a brown dward• AB Pic b companion is a BD• GSC 8047-0232 B companion is a BD
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.
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)
4th planet was discovered in 2010
HR 8799A Scaled-up version of the Solar System
If we replace HR8799 with our Sun…
Our Solar System Planets
Jupiter Neptune Uranus Saturn
5 AU 30 AU 19 AU 9.5AU
Observed HR 8799 planetary system
e b c d
14.5 68 38 24
After replacing the central star with our Sun
6.6 31 17 11
HR8799 is about 2.5 times more massive than our Sun.
Future
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
Gemini Planet Imager (34 million USD device)
Darwin
European missionNASA collaborationLaunch in 2015?
Future
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!
In summary…
Important ConceptsSolar 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 TermsHot JupitersAstrometryTransitPlanetesimal
Skip section 8-3
Chapter/sections covered in this lecture : sections 8-5 through 8-7